Arsenic in Human and Cow's Milk: a Reflection of Environmental Pollution

Arsenic, an environmental pollutant, is present in minute but invariable amounts in food, drinking water and ambient air. Izmir is founded on a land of long extinct volcanoes, with vast areas of lava ground suitable for agriculture. It is located at close vicinity to high thermal activity, e.g., hot springs and thermal baths. In the present study, total arsenic level in breast milk was assessed in randomly chosen 35 lactating women of different socioeconomic levels who live downtown in Izmir and in milk of 36 cows grazing on shoulder grass of highways with heavy traffic. Total arsenic was assessed on an atomic absorption spectrophotometer (AA-680 Shimadzu). Mean (± SEM) arsenic was found to be 4.219 ± 0.079 µg L^-1 in breast milk, and 4.932 ± 0.38 µg L^-1 in cow's milk. Conclusion: in Izmir, arsenic contamination of breast milk was not found so as to be considered noxious for suckling infants, whereas was found relatively higher in cow's milk. It would be prudent to remember breast and cow's milk arsenic contamination in breast fed or milk fed babies living in areas with higher thermal activity or in regions where ground water is with high arsenic content.     

Arsenic in field‐collected soil solutions and extracts of contaminated soils and its implication to soil standards

Large concentrations of arsenic in soils, sediments, and freshwaters require risk assessment across the Central Alps and other regions. We measured arsenic concentrations in soil samples collected from 38 sites located in the Austrian Central Alps that had been contaminated due to mining and smelter activities and geogenic mineralization. Medians and ranges of arsenic concentrations (in mg kg^—1) in the soil solid phase were: 77.1 (1—3000) for the total (As_t), 19.2 (0—726) for (NH₄)₂C₂O₄‐extractable (As_o), 2.35 (0—169) for (NH₄)₂HPO₄‐extractable (As_p), and 0.143 (0—11.1) for (NH₄)₂SO₄‐extractable (As_s) arsenic. Arsenic concentrations in soil solutions (As_sol) collected from organic surface layers and mineral horizons at five selected sites using suction cups fitted with nylon membranes ranged from 0 to 171 μg l^—1. Typically, the prevailing species of As in the soil solution was As(V). As_sol was correlated with As_s (As_sol = 0.279 + 15.6 As_s; r² = 0.938; n = 17) and As_t (As_sol = 1.272 + 0.043 As_t; r² = 0.833; n = 17). Using these empirical models, As_sol can be predicted quite accurately based on extraction with 0.05 M (NH₄)₂SO₄ or total arsenic concentrations in the soil. Linking these models to drinking water standards (DWS) we propose soil standards for freshwater protection that vary for As_s (mg kg^—1) between 0.62 (for DWS = 10 μg l^—1 WHO) and 3.19 (for DWS = 50 μg l^—1). Corresponding standards for As_t (mg kg^—1) are 203 (DWS = 10 μg l^—1) and 1133 (DWS = 50 μg l^—1). These considerations demonstrate that changes in legislation on DWS may have dramatic impact on As concentrations in soil that are acceptable for groundwater protection.     

Vegetables collected in the cultivated Andean area of northern Chile: total and inorganic arsenic contents in raw vegetables.

High levels of arsenic are found in the soil and water of the Second Region in Chile as a result of natural causes. Total and inorganic arsenic contents were analyzed in the edible part of 16 agricultural products (roots, stems, leaves, inflorescences, and fruits) grown in this area. The total arsenic contents varied in the range 0.008-0.604 microg g(-1) of wet weight (ww), below the maximum level allowed by Chilean legislation (1 microg(-1) of ww). Inorganic arsenic contents (range = 0.008-0.613 microg(-1) of ww) represented between 28 and 114% of total arsenic. The concentrations of total and inorganic arsenic found in edible roots and leaves were higher than those found in fruit. The highest concentrations were found in a sample of spinach. High quantities of this vegetable would have to be consumed (250 g/day) to reach the Provisional Tolerable Weekly Intake for inorganic arsenic. The vegetable group may make a considerable contribution to the total intake of inorganic arsenic.     

Bioavailability of inorganic arsenic in cooked rice: practical aspects for human health risk assessments

Arsenic is present in rice grain mainly as inorganic arsenic. Little is known about the effect of cooking on inorganic arsenic content in rice and its bioavailability. This study evaluated total arsenic and inorganic arsenic in rice cooked with arsenic-contaminated water, the bioaccessibility of As(III) and As(V) after simulated gastrointestinal digestion, and the extent of arsenic retention and transport by Caco-2 cells used as a model of intestinal epithelia. After cooking, inorganic arsenic contents increase significantly. After simulated gastrointestinal digestion, the bioaccessibility of inorganic arsenic reached 63-99%; As(V) was the main species found. In Caco-2 cells, arsenic retention, transport, and total uptake (retention + transport) varied between 0.6 and 6.4, 3.3 and 11.4, and 3.9 and 17.8%, respectively. These results show that in arsenic endemic areas with subsistence rice diets, the contribution of inorganic arsenic from cooked rice should be considered in assessments of arsenic health risk.     

Arsenic Concentrations in Groundwater,Soils, and Irrigated Rice in Southwestern Bangladesh

Arsenic (As) poisoning of groundwater in Bangladesh has become a major environmental and health issue. The extensive use of groundwater in irrigation of rice has resulted in elevated As in soils and crops. A study was undertaken to determine As concentrations in groundwater, soils, and crops in 16 districts of southwestern Bangladesh. Groundwater samples were collected from shallow-tube and hand-tube wells (STW and HTW) used for irrigation and drinking water. Soil and rice plants were sampled from the command area of the tube wells. Arsenic concentrations were determined using an atomic absorption spectrometer equipped with flow injection hydride generator. Groundwater samples contained <10 to 552 μg As L^?1. Arsenic concentrations in 59% of STW samples exceeded 50 μg As L^?1, the national standard for As in drinking water. Unlike groundwater, most of the surface water samples contained <10 μg As L^?1. Concentrations of As in the soils from the command area of the tube wells ranged from 4.5 to 68 mg kg^?1. More than 85% of the soils contained <20 mg As kg^?1. The mean As concentration in the rice grain samples was 0.23 mg kg^?1, which is much less than the maximum food hygiene standard. A positive relationship was observed between groundwater and soil As, implying that soil As level increases as a result of irrigation with contaminated water. However, irrigation water As did not show any relation with rice grain As. The findings suggest that surface water bodies are a safe source of irrigation water in the As-contaminated areas.     

Arsenic in Water,Soil, and Rice Plants in the Indo-Gangetic Plains of Northwestern India

Arsenic (As), which is present in all living tissues, water, and soil, is considered toxic to humans and animals. Because of the presence of arsenic-contaminated sites throughout the world, there is a renewed interest in studying the status of As in water, soil, and plants. Concentrations of As above the permissible limit have been reported in Lower Ganges Plains (West Bengal in India and Bangladesh). The present investigation aimed to examine the concentration of As in water, soil, and rice plants in the Upper/Trans-Ganges Plains covering Punjab in northwestern India. In total, 200 water samples were collected from different locations in Punjab. Corresponding soil, rice grain, and straw samples were collected from the same locations as the water samples had been collected. In addition to deep tube well water (>125 m deep), water samples from shallow hand pumps (<50 m deep) and canals were also collected. The samples were analyzed for total As concentration using an atomic absorption spectrophotometer equipped with a hydride generating system (AAS-HG). The concentration of As in tube well water samples varied from 5.33 to 17.27 μg As L^–1, with about 40% samples having As concentrations greater than the permissible limit (10 μg As L^–1). None of the hand pump and canal water samples had As concentrations greater than permissible limits. The As concentration of surface soils varied from 1.09 to 2.48 mg As kg^–1. There was no trend in the distribution of As with depth of soil. The concentration of As in rice straw varied from 4.05 to 15.06 μg As kg^–1 and that of grain from 1.48 to 6.87 μg As kg^–1. The concentration of As was lower in edible grain than in inedible straw. There was a positive and significant correlation between As concentration in tube well water and As concentration in surface soils. The buildup of As in soils was directly related to the As concentration of tube well waters. There was a significant correlation between As in water and As in plants. However, a nonsignificant correlation existed between As in soil and As in plants. This indicates that plants absorbed more As from irrigation water than that from soil. This also suggests that irrigation with such waters over a longer period of time may have detrimental effects on soil and on plants, animals, and humans. There is thus a need to continuously monitor the As concentration in undergroundwater.     

Heavy metal effects on soil populations and heavy metal tolerance of Rhizobium meliloti,nodulation, and growth of alfalfa

Effects of heavy metals on rhizobia and the symbiotic association with leguminous hosts are currently unclear. To investigate this problem, we examined Rhizobium meliloti (microsymbiont) and alfalfa (Medicago sativa) (macrosymbiont) collected from soils contaminated with varying concentrations of heavy metals (varying distances from a Zn smelter operating 90 yr.). Soil populations of R. meliloti were not correlated with metal concentrations in soil. The lowest rhizobial population was found in the soil with the highest extractable metal concentrations, but the highest populations were found in soil which was moderately contaminated. A greenhouse study in which alfalfa was grown in the same soils showed no significant trend for nodulation or nitrogenase activity of roots. Highest nodule number and nitrogenase activity were observed in those soils which had the lowest population of R. meliloti. When the heavy metal Minimum Inhibitory Concentration (MIC) of individual isolates was examined, no correlation was found between the MIC and soil metal concentration (total, or water or 0.01 M Ca(NO₃)₂ extractable).These results indicate that even in highly contaminated soils, metal activity was not high enough to exert an antagonistic influence on the soil rhizobial population or the symbiotic association between alfalfa and R. meliloti.     

滴灌苜蓿田间土壤水盐及苜蓿细根的空间分布

为了明确滴灌苜蓿土壤水、盐运移,细根分布及细根生物量动态,该文对苜蓿进行滴灌和漫灌试验,结果表明,漫灌水分集中在15 cm浅层土壤内且分布均匀,含水率在19.5%~20.5%之间。滴灌水分高值区集中在水平方向距滴头15 cm,深度为40 cm的土层中,含水率达到18.0%~20.0%。漫灌对0~25 cm深度土层盐分淋洗作用明显,土水比1:5土壤水提液的电导率由灌前的0.4~0.5 m S/cm下降到0.3 m S/cm以下;滴灌可使根区盐分下降至0.2 m S/cm,显著低于灌溉初始的盐分含量(P0.05)。与漫灌比较,滴灌苜蓿细根集中分布在水平方向距滴头0~30 cm,垂直深度0~50 cm范围内。生长季各时间节点滴灌细根总量高于漫灌,其平均值分别为211.6和198.3 g/m2。滴灌和漫灌各时间节点细根量表现出明显的波动,其范围分别在193.2~243.6和182.7~219.1 g/m2之间。在整个生长期内,滴灌活根量高于漫灌,且生长前期滴灌死根量变化较漫灌平稳。活细根和死细根之间的周转使得两者呈现出此消彼涨的状态,表明细根具有生长-凋亡-再生长的周期性。该研究可为滴灌技术在苜蓿栽培上的应用提供参考。     

Anion‐exchange membrane,water, and sodium bicarbonate extractions as soil tests for phosphorus

Abstract

Three techniques were evaluated as soil P tests for western Canadian soils: anion‐exchange membrane (AEM), water, and bicarbonate extraction. The AEM, water, and bicarbonate‐extractable total P represented novel approaches to compare to the widely used bicarbonate‐extractable inorganic P (traditional Olsen) soil test. In a range of Saskatchewan soils, similar trends in predicted relative P availability were observed for AEM, water extraction, bicarbonate‐extractable total P, and bicarbonate‐extractable organic P. Correlations between soil test values revealed AEM and water‐extractable P to be most closely correlated, consistent with the similar manner of P removal in the two tests.

Phosphorus availability, as predicted by the tests, was compared to actual P uptake by canola and wheat grown on 14 soils in a growth chamber experiment. P uptake by canola was highly correlated with AEM (r² = 0.86–0.90), water (0.87 ‐0.94), and bicarbonate‐extractable total (0.91) and inorganic (0.92) P. Uptake of P by wheat was not quite as highly correlated with test‐predicted values: AEM (r² = ‐0.73–0.78), water (0.72–0.77), bicarbonate total (0.82), bicarbonate‐inorganic P (0.75).

The similarity in coefficients of determination among test methods indicated nearly identical abilities of the tests to predict soil P availability in the range of soils examined. The AEM and water extractions, unlike bicarbonate, are largely independent of soil type and may prove superior when a wider range of soils is being tested. Bicarbonate‐extractable total P and water‐extractable P suffer limitations in analytical simplicity and cost. In testing for P alone, AEM was considered superior to the other methods due to low cost, simplicity, independence of soil type, and high correlation with plant uptake.     

Arsenic transport and transformation associated with MSMA application on a golf course green

The impact of extensively used arsenic-containing herbicides on groundwater beneath golf courses has become a topic of interest. Although currently used organoarsenicals are less toxic, their application into the environment may produce the more toxic inorganic arsenicals. The objective of this work was to understand the behavior of arsenic species in percolate water from monosodium methanearsonate (MSMA) applied golf course greens, as well as to determine the influences of root-zone media for United State Golf Association (USGA) putting green construction on arsenic retention and species conversion. The field test was established at the Fort Lauderdale Research and Education Center (FLREC), University of Florida. Percolate water was collected after MSMA application for speciation and total arsenic analyses. The results showed that the substrate composition significantly influenced arsenic mobility and arsenic species transformation in the percolate water. In comparison to uncoated sands (S) and uncoated sands and peat (S + P), naturally coated sands and peat (NS + P) showed a higher capacity of preventing arsenic from leaching into percolate water, implying that the coatings of sands with clay reduce arsenic leaching. Arsenic species transformation occurred in soil, resulting in co-occurrence of four arsenic species, arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in percolate water. The results indicated that substrate composition can significantly affect both arsenic retention in soil and arsenic speciation in percolate water. The clay coatings on the soil particles and the addition of peat in the soil changed the arsenic bioavailability, which in turn controlled the microorganism-mediated arsenic transformation. To better explain and understand arsenic transformation and transport after applying MSMA in golf green, a conceptual model was proposed.     

The excretion of citric and malic acid by proteoid roots of Lupinus albus L.; effects on soil solution concentrations of phosphate,iron, and aluminum in the proteoid rhizosphere in samples of an oxisol and a luvisol

Organic acid concentration in the proteoid rhizosphere of White Lupin in different soil samples (Oxisol-A_p = Ox, Luvisol-A_p and Luvisol-C = L_A and L_C) was determined in order to study the influence of root-released carboxylates on the mobilization of phosphate, aluminum, and iron in the rhizosphere. In the L_C, organic acids were accumulated as Casalts extractable with water. In the proteoid rhizosphere of this soil sample 55 μmol citrate and 8 μmol malate per g soil were found. In the Ox, no water extractable organic acids were present. However, determination of citrate in the solid phase of this soil by Diffuse Reflectance Infrared Fourier Transform Spectroscopy gave concentrations of 88 and 68 μmol citrate per g soil without and with P application, respectively. Displaced soil solution from the proteoid root rhizosphere of the Ox and the L_A increased in Fe and Al concentrations from <50 μmol/L (soil from reference pots without plants) to more than 600 μmol Fe+Al/L. The concentration of P was increased by a factor of 2 despite of P uptake by the proteoid roots. The mobilization of Al, Fe, and P is attributed to ligand exchange of phosphate against citrate and to the solubilization of Al and Fe as carboxylate complexes.     

Pressurized Hot Water and DTPA‐Sorbitol as Viable Alternatives for Soil Boron Extraction. II. Correlation of Soil Extraction to Responses of Boron‐Fertilized Alfalfa

Abstract

Pressurized hot water and DTPA‐Sorbitol are two relatively new, proposed alternative soil boron (B) extraction methods for which no data on yield or plant nutrient uptake have been reported for validation. Both methods initially have shown significant correlation with the hot water extraction method in untreated soils as well as soils incubated with various levels of B. The objective of the research was to extract samples of B‐treated soils by using all three extraction methods and correlate the B values obtained to yield, B tissue concentration, and total B removal of alfalfa (Medicago sativa). Greenhouse and field experiments on alkaline and limed acid soils naturally low in hot water‐extractable B were conducted to test alfalfa response to B fertilizer. In the greenhouse, highly significant relationships exist between plant uptake and extractable B with all three methods at varying levels of applied B, but no alfalfa yield response was observed. All three methods result in accurate predictions of plant B tissue concentrations and total B removal. The field experiment exhibited a significant positive relationship between total alfalfa yield and extractable B using hot water and pressurized hot water extractions. Extractable B using DTPA‐Sorbitol was not related to total alfalfa yield in the field experiment. This work, coupled with the earlier incubation studies, supports the pressurized hot water extraction method as an improvement over hot water in diverse soil types. The lack of relationship in the acid soil supports DTPA‐Sorbitol as an improvement over hot water in alkaline soils.     

Accumulation of Phosphorus and Arsenic in Two Perennial Grasses for Soil Remediation

Rice cutgrass (Leersia oryzoides Sw.) and tall fescue (Festuca arundinacea Schreb.) were assessed for potential for phytoremediation of arsenic (As) in a soil-based medium amended with phosphorus (P) in a greenhouse experiment. Arsenic was added at 30 mg kg^?1, and P concentrations ranged from 0 to 120 mg kg^?1. Plants were grown for 8 weeks. Rice cutgrass accumulated greater concentration and total amount of As in shoots or roots than fescue. Only the first increment of P fertilization increased As in shoots above that which accumulated without P fertilization. Phosphorus fertilization did not stimulate growth of either species. Most of the As remained in the roots of either species. Plant–soil accumulation ratios suggest that rice cutgrass has more potential in phytoremediation than fescue. Above a minimal amount, P fertilization did not enhance As accumulation in shoots and may not be useful in increasing the potential of either species to remediate soils.     

Arsenic Uptake by Two Hyperaccumulator Ferns from Four Arsenic Contaminated Soils

A greenhouse study was conducted to evaluate and compare arsenic accumulation from four arsenic contaminated soils by two arsenic hyperaccumulators, Pteris vittata and Pteris cretica. After growing in soils for six weeks, the plants were harvested and separated into above- and below-ground biomass. Total As, P, Ca, K, glutathione and biomass were measured for the plants, and total As, Mehlich-3 P and As, exchangeable K and Ca, and arsenic fractionation were performed for the soils. Pteris vittata had significantly higher total biomass (14 g/plant) and As accumulation than P. cretica. Arsenic accumulation in both ferns followed the arsenic concentrations in the soil. The P/As molar ratio in the fronds, growing in arsenic contaminated soils, ranged from 80 to 939 in P. vittata and 130 to 421 in P. cretica. Plant arsenic concentrations were significantly positively correlated with Mehlich-3 arsenic in the soils. Soil pH was also significantly correlated with Mehlich-3 arsenic before and after plant uptake. Plant As uptake was significantly correlated with exchangeable potassium in the soil before plant uptake. Glutathione availability was not implicated as a major detoxification mechanism in these ferns. Though both plants were effective in taking up arsenic from various arsenic contaminated soils, P. vittata was overall a better candidate for phytoremediation of arsenic contaminated soils.     

An integrated sampling/speciation method for inorganic arsenic in soil solution

Arsenic mobility, bioavailability, and toxicity in soil‐water systems are strongly affected by species distribution. In spite of species‐selective analytical tools, results may be biased by postsampling oxidation or reduction of compounds. The scope of this study was to delineate a speciation method for inorganic arsenic integrated with pore‐water sampling to prevent problems related to postsampling species transformation. Experiments were performed with exchange cartridges packed with quaternary amine (nitrate‐form) to separate anionic arsenate from uncharged arsenite. Standard solutions with varied As(III) : As(V) ratios as well as groundwater and soil‐solution samples were studied. Analyses were performed by ICP‐MS using either extraction cartridges directly coupled to the instrument or samples obtained by offline speciation tests. Results showed that As(III) passes the packed bed with the rinsing solution, while As(V) is retained on the column and can be released by elution with 0.25 M NH₄NO₃. Recoveries between 98% and 116% were insensitive to pH variation (pH 3–8) and competing anions. Groundwater samples from a contaminated site yielded recoveries between 92% and 125% when the sum of As(III) and As(V) was compared to total As. Integration of the speciation scheme with pore‐water sampling was tested in a soil‐column experiment. Soil material from a fen site with elevated geogenic As contents was subjected to a varying moisture regime. Reducing conditions during prolonged saturation caused a marked increase of As(III) concentrations. Conversely, when the soil was drained, total As levels decreased and were dominated by As(V). Overall, extraction results with standard solutions and natural samples indicate reliable performance of the method in experimental investigations and field studies.     

煤矸石土壤砷污染相关性分析

在对内蒙古自治区某矿区周边土壤环境总砷含量、全磷、有机质、含水率等项目测定的基础上,分析了土壤总砷含量、有效砷含量与土壤理化性质指标的相关性。同时,通过模拟研究区降水特点和降水量,采用淋溶试验装置,对由煤矸石和自然表层土壤组成的两组混合样品在不同pH值条件下砷的析出规律进行了实验研究。结果表明,研究区土壤有效态砷与总砷含量存在显著正相关关系;总砷含量与pH值、全磷存在一定的正相关性,与有机质和水解性氮之间的相关性不显著;土壤有效态砷含量与有机质含量呈正相关关系,与pH值呈一定的负相关关系。混合土层中砷的淋出量随淋溶液pH值的增加呈降低趋势,pH值越低,砷淋出量越高。     

Assessment of Arsenic Toxicity and Tolerance Characteristics of Bean Plants (Phaseolus Vulgaris) Exposed to Different Species of Arsenic

Experiments were conducted to evaluate the arsenic toxicity, its accumulation and phytoremediation potential of bean plants (Phaseolus vulgaris) grown in soils contaminated with different species of arsenic such as arsenite (As(III)), arsenate (As(V)) and dimethylarsinic acid (DMA). Bean plants were grown in soils amended by aqueous solutions of 20 and 50 mg kg^?1 of As (III), As(V) or DMA. Arsenic species negatively affected the yield and growth of the plant. The study demonstrated arsenic accumulation in the plant parts. The concentration of arsenic compounds in the shoots decreased in the order arsenate > arsenite > dimethylarsinic acid while in the roots as arsenite > arsenate > dimethylarsinic acid. Most arsenic is accumulated in the roots with limited transfer to shoots. Thus, bean plants can be considered as an arsenic excluder and has the potential for phytostabilization of arsenic contaminated sites. The study also reveals that removal of arsenic by boiling the vegetables with excess of water is not possible.     

Arsenic speciation in food and estimation of the dietary intake of inorganic arsenic in a rural village of West Bengal, India

Arsenic (As) species were quantified by HPLC-HG-AFS in water and vegetables from a rural area of West Bengal (India). Inorganic species predominated in vegetables (including rice) and drinking water; in fact, inorganic arsenic (i-As) represented more than 80% of the total arsenic (t-As) content. To evaluate i-As intake in an arsenic affected rural village, a food survey was carried out on 129 people (69 men and 60 women). The data from the survey showed that the basic diet, of this rural population, was mainly rice and vegetables, representing more than 50% of their total daily food intake. During the periods when nonvegetarian foods (fish and meat) were scarce, the importance of rice increased, and rice alone represented more than 70% of the total daily food intake. The food analysis and the food questionnaires administrated led us to establish a daily intake of i-As of about 170 microg i-As day (-1), which was above the tolerable daily intake of 150 microg i-As day (-1), generally admitted. Our results clearly demonstrated that food is a very important source of i-As and that this source should never be forgotten in populations depending heavily on vegetables (mainly rice) for their diet.     

Arsenic uptake,distribution, and accumulation in tomato plants: Effect of arsenite on plant growth and yield

The response of tomato (Lycopersicum esculentum Mill, cultivar Marmande) plants to different levels of arsenic (As) in nutrient solution was investigated—the processes of uptake, distribution and accumulation of As, and the effect of arsenite on yield and plant growth (plant height, diameter of stem, stem and root length, fresh and dry weight of root, stems, leaves, and fruit). The experiment was performed at three levels of As: 2, 5 and 10 mg/L [added as sodium arsenite (NaAsO₂)] in a nutrient solution, together with the corresponding control plants. Arsenic uptake depended on the As concentration in solution and As content in the roots increased as the time of treatment increased. The most important finding was the high toxicity of arsenite to roots. The concentration in stems, leaves, and fruit was correlated with the As level in the nutrient solution. Although the As level of 10 mg/L damaged the root membranes, resulting in a significant decrease in the upward transport of As. Arsenic exposure resulted in a drastic decrease in plant growth parameters (e.g., maximum decrease of 76.8% in leaf fresh weight) and in tomato fruit yield (maximum reduction of 79.6%). However, it is important to note that the As concentration in the fruits was not toxic or harmful for human consumption.     

Potentially hazardous element accumulation in rice tissues and their availability in soil systems after biochar amendments

Purpose

Biochar has shown to be a great product to control the bioavailability of potentially hazardous elements (PHE) in contaminated soils. Despite the advantages associated with the application of biochar in agricultural soils, relatively few studies have focused on the effects of biochar amendments on soil chemical properties, accumulation of arsenic, cadmium, zinc, and lead in rice tissues, and their availability in soil systems.

Materials and methods

The field experiment was conducted at the paddy soils in Hunan Province, China. The soil texture was sandy clay loam. Wheat-derived biochar was applied once to the experimental plots at the rates of 0, 10, 20, 30 and 40 t ha^?1, and referenced as A0, A10, A20, A30, and A40, respectively. For PHE determination, soil samples and plant samples were digested with a mixed solution of HCl:HNO₃ (4:1, V:V) and HCl:HClO₄ (4:1, V:V), respectively, and the arsenic, cadmium, zinc, and lead in the digest solution were measured by ICP-MS (Thermo Fisher Scientific, USA). The soil available fraction of PHE (arsenic, cadmium, zinc, and lead) was extracted by diethylenetriamine pentaacetic acid (DTPA) and measured by inductively ICP-MS.

Results and discussion

Biochar amendment increased chemical properties of soil organic matter, pH, electrical conductivity, cation exchange capacity, nitrate nitrogen, and available phosphorus. Soil DTPA extractable arsenic, cadmium, zinc, and lead concentrations were significantly reduced. Arsenic, cadmium, zinc, and lead in rice shoots, and arsenic, cadmium, and zinc in roots significantly decreased after amendment. Concentrations in rice tissues positively and negatively correlated with the soil available fraction of PHE and soil chemical properties, respectively. Soil electrical conductivity negatively correlated with the soil available fraction of PHE. Concentrations of arsenic, zinc, cadmium, and lead in rice roots declined relative to increases of cation exchange capacity (arsenic, zinc), available phosphorus (cadmium), and nitric nitrogen (lead) content. Similar relationships were observed between cation exchange capacity and PHE in shoots.

Conclusions

Biochar creates avoidance of PHE through regulating chemical properties through biochar sorption capacity. Cation exchange capacity, available phosphorus, and nitric nitrogen were the principle factors affecting roots uptake of arsenic, zinc, cadmium, and lead. Biochar soluble salts could decline availability of metals/metalloids in soils through precipitation. Wheat-derived biochar application is an alternative safe product to immobilize PHE in rice paddy soils by restricting the risk of PHE.