Leaching characteristic of toxic trace elements in soils amended by sewage sludge compost: A comparison of field and laboratory investigations

Long-term effect of municipal solid waste compost on the recovery of a potentially toxic element (PTE)-contaminated soil: PTE mobility, distribution and bioaccessibility

Compost from municipal solid waste (MSWC) can represent a resource for the environmental management of soils contaminated with potentially toxic elements (PTEs), since it can reduce their mobility and improve soil fertility. However, the long-term impact of compost on soil recovery has been poorly investigated. To this end, the influence of a MSWC added at different rates (i.e. 1.5, 3.0 and 4.5% w/w) to a multi-PTE-contaminated (e.g. Sb 412 mg kg-1, Pb 2664 mg kg-1 and Zn 7510 mg kg-1) sub-acidic soil (pH 6.4) was evaluated after 6 years since its addition. The MSWC significantly enhanced soil fertility parameters (i.e. total organic carbon, Olsen P and total N) and reduced the PTE labile fractions. The distribution maps of PTEs detected through µXRF analysis revealed the presence of Zn and Pb carbonates in the amended soils, or the formation of complexes between these PTEs and the functional groups of MSWC. A higher oral, inhalation and dermal bioaccessibility of each PTE was detected in the soil fine-grained fractions (< 2 and 2-10 µm) than in coarse particles (10-20 and 20-50 µm). The MSWC amendment generally did not modify the PTE bioaccessibility, while the relative bioaccessibility of cationic PTEs was greater than that of anionic ones (e.g. Cd > Zn > Pb > Sb > As). Pb and Sb showed the highest hazard quotients (e.g. 2.2 and 10 for Sb and Pb, respectively, in children). Overall, the results indicated that the MSWC used can be an effective option for the recovery of PTE-contaminated soils, even in the long term.

Recent progress on emerging technologies for trace elements-contaminated soil remediation

Abiotic stresses from potentially toxic elements (PTEs) have devastating impacts on health and survival of all living organisms, including humans, animals, plants, and microorganisms. Moreover, because of the rapid growing industrial activities together with the natural processes, soil contamination with PTEs has pronounced, which required an emergent intervention. In fact, several chemical and physical techniques have been employed to overcome the negative impacts of PTEs. However, these techniques have numerous drawback and their acceptance are usually poor as they are high cost, usually ineffectiveness and take longer time. In this context, bioremediation has emerged as a promising approach for reclaiming PTEs-contaminated soils through biological process using bacteria, fungus and plants solely or in combination. Here, we comprehensively reviews and critically discusses the processes by which microorganisms and hyperaccumulator plants extract, volatilize, stabilize or detoxify PTEs in soils. We also established a multi-technology repair strategy through the combination of different strategies, such as the application of biochar, compost, animal minure and stabilized digestate for stimulation of PTE remediation by hyperaccumulators plants species. The possible use of remote sensing of soil in conjunction with geographic information system (GIS) integration for improving soil bio-remediation of PTEs was discussed. By synergistically combining these innovative strategies, the present review will open very novel way for cleaning up PTEs-contaminated soils.

Conventional and Zero Tillage with Residue Management in Rice-Wheat System in the Indo-Gangetic Plains: Impact on Thermal Sensitivity of Soil Organic Carbon Respiration and Enzyme Activity

The impact of global warming on soil carbon (C) mineralization from bulk and aggregated soil in conservation agriculture (CA) is noteworthy to predict the future of C cycle. Therefore, sensitivity of soil C mineralization to temperature was studied from 18 years of a CA experiment under rice-wheat cropping system in the Indo-Gangetic Plains (IGP). The experiment comprised of three tillage systems: zero tillage (ZT), conventional tillage (CT), and strip tillage (ST), each with three levels of residue management: residue removal (NR), residue burning (RB), and residue retention (R). Cumulative carbon mineralization (C_t) in the 0-5 cm soil depth was significantly higher in CT with added residues (CT-R) and ZT with added residues (ZT-R) compared with the CT without residues (CT-NR). It resulted in higher CO₂ evolution in CT-R and ZT-R. The plots, having crop residue in both CT and ZT system, had higher (p < 0.05) Van't-Hoff factor (Q₁₀) and activation energy (Ea) than the residue burning. Notably, micro-aggregates had significantly higher Ea than bulk soil (~14%) and macro-aggregates (~40%). Aggregate-associated C content was higher in ZT compared with CT (p < 0.05). Conventional tillage with residue burning had a reduced glomalin content and β-D-glucosidase activity than that of ZT-R. The ZT-R improved the aggregate-associated C that could sustain the soil biological diversity in the long-run possibly due to higher physical, chemical, and matrix-mediated protection of SOC. Thus, it is advisable to maintain the crop residues on the soil surface in ZT condition (~CA) to cut back on valuable C from soils under IGP and similar agro-ecologies.

Impact of organic amendments on the bioavailability of heavy metals in mudflat soil and their uptake by maize

Organic amendments (OAs) can be a sustainable and effective method for mudflat soil improvement. A field experiment was conducted to investigate the potential of OA application to mudflat soil improvement. We measured the pH, soil organic matter (SOM), salinity, maize growth, and heavy metal (HM) accumulation in OA-applied soils, and maize tissues after three OAs, sewage sludge (SS), Chinese medical residue (CMR), and cattle manure (CM), were applied at the application rates of 0, 30, 75, 150, and 300 t ha^-1. OA application significantly increased the SOM and decreased the pH and salinity of mudflat soils. The maize biomass and HM contents in soil and maize increased after OA application. The bioavailability and bioconcentration of HMs were generally in the sequence of SS > CMR > CM. The average bioavailability ratios of HMs were in the order of Cd > Zn > Cu > Mn > Ni. The bioconcentration of Zn and Cd by maize was highest, followed by Mn, Cu, and Ni. SOM, pH, and salinity were the important factors regulating soil available HMs and, subsequently, HM accumulation in maize. Among the three OAs, SS is most effective in decreasing soil salinity, and increasing the SOM, bioavailability, and bioconcentration of HMs. On the other hand, CM was the best OA because it promoted significant maize growth yet maintained low HM contamination risk.

Functional Analysis of the C-5 Sterol Desaturase PcErg3 in the Sterol Auxotrophic Oomycete Pathogen Phytophthora capsici

Although sterols play an important role in most eukaryotes, some oomycetes, including Phytophthora spp., have lost the sterol synthesis pathway. Nevertheless, the ERG3 gene encoding C-5 sterol desaturase in the sterol synthesis pathway is still present in the genomes of Phytophthora spp. Phytophthora capsici, a destructive pathogen with a broad range of plant hosts, poses a significant threat to the production of agriculture. This study focused on the ERG3 gene in P. capsici (PcERG3) and explored its function in this pathogen. It showed that the PcERG3 gene could be expressed in all tested developmental stages of P. capsici, with sporangium and mycelium displaying higher expression levels. A potential substrate of Erg3 (stellasterol) was used to treat the P. capsici wild-type strain and a PcERG3Δ transformant, and their sterol profiles were determined by GC-MS. The wild-type strain could convert stellasterol into the down-stream product while the transformant could not, indicating that PcErg3 retains the C-5 sterol desaturase activity. By comparing the biological characteristics of different strains, it was found that PcERG3 is not important for the development of P. capsici. The pathogenicity of the PcERG3Δ transformants and the wild-type strain was comparable, suggesting that PcERG3 is not necessary for the interaction between P. capsici and its hosts. Further investigations revealed that the PcERG3Δ transformants and the wild-type strain displayed a similar level of tolerance to external adversities such as unsuitable temperatures, high osmotic pressures, and intemperate pH, signifying that PcERG3 is not essential for P. capsici to cope with these environmental stresses.

Toxicity and genotoxicity of domestic sewage sludge in the freshwater snail Biomphalaria glabrata (Say, 1818)

Waste produced in homes is one of the main sources of pollutants in freshwater ecosystems. Therefore, it is imperative to implement methodologies that aid in environmental monitoring procedures. The use of organisms as biomonitors has grown increasingly prevalent as they are models that provide data that can be adequately evaluated. In this work, we investigated the genotoxic and cytotoxic effects caused by domestic sewage sludge through an analysis of biomarkers in the mollusk Biomphalaria glabrata. For the tests, increasing concentrations of 50, 100, 150, and 500 mg L^-1 of domestic sewage sludge were standardized, in addition to control groups. Assays were performed after the mollusks were exposed to the domestic sewage sludge in acute (48 h) and chronic (15 d) manner. Toxicity tests were performed with embryonic and adult snails. The cytoplasmic and nuclear changes were analyzed in the hemocyte cells. Lastly, genotoxic damage was analyzed using the comet assay. Adult snails and embryos of B. glabrata showed no significant morphological changes. Domestic sludge caused deleterious effects on mollusks as confirmed after cell genotoxicity tests. Therefore, based on the results obtained from the analysis of B. glabrata hemocytes, we can affirm that domestic sewage sludge causes genotoxic and cytotoxic effects on mollusk cells. Therefore, it is possible to conclude that the mollusk Biomphalaria glabrata can be used as a good low-cost alternative to assist in the biomonitoring of freshwater environments. Graphical Abstract.

Evaluation of Land Potential for Use of Biosolids in the Coastal Mediterranean Karst Region

The aim of this study was to evaluate the potential of agricultural land in the coastal Adriatic Karst region (Šibenik region, Croatia) for biosolids application by integrating spatial data from different sources: digital maps and remote sensing, parcel identification system, GIS field observations and measurements focusing on specific land and soil properties. Due to the rapid development of the wastewater treatment industry, excessive accumulation of sewage sludge (SS) in wastewater treatment plants is a growing problem worldwide. Management options for land application of biosolids require a comprehensive characterization of both SS and SS-amended soils. The assessment of agricultural land in the study area for SS disposal was based on EU and national legislation. The evaluation revealed that agricultural land in the study area accounts for only 10% of the total area (25,736 ha), but only a quarter of the existing land (6065 ha) is suitable for biosolids application. Furthermore, the data indicate that the sewage sludge can be safely applied to the soil in terms of soil metals according to the Croatian legislation. The short-term potential of the soil to sustain this ecosystem service, namely soil improvement with biosolids, should be used to determine the inherent long-term potential based on resistance to soil degradation and resilience. However, caution is needed and the long-term effects should be investigated before biosolids are continuously used for soil application.

Effect of sewage sludge derived compost or biochar amendment on the phytoaccumulation of potentially toxic elements and radionuclides by Chinese cabbage

This study set out to evaluate the effect of using sewage sludge-derived compost (SSC) or biochar (SSB) as a soil amendment on the phytoaccumulation of potentially toxic elements, PTE (Cd, Cr, Cu, Ni, Pb, Zn) and natural radionuclides (²³⁸U and ²³²Th) by Chinese cabbage (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt) in terra rossa and rendzina soils, which are the two common soil types in Croatia. The experiment consisted of a greenhouse pot trial using a three-factor design where soil type, sludge post-stabilisation procedure and amendment rate (12 and 120 mgP/L) were the main factors. At harvest, the concentrations of analytes in the substrate, leaves and roots were measured, from which the edible tissue uptake (ETU) and concentration ratios (CR) were determined. Also, the average daily dose (ADD) and hazard quotient (HQ) were determined to assess the health risk, as well as soil contamination factor (CF). The results showed that neither adding SSC nor SSB affected the soil loading at the rates applied, suggesting a low risk of soil contamination (CF ≤ 1). The ETU of Cd, Cu, and Zn were 0.0061, 1.23, and 0.91 mg/plant from compost-amended soil and 0.0046, 0.78 and 0.65 mg/plant for biochar-amended soil, respectively. This difference suggests that their ETU was higher in compost-amended soils than in soils treated with biochar. The CR data indicate that the bioavailability of Cu (CR of 5.30) is highest at an amendment rate of 12 mgP/L, while for Zn (CR of 0.69), the highest bioaccumulation was observed with an amendment rate of 120 mgP/L. Translocation of Cr, Ni, Pb and ²³⁸U to the leaves was limited. Overall, the HQ (<1) for Cd, Cu and Zn in the edible parts confirmed that consuming Chinese cabbage does not threaten human health. Similarly, the daily intake of ²³²Th remained below the limit (3 μg) set by ICRP, suggesting no radiological risk. Finally, although the amendment rate, which was 10-times the amount stipulated in Croatian regulation and the CR ranged from 0.007 to 5.30, the precautionary principle is advised, and the long-term impact of sewage sludge derived compost or biochar on different plant groups (incl. root vegetables) at the field-scale is recommended.

Interactive assessment of lignite and bamboo-biochar for geochemical speciation, modulation and uptake of Cu and other heavy metals in the copper mine tailing

This study was designed to examine the combined effect of bamboo-biochar (BC) and water-washed lignite (LGT) at copper mine tailings (CuMT) sites on the concentration of Cu and other metals in pore water (PW), their bioavailability, and change in geochemical speciation. Rapeseed (first cropping-season) and wheat (second cropping-season) were grown for 40-days each and the influence of applied-amendments on both cropping seasons was observed and compared. A significant increase in pH, water holding capacity (WHC), and soil organic carbon (SOC) was observed after the applied amendments in second cropping-seasons. The BC-LGT significantly reduced the concentration of Cu in PW after second cropping seasons; however, the concentration of Pb and Zn were increased with the individual application of biochar and LGT, respectively. BC-LGT and BC-2% significantly reduced the bioavailability of Cu and other HMs in both cropping seasons. The treated-CuMT was subjected to spectroscopic investigation through X-ray photoelectron spectroscopy (XPS), Fourier transform Infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). The results showed that Cu sorption mainly involved the coordination with hydroxyl and carboxyl functional groups, as well as the co-precipitation or complexation on mineral surfaces, which vary with the applied amendment and bulk amount of Mg, Mn, and Fe released during sorption-process. The co-application of BC-LGT exerted significant effectiveness in immobilizing Cu and other HMs in CuMT. The outcomes of the study indicated that co-application of BC-LGT is an efficacious combination of organic and inorganic materials for Cu adsorption which may provide some new information for the sustainable remediation of copper mine tailing.

Rice Rhizospheric Effects on the Bioavailability of Toxic Trace Elements during Land Application of Biochar

Land application of biochar, the product of organic waste carbonization, can improve soil fertility as well as sequester carbon to mitigate climate change. In addition, biochar can greatly influence the bioavailability of toxic trace elements (TTEs) in soils resulting from its large internal surface areas, abundance in organic carbon, and ability to modify soil pH. Most research to date employs batch leaching tests to predict how biochar addition impacts TTE bioavailability, but these ex situ tests rarely considered the rhizospheric effect which might offset or intensify the changes induced by organic residue addition. This is especially so in rice rhizospheres because of strong clines in localized redox conditions. In this study, we adopted in situ high-resolution (HR) diffusive gradients in thin films (DGT) as well as rhizo-bag porewater sampling experiments to depict an overall picture of the difference in TTE (As, Cd, Cu, Ni, and Pb) bioavailability between the rice rhizosphere and bulk soils during land application of biochar. Porewater sampling experiments revealed that biochar additions stimulated TTE release due to the increase of dissolved organic carbon (DOC) and H⁺ concentrations. In the rhizosphere, although biochar still promoted As, Cd, and Ni release into porewaters, the rhizospheric effect was one of dampening/reduction compared with the bulk soil. When we focused on the localized changes of TTE bioavailability in the rhizosphere using an in situ HR-DGT approach, on the contrary, flux maxima of Cd, Cu, and Ni occurred near/on the root surface, and hot spots of As can be observed at peripheries of the rooting zone, which demonstrated the high heterogeneity and complexity of the rhizosphere's influence on TTE bioavailability.

Flow analysis of major and trace elements in residues from large-scale sewage sludge incineration

Increase of sewage sludge (SS) has led to the construction of more incineration plants, exacerbating to the production of SS incineration residues. However, few studies have considered the mass balance of elements in large-scale SS incineration plants, affecting the residues treatment and utilization. In this study, flow analysis was conducted for major and trace elements in the SS, the fly ash (sewage sludge ash, SSA) and bottom ash from two large-scale SS incineration plants. The elemental characteristics were compared with those of coal fly ash (CFA), and air pollution control residues from municipal solid waste incineration (MSWIA), as well as related criteria. The results showed that the most abundant major element in SSA was Si, ranging from 120 to 240 g/kg, followed by Al (76-348 g/kg), Ca (26-113 g/kg), Fe (35-80 g/kg), and P (26-104 g/kg), and the trace elements were mainly Zn, Ba, Cu, and Mn. Not all the major elements were derived from SS. Most trace elements in the SS incineration residues accounted for 82.4%-127% of those from SS, indicating that SS was the main source of trace elements. The partitioning of heavy metals in the SS incineration residues showed that electrostatic precipitator ash or cyclone ash with high production rates were the major pollutant sinks. The differences in some major and trace elements could be indicators to differentiate SSA from CFA and MSWIA. Compared with related land criteria, the pollutants in SSA should not be ignored during disposal and utilization.

Coal Fly Ash–Clay Based Geopolymer-Incorporating Electric Arc Furnace Dust (EAFD): Leaching Behavior and Geochemical Modeling

The recent recovery processes of electric arc furnace dust (EAFD) include stabilization within materials with potential uses in the construction sector. The stabilization of EAFD by alkaline activation of different alumina-silicates, resulting in low-cost and environmentally friendly materials. The leaching standards within the different European regulations allow evaluating waste materials and products. This work aims to study the introduction of EAFD in FA–clay geopolymers, assessing the environmental and geochemical behavior in two different scenarios, disposal, and utilization. For it, the compliance equilibrium-based batch test (EN 12457-2) and pH dependence test (EN 14429) have been used. The dosages of EAFD in the geopolymeric matrix are 5% to 20% with curing temperatures of 75 °C and 225 °C. The introduction of EAFD favors the development of the flexural strength. From the environmental point of view, metals related to EAFD, such as Zn, Pb, or Cu, are retained in the matrix. While As or Se, comes mainly from clay, present a high concentration. Therefore, the role of clay should be analyzed in future research. As expected by the high iron content in the EAFD, the iron complexes on the surface of the material are responsible for immobilization of metals in this type of matrix.

Effect of Biowastes on Soil Remediation, Plant Productivity and Soil Organic Carbon Sequestration: A Review

High anthropogenic activities are constantly causing increased soil degradation and thus soil health and safety are becoming an important issue. The soil quality is deteriorating at an alarming rate in the neighborhood of smelters as a result of heavy metal deposition. Organic biowastes, also produced through anthropogenic activities, provide some solutions for remediation and management of degraded soils through their use as a substrate. Biowastes, due to their high content of organic compounds, have the potential to improve soil quality, plant productivity, and microbial activity contributing to higher humus production. Biowaste use also leads to the immobilization and stabilization of heavy metals, carbon sequestration, and release of macro and micronutrients. Increased carbon sequestration through biowaste use helps us in mitigating climate change and global warming. Soil amendment by biowaste increases soil activity and plant productivity caused by stimulation in shoot and root length, biomass production, grain yield, chlorophyll content, and decrease in oxidative stress. However, biowaste application to soils is a debatable issue due to their possible negative effect of high heavy metal concentration and risks of their accumulation in soils. Therefore, regulations for the use of biowastes as fertilizer or soil amendment must be improved and strictly employed to avoid environmental risks and the entry of potentially toxic elements into the food chain. In this review, we summarize the current knowledge on the effects of biowastes on soil remediation, plant productivity, and soil organic carbon sequestration.

An analysis of the versatility and effectiveness of composts for sequestering heavy metal ions, dyes and xenobiotics from soils and aqueous milieus

The persistence and bioaccumulation of environmental pollutants in water bodies, soils and living tissues remain alarmingly related to environmental protection and ecosystem restoration. Adsorption-based techniques appear highly competent in sequestering several environmental pollutants. In this review, the recent research findings reported on the assessments of composts and compost-amended soils as adsorbents of heavy metal ions, dye molecules and xenobiotics have been appraised. This review demonstrates clearly the high adsorption capacities of composts for umpteen environmental pollutants at the lab-scale. The main inferences from this review are that utilization of composts for the removal of heavy metal ions, dye molecules and xenobiotics from aqueous environments and soils is particularly worthwhile and efficient at the laboratory scale, and the adsorption behaviors and effectiveness of compost-type adsorbents for agrochemicals (e.g. herbicides and insecticides) vary considerably because of variabilities in structure, topology, bond connectivity, distribution of functional groups and interactions of xenobiotics with the active humic substances in composts. Compost-based field-scale remediation of environmental pollutants is still sparse and arguably much challenging to implement if, furthermore, real-world soil and water contamination issues are to be addressed effectively. Hence, significant research and process development efforts should be promptly geared and intensified in this direction by extrapolating the lab-scale findings in a cost-effective manner.

Leaching behavior and potential ecological risk of heavy metals in Southwestern China soils applied with sewage sludge compost under acid precipitation based on lysimeter trials

The ecological risk of heavy metals (HM) resulting from the use of sewage sludge compost (SSC) as an amendment to flower garden soil (FGS) and to abandoned phosphate mine soil (APMS) influenced by acid rain were simulated in lysimeter trials and the potential ecological risk index (PERI) was evaluated with minor modifications. The use of SSC indeed increased the mobility and release of HMs in FGS and APMS under conditions of acid rain. The leaching dynamics of HMs was found to be influenced by Fe/Al oxides and organic matter (OM) in the soil. The application of SSC as a fertilizer to barren APMS dramatically decreased the mobility of Cr, Cu and Pb by 51-56% due to their retention by particulate organic matter, while the leaching of As, Cd and Ni was increased as the result of competition with OM for available Fe/Al oxides (As) and proton-metal exchange reactions that occurred in HM-OM complexes (Cd and Ni). The ecological risk of FGS and APMS resulting from HM migration was actually low (PERI = 0.07-0.12), but the increased potential ecological risk resulting from the use of SSC were estimated to be moderate (a 16.0-33.5% increase in PERI for SSC-amended FGS) or high (a 140% increase in PERI for SSC-amended APMS). Ni, Cd and Cu were identified as the three main HMs responsible for increasing the ecological risk in soil which was mainly composed of fine-grained particles, whereas Cd and As were key ecological risks HMs in soil that was mainly composed of coarse-grained particles.

Study of genotoxic and cytotoxic effects after acute and chronic exposures to industrial sewage sludge on Biomphalaria glabrata hemocytes

Industrial development has provided numerous benefits to improve quality of life in modern times, however, it has also led to the development and use of a large number of toxic chemicals which have caused damage to various ecosystems. Consequently, knowledge of techniques and organisms that can be used to monitor, identify and quantify environmental pollutants has become increasingly relevant. Therefore, the objective of this study was to use the mollusk Biomphalaria glabrata to analyze biomarker and biomonitoring parameters of industrial sewage sludge. To perform the tests, concentrations of 50, 100, 150 and 500 mg L^-1 of industrial sewage sludge were standardized. All the tests were performed after the animals were exposed to the sludge in acute and chronic forms. Embryos exposure to sludge did not show a significant percentage of the animals non-viable when compared to the control group. Subsequently, hemocytes were analyzed for the presence of cytoplasmic and nuclear alterations. Finally, the comet test was performed to quantify the genotoxic damage caused by exposure to industrial sludge. Analysis hemocytes showed a significant number of cellular alterations was observed, mainly due to the high frequency of apoptosis. Moreover, during the analysis of nucleoids several degrees of nuclear damage were identified, with the groups exposed to the highest concentrations presenting the greatest genotoxic damage. Thus, we can conclude that the parameters evaluated in the mollusk Biomphalaria glabrata have proven to be a good tool, along with other techniques and complementary organisms, to assist aspects related to biomonitoring of freshwater ecosystems.

An innovative modeling approach of linking land use patterns with soil antibiotic contamination in peri-urban areas

Due to the intensive use and continuous release, high and persistent concentrations of antibiotics are found in soils worldwide. This severe contamination elevates the risks associated with antibiotic exposure and resistance for soil ecosystems and human health. Estimating antibiotic concentrations in soils is a complex and important challenge because the limited information is available on antibiotic use and emission and the high exposure risk to human health occurred in peri-urban areas. In this study, soil antibiotic contamination was linked with land use patterns in a data-scarce peri-urban area in four different seasons, and we established a modeling framework based on land use to estimate spatially explicit distribution of antibiotics in soils. The soil antibiotic concentration was found to be substantially affected by surrounding land use patterns in buffer zones with a radius of 350 m. Agricultural land was the main source of antibiotics entering the soil. Notably, road networks also had considerable impacts on antibiotic residues in soils. Then, a statistical model was developed in describing the linkage between land use patterns and soil antibiotic concentration. Model evaluation suggested that the proposed model successfully simulated the variation of antibiotics in soil with good statistical performance (R² > 0.7). Finally, the model was extrapolated to investigate detailed distribution of antibiotics in soils. Clear spatial and seasonal dynamics can be found in soil antibiotic concentration. To our knowledge, this was the first attempt to adopt a model focusing on land use pattern to estimate the spatially explicit distribution of antibiotics in soils. Despite of some uncertainties, the research provides a land-use-based modeling approach as a reference for preventing and controlling soil antibiotic contamination in the future.

Improvement of chemical quality of percolated leachates by in situ application of aqueous organic wastes on sulfide mine tailings

One of the major environmental concerns in the mining industry is the generation of acid leachates from tailings deposits, which are highly concentrated in potentially hazardous elements. The continuous processing of these leachates in treatment plant is unsustainable, so the in situ chemical improvement of the mine wastes and their leachates, mainly with another waste produced in the mining area, can reduce treatment and operational costs. This study aimed to evaluate the effect of two types of domestic wastewaters (DWW) on the improvement of the chemical characteristics of the leachates generated from mine wastes containing sulfides. A mesocosm assay was performed under greenhouse and controlled conditions with mine wastes collected in La Zanja mining area (Peru). Three irrigation treatments were tested: untreated DWW, treated DWW and water as control. Percolated leachates of each treatment were collected once per week, for a period of 10 weeks. Electrical conductivity, pH and multi-elemental concentration were analysed. During the assay, the mine wastes generated acid leachates (≈4) with significant concentrations of elements (mg/L; Al: 1.4-30.0; Cd: 0.05-0.19; Cu: 5.7-22.1; Fe: 1.6-19.4; Mn: 2.6-26.0; Zn: 1.2-9.2) and sulfates (204.3-997.8 mg/L), which exceed the thresholds established by Peruvian legislations. After DWW application, pH in the leachates increased to ≈7 and concentrations of several studied elements (e.g. Al, As, Fe, Cu, Zn, Cd, Pb, Ni, Mn) and sulfates decreased (>70% depending on DWW type, element and sampling) compared to the control. This fact allowed that the Environmental Quality standards from Peru (except for Cu and Mn) were reached. However, an enrichment of Na and K was obtained at the same leachates. At short term, the DWW application (especially untreated) on the mine wastes containing sulfides was effective in the improvement of the general chemical quality of their leachates. Moreover, the combined management of these two studied wastes (domestic wastewater and mine wastes) represents a promising cost-effective strategy during mining operation.

Ionic speciation and risks associated with agricultural use of industrial biosolid applied in Inceptisol

The evaluation of the chemical leaching potential from soils amended with biosolid is of extreme importance for environmental safety of agricultural use of these residues. The objective of this study was to evaluate the polluting potential and possible risks associated with the agricultural use of biosolids generated by the polyethylene terephthalate (PET) fiber and resin industry through ionic speciation and analysis of the activity of chemical species present in the leached solution from Inceptisol treated with rates 0, 6, 12, 18, 24, 48, 96, and 144 Mg ha^-1 on dry basis. The experiment was conducted in a lysimeter and the treatments with three replications were distributed at random. Chemical leaching was made by application of CaC1₂ 0.01 mol L^-1 solutions in a volume fourfold higher than the water retention capacity of the soil, divided into five leaching events: 210, 245, 280, 315, and 350 days of incubation. Chemical species concentrations in collected leachates were used for ionic speciation by geochemical software Visual MINTEQA2 version 4.0. Impact factor of chemical species was calculated as the ratio between maximum concentration in the leach solution in the treated soil and control. Dissolved organic carbon had strong influence on Pb⁺² and Cu⁺² leaching, but these elements in free or complexed forms presented low activities in solution. Leaching of NO₃^-, Zn⁺², and Na⁺ represents the main environmental risk of agricultural use of this residue. However, these risks can be minimized if technical criteria and critical limits for the agronomic use of biosolids were observed.

Hydroxyapatite reduces potential Cadmium risk by amendment of sludge compost to turf-grass grown soil in a consecutive two-year study

Recycling of sludge compost to soil as conditioner is generally regarded as the best means of disposal. However, concerns regarding heavy metal residues and sludge toxicity have recently received increasing public attention. Cadmium (Cd) is a mobile metal commonly found in sludge; therefore, the risk posed by Cd contaminated sludge should be carefully assessed. In this report, the effects of addition of hydroxyapatite (HAP) with sludge compost amendment on potential Cd risk were investigated. The results of consecutive two years showed that exchangeable Cd content in treatment of sludge compost with 1.5% HAP decreased by 6.0% compared with single sludge compost treatment, and residual Cd increased by 7.6%. Compared with single sludge compost, the incremental rate of exchangeable Cd dropped by 38.3% and the reductive rate of residual Cd increased by 37.7% in response to 1.5% HAP addition, indicating that HAP played a role of decreasing Cd phytoavailability. The HAP reduced the amount of Cd uptaken by turf-grass in both root and leaf. Moreover, HAP remarkably improved the quality of turf grass grown in amended soil, including leaf greenness, green maintainable period and root strength. However, HAP did not attenuate the downward mobility of Cd. Taken these together, these findings indicated that HAP can be used as a potential candidate to control surface Cd risk of sludge compost amended soil rather than that from leachate.