Biochar-nanoparticle combinations enhance the biogeochemical recovery of a post-mining soil

Here we addressed the capacity of distinct amendments to reduce arsenic (As), copper (Cu), selenium (Se) and zinc (Zn) associated risks and improve the biogeochemical functions of post-mining soil. To this, we examined nanoparticles (NPs) and/or biochar effects, combined with phytostabilization using Lolium perenne L. Soil samples were taken in a former metal mine surroundings. Ryegrass seeds were sown in pots containing different combinations of NPs (zero-valent iron (nZVI) or hydroxyapatite (nH)) (0 and 2 %), and biochar (0, 3 and 5 %). Plants were grown for 45 days and the plant yield and element accumulation were evaluated, also soil properties (element distribution within the soil fractions, fertility, and enzymatic activities associated with microbiota functionality and nutrient cycling) were determined. Results showed biochar-treated soil had a higher pH, and much higher organic carbon (C) content than control soil and NP-treated soils, and it revealed increased labile C, total N, and available P concentrations. Soil treatment with NP-biochar combinations increased exchangeable non-acid cation concentrations and reduced exchangeable Na%, improved soil fertility, reduced sodicity risk, and increased ryegrass biomass. Enzymatic activities, particularly dehydrogenase and glucosidase, increased upon the addition of biochar, and this effect was fostered by NPs. Most treatments led to a significant reduction of metal(loid)s contents in biomass, mitigating contamination risks. The two different NPs had similar effects in many parameters, nH outperformed nZVI in terms of increased nutrients, C content, and enzymatic activities. On the basis of our results, combined biochar-NP amendments use, specially nH, emerges as a potential post-mining soil restoration strategy.

Effectiveness of cork and pine bark powders as biosorbents for potentially toxic elements present in aqueous solution

Cork oak and pine bark, two of the most prolific byproducts of the European forestry sector, were assessed as biosorbents for eliminating potentially toxic elements (PTEs) from water-based solutions. Our research suggests that bioadsorption stands out as a viable and environmental eco-friendly technology, presenting a sustainable method for the extraction of PTEs from polluted water sources. This study aimed to evaluate and compare the efficiency of cork powder and pine bark powder as biosorbents. Specifically, the adsorption of Fe, Cu, Zn, Cd, Ni, Pb and Sn at equilibrium were studied through batch experiments by varying PTEs concentrations, pH, and ionic strength. Results from adsorption-desorption experiments demonstrate the remarkable capacity of both materials to retain the studied PTE. Cork powder and pine bark powder exhibited the maximum retention capacity for Fe and Cd, while they performed poorly for Pb and Sn, respectively. Nevertheless, pine bark showed a slightly lower retention capacity than cork. Increasing the pH resulted in cork showing the highest adsorption for Zn and the lowest for Sn, while for pine bark, Cd was the most adsorbed, and Sn was the least adsorbed, respectively. The highest adsorption of both materials occurred at pH 3.5-5, depending on the PTE tested. The ionic strength also influenced the adsorption of the various PTEs for both materials, with decreased adsorption as ionic strength increased. The findings suggest that both materials could be effective for capturing and eliminating the examined PTEs, albeit with different efficiencies. Remarkably, pine bark demonstrated superior adsorption capabilities, which were observed to vary based on the specific element and the experimental conditions. These findings contribute to elucidating the bio-adsorption potential of these natural materials, specifically their suitability in mitigating PTEs pollution, and favoring the recycling and revalorization of byproducts that might otherwise be considered residue.

Mercury mobilization in shrubland after a prescribed fire in NE Portugal: Insight on soil organic matter composition and different aggregate size

Soils constitute the major reservoir of mercury (Hg) in terrestrial ecosystems, whose stability may be threatened by wildfires. This research attempts to look at the effect of prescribed fire on the presence of Hg in a shrubland ecosystem from NE Portugal, delving into its relationship with soil aggregate size and the molecular composition of soil organic matter (SOM). During the prescribed fire, on average 347 mg Hg ha-1 were lost from the burnt aboveground biomass of shrubs and 263 mg Hg ha-1 from the combustion of the soil organic horizon. Overall, Hg concentration and pools in the mineral soil did not show significant changes due to burning, which highlights their role as long-term Hg reservoirs. The higher Hg concentrations found in smaller aggregates (<0.2 mm) compared to coarser ones (0.5-2 mm) are favored by the higher degree of organic matter decomposition (low C/N ratio), rather than by greater total organic C contents. The Hg-enriched finest fraction of soil (<0.2 mm) could be more prone to be mobilized by erosion, whose potential arrival to water bodies increases the environmental concern for the Hg present in fire-affected soils. The SOM quality (molecular composition) and the main organic families, analyzed by Fourier-transform infrared spectroscopy in combination with multivariate statistical analysis, significantly conditioned the retention/emission of Hg in the uppermost soil layers. Thus, before the fire, Hg was strongly linked to lipid and protein fractions, while Hg appeared to be linked to aromatic-like compounds in fire-affected SOM.

Use of metal nanoparticles in agriculture. A review on the effects on plant germination

Agricultural nanotechnology has become a powerful tool to help crops and improve agricultural production in the context of a growing world population. However, its application can have some problems with the development of harvests, especially during germination. This review evaluates nanoparticles with essential (Cu, Fe, Ni and Zn) and non-essential (Ag and Ti) elements on plant germination. In general, the effect of nanoparticles depends on several factors (dose, treatment time, application method, type of nanoparticle and plant). In addition, pH and ionic strength are relevant when applying nanoparticles to the soil. In the case of essential element nanoparticles, Fe nanoparticles show better results in improving nutrient uptake, improving germination, and the possibility of magnetic properties could favor their use in the removal of pollutants. In the case of Cu and Zn nanoparticles, they can be beneficial at low concentrations, while their excess presents toxicity and negatively affects germination. About nanoparticles of non-essential elements, both Ti and Ag nanoparticles can be helpful for nutrient uptake. However, their potential effects depend highly on the crop type, particle size and concentration. Overall, nanotechnology in agriculture is still in its early stages of development, and more research is needed to understand potential environmental and public health impacts.

Adsorption of antibiotics on bio-adsorbents derived from the forestry and agro-food industries

Antibiotic consumption at high levels in both human and veterinary populations pose a risk to their eventual entry into the food chain and/or water bodies, which will adversely affect the health of living organisms. In this work, three materials from forestry and agro-food industries (pine bark, oak ash and mussel shell) were investigated as regards their potential use as bio-adsorbents in the retention of the antibiotics amoxicillin (AMX), ciprofloxacin (CIP) and trimethoprim (TMP). Batch adsorption/desorption tests were conducted, adding increasing concentrations of the pharmaceuticals individually (from 25 to 600 μmol L-1), reaching maximum adsorption capacities of ≈ 12000 μmol kg-1 for the three antibiotics, with removal percentages of ≈ 100% for CIP, 98-99% adsorption for TMP onto pine bark, and 98-100% adsorption for AMX onto oak ash. The presence of high calcium contents and alkaline conditions in the ash favored the formation of cationic bridges with AMX, whereas the predominance of hydrogen bonds between pine bark and TMP and CIP functional groups explain the strong affinity and retention of these antibiotics. The Freundlich's model provided the best prediction for AMX adsorption onto oak ash and mussel shell (heterogeneous adsorption), whereas the Langmuir's model described well AMX adsorption onto pine bark, as well as CIP adsorption onto oak ash (homogeneous and monolayer adsorption), while all three models provided satisfactory results for TMP. In the present study, the results obtained were crucial in terms of valorization of these adsorbents and their subsequent use to improve the retention of antibiotics of emerging concern in soils, thereby preventing contamination of waters and preserving environment quality.

Clarithromycin as soil and environmental pollutant: Adsorption-desorption processes and influence of pH

Antibiotics pollution is a growing environmental issue, as high amounts of these compounds are found in soil, water and sediments. This work studies the adsorption/desorption of the macrolide antibiotic clarithromycin (CLA) for 17 agricultural soils with different edaphic characteristics. The research was carried out using batch-type experiments, with an additional assessment of the specific influence of pH for 6 of the soils. The results show that CLA adsorption reaches between 26 and 95%. In addition, the fit of the experimental data to adsorption models provided values between 1.9 and 19.7 Ln μmol1-n kg-1 for the KF, Freundlich affinity coefficient, and between 2.5 and 10.5 L kg-1 for Kd, distribution constant of Linear model. Regarding the linearity index, n, it varied between 0.56 and 1.34. Desorption showed lower scores than adsorption, with an average of 20%, and with values of 3.1 and 93.0 Ln μmol1-n kg-1 for KF(des) and 4.4 and 95.0 L kg-1 for Kd(des). The edaphic characteristics with the highest influence on adsorption were the silt fraction content and the exchangeable Ca content, while in the case of desorption, they were the total nitrogen, organic carbon, and exchangeable Ca and Mg contents. Regarding the pH, within the range studied (between 3 and 10), its value did not decisively affect the adsorption/desorption process. Overall, the set of these results could be of help to program appropriate measures leading to the retention/elimination of this antibiotic when it reaches the environment as a pollutant.

Variation of Hg concentration and accumulation in the soil of maritime pine plantations along a coast-inland transect in SW Europe

Climatic conditions have been shown as a major driver of the fate of Hg in forest ecosystems at a global scale, but less is known about climatic effects at shorter scales. This study assesses whether the concentration and pools of Hg in soils collected from seventeen Pinus pinaster stands describing a coastal-inland transect in SW Europe vary along a regional climatic gradient. In each stand, samples of the organic subhorizons (OL, OF + OH) and the mineral soil (up to 40 cm) were collected and some general physico-chemical properties and total Hg (THg) were analyzed. Total Hg was significantly higher in the OF + OH than in the OL subhorizons (98 and 38 μg kg^-1, respectively), favored by a greater organic matter humification in the former. In the mineral soil, mean THg values decreased with depth, ranging from 96 μg kg^-1 in the 0-5 cm layers to 54 μg kg^-1 in the deepest layers (30-40 cm), respectively. The average Hg pool (PHg) was 0.30 mg m^-2 in the organic horizons (92% accumulated in the OF + OH subhorizons), and 27.4 mg m^-2 in the mineral soil. Changes in climatic factors, mainly precipitation, along the coast-inland transect resulted in a remarkable variation of THg in the OL subhorizons, consistent with their role as the first receiver of atmospheric Hg inputs. The high precipitation rate and the occurrence of fogs in coastal areas characterized by the oceanic influence would explain the higher THg found in the uppermost soil layers of pine stands located close to the coastline. The regional climate is key to the fate of mercury in forest ecosystems by influencing the plant growth and subsequent atmospheric Hg uptake, the atmospheric Hg transference to the soil surface (wet and dry deposition and litterfall) and the dynamics that determine net Hg accumulation in the forest floor.

Direct toxicity of six antibiotics on soil bacterial communities affected by the addition of bio-adsorbents

Reducing the toxicity caused by antibiotics on bacterial communities in the soil is one of the great challenges of this century. For this, the effectiveness of amending the soil with different bioadsorbents such as crushed mussel shell (CMS), pine bark (PB) and biomass ash (BA), as well as combinations of them (CMS + PB and PB + BA) was studied at different doses (0 g kg^-1 to 48 g kg^-1). Soil samples were spiked, separately, with increasing doses (0-2000 mg kg^-1) of cefuroxime (CMX), amoxicillin (AMX), clarithromycin (CLA), azithromycin (AZI), ciprofloxacin (CIP) and trimethoprim (TMP). Their toxicity on bacterial growth was estimated using the tritium-labeled leucine (³H) incorporation method. Toxicity was observed to behave differently depending on the antibiotic family and bioadsorbent, although in different magnitude and at different doses. The toxicity of β-lactams (AMX and CXM) was reduced by up to 54% when the highest doses of bio-adsorbents were added due to the increase in pH (CMS and BA) and carbon (PB) contribution. Macrolides (CLA and AZI) showed slight toxicity in un-amended soil samples, which increased by up to 65% with the addition of the bio-adsorbents. The toxicity of CIP (a fluoroquinolone) increased with the dose of the bio-adsorbents, reaching up to 20% compared with the control. Finally, the toxicity of TMP (a diaminopyrimidine) slightly increased with the dose of bio-adsorbents. The by-products that increase soil pH are those that showed the highest increases of CLA, AZI, CIP and TMP toxicities. These results could help to prevent/reduce environmental pollution caused by different kinds of antibiotics, selecting the most appropriated bio-adsorbents and doses.

Use of Three Different Nanoparticles to Reduce Cd Availability in Soils: Effects on Germination and Early Growth of Sinapis alba L

Globally, cadmium (Cd) is one of the metals that causes the most significant problems of contamination in agricultural soils and toxicity in living organisms. In this study, the ability of three different nanoparticles (dose 3% w/w) (hydroxyapatite (HANPs), maghemite (MNPs), or zero-valent iron (FeNPs)) to decrease the availability of Cd in artificially contaminated agricultural soil was investigated. The effect of Cd and nanoparticles on germination and early growth of Sinapis alba L. was also assessed by tolerance/toxicity bioassays. The available Cd contents in the contaminated soil decreased after treatment with the nanoparticles (available Cd decreased with HANPs: >96.9%, MNPs: >91.9%, FeNPs: >94%), indicating that these nanoparticles are highly efficient for the fixation of available Cd. The toxicity/tolerance bioassays showed different behavior for each nanoparticle. The HANPs negatively affected germination (G(%): 20% worsening compared to control soil), early root growth (G_index: -27.7% compared to control soil), and aerial parts (Ap_index: -12%) of S. alba, but showed positive effects compared to Cd-contaminated soils (G_index: +8-11%; Ap_index: +26-47%). MNP treatment in Cd-contaminated soils had a positive effect on germination (G(%): 6-10% improvement) and early growth of roots (G_index: +16%) and aerial parts (Ap_index: +16-19%). The FeNPs had a positive influence on germination (G(%): +10%) and growth of aerial parts (Ap_index: +12-16%) but not on early growth of roots (G_index: 0%). These nanoparticles can be used to reduce highly available Cd contents in contaminated soils, but MNPs and FeNPs showed the most favorable effects on the early growth and germination of S. alba.

Mercury in a birch forest in SW Europe: Deposition flux by litterfall and pools in aboveground tree biomass and soils

Atmospheric mercury (Hg) is largely assimilated by vegetation and subsequently transferred to the soil by litterfall, which highlights the role of forests as one of the largest global Hg sinks within terrestrial ecosystems. We assessed the pool of Hg in the aboveground biomass (leaves, wood, bark, branches and twigs), the Hg deposition flux through litterfall over two years (by sorting fallen biomass in leaves, twigs, reproductive structures and miscellaneous) and its accumulation in the soil profile in a deciduous forest dominated by Betula alba from SW Europe. The total Hg pool in the aboveground birch biomass was in the range 532-683 mg ha^-1, showing the following distribution by plant tissues: well-developed leaves (171 mg ha^-1) > twigs (160 mg ha^-1) > bark (159 mg ha^-1) > bole wood (145 mg ha^-1) > fine branches (25 mg ha^-1) > thick branches (24 mg ha^-1) > newly sprouted leaves (20 mg ha^-1). The total Hg deposition fluxes through litterfall were 15.4 and 11.7 μg m^-2 yr^-1 for the two years studied, with the greatest contribution coming from birch leaves (73 %). In the soil profile, the pool of Hg in the mineral soil (37.0 mg m^-2) was an order of magnitude higher than in the organic horizons (1.0 mg m^-2), mostly conditioned by parameters such as soil bulk density and thickness, total C and N contents and the presence of certain Al compounds.

Do heavy metals affect bacterial communities more in small repeated applications or in a single large application?

Heavy metals from anthropogenic sources accumulate slowly but steadily, leading to high metal concentration levels in soil. However, the effect of each heavy metal on soil bacterial communities is usually assessed in laboratories by a single application of individually spiked metals. We evaluated the differences between single individual application and repeated individual applications of Cr, Cu, Ni, Pb, and Zn on bacterial communities, through pollution-induced community tolerance (PICT), using bacterial growth as the endpoint (³H-leucine incorporation method). We found that PICT development was higher when soil was spiked in individual single application than individual repeated applications for Cu, Ni and Zn. In contrast, bacterial communities did not show different tolerance between singly or repeatedly when soil was spiked with Cr. In the case of Pb any increase of bacterial community tolerance to this metal was found despite high doses applied (up to 2000 mg kg^-1). These results are relevant for the interpretation of the effects of heavy metals on soil microbes in order to avoid laboratory overestimations of the real effects of heavy metals on soil microbes.

Needle age and precipitation as drivers of Hg accumulation and deposition in coniferous forests from a southwestern European Atlantic region

Vegetation and climate are critical in the biogeochemical cycle of Hg in forest ecosystems. The study assesses the influence of needle age and precipitation on the accumulation of Hg in needle biomass and its deposition by litterfall in thirty-one pine plantations spread throughout two biogeographical regions in SW Europe. Well-developed branches of Pinus pinaster were sampled and pine needles were classified according to 4 age classes (y₀, y₁, y₂, y₃). The concentration of total Hg (THg) was analyzed in the samples and Hg content in needle biomass and its deposition by litterfall were estimated. The concentration of total Hg (THg) increased with needle age ranging from 9.1 to 32.7 μg Hg kg^-1 in the youngest and oldest needles, respectively. The rate of Hg uptake (Hg_R) three years after needle sprouting was 10.2 ± 2.3 μg Hg kg^-1 yr^-1, but it decreased with needle age probably due to a diminution in photosynthetic activity as needles get older. The average total Hg stored in needle biomass (Hg_Wt) ranged from 5.6 to 87.8 mg Hg ha^-1, with intermediate needle age classes (y₁ and y₂) accounting for 70% of the total Hg stored in the whole needle biomass. The average deposition flux of Hg through needle litterfall (Hg_Lt) was 1.5 μg Hg m^-2 yr^-1, with the y₂ and y₃ needles contributing most to the total Hg flux. The spatial variation of THg, Hg_Wt and Hg_Lt decreased from coastal pine stands, characterized by an oceanic climate, to inland pine stands, a feature closely related to the dominant precipitation regime in the study area. Climatic conditions and needle age are the main factors affecting Hg accumulation in tree foliage, and should be considered for an accurate assessment of forest Hg pools at a regional scale and their potential consequences in the functioning of terrestrial ecosystems.

Influence of pH on the adsorption-desorption of doxycycline, enrofloxacin, and sulfamethoxypyridazine in soils with variable surface charge

In this research, the adsorption/desorption of the antibiotics doxycycline (DC), enrofloxacin (ENR), and sulfamethoxypyradazine (SMP) was studied in 6 agricultural soils with predominance of variable charge, both before and after removing organic matter by calcination. DC adsorption was high at acidic pH, and decreased at pH values above 8. Removal of organic matter with calcination caused just a slight decrease in adsorption, and even in some soils adsorption was similar to that in non-calcined samples. The adsorption coefficients (K_d) were higher for the DC^- species compared to DC⁺, DC⁰ and DC^2-. Regarding DC desorption, the values were very low throughout the pH range covered in the study (2-12), both in the calcined samples and in those not subjected to calcination. ENR showed a similar behavior to DC regarding the effect of pH, since ENR adsorption also decreased at basic pH, but the effect of removing organic matter was different, as it caused a clear decrease in ENR adsorption. The species with the highest K_d was in this case ENR⁰, although ENR⁺ is also quantitatively important as regards K_d value in calcined samples. For this antibiotic, no differences in desorption were observed between calcined and non-calcined samples. Finally, SMP adsorption also decreased as pH increased, and, in addition, similarly to what happened with ENR, in general, there was a strong decrease in SMP adsorption when organic matter was removed. The species with the highest K_d in this case was SMP⁺ in non-calcined samples, but SMP⁰ and SMP^- become more relevant in calcined samples. The percentages of SMP desorption were higher than those for the other two antibiotics, and an increase occurs at intermediate pH values, being higher for calcined samples. These results can be considered relevant in terms of increasing the knowledge as regards the possible evolution and fate of the three antibiotics studied. Specifically, for different pH conditions and with different organic matter contents, when they reach soils and other environmental compartments after being discharged as contaminants. This could have important repercussions on public health and the overall environment.

Competitive adsorption and desorption of tetracycline and sulfadiazine in crop soils

In view of the environmental issues caused by antibiotics, this research studies competitive adsorption/desorption for tetracycline (TC) and sulfadiazine (SDZ) in agricultural soils. Competitive adsorption was studied in binary systems (adding equal concentrations of both antibiotics). In addition, it was compared with results from simple systems. In all cases, batch-type adsorption/desorption experiments were carried out. In the binary systems, for the highest antibiotic concentration added, adsorption percentages were always higher for TC (close to 100%) than for SDZ (10-90%). In these systems, TC desorption was lower than 5% for all soils, and generally <10% for SDZ. Comparing TC and SDZ adsorption for the different systems, SDZ was clearly affected by the presence of TC, with SDZ adsorption percentages being was much higher (with differences generally above 65%) in the binary than in the simple systems. On the contrary, comparing the results of TC adsorption in simple and binary systems, TC was not affected by the presence of SDZ, obtaining similar adsorption percentages in both systems. K_d and K_F values (in the Linear and Freundlich models), were higher in the simple systems in the case of TC, which could be due to competition with SDZ, while for SDZ K_d and K_F were higher in the binary systems, with a synergistic effect of TC favoring SDZ adsorption. Regarding desorption, it reached 100% for SDZ in some soils in simple systems, dropping to 10% in the presence of TC. TC desorption was <4%, not affected by SDZ. The results indicate that environmental risks would be higher for SDZ, showing differences when both antibiotics are present. This can be considered relevant as regards public health and environmental preservation, in view of direct toxicities and the promotion of resistance to antibiotics associated with the presence of these contaminants in the environment.

Influence of soil properties on the development of bacterial community tolerance to Cu, Ni, Pb and Zn

Pollution-Induced Community Tolerance (PICT) is a helpful and sensitive methodology to evaluate the effect of metal pollution in soils using microorganisms as indicators. PICT was used to determine the increase of bacterial community tolerance to Cu, Ni, Pb and Zn (Δlog IC₅₀), and to assess the influence of soil properties on the development of bacterial community tolerance to Cu, Ni, Pb, and Zn. Soil samples showed a wide range of properties, such as pH (3.96-7.47), texture (13.8-31.7% clay) or organic matter (9.7-30.7%). Bacterial growth measured by the [³H]-leucine incorporation method was used as the PICT endpoint. Bacterial communities generally developed tolerance in response to Cu, Ni and Zn additions to soils. However, bacterial communities showed no tolerance to Pb, probably due to high Pb sorption in studied soils. Soil properties influenced the development of bacterial community tolerance to Cu, Ni and Zn. Effective cation exchange and a soil sorption parameter (Freundlich's linearity index) were the selected variables to estimate Δlog IC₅₀ to Cu (R² = 0.65). Clay content and Ni-soluble are the main factors to estimate Δlog IC₅₀ to Ni (R² = 0.63). Organic matter content and a sorption parameter (maximum sorption capacity of the soil from Langmuir equation) are the soil properties to estimate Δlog IC₅₀ to Zn (R² = 0.45). Most of the variables exerted their effect in soil, i.e. PICT selection phase. However, clay content affected bacterial community tolerance determination (PICT detection phase), leading to overestimated measurements of bacterial community tolerance.

Effects of ciprofloxacin, trimethoprim, and amoxicillin on microbial structure and growth as emerging pollutants reaching crop soils

The presence of emerging pollutants, and specifically antibiotics, in agricultural soils has increased notably in recent decades, causing growing concern as regards potential environmental and health issues. With this in mind, the current study focuses on evaluating the toxicity exerted by three antibiotics (amoxicillin, trimethoprim, and ciprofloxacin) on the growth of soil bacterial communities, when these pollutants are present at different doses, and considered in the short, medium, and long terms (1, 8 and 42 days of incubation). Specifically, the research was carried out in 12 agricultural soils having different physicochemical characteristics and was performed by means of the leucine (³H) incorporation method. In addition, changes in the structure of soil microbial communities at 8 and 42 days were studied in four of these soils, using the phospholipids of fatty acids method for this. The main results indicate that the most toxic antibiotic was amoxicillin, followed by trimethoprim and ciprofloxacin. The results also show that the toxicity of amoxicillin decreases with time, with values of Log IC₅₀ ranging from 0.07 ± 0.05 to 3.43 ± 0.08 for day 1, from 0.95 ± 0.07 to 3.97 ± 0.15 for day 8, and from 2.05 ± 0.03 to 3.18 ± 0.04 for day 42, during the incubation period. Regarding trimethoprim, 3 different behaviors were observed: for some soils the growth of soil bacterial communities was not affected, for a second group of soils trimethoprim toxicity showed dose-response effects that remained persistent over time, and, finally, for a third group of soils the toxicity of trimethoprim increased over time, being greater for longer incubation times (42 days). As regards ciprofloxacin, this antibiotic did not show a toxicity effect on the growth of soil bacterial communities for any of the soils or incubation times studied. Furthermore, the principal component analysis performed with the phospholipids of fatty acids results demonstrated that the microbial community structure of these agricultural soils, which persisted after 42 days of incubation, depended mainly on soil characteristics and, to a lesser extent, on the dose and type of antibiotic (amoxicillin, trimethoprim or ciprofloxacin). In addition, it was found that, in this research, the application of the three antibiotics to soils usually favored the presence of fungi and Gram-positive bacteria.

Potential of low-cost bio-adsorbents to retain amoxicillin in contaminated water

Sewage sludge as agricultural amendment is the main route of human-medicine antibiotics to enter soils. When reaching environmental compartments, these compounds can cause significant risks to human and ecological health. Specifically, the antibiotic amoxicillin (AMX) is highly used in medicine, and the fact that more than 80% of the total ingested is excreted increases the chances of causing serious environmental and public health problems. As the use of low-cost bio-adsorbents could help to solve these issues, this research focuses on the retention of AMX onto four by-products of the forestry industry (eucalyptus leaf, pine bark, pine needles, and wood ash) and one from food industry (mussel shell). To carry out this study, batch-type tests were performed, where increasing concentrations of the antibiotic (0, 2.5, 5, 10, 20, 30, 40 and 50 μmol L^-1) were added to samples of 0.5 g of each bio-adsorbent. Eucalyptus leaf, pine needle and wood ash showed adsorption scores higher than 80%, while it was up to 39% and 48% for pine bark and mussel shell, respectively. For pine bark, wood ash and mussel shell, adsorption data showed good adjustment to the Freundlich and Linear models, while pine needles and eucalyptus leaf did not fit to any model. There was not desorption when the maximum concentration of AMX (50 μmol L^-1) was added. Overall, eucalyptus leaf, pine needles and wood ash can be considered good bio-adsorbents with high potential to retain AMX, which has significant implications regarding their eventual use to reduce risks of environmental pollution by this antibiotic.

The role of afforestation species as a driver of Hg accumulation in organic horizons of forest soils from a Mediterranean mountain area in SW Europe

Forest areas are a primary sink of atmospheric mercury (Hg) within terrestrial ecosystems, whereas forest vegetation plays a key role in atmospheric Hg transfer to soil horizons. This study assessed variations in total Hg contents (Hg_T) and accumulation (Hg_Res) in the soil organic horizons of a forest area in NE Portugal, where post-wildfire afforestation led to the substitution of the native deciduous species (Quercus pyrenaica) by fast-growing coniferous species (Pseudotsuga menziesii and Pinus nigra). The study also evaluated, for each species, the links between Hg contents and other biophilic elements of soil organic matter (C, N, S) present in organic subhorizons (OL, OF, OH). Mean Hg_T in the organic horizons of the different tree species follow the sequence: P. nigra (88 μg kg^-1) < Q.pyrenaica (101 μg kg^-1) <P. menziesii (141 μg kg^-1). The highest Hg_Res for the entire organic horizon was found under P. menziesii (471 μg m^-2), followed by P. nigra (253 μg m^-2) and Q. pyrenaica (189 μg m^-2). Among the organic subhorizons, values of Hg_T and Hg_Res follow the sequence OL < OF < OH, which is consistent with the degree of organic matter humification. Indeed, Hg_T and Hg_Res correlated significantly with the C/N and C/S ratios for all species and organic subhorizons, suggesting that the quality of organic matter may influence strongly the Hg fate in these forest soils. Soils from P. menziesii plots have shown an Hg_Res 2.5 times higher than in plots dominated by the native Q. pyrenaica. Hg accumulation in the organic horizons, promoted in the coniferous species, may increase the risk of Hg mobilization due to wildfires and forest management practices. Therefore, forest management plans should select cautiously the tree species for afforestation in order to minimize adverse environmental effects caused by changes in the biogeochemical cycle of contaminants such as Hg.

Relevance of sorption in bio-reduction of amoxicillin taking place in forest and crop soils

The fate of antibiotics reaching soils is a matter of concern, given its potential repercussions on public health and the environment. In this work, the potential bio-reduction of the antibiotic amoxicillin (AMX), affected by sorption and desorption, is studied for 17 soils with clearly different characteristics. To carry out these studies, batch-type tests were performed, adding increasing concentrations of AMX (0, 2.5, 5, 10, 20, 30, 40, and 50 μmol L^-1) to the soils. For the highest concentration added (50 μmol L^-1), the adsorption values for forest soils ranged from 90.97 to 102.54 μmol kg^-1 (74.21-82.41% of the amounts of antibiotic added), while the range was 69.96-94.87 μmol kg^-1 (68.31-92.56%) for maize soils, and 52.72-85.40 μmol kg^-1 (50.96-82.55%) for vineyard soils. When comparing the results for all soils, the highest adsorption corresponded to those more acidic and with high organic matter and non-crystalline minerals contents. The best adjustment to adsorption models corresponded to Freundlich's. AMX desorption was generally <10%; specifically, the maximum was 6.5% in forest soils, and 16.9% in agricultural soils. These results can be considered relevant since they cover agricultural and forest soils with a wide range of pH and organic matter contents, for an antibiotic that, reaching the environment as a contaminant, can pose a potential danger to human and environmental health.

Amoxicillin Retention/Release in Agricultural Soils Amended with Different Bio-Adsorbent Materials

The antibiotic amoxicillin (AMX) may reach soils and other environmental compartments as a pollutant, with potential to affect human and environmental health. To solve/minimize these hazards, it would be clearly interesting to develop effective and low-cost methods allowing the retention/removal of this compound. With these aspects in mind, this work focuses on studying the adsorption/desorption of AMX in different agricultural soils, with and without the amendment of three bio-adsorbents, specifically, pine bark, wood ash and mussel shell. For performing the research, batch-type experiments were carried out, adding increasing concentrations of the antibiotic to soil samples with and without the amendment of these three bio-adsorbents. The results showed that the amendments increased AMX adsorption, with pine bark being the most effective. Among the adsorption models that were tested, the Freundlich equation was the one showing the best fit to the empirical adsorption results. Regarding the desorption values, there was a decrease affecting the soils to which the bio-adsorbents were added, with overall desorption not exceeding 6% in any case. In general, the results indicate that the bio-adsorbents under study contributed to retaining AMX in the soils in which they were applied, and therefore reduced the risk of contamination by this antibiotic, which can be considered useful and relevant to protect environmental quality and public health.

Time-course evolution of bacterial community tolerance to tetracycline antibiotics in agricultural soils: A laboratory experiment

The presence of antibiotics in soils may increase the selection pressure on soil bacterial communities and cause tolerance to these pollutants. The temporal evolution of bacterial community tolerance to different concentrations of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) was evaluated in two soils. The results showed an increase of soil bacterial community tolerance to TC, CTC and OTC only in samples polluted with the highest antibiotic concentrations tested (2000 mg kg^-1). The magnitude of those increases was higher in the soil with the lower organic carbon content (1.6%) than in the soil with an organic carbon content reaching 3.4%. In the soil with low organic carbon content, the time-course evolution showed a maximum increase in the tolerance of bacterial communities to tetracycline antibiotics between 45 and 100 incubation days, while for longer incubation times (360 days) the tolerance decreased. In the soil with high organic carbon content, a similar behavior was found for OTC. However, for CTC and TC, slightly increases and decreases (respectively) were found in the bacterial community tolerance at intermediate incubation times, followed by values close to zero for TC after 360 days of incubation, while for CTC they remained higher than in the control. In conclusion, soil pollution due to tetracyclines may cause bacterial community tolerance to these antibiotics when present at high concentrations. In addition, the risk is higher in soils with low organic matter content, and it decreases with time.

Sulfadiazine removal using green zero-valent iron nanoparticles: A low-cost and eco-friendly alternative technology for water remediation

In this work, the effectiveness of green zero-valent iron nanoparticles (gnZVIs) for the removal of the antibiotic sulfadiazine (SDZ) from water via adsorption and reduction was tested. Additionally, the effectiveness of this material as a catalyst for the Fenton and photo-Fenton processes was also investigated. This represents the first study concerning the use of gnZVIs for the degradation of a sulfonamide antibiotic. The results obtained indicate that gnZVIs were able to remove up to 58% of SDZ via adsorption and up to 69% via adsorption plus reduction using a SDZ/Fe³⁺ molar ratio of 1:61.6. Furthermore, gnZVIs showed strong effectiveness as a catalyst for the Fenton and photo-Fenton reactions, with complete SDZ removal in 8 h and 5 min, respectively, using a SDZ/Fe³⁺/H₂O₂ molar ratio of 1:38.4:38.4. These results demonstrate that the use of gnZVIs constitutes an attractive and potential alternative technology for water remediation, reducing environmental impact and operational costs.

How to study SARS-CoV-2 in soils?

Wastewater based epidemiology is increasingly being considered as a potentially useful tool for early warning about eventual new COVID-19 outbreaks. In addition, some authors are investigating on the detection and quantification of SARS-CoV-2 in sewage sludge. However, no paper has been published up to date indicating how this virus could be quantified in soil samples. In view of that, we review available data searching for methodological approaches that could guide on the quantification of SARS-CoV-2 (and even other pathogenic microorganisms) in soils.

SARS-CoV-2 and other main pathogenic microorganisms in the environment: Situation in Galicia and Spain

In the context of the current COVID-19 pandemic, and mostly taking a broad perspective, it is clearly relevant to study environmental factors that could affect eventual future outbreaks due to coronaviruses and/or other pathogenic microorganisms. In view of that, the authors of this manuscript review the situation of SARS-CoV-2 and other main pathogenic microorganisms in the environment, focusing on Galicia and Spain. Overall, in addition to showing local data, it is put in evidence that, summed to all efforts being carried out to treat/control this and any other eventual future epidemic diseases, both at local and global levels, a deep attention should be paid to ecological/environmental aspects that have effects on the planet, its ecosystems and their relations/associations with the probability of spreading of eventual future pandemics.

Environmental relevance of adsorption of doxycycline, enrofloxacin, and sulfamethoxypyridazine before and after the removal of organic matter from soils

In this work batch-type experiments were used to study the adsorption of the antibiotics doxycycline (DC), enrofloxacin (ENR), and sulfamethoxypyridazine (SMP) in cultivation soils, before and after the removal of soil organic matter. Organic matter removal by calcination resulted not only in C and N removal, but also in increased soil pH, exchangeable basic cations and surface area values. The results indicate a very different behavior depending on the type of antibiotic, showing the adsorption sequence DC > ENR > SMP. Specifically, DC adsorption was very high in untreated soil samples (with organic matter), and was still high (although decreased) after the removal of soil organic matter. Furthermore, the adsorption behavior of DC was clearly dependent on the pH of the medium. Regarding ENR, it also showed high adsorption, although to a lesser extent than DC. However, when soil organic matter was removed, ENR adsorption significantly decreased in all soil samples. As regards SMP, it was adsorbed to a much lesser extent, and the removal of soil organic matter caused an additional drastic decrease in adsorption, reaching negligible values in some samples. Desorption followed the reverse sequence of adsorption, specifically in the order DC < ENR < SMP. In the case of DC, desorption was negligible, both in samples with and without organic matter, while for ENR and SMP, desorption clearly increased for soil samples where organic matter was removed. These results may be of relevance as regards environmental quality and public health, especially to facilitate a correct use of soils and organic amendments in areas that receive the application of substances containing the investigated antibiotics.

Photodegradation of Ciprofloxacin, Clarithromycin and Trimethoprim: Influence of pH and Humic Acids

In view of the rising relevance of emerging pollutants in the environment, this work studies the photodegradation of three antibiotics, evaluating the effects of the pH of the medium and the concentration of dissolved organic matter. Simulated light (with a spectrum similar to that of natural sunlight) was applied to the antibiotics Ciprofloxacin (Cip), Clarithromycin (Cla) and Trimethoprim (Tri), at three different pH, and in the presence of different concentrations of humic acids. The sensitivity to light followed the sequence: Cip > Cla > Tri, which was inverse for the half-life (Tri > Cla > Cip). As the pH increased, the half-life generally decreased, except for Cla. Regarding the kinetic constant k, in the case of Cip and Tri it increased with the rise of pH, while decreased for Cla. The results corresponding to total organic carbon (TOC) indicate that the complete mineralization of the antibiotics was not achieved. The effect of humic acids was not marked, slightly increasing the degradation of Cip, and slightly decreasing it for Tri, while no effect was detected for Cla. These results may be relevant in terms of understanding the evolution of these antibiotics, especially when they reach different environmental compartments and receive sunlight radiation.

Comparing the effect of Cu-based fungicides and pure Cu salts on microbial biomass, microbial community structure and bacterial community tolerance to Cu

The effect of Cu on three different microbial endpoints was studied using different Cu sources, in order to check the usefulness of pure Cu salts to estimate the toxicity of commercial Cu fungicides on soil microbes. Cu additions caused similar dose-response curves of substrate induced respiration (SIR) decreases regardless of Cu source, i.e. the use of pure Cu salts to estimate the effect of Cu fungicides on microbial biomass using SIR may be useful. Phospholipid fatty acid (PLFA) analysis showed that the Cu source was more important for the microbial community structure than Cu concentration. Thus, the use of Cu salts to infer the effects of Cu fungicides on microbial community structure using PLFA analysis is not recommended, since effects of Cu concentration will be confounded with Cu source. Analyzing pollution induced community tolerance (PICT) to Cu showed that the use of pure Cu salts may overestimate Cu effects if Cu salt additions modified the soil pH. The highest doses of Cu salts increased bacterial community tolerance to Cu between 300 and 600 times, while commercial Cu fungicide increases were between 20 and 160 times. Therefore, the use of pure Cu salts to estimate the Cu fungicides effects on soil microbes is not recommended for PLFAs analyses, not suitable for PICT at high Cu concentrations, while useful for SIR.

Sulfadiazine, sulfamethazine and sulfachloropyridazine removal using three different porous materials: Pine bark, "oak ash" and mussel shell

This work focuses on studying the efficacy of three different by-products to adsorb three antibiotics (sulfadiazine, SDZ; sulfamethazine, SMT; sulfachloropyridazine, SCP). These antibiotics can be considered pollutants of the environment when they reach water, as well as in cases where they are spread on soils through irrigation or contained in sewage sludge or livestock manure. In this study, batch-type adsorption/desorption experiments were performed for each of the three sulfonamides, adding 7 different concentrations of the antibiotics, going from 1 to 50 μmol L^-1, and with contact time of 24 h. The results indicate that pine bark is the most efficient bioadsorbent among those studied, as it adsorbs up to 95% of the antibiotics added, while desorption is always less than 11%. However, for "oak ash" and mussel shell the adsorption is always lower than 45 and 15%, respectively, and desorption is high, reaching up to 49% from "oak ash" and up to 81% from mussel shell. Adsorption data showed good fitting to the Linear and Freundlich models, with R² values between 0.98 and 1.00 in both cases. K_d and K_F adsorption parameters showed similar values for the same sorbent materials but were much higher for pine bark than for the other two bioadsorbents. The Freundlich's n parameter showed values in the range 0.81-1.28. The highest K_F values (and therefore the highest adsorption capacities) were obtained for the antibiotic SCP in pine bark. Pine bark showed the highest capacity to adsorb each of the antibiotics, increasing as a function of the concentration added. When the concentration of sulfonamide added was 50 μM, the amounts adsorbed were 780 μmol kg^-1 for SDZ, 890 μmol kg^-1 for SMT, and 870 μmol kg^-1 for SCP. "Oak ash" and mussel shell have low adsorption capacity for all three sulfonamides, showing values always lower than 150 μmol kg^-1 (oak ash) and 20 μmol kg^-1 (mussel shell) when a concentration of 50 μmol L^-1 of antibiotic is added. The results of this study could aid to make an appropriate management of the by-products studied, in order to facilitate their valorization and recycling in the treatment of environmental compartments polluted with sulfonamide antibiotics.

Use of waste materials to prevent tetracycline antibiotics toxicity on the growth of soil bacterial communities

The increase of concentrations of tetracycline antibiotics in agricultural soils worldwide is of special concern, due to its potential toxic effects on soil bacterial communities. In the present work, the reuse of two waste/by-product materials as soil amendments was tested as a preventive practice for reducing tetracycline antibiotics toxicity in soils. Pine bark (PB), with high percentage of organic carbon, and crushed mussel shell (CMS), a frequent natural liming material, were added to 4 soils in doses 0, 6, 12 and 48 g of by-product per kg^-1 of soil (dry weight) of each one (separately). The soils and soil-waste mixtures were then spiked with tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC). After one day of incubation, the bacterial growth was estimated in soils and soil-mixtures using the leucine incorporation technique. The addition of PB to the soils showed two different behaviors, depending on the antibiotics. The toxicity of TC and OTC decreased with the addition of PB (toxicities going from 6 to 25% and from 5 to 36%, respectively). However, CTC toxicity did not change, or even increased in response to the PB amendment. Regarding soil amendment with CMS, it was not effective to prevent the toxicity of any of the three antibiotics studied.

Soil properties influencing Hg vertical pattern in temperate forest podzols

Mercury content of twelve podzols from NW Spain was studied to elucidate the main soil properties involved in the Hg accumulation of these soils. The highest average Hg concentrations (Hg_T) were found in the Bh and Bs horizons (64 and 105 μg kg^-1), whereas the lowest occurred in the E horizons (15 μg kg^-1). Moderate values of Hg_T were obtained for the A and C horizons (38 and 52 μg kg^-1). The Hg enrichment factors revealed that the predominant origin of Hg in these soils is the atmosphere instead of the parent material. As it was shown by the PCA performed (which explained 82% of the variance of the data), the main soil characteristics involved in the pedogenetic processes of the studied podzols are organic matter and Al and Fe compounds. The stepwise linear regressions made described between 54% and 84% of the predicted Hg depending on the soil horizon. Besides a complex ensemble of biogeochemical reactions involved in the balance between input and outputs of Hg, the most influencing variable in the A horizons was organic C, moderate stability Al-humus complexes in the E horizons, Fe-humus complexes and pH_w in the Bh horizons, Al-humus compounds in the Bs horizons and crystalline Al and Fe compounds in the C horizons. Therefore, Hg is mobilized from the A and E horizons bound to dissolved organic matter and precipitated in the illuvial horizons due to the saturation of the organic matter with metals. The immobilization of Hg in the subsuperficial horizons of podzols leads to different environmental benefits derived from the removal of Hg from the A horizons, more exposed to climate-induced and land use/cover changes that could potentially modify the dynamics of Hg in those superficial horizons.

SARS-CoV-2 and other pathogens could be determined in liquid samples from soils

In the current COVID-19 pandemic, SARS-CoV-2 has been quantified in wastewater in various countries, and wastewater based epidemiology has been proposed as a potential early warning tool for new outbreaks. However, even taking into account that poorly treated wastewater and sewage sludge may be spread on soils, there is no published paper dealing with the quantification of the virus in soil-related liquid samples, as could be runoff, leachates, or soil solution. To fill this gap, the authors of this piece propose reflections on the development of a methodological approach for the quantification of SARS-CoV-2 (and eventually other pathogens) in soil-related liquid samples.

The Toxicity Exerted by the Antibiotic Sulfadiazine on the Growth of Soil Bacterial Communities May Increase over Time

The toxicity exerted by the antibiotic sulfadiazine on the growth of soil bacterial communities was studied in two agricultural soils for a period of 100 days. In the short-term (2 days of incubation), the effect of sulfadiazine on bacterial growth was low (no inhibition or inhibition <32% for a dose of 2000 mg·kg-1). However, sulfadiazine toxicity increased with time, achieving values of 40% inhibition, affecting bacterial growth in both soils after 100 days of incubation. These results, which were here observed for the first time for any antibiotic in soil samples, suggest that long-term experiments would be required for performing an adequate antibiotics risk assessment, as short-term experiments may underestimate toxicity effects.

Single and simultaneous adsorption of three sulfonamides in agricultural soils: Effects of pH and organic matter content

Veterinary antibiotics reaching the environment have become a matter of global concern, since they can cause serious negative impacts on human and ecological health. Therefore, a deep understanding of their behavior and fate once they reach the soil environment is of utmost importance to design and implement appropriate measures that could reduce their potential risks. With this aim, batch-type experiments were carried out to study competitive adsorption and desorption for three sulfonamide antibiotics (sulfadiazine -SDZ-, sulfamethazine -SMT-, and sulfachloropyridazine -SCP-) in six crop soils presenting different characteristics. The results obtained showed that sulfonamides have a low retention in soils, with average adsorption percentages of 40% for SDZ, 44% for SMT and 54% for SCP, and with desorption percentages up to 36% for SDZ and SCP and up to 29% for SMT. The retention of sulfonamides was strongly influenced by the soil organic carbon content (SOC), with higher adsorption and less desorption associated to higher SOC contents. In addition, the hydrophobicity of sulfonamides also had an influence, as higher hydrophobicity resulted in higher affinity for soils, showing the affinity sequences: SDZ ~ SMT <SCP in acid soils, and SDZ ~ SCP <SMT in neutral soils. The results obtained in the ternary systems were very similar to those found in simple systems, indicating the absence of substantial competition for adsorption sites among the three sulfonamides. Despite the low competition among them, these antibiotics have high mobility in soils and, therefore, they imply a significant risk of contamination of water bodies, as well as of entering the food chain, generating serious hazards for human and environmental health. Therefore, fertilization of soils with sulfonamide polluted manures should be controlled, implementing new measurements for the pretreatment of manures before their application, thus contributing to a reduction of potential risks.

Use of biomass ash to reduce toxicity affecting soil bacterial community growth due to tetracycline antibiotics

Tetracycline antibiotics (TA) used in veterinary medicine reach terrestrial ecosystems mostly via the repeated applications of animal manures and slurries on agricultural soils, where they may cause toxic effects on bacterial communities. In the current work, we studied the efficacy of adding doses of 0, 6, 24 and 48 g kg^-1 of biomass ash (BA) to four different soils to reduce potential negative effects of tetracycline antibiotics. Specifically, soil samples were polluted with different concentrations of tetracycline, oxytetracycline or chlortetracycline, and the bacterial community growth was estimated using the ³H leucine incorporation technique. Soil amendment with BA increased soil pH (1.3-4.8 units), total carbon (0.7-5.8 g kg^-1) and Fe and Al oxides concentrations (0.25-3.98 g kg^-1), as well as bacterial activity (1-9 times compared to the control). In addition, BA amendment at high doses (24 or 48 g kg^-1) resulted in a similar toxicity decrease for the three antibiotics, but with variations among soils. The reductions in antibiotics toxicity were very variable, ranging between 5% and 100% (total recovery). In view of that, the spreading of BA could be interesting as management practice to reduce risks of soil pollution and subsequent toxicity on bacterial communities due to tetracycline antibiotics.

Litterfall Hg deposition to an oak forest soil from southwestern Europe

Litterfall constitutes one of the main vectors for mercury (Hg) transfer to forested ecosystems, so we studied the deposition of Hg through senescent vegetation (oak leaves, twigs and miscellaneous) in a deciduous forest plot of Southwest Europe dominated by Quercus robur in 2015 and 2016. Total Hg concentrations increased in the following order: bole wood (1.4 μg kg^-1) < bark (8.3 μg kg^-1) < twigs (12.2 μg kg^-1) < miscellaneous (36.0 μg kg^-1) < oak leaves (39.3 μg kg^-1) < mineral soil (42.4 μg kg^-1) < Oi horizons (48.7 μg kg^-1) < Oe + Oa horizons (71.6 μg kg^-1). Mercury accumulation rates in oak leaves during the growing season were 0.15-0.18 μg kg^-1 day^-1. Mercury deposition fluxes were 26 and 21 μg m^-2 yr^-1 for 2015 and 2016, respectively, with oak leaves being the fraction that contributed the most. Mercury determination in litterfall sorted biomass fractions lead to a more accurate estimation of the total annual Hg deposition fluxes through litterfall. Higher Hg content was obtained for organic horizons (average of 60.2 μg kg^-1) than for mineral soil (mean of 42.4 μg kg^-1), but the soil Hg pool was higher in the latter. The results confirmed the necessity of taking into account the Hg pool in the deeper mineral soil layers as they accumulate substantial quantities of Hg associated to organic C and Al compounds, preventing its mobilization to other compartments of the terrestrial ecosystems.

Adsorption-desorption of doxycycline in agricultural soils: Batch and stirred-flow-chamber experiments

With the aim of obtaining information about the environmental fate and dynamics of the antibiotic doxycycline (DC) when it reaches soil, adsorption and desorption processes were studied for this compound in 20 agricultural soils, by means of batch-type and stirred-flow-chamber experiments. The results indicate that the studied soils adsorbed high amounts of DC, with adsorption percentages >91% in all cases. In addition, adsorption results were satisfactorily modeled, with good fittings to the Langmuir and Freundlich equations, with the values for Langmuir's maximum adsorption capacity (q_max) varying between 14,692 and 26,141 μmol kg^-1 (average 17,816), and between 1,906 and 13,120 Lⁿ μmol^1-n kg^-1 (average 6,969) for the Freundlich affinity coefficient, which are very high. The soil variables most related to the adsorption of the antibiotic were linked to organic matter (specifically, soil organic carbon-SOC- and soil nitrogen -N- contents), and to the clay fraction, as well as to cation exchange capacity, being the soils with a greater content in these variables those that presented a greater adsorption. FTIR results shown that DC adsorption mechanisms were based on interactions such as hydrogen bonds and π-π interactions between the antibiotic and soils. Desorption was very low, reaching values between 1 and 2% in batch experiments, and between 5 and 15% in stirred flow chamber experiments, which indicates a strong hysteresis affecting adsorption and desorption processes. This fact can be considered positively, as these soils could retain DC very strongly, thus reducing risks to human and ecological health.

Estimation of adsorption/desorption Freundlich's affinity coefficients for oxytetracycline and chlortetracycline from soil properties: Experimental data and pedotransfer functions

Tetracycline antibiotics spread in the environment constitute a real threat, causing risks that should be controlled. Retention/release of these compounds after interacting with soil components are the main process governing their entry into water bodies, plant uptake, and availability for soil microorganisms. In this work, batch-type experiments were performed to study adsorption/desorption of oxytetracycline (OTC) and chlortetracycline (CTC) in 63 crop soils. The Freundlich model satisfactory described adsorption curves, showing strong affinity of both antibiotics to soils, with adsorption coefficient (K_F(ads)) values between 1015 and 9733 Lⁿ μmol^1-n kg^-1 for OTC, and between 1099 and 11344 Lⁿ μmol^1-n kg^-1 for CTC. Desorption percentages were always lower than 10%, indicating that adsorption is highly irreversible. Furthermore, the desorption coefficient (K_F(des)) correlated positive and significantly with K_F(ads), showing that those soils characterized by higher adsorption were also those showing less desorption. Soil organic carbon (SOC) was the soil characteristic that most explained the variance of K_F, both for adsorption and desorption, which caused that soils with higher SOC scores showed higher adsorption and lower desorption for both antibiotics. Pedotransfer functions were developed for OTC and CTC, and resulted effective to satisfactory predict K_F(ads) and K_F(des) values. These equations would facilitate an easy identification of soils vulnerable to antibiotics pollution, which would allow to program appropriate management practices to decrease undesirable effects on the environment and on public health.

Effects of pine bark amendment on the transport of sulfonamide antibiotics in soils

In the present work, laboratory column experiments were carried out to study the effect of pine bark amendment (at doses of 0, 12, 48 and 96 Mg ha^-1) on the transport of three sulfonamide antibiotics (sulfadiazine -SDZ-, sulfamethazine -SMT-, and sulfachloropyridazine -SCP-) through two crop soils. All three sulfonamides showed high mobility in the unamend soils, with absence of retention in most cases. However, some differences were detected regarding the degree of interactions between sulfonamides and soils, being higher for soil 1, which was attributed to its higher organic carbon content. For both soils, interactions with the antibiotics studied followed the sequence SDZ < SMT < SCP, indicating an increase as a function of the hydrophobicity of sulfonamides. Pine bark amendment significantly increased the retention of the three sulfonamides in both soils. Specifically, in the case of soil 1, the incorporation of the highest dose of pine bark (96 Mg ha^-1) caused that retention increased from 0% to 70.3% for SDZ, from 2.7% to 71.3% for SMT, and from 0% to 85.4% for SCP. This effect of pine bark is mainly attributed to its high organic carbon content (48.6%), including substances with potential to interact and retain antibiotics, as well as to its acidic pH (4.5). Therefore, pine bark amendment would be an effective alternative to reduce the transport of sulfonamides in soils and, thus, decrease risks of passing to other environmental compartments, as well as harmful effects on the environment and public health.

Adsorption/desorption of three tetracycline antibiotics on different soils in binary competitive systems

Taking into account environmental and public health issues due to emerging pollutants, and specifically to antibiotics spread into environmental compartments, this work focused on the competition among three tetracycline antibiotics (tetracycline, CT; oxytetracycline, OTC; and chlortetracycline, CTC) for adsorption sites in six different soils. Batch-type adsorption/desorption tests were carried out, with 24 h as contact time. The six soils were from two different farming areas, and were selected according to pH values and organic matter contents. Binary systems (pairs of antibiotics present simultaneously) were used to study competition, setting the dose of one antibiotic at 200 μmol L^-1, and varying the concentration of another from 50 to 600 μmol L^-1. In the case of the concentration of 200 μmol L^-1, the results of the binary systems were also compared with those obtained in simple and ternary systems. The results showed that those soils with the highest organic matter content (soils 50AL and 71S) adsorbed 100% of the three antibiotics, with desorption being <10% in all cases. The other four soils showed some degree of competition for adsorption sites in binary systems, with adsorption decreasing between 25 and 47% compared to simple systems, and with desorption increasing, especially in soils with higher pH and less organic matter. This competition was even more pronounced in ternary systems, affecting to these same soils, while the effects were very scarce in soils with higher organic matter content. The results indicate that most of the studied soils have high adsorption capacity for tetracycline antibiotics, retaining them with high energy even in the case of multiple systems. It was also shown that hysteresis affected adsorption/desorption processes. These results have relevance at environmental and social levels, given the growing concern regarding antibiotics pollution, and the need of promoting their retention and inactivation when spread in environmental compartments.

Influence of mussel shell, oak ash and pine bark on the adsorption and desorption of sulfonamides in agricultural soils

Taking into account the high mobility and environmental risks due to sulfonamide antibiotics as emerging pollutants, batch-type experiments were performed to study adsorption/desorption of three sulfonamides (sulfadiazine -SDZ-, sulfamethazine -SMT- and sulfachloropyridazine -SCP-) in three agricultural soils. The study was carried out both for un-amended and amended soil samples, using different doses (0, 12, 24 and 48 Mg ha^-1) of three different by-products (mussel shell, oak ash and pine bark). Adsorption on un-amended soils was rather low, with percentages between 11 and 45% for SDZ, 20-64% for SMT, and 19-65% for SCP. Both the Linear and Freundlich models fitted well to adsorption curves. In the case of un-amended soils, and regarding the Linear model, the values of the coefficient of distribution (K_d, expressed in L kg^-1) were between 0.6 and 1.3 for SDZ, between 0.7 and 1.1 for SMT, and between 0.6 and 2.6 for SCP. As regards the Freundlich model, the values of the adsorption constant (K_F, expressed in L^1/n μmol^1-1/n kg^-1), were in the range 0.4-1.9 for SDZ, 0.9-2.9 for SMT, and 1.2-3.8 for SCP. Simultaneously, desorption percentages were high, reaching 13.7-47.7% for SDZ, 12.6-35.1% for SMT, and 13.7-34.3% for SCP, when the highest initial antibiotic concentration (50 μmol L^-1) was added, thus indicating low retention and high mobility for these compounds in soils. Mussel shell and oak ash amendments did not increase retention of any of the three sulfonamides. However, the incorporation of pine bark resulted in an increase in the adsorption and decrease in desorption for all three antibiotics. Specifically, for soils amended with pine bark at 48 Mg ha^-1, K_d values (expressed in L kg^-1) were between 2.1 and 2.9 for SDZ, between 3.4 and 3.6 for SMT, and between 2.5 and 8.2 for SCP. Regarding K_F (expressed in L^1/n μmol^1-1/n kg^-1), its values ranged from 5.6 to 6.3 for SDZ, 6.2-8.8 for SMT, and 5.3-7.1 for SCP. These scores were clearly higher than those of un-amended soils, and pine bark amendment also resulted in lower desorption percentages, ranging 8.7-11.4% for SDZ, 4.0-10.7% for SMT, and 6.5-16.9% for SCP. This positive effect on the retention of sulfonamides due to pine bark can be attributed to its high organic carbon content (48.6%), as well as to its acidic pH_w (4.0). Therefore, pine bark amendment can be considered an effective alternative to increase the retention of sulfonamides in soils, thus reducing their bioavailability and transport to other environmental compartments, and subsequent risks of negative impacts on human and environmental health.

Modelling Hg mobility in podzols: Role of soil components and environmental implications

A high-resolution soil sampling has been applied to two forest podzols (ACB-I and ACB-II) from SW Europe in order to investigate the soil components and processes influencing the content, accumulation and vertical distribution of Hg. Total Hg contents (THg) were 28.0 and 23.6 μg kg^-1 in A horizons of ACB-I and ACB-II, then they strongly decreased in the E horizons and peaked in the Bhs horizons of both soils (55.3 and 63.0 μg kg^-1). THg decreased again in BwC horizons to 17.0 and 39.8 μg kg^-1. The Bhs horizons accounted for 46 and 38% of the total Hg stored (ACB-I and ACB-II, respectively). Principal component analysis (PCA) and principal components regression (PCR), i.e. using the extracted components as predictors, allowed to distinguish the soil components that accounted for Hg accumulation in each horizon. The obtained model accurately predicted accumulated Hg (R² = 0.845) through four principal components (PCs). In A horizons, Hg distribution was controlled by fresh soil organic matter (PC4), whereas in E horizons the negative values of all PCs were consistent with the absence of components able to retain Hg and the corresponding very low THg concentrations. Maximum THg contents in Bhs horizons coincided with the highest peaks of reactive Fe and Al compounds (PC1 and PC2) and secondary crystalline minerals (PC3) in both soils. The THg distribution in the deepest horizons (Bw and BwC) seemed to be influenced by other pedogenetic processes than those operating in the upper part of the profile (A, E and Bhs horizons). Our findings confirm the importance of soils in the global Hg cycling, as they exhibit significant Hg pools in horizons below the uppermost O and A horizons, preventing its mobilization to other environmental compartments.

Adsorption/desorption of sulfamethoxypyridazine and enrofloxacin in agricultural soils

Adsorption and desorption processes were studied for the antibiotics sulfamethoxypyridazine (SMP) and enrofloxacin (ENR) in 20 agricultural soils devoted to wheat-potato and vine cultivation. Batch experiments were used to conduct kinetic studies, as well as to evaluate adsorption and desorption for different concentrations of antibiotics. The results indicated that adsorption curves were linear for SMP, while presented a certain curvature in the case of ENR. The adsorption of both antibiotics was fitted to a linear equation and to the Freundlich model. In the case of the linear equation, the values of the distribution coefficient K_d were lower for SMP (0.9-26.0 L kg^-1) than for ENR (121-2345 L kg^-1). In the Freundlich model, the values of the adsorption constant K_F ranged between 1.7 and 34.0 Lⁿ μmol^1-n kg^-1 for SMP, and between 829 and 3019 Lⁿ μmol^1-n kg^-1 for ENR. A multiple regression analysis showed that, in the case of SMP, 78% of the variance of the adsorption parameter K_d was explained by soil organic carbon (SOC) and exchangeable magnesium (Mg_e) contents, while for ENR no significant relation was found. In addition, for SMP, 66% of the variance of K_F was explained by SOC, and for ENR 45% of the variability of K_F was explained by nitrogen content. Desorption rates were higher for SMP (reaching up to 24%) than for ENR (which reached up to 7%). Desorption percentages showed a potential relation with the adsorption parameter K_d for both SMP and ENR. These results could be useful to elucidate the evolution and dynamics of these emerging pollutants in soils and other environmental compartments, which could be of aid in controlling public health risks associated to them.

Comparison of Cu salts and commercial Cu based fungicides on toxicity towards microorganisms in soil

Microbial responses to Cu pollution as a function of Cu sources (Cu salts and commercial Cu fungicides) were assessed in a soil using basal soil respiration, and bacterial and fungal community growth, as endpoints. The soil was amended with different concentrations (0-32 mmol Cu kg^-1) of Cu nitrate, Cu sulfate, Bordeaux mixture and 3 types of Cu oxychloride. Cu salts decreased soil pH, while this was not found with the other Cu sources. This difference in soil pH effects caused differences in the respiration, bacterial growth and fungal growth response. Basal soil respiration was negatively affected by Cu addition when the soil was spiked with Cu salts, but almost unaffected by commercial Cu fungicides. Bacterial growth was significantly and negatively affected by Cu addition for all the Cu sources, but Cu toxicity was higher for Cu salts than for commercial Cu fungicides. Fungal growth response was also different for Cu salts and commercial Cu fungicides, but only in the long-term. High Cu amendments using Cu salts stimulated fungal growth, whereas for commercial Cu fungicides, these concentrations inhibited fungal growth. Thus, the use of products similar to those used in commercial fungicides is a recommended practice for Cu risk assessments in soil.

Competitive adsorption/desorption of tetracycline, oxytetracycline and chlortetracycline on pine bark, oak ash and mussel shell

We studied competitive adsorption for the tetracycline antibiotics (TCs) tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) on three bio-adsorbents (mussel shell, oak wood ash, and pine bark). The results were compared for individual systems (with antibiotics added separately) and ternary systems (with all three antibiotics added simultaneously). In all cases batch-type experiments were carried out, with 24 h of contact time. In the individual systems, concentrations of 200 μmol L^-1 were used for each of the three antibiotics, separately. In the ternary system, all three TCs were added simultaneously, using the following total concentrations: 50, 100, 200, 400, 600 μmol L^-1, each antibiotic being 1/3 of the total. Taking into account that ionic strength of a solution is related to a measure of the concentration of ions in that solution, the use of individual and ternary systems allows to compare, for each antibiotic, systems having equal concentrations and similar ionic strength (concentrations of 200 μmol L^-1), and systems having different concentrations and ionic strength (200 μmol L^-1 in the individual systems, and 600 μmol L^-1 in the ternary systems, resulting from the sum of 200 μmol L^-1 corresponding to each of the three antibiotics). Adsorption/desorption results indicated that these processes were in all cases closely related to pH values, and to carbon and non-crystalline minerals contents in the bio-adsorbents. Both oak ash and pine bark adsorbed close to 100% of TCs in individual and ternary systems, with desorption <4% for oak ash, and <12% for pine bark. However, mussel shell gave clearly poorer results, only relatively acceptable for CTC, with adsorption <56% and desorption even >30% for TC and OTC. In view of the results, oak ash and pine bark can be recommended as effective bio-adsorbents for the three TCs studied, and could be useful to retain/inactive them in wastes, and soil or liquid media receiving these emerging pollutants, thus reducing risks of damage for public health and the environment.

Pedotransfer functions to estimate the adsorption and desorption of sulfadiazine in agricultural soils

Batch-type experiments were used to study adsorption-desorption of sulfadiazine in 50 crop soils exposed to antibiotic pollution due to the spreading of animal manure or slurry. Adsorption and desorption curves were linear, and were satisfactorily described using the linear and Freundlich equations. The Freundlich adsorption constant (K_F(ad)) showed low values (between 0.4 and 9.0 L^1/n μmol^1-1/n kg^-1), which were similar to those of the adsorption constant for the linear model (K_d(ad), between 0.3 and 12.0 L kg^-1). Furthermore, the desorption constant for the linear model (K_d(des)) showed higher values than those of K_d(ad), ranging between 1.6 and 29.3 L kg^-1, while the values of the Freundlich desorption constant (K_F(des)) ranged from 0.10 to 36.8 L^1/n μmol^1-1/n kg^-1. The percentages of adsorption were very variable, ranging from 10 to 87%. The soil characteristics that most influenced adsorption-desorption were those related to soil organic matter (organic carbon and nitrogen contents), as well as the effective cation exchange capacity, and pH. In addition, statistically robust pedotransfer functions were obtained, allowing prediction of adsorption-desorption behavior for sulfadiazine from readily determinable soil parameters, such as pH or organic carbon content.

Competitive adsorption of tetracycline, oxytetracycline and chlortetracycline on soils with different pH value and organic matter content

Antibiotics spread into the environment can cause soil and water degradation. Specifically, tetracycline antibiotics (TCs) are among those most consumed in veterinary medicine, and near 90% of the doses administered to animals are excreted as original compounds, due to poor absorption. In this study we investigated competitive soil adsorption/desorption for three tetracycline antibiotics (tetracycline: TC, oxytetracycline: OTC, and chlortetracycline: CTC), usually spread on soils by slurry fertilization, affecting to soil degradation due to chemical pollution. The study was carried out on six soils selected according to their pH values (4.49-7.06), and organic matter contents (1.07-10.92%). The competitive experiments were performed in ternary systems (adding all three TCs simultaneously, using five equal and increasing concentrations, from 17 to 200 μmol L^-1). The results were compared with those obtained in simple systems (adding individual antibiotics separately), for the same final concentration (in this case, 200 μmol L^-1) and for different concentrations (200 μmol L^-1 in the simple systems, versus 600 μmol L^-1 in the ternary systems, resulting from the sum of 200 μmol L^-1 of each of the three antibiotics). In all cases, batch-type adsorption/desorption experiments were carried out, with 24 h as contact time. Those soils with higher organic matter content adsorbed 100% of the TCs, with desorption being always lower than 3%. In soils with less organic matter, adsorption decreased as the dose of added antibiotic increased, due to competition for adsorption sites. CTC was the most retained among the three TCs (up to 20% more than the other when high doses of antibiotic were added). In the simple systems, percentage adsorption was always high (>85%) for the three TCs; however, percentage adsorption decreased in the ternary systems, reaching just 65% and 40% (for equal and different ionic strength, respectively) in soils with low organic matter contents. These results show the environmental and public health relevance of competition among the three TCs. In fact, the highest risk of entering the food chain takes place when these antibiotics are spread together on soils with low organic matter content, especially in the case of TC and CTC, which are the least adsorbed and the most desorbed molecules.

Adsorption/desorption and transport of sulfadiazine, sulfachloropyridazine, and sulfamethazine, in acid agricultural soils

Batch-type experiments were used to study adsorption-desorption of three sulfonamides: sulfadiazine (SDZ) sulfachloropyridazine (SCP), and sulfamethazine (SMT), in five crop soils, whereas laboratory soil column experiments were employed to obtain data on transport processes. Adsorption results were satisfactorily adjusted to Linear and Feundlich equations, with R² values above 0.95. Adsorption followed the sequence SDZ < SMT < SCP, showing higher values for soils with higher levels of organic carbon (OC) content. Conversely, desorption was higher in soils with less OC, and lower in soils with higher OC contents. The temporal moment analysis method gave values for the transport parameters τ and R which were significantly correlated with soil parameters related to organic matter, specifically OC and N concentrations. The higher retention of the three sulfonamides in soils with high organic matter content is a relevant fact, with value when programming management practices in agricultural soils, and specifically in relation to the spreading of animal manures, slurries, or waste containing these emerging pollutants.

Experimental data and model prediction of tetracycline adsorption and desorption in agricultural soils

In this work, tetracycline (TC) adsorption and desorption were studied, and the soil properties that most influenced the process were identified. Batch experiments were carried out on 63 crop soil samples, which showed a wide range of values in their physicochemical characteristics. Adsorption curves fit well to the Freundlich equation, with K_F values varying between 901 and 9202 Lⁿ μmol^1-n kg^-1. K_d values ranged between 53 and 6899 L kg^-1 for an initial concentration (C_o) of 400 μM, whereas the adsorption capacity (q_a) ranged from 8541 to 14,852 μmol kg^-1. TC retention on soils was high, with adsorption values always higher than 58%, and desorption values lower than 9%. Bivariate correlations and multiple linear regressions were performed to identify those soil variables having a greater influence on TC adsorption and desorption. The results indicate that organic carbon, clay, exchangeable aluminum, available phosphorus, effective cation exchange capacity content, and pH are the main characteristics affecting TC adsorption and desorption. The models, developed by means of multiple linear regression, gave satisfactory and robust predictions for TC adsorption and desorption, using easily determinable soil characteristics as input.

Copper and zinc in rhizospheric soil of wild plants growing in long-term acid vineyard soils. Insights on availability and metal remediation

Total and available Cu and Zn levels were assessed in plant biomass, as well as in two rhizosphere fractions (tightly adhering rhizosphere (TAR), and loosely adhering rhizosphere (LAR)), in wild plants species from vineyard soils. Both TAR and LAR fractions were enriched in total Cu and Zn (1.7 and 1.6 times, respectively), and in available Cu and Zn (2.2 and 19.5 times, respectively), with the former being significantly higher for TAR than for LAR fractions. Mean values for total Cu accumulation in root and aerial biomass of the studied wild plants were 84 and 66 mg kg^-1, respectively, being 57 and 79 mg kg^-1 for Zn. No correlations were found among metal contents in plant biomass and available Cu and Zn concentrations in the rhizosphere fractions. Translocation factor (TF) values for Zn (range 1.0-3.5) indicate preferential accumulation in the aerial biomass in all the studied wild plants. On the contrary, TF for Cu shows a greater variability, depending on plant species, and ranging from 0.2 to 5.9. Regarding bioaccumulation factor (BAF), ranges were 0.03-0.27 and 0.13-0.58, for Cu and Zn, respectively. Results suggest that D. sanguinalis, P. hieracioides, S. viridis, and T. barbata could be useful for Cu remediation in the studied soils, by means of phytostabilization processes.

Controlling risks of P water pollution by sorption on soils, pyritic material, granitic material, and different by-products: effects of pH and incubation time

Batch experiments were used to test P sorbent potential of soil samples, pyritic and granitic materials, mussel shell, mussel shell ash, sawdust, and slate waste fines for different pH and incubation times. Maximum P sorption varied in a wide range of pH: < 4 for pyritic material, 4-6 for forest soil, > 5 for slate fines, > 6 for shell ash, and pH 6-8 for mussel shell. P sorption was rapid (< 24 h) for forest soil, shell ash, pyritic material, and fine shell. On the opposite side, it was clearly slower for vineyard soil, granitic material, slate fines, pine sawdust, and coarse shell, with increased P sorption even 1 month later. For any incubation time, P sorption was > 90% in shell ash, whereas forest soil, pyritic material, and fine shell showed sorption rates approaching 100% within 24 h of incubation. These results could be useful to manage and/or recycle the sorbents tested when focusing on P immobilization or removal, in circumstances where pH changes and where contact time may vary from hours to days, thus aiding to diminish P pollution and subsequent eutrophication risks, promoting conservation and sustainability.