The impact of sewage irrigation on the uptake of mercury in corn plants (Zea mays) from suburban Beijing

The impact of sewage irrigation on the uptake and translocation of mercury (Hg) in corn plants (Zea mays) was investigated. Corn plants were harvested the same day from two nearby fields in suburban Beijing, one irrigated historically with sewage effluent, and one irrigated solely with groundwater. Hg content was analyzed in the soil, roots and stems, while percent moisture and soil organic content were analyzed in the soil samples. The concentration of Hg in the soil and roots, and the soil organic content were not significantly different between the two fields, despite the historic practice of sewage irrigation. Hg content in roots was positively correlated with soil Hg concentration (r=0.95, n=6). The transfer coefficients between roots and stems were significantly higher in the control site (control: 2.06, sewage-irrigated: 0.44, p<0.05), indicating that the barrier effect of the roots was not consistent between the two fields.     

Human health risk from Heavy metal via food crops consumption with wastewater irrigation practices in Pakistan

The current study was designed to investigate the potential human health risks associated with consumption of food crops contaminated with toxic heavy metals. Cadmium (Cd) concentration in surface soils; Cd, lead (Pb) and chromium (Cr) in the irrigation water and food crops were above permissible limits. The accumulation factor (AF) was >1 for manganese (Mn) and Pb in different food crops. The Health Risk Index (HRI) was >1 for Pb in all food crops irrigated with wastewater and tube well water. HRI >1 was also recorded for Cd in all selected vegetables; and for Mn in Spinacia oleracea irrigated with wastewater. All wastewater irrigated samples (soil and food crops) exhibited high relative contamination level as compared to samples irrigated with tube well water. Our results emphasized the need for pretreatment of wastewater and routine monitoring in order to avoid contamination of food crops from the wastewater irrigation system.     

某矿区土壤和地下水重金属污染调查与评价

为了解湘南某矿区土壤和地下水重金属污染状况，对该矿区东河流域附近重金属污染源进行了调查，同时，对地下水和土壤样品进行了采样分析，结果表明：（1）该矿区东河流域附近的主要污染源有18个，其中有色金属选厂、尾矿库、采矿场和冶炼厂是排放重金属较多的污染源；（2）20个采样点中土壤重金属Pb、Cd、Zn、As和Hg大部分超过国家土壤环境质量标准（GB15618-1995），综合污染指数P综〉1，该矿区主要的重金属污染元素为Cd、As和Hg，且土壤中Cd、Zn和As的含量两两之间存在着极显著的正线性相关关系；（3）重金属元素在土壤中的纵向迁移不明显，该矿区附近20个采样点的地下水并未受到污染，综合污染指数P综〈1。20个采样点地下水Pb、Cd、Zn、As、Hg浓度均能达到地下水质量标准（GB／T14848．9）中的Ⅲ类标准。     

Risk assessment of potentially toxic element pollution in soils and rice (Oryza sativa) in a typical area of the Yangtze River Delta

Soil pollution with potentially toxic elements (PTEs) resulting from rapid industrial development has caused major concerns. Selected PTEs and their accumulation and distribution in soils and rice (Oryza sativa) collected from Changshu, east China, were analyzed to evaluate the potential health risk to the local population. The soils were primarily contaminated with Hg, followed by Cu, Cd, Pb, and Zn. The concentrations of Pb, Hg, and Cd of 46, 32, and 1 rice samples exceeded their national maximum allowable levels in foods, respectively. Spatial distributions of total Cr, Cu, Pb, Zn, and Cd in soils shared similar geographical trends. The risk assessment of PTEs through rice consumption suggests that the concentrations of Cu, Pb, and Cd in some rice samples exceed their reference oral dose for adults and children. In general, there was no target hazard quotient value of any individual element that was greater than 1, but hazard index values for adults and children were 1.726 and 1.523, respectively.     

Effects of irrigation with raw and differentially diluted sewage and application of primary settled sewage-sludge on wheat plant growth, crop yield, enxymatic changes and trace element uptake

An increase in the concentration of Cu, Zn, Cr and Mn, and a decrease in the activities of aspartate amino transferase, alanine amino transferase and peroxidase were observed in the different fractions of wheat plants, following raw and differentially diluted (66% and 50%) sewage irrigation and dry primary settled sewage-sludge amendments of soils. The grain enrichment efficiencies for Cu, Zn and Mn were significantly low under all experimental conditions. On the other hand, the grain enrichment efficiency for Cr was low under all sewage irrigation conditions only. Except in the earheads of wheat plants from sludge-amended soil, catalase activities were significantly low in roots, stems and earheads of wheat plants, under all other treatment conditions investigated. The decrease in the proteinase activity was statistically significant in roots and earheads of sewage-irrigated plants; the activity in the stem was low following irrigation with raw and 66% sewage only. Proteinase activity was also significantly low in all fractions of wheat plants harvested from soil amended with 20 tonnes of sludge per hectare. The observed results appear to be due to an overall decrease in the metabolic status of the plants following sewage irrigation and sludge amendment of soils. Grain yields, however, were not reduced despite this metabolic effect.     

Potential risk assessment of heavy metals by consuming shellfish collected from Xiamen, China

Concentrations of Hg, Pb, Cd, and Cr in 240 shellfish including oyster, short-necked clam, razor clam, and mud clam collected from six administrative regions in Xiamen of China were measured. The daily intakes of heavy metals through the consumption of shellfish were estimated based on both of the metal concentrations in shellfish and the consuming amounts of shellfish. In addition, the target hazard quotients (THQ) were used to evaluate the potential risk of heavy metals in shellfish on human body. Results showed that the concentrations of heavy metals in shellfish ranged at the following sequence: Cr > Cd > Pb > Hg. The concentrations of Hg and Pb in most samples were below the limits (0.3 mg?kg^?1 for Hg and 0.5 mg?kg^?1 for Pb) of national standard (GB 18406.4-2001) set in China. About 57 % of samples were found to contain more than 0.1 mg?kg^?1 of Cd, in which the highest level was found in oyster from Xiangan with a value of 1.21 mg?kg^?1. The average concentrations of Cd in oyster and mud clam samples were 0.338 and 0.369 mg?kg^?1, respectively, which were significantly higher (p?<?0.05) than those in the samples of short-necked clam and razor clam. The highest concentration of Cr was found to present in short-necked clam from Jimei with a value of 10.4 mg?kg^?1, but a mean value of 1.95 mg?kg^?1 in all the shellfish was observed, and no significant difference was found among the different sampling regions. The calculated daily intakes of Hg, Pb, Cd, and Cr through consuming the shellfish were 0.005, 0.122, 0.137, and 1.20 μg?kg^?1 day^?1, respectively, which accounted for 2.19, 3.42, 13.7, and 40.1 % of the corresponding tolerable limits suggested by the Joint FAO/WHO Expert Committee on Food Additives. The THQ values of the four metals were far below 1 for most samples, except for those of Cd and Cr in the four shellfish species with the mean values of 0.132 and 0.385, respectively. The highest THQ values of Cd were observed in the species of oyster (0.719) and mud clam (0.568). But the high THQ values of Cr observed in all the four species were derived from the applied reference dose (RfD) data of Cr(VI) due to the unavailable RfD value of total Cr. The results indicate that the intakes of heavy metals by consuming shellfish collected from Xiamen of China do not present an appreciable hazard risk on human health, but attention should be paid to consuming those with relatively high THQ values, such as oyster, mud clam, and short-necked clam.     

Metal contents and potential health risk assessment of crops grown in a former mining district (Romania)

ABSTRACT

The Cd, Cu, Pb and Zn contents in home-grown crops in a former mining district were determined in order to evaluate the non-carcinogenic long-term potential health risk related to crop consumption. The potential health risk was investigated by estimating the daily intake and the hazard quotients. For all crop categories, the daily intake and the target hazard quotient were below the threshold values for Cd, Cu, and Zn. The daily intake of Pb exceeded the oral reference dose, while the target hazard quotient for vegetables was above 1, indicating a potential health risk. The total target hazard quotient for the individual metals decreased in the following order: Pb>Cd>Cu>Zn. This study confirmed that the daily consumption of crops grown in contaminated soils could pose health risks to humans.     

High levels of heavy metals in rice (Oryza sativa L.) from a typical E-waste recycling area in southeast China and its potential risk to human health

Very few studies have investigated the heavy metal contents in rice samples from a typical E-waste recycling area. In this study, 10 heavy metals (As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Ni and Pb) in 13 polished rice and relevant hull samples, six relevant paddy soil samples were investigated. The geometric mean concentrations of Cd, Cu and Hg in soil samples were 1.19, 9.98 and 0.32 microg g(-1), respectively, which were 4.0, 2.0 and 1.1-folds of the maximum allowable concentration (MAC) (0.30, 50.00, 0.30 microg g(-1), respectively) for Chinese agricultural soils. The analyzed metal concentrations were significantly different between rice and relevant hull except for As, Cd and Hg (p<0.05). All metal concentrations, except for Co, in rice hull were higher than those in polished rice. The geometric mean of Pb in polished rice reached 0.69 microg g(-1), which was 3.5-folds higher than the MAC (0.20 microg g(-1)) by the safety criteria for milled rice. Cd contents in 31% of the rice samples exceeded the national MAC (0.20 microg g(-1)), and the arithmetic mean also slightly exceeded national MAC. In addition, Cd and Pb contents in local rice were much higher than commercial rice samples examined in this work and previous studies. Comparing the tolerable daily intakes given by FAO/WHO with the mean estimated daily intakes; Pb daily intake through rice consumption in this area was 3.7 microg day(-1)kg(-1) body weight (bw), which already exceeded the FAO tolerable daily intake, and the Cd daily intake (0.7 microg day(-1)kg(-1) bw) through rice had already taken up 70% of the total tolerable daily intake (1 microg day(-1)kg(-1) bw). The daily intake of Hg and As through rice was much lower than the tolerable daily intakes, but bioaccumulation of Hg through the food chain and intake of As from other food stuff should also be of concern.     

Genotypic and environmental variation in chromium, cadmium and lead concentrations in rice

Genotypic and environmental variation in Cr, Cd and Pb concentrations of rice grains and the interaction between these metals were investigated by using 138 rice genotypes grown in three contaminated soils. There were significant genotypic differences in the three heavy metal concentrations of rice grains, with the absolute difference among 138 genotypes in grain Cr, Cd and Pb concentrations being 24.5-, 9.1- and 23.8-folds, respectively, under the slightly contaminated soil (containing 4.61mgkg(-1) Cr, 1.09mgkg(-1) Cd and Pb 28.28mgkg(-1), respectively). A highly significant interaction occurred between genotype and environment (soil type) in the heavy metal concentrations of rice grains. Cr concentration in rice grains was not correlated with Cd and Pb concentration. However, there was a significant correlation between Cd and Pb in slightly and highly contaminated soils. The results suggest the possibility to develop the rice cultivars with low Cd and Pb concentrations in grain.     

Arsenic and other heavy metals in soils from an arsenic-affected area of West Bengal,India

Domkal is one of the 19, out of 26 blocks in Murshidabad district where groundwater contains arsenic above 0.05 mg/l. Many millions of cubic meters of groundwater along with arsenic and other heavy metals are coming out from both the hand tubewells, used by the villagers for their daily needs and shallow big diameter tubewells, installed for agricultural irrigation and depositing on soil throughout the year. So there is a possibility of soil contamination which can moreover affect the food chain, cultivated in this area. A somewhat detailed study was carried out, in both micro- and macrolevel, to get an idea about the magnitude of soil contamination in this area. The mean concentrations (mg/kg) of As (5.31), Fe (6740), Cu (18.3), Pb (10.4), Ni (18.8), Mn (342), Zn (44.3), Se (0.53), Mg (534), V (44.6), Cr (33.1), Cd (0.37), Sb (0.29) and Hg (0.54) in fallow land soils are within the normal range. The mean As (10.7), Fe (7860) and Mg (733) concentrations (mg/kg) are only in higher side whereas Hg (0.17 mg/kg) is in lower side in agricultural land soils, compared to the fallow land soils. Arsenic concentrations (11.5 and 28.0 mg/kg respectively) are high in those agricultural land soils where irrigated groundwater contains high arsenic (0.082 and 0.17 mg/l respectively). The total arsenic withdrawn and mean arsenic deposition per land by the 19 shallow tubewells per year are 43.9 kg (mean: 2.31 kg, range: 0.53-5.88 kg) and 8.04 kg ha(-1) (range: 1.66-16.8 kg ha(-1)) respectively. For the macrolevel study, soil arsenic concentration decreases with increase of distance from the source and higher the water arsenic concentration, higher the soil arsenic at any distance. A proper watershed management is urgently required to save the contamination.     

Analytical methods and validation for determining trace elements in red wines

The objective of this work is to quantify As, Hg, Cd, Ni and Pb in Portuguese red wines. First, the methods for the quantification of trace elements in red wines were validated. Several pre-treatments were compared, namely a pre-digestion process with HNO₃, a pre-oxidation step with H₂O₂, and a spiking step of wine samples with a known concentration of the trace elements analyzed. Except for As, it was determined that the quantification of the trace elements does not require a pre-digestion process with HNO₃. For all of the trace elements analyzed, a pre-oxidation step with H₂O₂ may enable an accurate quantification. The techniques chosen for the quantification of trace elements were hydride generation atomic absorption spectrometry (HGAAS) for As and Hg, electrothermal atomic absorption spectrometry (ETAAS) for Cd, and flame atomic absorption spectrometry (FAAS) for Ni and Pb. In the second stage of this work, 25 Portuguese red wines spanning all of the red wine-producing regions were analyzed for all of the five trace elements referred to above. Only Cd and Pb have shown concentrations above the limit values defined by the “Organization Internationale de la Vigne et du Vin.” The Target Hazard Quotient (THQ) equation was used to determine in which wine-producing regions that wine consumption can be a problem for public health in terms of the concentrations of the five trace elements analyzed. THQ values have indicated that for the universe of the 25 red wines analyzed no region produces wines that can pose problems for public health, when the Portuguese red wine standard consumption is considered.     

Concentration and health risk evaluation of heavy metals in market-sold vegetables and fishes based on questionnaires in Beijing,China

Concentrations of heavy metals (As, Cd, Pb, Cu, Ni, Fe, Mn, and Zn) in market vegetables and fishes in Beijing, China, are investigated, and their health risk to local consumers is evaluated by calculating the target hazard quotient (THQ). The heavy metal concentrations in vegetables and fishes ranged from not detectable (ND) to 0.21 mg/kg fresh weight (f.w.) (As), ND to 0.10 mg/kg f.w. (Cd), and n.d to 0.57 mg/kg f.w. (Pb), with average concentrations of 0.17, 0.04, and 0.24 mg/kg f.w., respectively. The measured concentrations of As, Cd, Pb, Cu, Ni, Fe, Mn, and Zn are generally lower than the safety limits given by the Chinese regulation safety and quality standards of agriculture products (GB2762-2012). As, Cd, and Pb contaminations are found in vegetables and fishes. The exceeding standard rates are 19 % for As, 3 % for Cd, and 25 % for Pb. Pb contaminations are found quite focused on the fish samples from traditional agri-product markets. The paper further analyzed the health risk of heavy metals in vegetables and fishes respectively from supermarkets and traditional agri-product markets; the results showed that the fishes of traditional agri-product markets have higher health risk, while the supermarkets have vegetables of higher heavy metal risk, and the supervision should be strengthened in the fish supply channels in traditional agri-product markets.     

Health risk assessment of heavy metals in soil-plant system amended with biogas slurry in Taihu basin,China

Biogas slurry is a product of anaerobic digestion of manure that has been widely used as a soil fertilizer. Although the use for soil fertilizer is a cost-effective solution, it has been found that repeated use of biogas slurry that contains high heavy metal contents can cause pollution to the soil-plant system and risk to human health. The objective of this study was to investigate effects of biogas slurry on the soil-plant system and the human health. We analyzed the heavy metal concentrations (including As, Pb, Cu, Zn, Cr and Cd) in 106 soil samples and 58 plant samples in a farmland amended with biogas slurry in Taihu basin, China. Based on the test results, we assessed the potential human health risk when biogas slurry containing heavy metals was used as a soil fertilizer. The test results indicated that the Cd and Pb concentrations in soils exceeded the contamination limits and Cd exhibited the highest soil-to-root migration potential. Among the 11 plants analyzed, Kalimeris indica had the highest heavy metal absorption capacity. The leafy vegetables showed higher uptake of heavy metals than non-leafy vegetables. The non-carcinogenic risks mainly resulted from As, Pb, Cd, Cu and Zn through plant ingestion exposure. The integrated carcinogenic risks were associated with Cr, As and Cd in which Cr showed the highest risk while Cd showed the lowest risk. Among all the heavy metals analyzed, As and Cd appeared to have a lifetime health threat, which thus should be attenuated during production of biogas slurry to mitigate the heavy metal contamination.     

Health risks of heavy metals in contaminated soils and food crops irrigated with wastewater in Beijing, China

Consumption of food crops contaminated with heavy metals is a major food chain route for human exposure. We studied the health risks of heavy metals in contaminated food crops irrigated with wastewater. Results indicate that there is a substantial buildup of heavy metals in wastewater-irrigated soils, collected from Beijing, China. Heavy metal concentrations in plants grown in wastewater-irrigated soils were significantly higher (P相似文献   

Survey of heavy metal pollution and assessment of agricultural soil in Yangzhong district, Jiangsu Province, China

We investigated concentrations of Hg, Cd, Pb, Zn, Cu, As, Ni, and Cr in samples of soil, cereal, and vegetables from Yangzhong district, China. Compared to subsoils, the sampled topsoils are enriched in Hg, Cd, Cu, Pb, Zn, and As. High levels of Cd and Hg are observed in most agricultural soils. Concentrations of Cr and Ni show little spatial variation, and high Cu, Pb, and Zn contents correspond well to areas of urban development. High As contents are primarily recorded at the two ends of the sampled alluvion. The contents of Cd, Hg, and total organic carbon (TOC) increase gradually to maximum values in the upper parts of soil profiles, while Cr and Ni occur in low concentrations within sampled profiles. As, Pb, Cu, and Zn show patterns of slight enrichment within the surface layer. Compared to data obtained in 1990, Cd and Hg show increased concentrations in 2005; this is attributed to the long-term use of agrochemicals. Cr and Ni contents remained steady over this interval because they are derived from the weathering of parent material and subsequent pedogenesis. The measured As, Cu, Pb, and Zn contents show slight increases over time due to atmospheric deposition of material sourced from urban anthropogenic activity. Low concentrations of heavy metals are recorded in vegetables and cereals because the subalkaline environment of the soil limits their mobility. Although the heavy metal concentrations measured in this study do not pose a serious health risk, they do affect the quality of agricultural products.     

Heavy metal content in vegetables and fruits cultivated in Baia Mare mining area (Romania) and health risk assessment

Information about heavy metal concentrations in food products and their dietary intake are essential for assessing the health risk of local inhabitants. The main purposes of the present study were (1) to investigate the concentrations of Zn, Cu, Pb, and Cd in several vegetables and fruits cultivated in Baia Mare mining area (Romania); (2) to assess the human health risk associated with the ingestion of contaminated vegetables and fruits by calculating the daily intake rate (DIR) and the target hazard quotient (THQ); and (3) to establish some recommendations on human diet in order to assure an improvement in food safety. The concentration order of heavy metals in the analyzed vegetable and fruit samples was Zn?>?Cu?>?Pb?>?Cd. The results showed the heavy metals are more likely to accumulate in vegetables (10.8–630.6 mg/kg dw for Zn, 1.4–196.6 mg/kg dw for Cu, 0.2–155.7 mg/kg dw for Pb, and 0.03–6.61 mg/kg dw for Cd) than in fruits (4.9–55.9 mg/kg dw for Zn, 1.9–24.7 mg/kg dw for Cu, 0.04–8.82 mg/kg dw for Pb, and 0.01–0.81 mg/kg dw for Cd). Parsley, kohlrabi, and lettuce proved to be high heavy metal accumulators. By calculating DIR and THQ, the data indicated that consumption of parsley, kohlrabi, and lettuce from the area on a regular basis may pose high potential health risks to local inhabitants, especially in the area located close to non-ferrous metallurgical plants (Romplumb SA and Cuprom SA) and close to T?u?ii de Sus tailings ponds. The DIR for Zn (85.3–231.6 μg/day kg body weight) and Cu (25.0–44.6 μg/day kg body weight) were higher in rural areas, while for Pb (0.6–3.1 μg/day kg body weight) and Cd (0.22–0.82 μg/day kg body weight), the DIR were higher in urban areas, close to the non-ferrous metallurgical plants SC Romplumb SA and SC Cuprom SA. The THQ for Zn, Cu, Pb, and Cd was higher than 5 for <1, <1, 12, and 6 % of samples which indicates that those consumers may experience major health risks.     

Metal contents of marine turtle eggs (Chelonia mydas; Lepidochelys olivacea) from the tropical eastern pacific and the implications for human health

Concentrations of eight elements were measured in Chelonia mydas and Lepidochelys olivacea eggs collected along the Pacific coast of Panama. Manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), and mercury (Hg) concentrations were similar to previous reports of these species from around the world, while lead (Pb) was lower than previous reports. Cd posed the highest health risk to people who regularly eat the eggs, with average consumption rates leading to target hazard quotients (THQ) of up to 0.35 ± 0.15. Our conclusions indicate that current turtle egg consumption in isolated, coastal Pacific communities may pose a health concern for young children, and that youth and young adults should limit their consumption of turtle eggs to reduce their total intake of nonessential metals.     

Natural pollution caused by the extremely acidic crater lake Kawah Ijen, East Java, Indonesia

Background. Aims and Scope Lakes developing in volcano craters can become highly acidic through the influx of volcanic gases, yielding one of the chemically most extreme natural environments on earth. The Kawah Ijen crater lake in East Java (Indonesia) has a pH 〈 0.3. It is the source of the extremely acid and metal-polluted river Banyupahit (45 km). The lake has a significant impact on the river ecosystem as well as on a densely populated area downstream, where agricultural fields are irrigated with water with a pH between 2.5 and 3.5. The chemistry of the river water seemed to have changed over the past decade and the negative effect in the irrigation area increased. A multidisciplinary approach was used to investigate the altered situation and to get insight in the water chemistry and the hydrological processes influencing these alterations. Moreover, a first investigation of the effects of the low pH on ecosystem health and human health was performed. Methods Water samples were taken at different sites along the river and in the irrigation area. Sampling for macroinvertebrates was performed at the same sites. Samples of soil and crop were taken in the irrigation area. All samples were analysed for metals (using ICP-AES) and other elements, and concentrations were compared to local and international standards. Results and Discussion The river carries a very high load of SO4, NH4, PO4, Cl, F, Fe, Cu, Pb, Zn, Al and other potentially toxic elements. Precipitation and discharge data over the period of 1980 – 2000 clearly show that the precipitation on the Ijen plateau influences water chemistry of the downstream river. Metal concentrations in the river water exceed the concentrations mentioned in Indonesian and international quality guidelines, even in the downstream river and the irrigation area. Some metal concentrations are extremely high, especially iron (up to 1600 mg/l) and aluminium (up to 3000 mg/l). The food-webs in the acidic parts of the river are highly underdeveloped. No invertebrates were present in the extremely acid water and, at pH 2.3, only chironomids were found. This also holds true for the river water with pH 3.3 in the downstream area. Agricultural soils in the irrigation area have a pH of 3.9 compared to a pH of 7.0 for soils irrigated with neutral water. Decreased yields of cultivated crops are probably caused by the use of Al containing acid irrigation water. Increased levels of metals (especially Cd, Co, Ni and Mn) are found in different foodstuffs, but still remain within acceptable ranges. Considering local residents” diets, Cd levels may lead to an increased risk for the human health. Fluoride exposure is of highest concern, with levels in drinking water exceeding guideline values and a lot of local residents suffering from dental fluorosis. Conclusions, Recommendations and Outlook In short, our data indicate that the Ijen crater lake presents a serious threat to the environment as well as human health and agricultural production.     

The effect of municipal sludge compost on the mobility and bioavailability of Cd in a sierozem-wheat system in an arid region northwest of China

The effect of sewage sludge on the mobility and the bioavailability of trace metals in plant-soil systems have aroused wide interested and been widely explored. Based on a wheat-cultivating experiment, the effect of municipal sludge compost (MSC) on the mobility and bioavailability of Cd in a soil-wheat system was studied. With the application of MSC, soil organic matter (SOM), total nitrogen (TN), and total phosphorus (TP) in the soil increased significantly, while concentrations of trace metals (Cu, Zn, Ni, Pb, Cd) were below the China’s minimum thresholds. The application of MSC could improve wheat growth. The application of MSC at the rate of 0.5 % had no significant effect on the chemical fraction distribution of Cd in soil. In two soil treatments, Cd mainly existed in the labile chemical fractions (exchangeable chemical fraction (EXCF) and carbonate chemical fraction (CABF)). However, the application of MSC could reduce accumulation of Cd by wheat. Cd contents in each part of the MSC-applied wheat were significantly less than that of non-MSC-applied wheat. In the tested soils, the extractable concentrations decreased in the order: EDTA > MgCl₂ ≈ NH₄OAc > DTPA. There were no significant differences between soil treatments in the amounts of extractable Cd when the extraction was done under neutral conditions, although significant differences were observed when the extraction was done under alkaline conditions. In this study, the DTPA extraction procedure provided a good indication of Cd bioavailability. Our results suggest that, in the short term at least, amending soils with MSC may benefit crop dry matter production while not increasing the risk of human exposure to Cd through consumption of wheat grown on MSC-amended soils.     

Accumulation of potentially toxic elements in plants and their transfer to human food chain

Abstract

Contaminated soils can be a source for crop plants of such elements like As, Cd, Cr, Cu, Ni, Pb, and Zn. The excessive transfer of As, Cu, Ni, and Zn to the food chain is controlled by a “soil‐plant barrier”; however, for some elements, including Cd, the soil‐plant barrier fails. The level of Cd ingested by average person in USA is about 12 μg/day, which is relatively low comparing to Risk Reference Dose (70 μg Cd/day) established by USEPA. Food of plant origin is a main source of Cd intake by modern society. Fish and shellfish may be a dominant dietary sources of Hg for some human populations. About half of human Pb intake is through food, of which more than half originates from plants. Dietary intake of Cd and Pb may be increased by application of sludges on cropland with already high levels of these metals. Soils amended with sludges in the USA will be permitted (by USEPA‐503 regulations) to accumulate Cr, Cd, Cu, Pb, Hg, Ni, and Se, and Zn to levels from 10 to 100 times the present baseline concentrations. These levels are very permissive by international standards. Because of the limited supply of toxicity data obtained from metals applied in sewage sludge, predictions as to the new regulations will protect crop plants from metal toxicities, and food chain from contamination, are difficult to make.