Historical arsenic contamination of soil due to long-term phosphate fertiliser applications

Size-resolved distribution of trace elements in lysimeter soil solutions under contrasting long-term agricultural management to assess their bioavailability

The chemical species of trace elements (TEs) in agricultural soils is highly variable under diverse conditions, requiring tools with clear resolution and minimal disturbance for exploration. A novel surgical (316L) stainless steel (SS) lysimeter with a 5 μm pore size was developed to collect field soil solutions. The size-resolved distribution of TEs were characterized into total (nitric acid digestion), particulate (0.45-5 μm), dissolved (<0.45 μm), colloidal (1 kDa to 0.45 μm), and mainly ionic (<1 kDa) fractions in the lysimeter soil solutions. Total concentrations of TEs (dry weight basis) in acid digested Gray Luvisolic soils were analyzed. Most TEs in lysimeter soil solutions were present in particulate phases, relevant to their geochemical affinities and occurrences in soil minerals. Among dissolved fractions, As, Ba, Co, Li, Mn, Tl, and V existed as mainly ionic species in the soil solutions. Copper, Pb, Al, Th, and U showed variable associations with dissolved organic matter (DOM) and/or inorganic colloids among agricultural treatments. Inorganic NPKS or NKS fertilizer applications with lower pH (5.25-5.74) enhanced mobility and potential bioavailability of Ba, Co, Li, Mn, and Pb present in mainly ionic species, compared with other locations (pH 5.82-6.37). Manure application exhibited a dual effect, potentially increasing bioavailability for As, Tl, and V due to probably enhanced cation exchange capacity (CEC), while also facilitating specific adsorption of Cu and U on DOM, potentially reducing their bioavailability depending on DOM molecular weight. Colloidal and ionic Al and Th concentrations were higher in forest soils than agricultural soils, with extremely low potential bioavailability of Th attributed to strong precipitation with inorganic colloids and adsorption on DOM. The lysimeter sampling and size fractionation method provided a clear insight into agricultural effects on TE distributions and enhancing understanding of agricultural soil health in terms of TE bioavailability in situ.

Nutrient addition alters plant community productivity but not the species diversity of a mountain meadow in Tajikistan

Introduction

Tajikistan is a typical mountainous country covered by different mountain grasslands that are important pasture resources. Recently, grassland degradation has become widespread due to climate change and human activities and fertilization has been used to improve grassland production. However, fertilizer inputs can substantially alter species diversity, but it is uncl\ear how productivity and species diversity respond to nutrient enrichment in the mountain meadows of Tajikistan.

Methods

Therefore, a 5-year (2018-2022) continuous in-situ mineral fertilizer experiment was conducted to examine the effects of three nitrogen (N) levels (0, 30, and 90 kg N ha-1 year-1), two phosphorus (P) levels (0 and 30 kg P ha-1 year-1), and their combinations on above-ground biomass (AGB) and species diversity in a mountain meadow grassland in Ziddi, Varzob region, Tajikistan. Five species diversity metrics-Margalef's species richness (Dma), the Shannon-Wiener index (H), the Simpson index (C), Pielou's equitability index (Epi), and the Evar Species Evenness index (Evar)-were used to measure species diversity.

Results and discussions

The results indicated that the addition of different N and P amounts and their various combinations considerably increased both total and dominant species AGB, with the highest increase occurring in the N90P30 (90 kg N ha-1 year-1 combined with 30 kg P ha-1 year-1) treatment in 2022; during the experiment, the importance value of Prangos pabularia (dominant species) first decreased and then increased, but its dominant status did not change or fluctuate among the years. Furthermore, N, P, and their different combinations had no significant effect on species diversity (Dma, H, C, Epi, and Evar). All the species diversity indexes fluctuated among years, but there was no interaction with mineral fertilizer addition. Total AGB had a negative relationship with species diversity and low concentration N fertilizer addition (N30; P30) strengthened this negative trend. However, this trend decreased under the high N fertilizer condition (N90P30). Overall, nutrient addition to the natural mountain grassland of the Varzob region improved AGB, which meant that there was more forage for local animals. Mineral fertilizers had no significant effect on species diversity, but may enhance P. pabularia dominance in the future, which will help maintain the stability of the plant community and improve the quality of the forage because P. pabularia is an excellent and important winter fodder. Our study suggests that scientific nutrient management could effectively promote grassland production, conserve plant variety, and regenerate degraded grassland, which will counteract the desertification process in northwest Tajikistan mountain meadows.

Evidence for the accumulation of toxic metal(loid)s in agricultural soils impacted from long-term application of phosphate fertilizer

Phosphate fertilizers may contain elevated concentrations of toxic metals and metalloids and therefore, their excessive application can result in the accumulation of both phosphorus (P) and metal(loid)s in agricultural soils. This study aims to investigate the occurrence, distribution, and potential plant-availability of metal(loid)s originating from phosphate fertilizer in a long-term experimental field at the Tidewater Research Station in North Carolina, where topsoil (10-20 cm deep) and subsoil (up to 150 cm deep) samples were collected from five plots with consistent and individually different application rates of P-fertilizer since 1966. We conducted systematic analyses of P and metal(loid)s in bulk soils, in the plant available fraction, and in four sequentially extracted soil fractions (exchangeable, reducible, oxidizable, and residual). The results show that P content in topsoils were directly associated with the rate of P-fertilizer application (ρ = 1, p < 0.05). Furthermore, P concentrations were highly correlated with concentrations of Cd, U, Cr, V, and As in the bulk topsoil (ρ > 0.58, p < 0.05), as well as the potential plant-available fraction (ρ > 0.67, p < 0.01), indicating the accumulation of the fertilizer-derived toxic metal(loid)s in the topsoil. Significant correlations (p < 0.001) of metal(loid)s concentrations between the bulk soil and the potential plant-available fraction raises the possibility that P-fertilizer application could increase the accumulation of toxic metal(loid)s in plants, which could increase human exposure. Results from sequential leaching experiments revealed that large portions of the trace elements, in particular Cd, occur in the soluble (exchangeable and reducing) fractions of topsoil with higher P-fertilizer input, whereas the levels of redox-sensitive elements (As, V, U, Cr) were higher in the reducible and oxidizable fractions of the soils. Overall, the data presented in this study demonstrate the effect of long-term P-fertilizer application on the occurrence and accumulation of a wide range of toxic metal(loid)s in agricultural topsoil.

Phosphate deficiency modifies lipid composition and seed oil production in camelina

Camelina (Camelina sativa) is an emerging industrial oilseed crop because of its potential for double cropping, fallow year production, growth on marginal lands, and multiple uses of seed oils and meals. To realize the potential for sustainable production of camelina, a better understanding of how camelina seed oil production and composition respond to low input environments is desired. Phosphorus (P) is one of the least available essential macronutrients to plants with finite worldwide supply. This study investigated seed oil production and lipid composition of camelina in field settings and under greenhouse conditions in response to P deficiency. Lipidomic profiling reveals that P deficiency in field settings triggered extensive leaf lipid remodeling that decreased the ratio of phospholipids to non-P-containing galactolipids from 30% to 5% under P sufficient to deficient conditions. P deficiency increased seed oil content per seed weight by approximately 25% and 20% in field and greenhouse settings, respectively. In addition, P deficiency altered seed fatty acid composition, with increases in monounsaturated 18:1 and 20:1 and decreases in polyunsaturated 18:3. Total seed production was decreased by 10- to 15-fold under P deficiency and the decrease resulted from reduced seed numbers without affecting seed weight. The results from field and greenhouse conditions indicate that P deficiency increases seed oil content, alters fatty acid composition, and decreases greatly seed production, suggesting that achieving a high yield and quality of camelina seed oil is positively linked to P status of soil.

Accumulation and speciation of arsenic in Eisenia fetida in sodium arsenite spiked soils - A dynamic interaction between soil and earthworms

Arsenic (As) is a toxic metalloid that is a significant global pollutant of the environment and a persistent bioaccumulation carcinogen. Earthworms are frequently employed as sentinel organisms to investigate the bioavailability of As in contaminated soils. However, the process of As accumulation in earthworms and the mechanism of transformation of As species in their bodies are not well understood. The accumulation of As and variation of As species in the earthworms (Eisenia fetida) exposed to sodium arsenite (0, 20, and 80 mg kg^-1 As) were investigated in this study. The total As concentration of earthworms in the three treatments at various sample times was dose-dependent on soil As content. After 56 days of exposure, the high concentration treatment had the highest total As content (772 ± 21 mg kg^-1) in earthworms, followed by the low concentration treatment (579 ± 42 mg kg^-1) and control (31 ± 1 mg kg^-1). During 56 days, the proportion of trivalent As in earthworms increased from 70% to more than 90%, while pentavalent As decreased by 11-18%. On day 28, the sum of the four organic As species reached a maximum (<1%). Changes in soil As species and an increase in bioavailable As cause earthworms to accumulate more As. The total As in soil after 56 days of exposure was 9.51 ± 0.50, 25.6 ± 0.60, and 82.8 ± 0.28 mg kg^-1, which was not significantly different from the total As in soil before the experiment. These findings are useful in assessing the risk of earthworm exposure to sodium arsenite in the soil.

Arsenic biotransformation genes and As transportation in soil-rice system affected by iron-oxidizing strain (Ochrobactrum sp.)

Arsenic (As) biotransformation in soil affects As biogeochemical cycling and is associated with As accumulation in rice. After inoculation with 1% iron-oxidizing bacteria (FeOB) in paddy soil, As speciation, As biotransformation genes in soil, As/Fe in Fe plaques, and As accumulation in rice were characterized. Compared with the control, the available As concentrations in soils decreased while amorphous and poorly crystalline Fe-Al oxidized As and crystalline Fe-Al oxidized As fractions increased of F (FeOB) and RF (rice and FeOB) treatments. Fe concentrations increased and positively correlated with As concentrations in Fe plaques on the rice root surface (***P < 0.001). Compared with R (rice), Monomethyl As (MMA), dimethyl As (DMA), arsenate (As(V)), and arsenite (As(III)) concentrations in rice plants showed a downwards trend of RF treatment. The As concentration in grains was below the National Standard for Food Safety (GB 2762-2017). A total of 16 As biotransformation genes in rhizosphere soils of different treatments (CK, F, R and RF were quantified by high-throughput qPCR (HT-qPCR). Compared with the control, the As(V) reduction and As transport genes abundance in other treatments increased respectively by 54.54%-69.17% and 54.63%-73.71%; the As(III) oxidation and As (de) methylation genes did not change significantly; however, several As(III) oxidation genes (aoxA, aoxB, aoxS, and arsH) increased. These results revealed that FeOB could reduce, transport As, and maybe also oxidize As. In addition, As(III) oxidation gene (aoxC) in rhizosphere soil was more abundant than in non-rhizosphere soil. It indicated that radial oxygen loss (ROL) promoted As(III) oxidation in rhizosphere soils. The results provide evidence for As biotransformation by ROL and FeOB in soil-rice system. ROL affects As oxidation and immobilization, and FeOB affects As reduction, transportation and may also affect As oxidation.

Assessment of Potentially Toxic Elements in the Urban Soil and Plants of Kirkuk City in Iraq

Kirkuk city is known for its industrial activities, especially oil and cement production, as well as its road traffic. The aim of this study was to assess potentially toxic elements (PTEs) in the soil and plants from urban areas by measuring pollution indices and estimating the effect that this pollution has on the environment. Leaf and soil samples were taken from 10 different locations in Kirkuk. These samples were pre-treated using the acid digestion method and concentrations of 12 elements were determined using inductively coupled plasma mass spectrometry (ICP-MS). The results indicate a high content of aluminum and magnesium (mg/kg) in the soil samples from all study sites. For leaf samples, the results showed a moderate to low amount of magnesium and aluminum. Based on our results, the PTE concentrations were found in the following order—Mg > Al > Ni > Cu > Cr > Pb > Co > As > Se > Cd > Hg > Ti—in leaf samples from all 10 study sites. However, in the soil samples, PTE concentrations were in the following order—Mg > Al > Cr > Ni > Cu > Pb > Co > As > Se > Ti > Cd > Hg—from all study sites. Pollution indices showed a moderate level of contamination of Pb, Cd, and Ni, and a high level of contamination of As and Hg in plant and soil samples from all study sites in Kirkuk city.

Evaluation of single and joint toxicity of perfluorooctanoic acid and arsenite to earthworm (Eisenia fetida): A multi-biomarker approach

Perfluorooctanoic acid (PFOA) and arsenic are ubiquitous environmental contaminants and could co-exist in soil. However, data on their possible combined toxic effects on terrestrial organisms are still lacking. In this study, we exposed earthworm Eisenia fetida to artificial soil spiked with different sub-lethal levels of PFOA, arsenite (As(III)) or their mixture for 28 days. The bioaccumulation and multi-biomarker responses in the earthworms were measured. Results showed that the co-existence of PFOA and As(III) in soil enhanced the bioaccumulation of arsenic while reduced the bioaccumulation of PFOA. Most selected biomarkers exhibited significant responses at higher exposure levels and indicated oxidative damages. Biomarker Response Index (BRI) was used to integrate the multi-biomarker responses and the results showed significant dose-effect relationships between biological health status and exposure levels. Moreover, variation analysis of multi-biomarkers and BRI proved that As(III) exhibited more toxicity than PFOA to the earthworms. Based on BRI results, Effect Addition Index (EAI) was calculated to evaluate the joint effects of the two toxicants. According to EAI, the joint toxicity of PFOA and As(III) was related to exposure concentration, changing from synergism to slight antagonism with the increase of exposure level. These results provide valuable toxicological information for the risk assessment of co-exposure to PFOA and arsenic in the soil environment. Moreover, this study proved that BRI is an effective tool to integrate multi-biomarker responses, and its combination with EAI provides a useful combined approach to evaluate the joint effects of mixed contamination systems.

Immobilized phosphate-binding protein can effectively discriminate against arsenate during phosphate adsorption and recovery

There is a strong impetus to establish a circular phosphorus economy by securing internally renewable phosphate (P_i ) resources for use as agricultural fertilizers. Reversible P_i adsorption technologies such as ion exchange can remove and recover P_i from water/wastewater for reuse. However, existing reversible adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity between As(V) and P_i chemical structure. If As(V) is co-recovered with P_i , the value of the recovered products for agricultural reuse is low. The objective of this study was to construct an immobilized phosphate-binding protein (PBP)-based P_i removal and recovery system and analyze its selectivity for P_i adsorption in the presence of As(V). A range of conditions was tested, including independent, sequential, and simultaneous exposure of the two oxyanions to immobilized PBP (PBP resin). The purity of the recovered P_i product was assessed after inducing controlled desorption of the adsorbed oxyanions at high pH (pH 12.5). P_i constituted more than 97% of the adsorbed oxyanions in the recovered product, even when As(V) was initially present at twofold higher concentrations than P_i . Therefore, PBP resin has potential to selectively remove P_i , as well as release high-purity P_i free of As(V) contamination suitable for subsequent agricultural reuse. PRACTITIONER POINTS: Existing reversible phosphate (P_i ) adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity in their chemical structure. Co-recovery of As(V) with P_i can reduce the recovered product's reuse as a fertilizer. An immobilized phosphate-binding protein (PBP)-based system can be highly selective for P_i even in the presence of As(V). P_i constituted more than 97% of the recovered product, even when As(V) was present at 2-fold higher concentrations than P_i . Immobilized PBP offers advantages over existing P_i adsorbents by providing high-purity P_i products free of As(V) contamination for reuse.

The Pedosphere as a Sink, Source, and Record of Anthropogenic and Natural Arsenic Atmospheric Deposition

The Anthropocene has led to global-scale contamination of the biosphere through diffuse atmospheric dispersal of arsenic. This review considers the sources arsenic to soils and its subsequent fate, identifying key knowledge gaps. There is a particular focus on soil classification and stratigraphy, as this is central to the topic under consideration. For Europe and North America, peat core chrono-sequences record massive enhancement of arsenic depositional flux from the onset of the Industrial Revolution to the late 20th century, while modern mitigation efforts have led to a sharp decline in emissions. Recent arsenic wet and dry depositional flux measurements and modern ice core records suggest that it is South America and East Asia that are now primary global-scale polluters. Natural sources of arsenic to the atmosphere are primarily from volcanic emissions, aeolian soil dust entrainment, and microbial biomethylation. However, quantifying these natural inputs to the atmosphere, and subsequent redeposition to soils, is only starting to become better defined. The pedosphere acts as both a sink and source of deposited arsenic. Soil is highly heterogeneous in the natural arsenic already present, in the chemical and biological regulation of its mobility within soil horizons, and in interaction with climatic and geomorphological settings. Mineral soils tend to be an arsenic sink, while organic soils act as both a sink and a source. It is identified here that peatlands hold a considerable amount of Anthropocene released arsenic, and that this store can be potentially remobilized under climate change scenarios. Also, increased ambient temperature seems to cause enhanced arsine release from soils, and potentially also from the oceans, leading to enhanced rates of arsenic biogeochemical cycling through the atmosphere. With respect to agriculture, rice cultivation was identified as a particular concern in Southeast Asia due to the current high arsenic deposition rates to soil, the efficiency of arsenic assimilation by rice grain, and grain yield reduction through toxicity.

Cadmium transport in red paddy soils amended with wheat straw biochar

Cadmium (Cd) can be leached from soil into the groundwater and exhibit its adverse effect on the health of animals and humans. While previous studies have studied the process of Cd transport in water-saturated sand columns, literature regarding Cd transport in soil is scarce. The aim of this experiment was to investigate the transport of Cd in soil columns and biochar application rate effects on the mobility and distribution of Cd in soil. The red paddy soil was collected from the paddy of Changsha County, Hunan Province in southern China. Batch sorption and column experiments were conducted to study the adsorption isotherms of Cd²⁺ and its mobility at different biochar application rate treatments (0, 0.5, 1, 1.5, and 2%) referenced here as A0, A10, A20, A30, and A40, respectively. The Cd concentration of in effluent samples and digestion solutions was measured by inductively coupled plasma optical emission spectrometer (ICP-OES, Thermo Fisher Scientific, USA). After finishing the column experiment, columns were dissected into five layers (1-cm segments), the Cd fractions in soil were performed by the European Community Bureau of Reference (BCR). The amount of Cd sorption among treatments decreased in the order of A40 > A30 > A20 > A10 > A0, and the Langmuir model was more suitable to study the Cd²⁺ adsorption on biochar-amended soil than Freundlich model. Breakthrough curves showed that increasing biochar application rate increased the initial breakthrough time, whereas the pore-water velocity and dispersion coefficient were 81.0 and 99.8% lower in the A40 treatments than in the A0 treatments, respectively. Increasing biochar application rate enhanced the pH but reduced redox potential (Eh) in the most of effluents. Compared with A0, the concentration of Cd retained in soil columns increased by 86.6% in the A40 treatments. However, BCR sequential extractions showed that biochar addition in A40 treatments increased the acid soluble fraction but reduced the reducible fraction. In A40 treatments, compared with the 0-1-cm soil layer, the relative Cd concentration (N/Ni) in the 1-2-, 2-3-, 3-4-, and 4-5-cm soil layers increased by 5.4, 10.9, 14.3, and 21.9%, respectively. Biochar application in A40 treatments showed strong capacity for retarding Cd transport in soil, while the potential mobility of Cd in soil should be considered.

Impacts of Long- and Short-Term of Irrigation with Treated Wastewater and Synthetic Fertilizers on the Growth, Biomass, Heavy Metal Content, and Energy Traits of Three Potential Bioenergy Crops in Arid Regions

The availability of suitable water is an important factor for increasing the cultivated areas and sustainability in arid (i.e., less than 200 mm precipitation per year) and semiarid regions (i.e., 200–700 mm precipitation per year). Therefore, this study aimed to analyze the impact of treated wastewater (TWW) and groundwater (GW) as well as synthetic fertilizers (50% and 100% of the recommended NPK dose; 150–150–60 kg N–P2O5–K2O ha−1) on the growth, biomass, energy traits, and macro and trace elements of maize (Zea mays L.), sorghum (Sorghum bicolor L.), and pearl millet (Pennisetum glaucum L) grown in old cultivated (first location; L1) and virgin soil (L2 and L3) as potential bioenergy crops. The soil in L1 has been irrigated with treated wastewater for the last 15 years and continued to be irrigated with treated wastewater in this investigation. The virgin soil was divided into two parts: the first part was irrigated with TWW, and the second part was irrigated with GW. The experiments were laid out in a split-plot with a randomized complete block design with water treatments (TWW in old and virgin soil, and GW in virgin soil) in main plots, and the two treatments of fertilization (50% and 100% of the recommended NPK dose) were distributed randomly in subplots. Compared with the crops irrigated with GW, the crops irrigated with TWW, whether grown on old or virgin soil, showed higher plant height, total chlorophyll content, leaf area per plant, total biomass, energy content, and gross energy with low ash. They also contained higher (but lower than permissible limits) concentrations of macro-elements (NPK) and trace elements (Fe, Mn, Cu, Zn, Cd, Pb, Ni, and Co). In addition, the application of a 50% recommended dose of NPK with TWW showed equivalent results to a 100% recommended dose of NPK on all measured parameters with few exceptions. In conclusion, the TWW can be used to irrigate field crops allocated for bioenergy production in arid regions because it does not harm the plants and environment. In addition, the 50% recommended dose of NPK fertilizer exerted no negative effects on the growth and energy production of field crops, thereby protecting the environment and reducing the leaching of excessive fertilizers into GW.

Nanominerals assemblages and hazardous elements assessment in phosphogypsum from an abandoned phosphate fertilizer industry

The present work investigates hazardous elements and nanomineralogical assemblages of phosphogypsum waste from an abandoned phosphate fertilizer industry located in Santa Catarina state (Brazil). Correlations between the chemical composition, nanominerals, and ultrafine particles are discussed. Multifaceted physical-geochemical study provided a careful understanding of the nanomineralogical assemblage of the phosphogypsum waste. The electron beam investigation revealed the presence of many hazardous elements in the ultrafine particles. Cr, Pb, Mn, Se, Sr, and Zr, among others, were found in individual ultrafine particles and nanominerals in all studied samples. Besides that, rare earth elements were found in different concentration ranges, being Ce, La, and Nd, the rare earth elements, found in the higher concentrations, above 900 mg kg^-1. The data supplied by this article are important to characterize the phosphogypsum waste, assessing the potential hazard to the environment and human health, and also, provides information to enable the designing of alternatives to manage this waste.

Changes of oxygen isotope values of soil P pools associated with changes in soil pH

Field data about the effect of soil pH on phosphorus (P) cycling is limited. A promising tool to study P cycling under field conditions is the ¹⁸O:¹⁶O ratio of phosphate (δ¹⁸O_P). In this study we investigate whether the δ¹⁸O_P can be used to elucidate the effect of soil pH on P cycling in grasslands. Soils and plants were sampled from different fertilisation and lime treatments of the Park Grass long term experiment at Rothamsted Research, UK. The soils were sequentially extracted to isolate different soil P pools, including available P and corresponding δ¹⁸O_P values were determined. We did not observe changes in plant δ¹⁸O_P value, but soil P δ¹⁸O_P values changed, and lower δ¹⁸O_P values were associated with higher soil pH values. At sites where P was not limiting, available P δ¹⁸O_P increased by up to 3‰ when lime was applied. We show that the δ¹⁸O_P method is a useful tool to investigate the effect of pH on soil P cycling under field conditions as it highlights that different soil processes must govern P availability as pH shifts. The next challenge is now to identify these underlying processes, enabling better management of soil P at different pH.

The Effect of Fertilizers on Biomass and Biodiversity on a Semi-Arid Grassland of Northern China

Semi-arid grassland in northern China faces degradation and desertification problems, with fertilizer application appearing to be a potential solution by improving soil fertility and plant fields or biodiversity. In this study, mineral and organic fertilizers were used in a semi-arid natural grassland in Hebei Province for three years. The plant characteristics, biomass and species diversity index were assessed and analyzed. In the years 2016 and 2017, mineral fertilizers (RC) significantly increased the total aboveground biomass and the aboveground biomass, natural height, density and coverage of Leymus chinensis compared with organic fertilizers (RO), especially at a moderate application rate (RC2). Leymus chinensis was first divided into its own group and then separated into four groups via cluster tree analysis. The importance values of Leymus chinensis showed continuous increases in mineral fertilizer treatments, but not for organic fertilizers. Margalef’s species richness indexes increased significantly (to 2.09) in the organic treatment (RO1) when compared with RC2. Thus, it was concluded that mineral fertilizers could enhance the position of Leymus chinensis in the natural grassland, while organic fertilizers could promote species biodiversity. This study also provides recommendations regarding the use of fertilizers for the purposes of increasing plant biomass and biodiversity in semi-arid grasslands of northern China.

Pollution Assessment of Trace Elements in Agricultural Soils around Copper Mining Area

Agricultural soils from Dongchuan copper mining area were sampled and analyzed to determine the concentrations of selected trace elements, namely As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. The main objectives of this study were: (1) To determine the levels of trace elements and their spatial distribution in soils; (2) to evaluate the potential ecological risk; and (3) to identify the main sources of risk element pollution. The environmental risks were assessed using five different contamination and pollution indexes. Descriptive and exploratory statistical analyses were performed to identify the relations among the trace elements in soils and possible sources of pollution. Although the values of As, Cu and Zn in the soils were significantly higher than Yunnan background values and exceeded the limits of the Chinese national standards in several sampling points, the most serious threat for the ecosystem and human health was represented by Cd. The main sources of Cu and As were identified mining activities, airborne particulates from smelters and the weathering of tailings, and partly also agricultural fertilizers. The major source of Cd was agricultural fertilizers and partly sources associated with mining and smelting activities.

Fertilizer application in rural cropland drives cadmium enrichment in bats dwelling in an urban area

The transfer of pollutants from chemical fertilizers through food webs within cropland is well documented; however, its impacts on the wild animals that forage on croplands but roost in other locations remain poorly understood. The potential for this cross-ecosystem 'spillover' of pollutants is greatest for bats, some of which exploit urban settlements as roosting niches but must travel long distances to reach croplands as foraging niches. Here, we used hairs from a colony of insectivorous bats, Chinese Noctule (Nyctalus plancyi), from an urban area in Southwest China to assess whether exposure to heavy metals/metalloids by the bats varied from 1975 to 2016. Historical changes occurred in hair cadmium (Cd) concentrations in adult females, which was exclusively explained by the regional fertilizer application intensity (FAI), even considering the potential impacts of Cd emissions in urban areas, as indicated by camphor trees (Cinnamomum camphora) near the bats' roosting niche, and the potential impacts of Cd in industrial wastewater, as documented in authorized databases. Therefore, the data from this bat colony, as urban dwellers, indicates Cd accumulation and cross-ecosystem transfer from rural croplands to an urban area.

Influence of calcium and phosphate on pH dependency of arsenite and arsenate adsorption to goethite

In the environment, simultaneous presence of arsenic (As) of different oxidation states is common, which hampers our understanding of As behavior. In the current study, the pH dependency of arsenite (As(III)) and arsenate (As(V)) adsorption to goethite under the influence of calcium (Ca²⁺) (as a major cation) and phosphate (PO₄^3-) (as a major anion) was studied, and the reliability of the CD-MUSIC model prediction was tested. The results show that the presence of the major ions led in general to a weaker and more complicated pH dependency of As adsorption. Calcium promoted As(V) adsorption especially at high pH, which can reverse the direction of the pH dependency. The presence of Ca²⁺ can even decrease As(III) adsorption when As(V) and/or PO₄^3- are present. Phosphate competed strongly with both As(III) and As(V) in their adsorption, especially at intermediate and low pH. In the multi-component system, As(III) adsorbs weaker than As(V) over the environmental relevant pH range, therefore it is often the dominant As species in solution and soluble As(III) concentration generally decreases with increasing pH. In the same pH range, As(V) adsorption shows a complicated pH dependency. Soluble As(V) reaches a minimum around pH 6 at high concentration of major bivalent cations (e.g. Ca²⁺), whereas soluble As(V) will decrease with pH at low bivalent cation concentrations. The experimental results can be reliably predicted and explained with the CD-MUSIC model. The outcome of this study can provide understanding needed in the risk assessment and remediation of As contaminated soils and water.

Opportunities and challenges in the use of mineral nutrition for minimizing arsenic toxicity and accumulation in rice: A critical review

Growing rice on arsenic (As)-contaminated soil or irrigating with As-contaminated water leads to significant accumulation of As in grains. Moreover, rice accumulates more As into grains than other cereal crops. Thus, rice consumption has been identified as a major route of human exposure to As in many countries. Inorganic As species are carcinogenic and could pose a considerable health risk to humans even at low dietary concentration. Genotypic variation and concentration of nutrients such as iron, manganese, phosphate, sulfur and silicon are the two main factors that affect As accumulation in rice grains. Therefore, in addition to better growth and yield of plants, application of specific nutrients in optimum quantities offers an added benefit of decreasing As content in rice grains. These nutrient elements influence speciation of As in rhizosphere, compete with As for root uptake and interfere with As translocations to the shoot and ultimately accumulation in grains. This papers critically appraises the methods, forms and rate of application, mechanisms and extent of efficiency of different mineral nutrients in decreasing As accumulation in rice grains.

Chemical reactive features of novel amino acids intercalated layered double hydroxides in As(III) and As(V) adsorption

Layered double hydroxides (LDHs) intercalated with amino acids such as methionine (Met) were synthesized as new adsorbents to remediate arsenic-polluted water. This Zn₂Al-Met-LDHs, identified with the formula of Zn_0.7Al_0.3(OH)₂(Met)_0.3·0.32H₂O, has good thermal stability. Adsorption experiments with Zn₂Al-Met-LDHs showed that the residual arsenic in solution could be reduced below the regulation limit, and this adsorption process fitted Langmuir isotherm and the pseudo-second-order kinetics well. A remarkably high removal efficiency and the maximum adsorption capacity for As(III) were achieved, 96.7% and 94.1 mg/g, respectively, at 298 K. The desorption efficiency of As(III) from the arsenic-saturated Zn₂Al-Met-LDHs (<8.7%), far less than that of As(V), promises a specific and reliable uptake of As(III) in sorts of solutions. More importantly, a complete and in-depth spectra analysis through FTIR, XPS and NMR was conducted to explain the excellent performance of Zn₂Al-Met-LDHs in arsenic removal. Herein, two special chemical reactions were proposed as the dominant mechanisms, i.e., hydrogen bonding between the carboxyl group of the host Met and the hydroxyl group of As(III) or As(V), and the formation of a chelate ring between the guest As(III) and the S, N bidentate ligands of the intercalated Met in the LDHs.

Toxicological and biochemical responses of the earthworm Eisenia fetida exposed to contaminated soil: Effects of arsenic species

Arsenic is a pollutant that can be detected in different chemical forms in soil. However, the toxicological effects of different arsenic species on organisms have received little attention. In this study, we exposed earthworms Eisenia fetida to artificial soils contaminated by arsenite [As(III)], arsenate [As(V)], monomethylarsonate (MMA) and dimethylarsinate (DMA) for 28 and 56 days. Three biomarkers including lipid peroxidation (LPO), metallothioneins (MTs) and lysosomal membrane stability (LMS) were analyzed in the organisms. In addition, the contents of total arsenic and arsenic species in earthworms were also determined to investigate the effects of bioaccumulation and biotransformation of arsenic on biomarkers and to evaluate the dose-response relationships. The results showed that the relationship between the three biomarkers and the two inorganic arsenic species were dose dependent, and the correlation levels between the biomarkers and As(III) were higher than that between the biomarkers and As(V). Trivalent arsenic species shows more toxicity than pentavalent arsenic on the earthworms at molecular and subcellular level, including oxidative damage, MTs induction and lysosomal membrane damage. The toxicity of MMA and DMA was lower than inorganic arsenic species. However, the occurrence of demethylation of organic arsenics could lead to the generation of highly toxic inorganic arsenics and induce adverse effects on organisms. The biotransformation of highly toxic inorganic arsenics to the less toxic organic species in the earthworms was also validated in this study. The biomarker responses of the earthworm to different arsenic species found in this study could be helpful in future environment monitoring programs.

Accumulation, biotransformation, and multi-biomarker responses after exposure to arsenic species in the earthworm Eisenia fetida

Earthworms (Eisenia fetida) were exposed to OECD soils contaminated with arsenite (29.3 mg kg-1), arsenate (35.2 mg kg-1), monomethylarsonate (342.5 mg kg-1) and dimethylarsinate (373.0 mg kg-1) for 64 days. The exposure concentration for the four arsenic species was set at one-tenth of 14 d-LC50 in order to compare their toxicity. Eight biomarkers including superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, glutathione reductase, reduced glutathione, lipid peroxidation and metallothioneins were analyzed in the organisms. A multi-biomarker approach, the integrated biomarker response (IBR) index, was adopted to summarize the multi-biomarker responses to a single value, reflecting the integrated stress of different arsenic species on earthworms. Furthermore, total arsenic and arsenic speciation were analyzed in earthworm tissue to evaluate the relationship between arsenic accumulation and biomarker responses at the molecular and subcellular levels and to observe the role of arsenic biotransformation in earthworms. The results showed that the toxicity of the four arsenic species was ranked as: arsenite > arsenate > monomethylarsonate and dimethylarsinate. Although organic arsenics showed a low degree of biotoxicity, they could be turned into highly toxic inorganic arsenics under the effect of demethylation, which caused a toxic effect on organisms. The biomarker responses indicated that a sub-lethal dose of both arsenite and arsenate could trigger the response of the antioxidant defense system and cause oxidative damage when the protective capacity of the system was exhausted. Arsenic in earthworms could be detoxified during the process of biotransformation, where inorganic arsenics were converted into organic arsenics, which would then be excreted out. Based on these results, it was proved that different arsenic species showed different degrees of toxicity. Therefore, arsenic species should be differentiated in order to obtain accurate results in quality/risk assessment programs.

Trace elements in rock phosphates and P containing mineral and organo-mineral fertilizers sold in Germany

68 rock phosphates and 162 P containing (organo-)mineral fertilizers sold in Germany were evaluated with regard to trace element contents. While Al, As, B, Be, Cd, Cr, Mo, Ni, Pb, Sb, Se, Tl, U, and Zn were higher in sedimentary than in igneous rock phosphates, the opposite was true for Co, Cu, Sn, Mn, Ti, Fe, and Sr. Comparing element concentrations to the currently valid legal limit values defined by the German Fertilizer Ordinance, it was found that some PK and many straight P fertilizers (superphosphate, triple superphosphate, partly acidulated rock phosphates) exceeded the limit of 50 mg Cd/kg P2O5. Mean values for As, Ni, Pb, and Tl remained below legal limits in almost all cases. While no legal limit has been defined for U in Germany yet, the limit of 50 mg U/kg P2O5 for P containing fertilizers proposed by the German Commission for the Protection of Soils was clearly exceeded by mean values for all fertilizer types analyzed. A large share of the samples evaluated in this work contained essential trace elements at high concentrations, with many of them not being declared as such. Furthermore, trace elements supplied with these fertilizers at a fertilization rate leveling P uptake would exceed trace element uptake by crops. This may become most relevant for B and Fe, since many crops are sensitive to an oversupply of B, and Fe loads exceeding plant uptake may immobilize P supplies for the crops by forming Fe phosphate salts. The sample set included two products made from thermochemically treated sewage sludge ash. The products displayed very high concentrations of Fe and Mn and exceeded the legal limit for Ni, emphasizing the necessity to continue research on heavy metal removal from recycled raw materials and the development of environmentally friendly and agriculturally efficient fertilizer products.

Lysosomal membrane response of the earthworm, Eisenia fetida, to arsenic species exposure in OECD soil

The NRRT assay was sensitive for toxicity assessment of inorganic arsenic pollution and it was affected more by As(iii) than by As(v).

Is soil dressing a way once and for all in remediation of arsenic contaminated soils? A case study of arsenic re-accumulation in soils remediated by soil dressing in Hunan Province, China

The investigation of arsenic (As) re-accumulation in an area previously remediated by soil dressing will help in sustainable controlling the risks of As to local ecosystems and should influence management decisions about remediation strategies. In this study, As content in an area remediated by soil dressing and the possible As accumulation risk in agricultural products were investigated. The results indicated that after 7 years of agricultural activities, the average As content (24.6 mg kg(-1)) in surface soil of the investigated area increased by 83.6% compared with that (13.4 mg kg(-1)) in clean soil. Of the surface soil samples (n = 88), 21.6% had As levels that exceeded the limits of the Environmental Quality Standard for Soils of China (GB 15618-1995) and 98.9% of the surface soil samples with As contents exceeding that in clean soil was observed. Soil dressing might be not a remediation method once and for all in some contaminated areas, even though no significant difference in available As content was found between clean (0.18 mg kg(-1)) and surface (0.22 mg kg(-1)) soils. The foreign As in surface soil of the investigated area mainly specifically sorbed with soil colloid or associated with hydrous oxides of Fe and Al, or existed in residual fraction. The upward movement of contaminated soil from the deeper layers and the atmospheric deposition of slag particles might be responsible for the re-accumulation of As in the investigated area. Decreases in soil pH in the investigated soils and the fact that no plant samples had As levels exceeding the limits of the National Food Safety Standards for Contaminants of China (GB 2762-2012) were also observed.