Temporal-spatial distribution and variability of cadmium contamination in soils in Shenyang Zhangshi irrigation area,China

Heavy metal contamination in soils has been of wide concern in China in the last several decades. The heavy metal contamination was caused by sewage irrigation, mining and inappropriate utilization of various agrochemicals and pesticides and so on. The Shenyang Zhangshi irrigation area （SZIA） in China is a representative area of heavy metal contamination of soils resulting from sewage irrigation for about 30 years duration. This study investigated the spatial distribution and temporal variation of soil cadmium contamination in the SZIA. The soil samples were collected from the SZIA in 1990 and 2004; Cd of soils was analyzed and then the spatial distribution and temporal variation of Cd in soils was modelled using kriging methods. The kriging map showed that long-term sewage irrigation had caused serious Cd contamination in topsoil and subsoil. In 2004, the Cd mean concentrations were 1.698 and 0.741 mg/kg, and the maxima 10.150 and 7.567 mg/kg in topsoils （0-20 cm） and subsoils （20-40 cm） respectively. These values are markedly more than the Cd levels in the second grade soil standard in China. In 1990, the Cd means were 1.023 and 0.331 mg/kg, and the maxima 9.400 and 3.156 mg/kg, in topsoils and subsoils respectively. The soil area in 1990 with Cd more than 1.5 mg/kg was 2701 and 206.4 hnl2 in topsoils and subsoils respectively; and in 2004, it was 7592 and 1583 hm^2, respectively. Compared with that in 1990, the mean and maximum concentration of Cd, as well as the soil area with Cd more than 1.5 mg/kg had all increased in 2004, both in topsoils and subsoils.

Relationships among Environmental Lead in Playground Soils and Dust and Blood Lead of Children in Muncie, Indiana, USA

The present study was designed to assess lead levels in playground soil and accumulated dust on playground equipment and then correlate those environmental lead measurements with children’s blood lead in the surrounding neighborhoods. Soil lead and surface dust were collected from 14 playgrounds in Muncie, Indiana, and blood lead levels were calculated for nearby children. Correlation analyses revealed a moderate positive association between dust Pb and soil Pb with a correlation coefficient r = 0.46 (p = 0.099). The relationship between settled dust on playground equipment and composite blood lead level also showed a medium positive correlation, indicated by r = 0.36 (p = 0.202). A positive correlation was also observed between soil Pb and composite blood lead values, as evidenced by r = 0.51 (p = 0.061). Furthermore, the assessment of spatial autocorrelation using Moran’s I index indicated no significant spatial clustering for the variables studied (dust Pb, soil Pb, and blood Pb). Correlation analysis showed a connection between lead levels in soil and dust, but no significant links were found between soil lead and blood lead and between dust lead and blood lead. These results suggest that environmental lead in parks has a limited impact on children’s blood lead levels nearby. Spatial autocorrelation analysis also revealed no significant spatial patterns among variables—dust, soil, and blood lead. Given these findings, it is recommended to seek expertise from qualified professionals and further perform comprehensive testing and analysis to investigate potential lead sources in children’s blood. The outcomes of this study offer valuable insights into assessing playground environmental lead contamination, contributing to future research priorities in this area. Specifically, future studies could focus on collecting larger sample sizes and characterizing blood lead in children who frequently use playgrounds rather than those who live nearby but may or may not use the playgrounds.

Spatial Availability of Nitrogen and Pesticides in the Surface Layers of Agricultural Soils of Tropical Hydrosystems in the Wet Season: Case of the BéréWatershed in Côte d’Ivoire (West Africa)

The objective of this study was to assess the contribution of the spatial organization of cropping systems and the physicochemical properties of surface layers of the agricultural zones soils in tropical hydrosystems to the spatial availability of nitrogen and pesticides during the wet season, such as the Béré watershed (BW) in C?te d’Ivoire. For this purpose, after mapping the spatial distribution of the BW cropping systems based on the likelihood classification methodology of satellite images of the study area, 27 samples from the 0 - 20 cm horizon of the soil surface layers of the agricultural areas were taken during the wet and agricultural season of the year 2016. The Kjeldahl method has been used to evaluate the total nitrogen concentration and high-performance liquid chromatography (HPLC) chain made it possible for the analysis of pesticide residues in the soil solutions. Geostatistical analysis and processing of spatial data and physicochemical and agrochemical soil parameters revealed that two major agricultural areas stand out in the BW, namely the Béré upstream watershed (BUW) dominated at 32.65% by annual croppings (maize, cotton, rainfed or lowland rice, market gardening, etc.) and the Béré downstream watershed (BDW) by large areas of perennial croppings (cashew nuts, cocoa, etc.), i.e. 21.47%. Agricultural soils in BW are usually of the moderately desaturated ferralitic type with a low acid pH and a quite strong temperature, such as those of tropical soils’ characteristics. However, agricultural soils in the BUW are characterized by higher proportions of sand and coarse sand. The parameters such as total porosity, cation exchange capacity, clay, organic matter, silt, fine silt, coarse silt, and potassium ions, are higher in the soils of the agricultural area of the BDW. Moreover, soils in the agricultural areas of the BUW are less rich in total nitrogen (0.84 g·kg-1) in contrast to those of the BDW (1.2 g·kg-1). On the other hand, the median concentrations of total pesticides remain very high in the BUW (193.80 μg·kg-1) in front of those of the BDW (94.81 μg·kg-1). In addition, the biological family of herbicides was the most notable in BW. The chemical families of triazines (100% detection;79.37 μg·kg-1) are the most important in the agricultural area of the BUW with the very significant presence of active molecules of pesticides such as simazine (92.86% detection;13.17 μg·kg-1). However, in the BDW, urea substitute (100% detection;44.02 μg·kg-1) dominate, including the active substance chlortoluron (84.62% detection;10.12 μg·kg-1). The presence and abundance of nitrogen and pesticides in the soils of the agricultural areas of BW are strongly linked to the intensive use of these agrochemicals in cropping systems in recent decades in West African countries, even though most of the active molecules found are forbidden in several countries, especially in European countries. These are applied to tropical agricultural soils with physicochemical characteristics favorable to their retention in wet weather, as confirmed by the case of BW’s agricultural soils. Therefore, the BW’s water resources present worrying risks of contamination during rainy events that deserve to be assessed and monitored. Hence the need to take mitigating measures to this effect in order to preserve the quality of the environment.

Distribution of Cu and Pb in particle size fractions of urban soils from different city zones of Nanjing, China

Soil samples from 4 defined city zones of Nanjing were randomly collected at 0-5 cm and 5-20 cm intervals and size fractions of soil particles were separated from undisturbed bulk soils by low energy dispersion procedure. The total contents of Cu and Pb in the different particle size fractions of the urban soils were analyzed by HNO3-HF-HClO4 digestion and flame atomic absorption spectrophotometer determination. The total content of Cu and Pb in soil particle size fractions varied with their size and with city zones as well. Both the content and variation with the size fractions of Pb was bigger than of Cu supporting our previous finding that there was Pb pollution to different degrees in the urban soils although the two elements were generally enriched in clay-sized fraction. Contaminated Pb tended to be preferentially enriched in the size fraction of 2000-250 μm and clay-sized fraction. While the size fractions of the soils from newly developed and preserved area contained smaller amount of Cu and Pb, the partitioning of them in coarse and fine particle size fractions were insignificant compared to that from inner residence and commercial area. The very high Pb level over 150 mg/kg of the fine particle fractions from the soils of the inner city could be a cause of high blood Pb level reported of children from the city as acute exposure to Pb of fine particles of the urban soil might occur by soil ingestion and inhalation by young children. Thus, much attention should be paid to the partitioning of toxic metals in fine soil particles of the urban soils and countermeasures against high health risk of Pb exposure by soil ingestion and dust inhalation should be practiced against the health problem of blood Pb for young children from the cities.

Potential of weed species applied to remediation of soils contaminated with heavy metals

To screen out a series of ideal plants that can effectively remedy contaminated soils by heavy metals is the main groundwork of phytoremediation engineering and the first step of its commercial application on a large scale. In this study, accumulation and endurance of 45 weed species in 16 families from an agricultural site were in situ examined by using the pot-culture field experiment, and the remediation potential of some weed species with high accumulation of heavy metals was assayed. The results showed that Solanum nigrum and Conyza canadensis can not only accumulate high concentration of Cd, but also strongly endure to single Cd and Cd-Pb-Cu-Zn combined pollution. Thus 2 weed species can be regarded as good hyperaccumulators for the remediation of Cd-contaminated soils. Although there were high Cd-accumulation in Artemigia selengensis, Znula britannica and Cephalanoplos setosum, their biomass was adversely affected due to action of heavy metals in the soils. If the problem of low endurance to heavy metals can be solved by a reinforcer, 3 weed species can be perhaps applied commercially.

Pesticide soil contamination mainly affects earthworm male reproductive parameters

Aim: To explore the effect of exposure to commercial Parathion~ (Pc) on the reproductive parameters (sperm and cocoon production and genotoxicity on male germ cells), the survival, the body weight and the gross anatomical changes in Eiseniafoetida. Methods: Three doses of Pc(1478, 739 and 444 mg/kg of soil) and three time intervals of exposure (5, 15 and 30 days) were used. Results: All treated animals were affected. An acute genotoxic effect, revealed by DNA fragmentation (comet assay), was seen by 5 days. Alterations in reproductive parameters were conspicuous in regard to the number of sperm, cocoons and worms born, and the histological observation of the gonads and seminal receptacles. In addition, the body weight and survival rate were decreased. Neuromuscular function was also affected. Conclusion: Earthworms are suitable bioindicators of chemical contamination of the soil, their advantage being their easy and economical handling

Microbial changes in rhizospheric soils contaminated with petroleum hydrocarbons after bioremediation

Effects of bioremediation on microbial communities in soils contaminated with petroleum hydrocarbons are a scientific problem to be solved. Changes in dominate microbial species and the total amount of microorganisms including bacteria and fungi in rhizospheric soils after bioremediation were thus evaluated using field bioremediation experiments. The results showed that there were changed dominant microorganisms including 11 bacterial strains which are mostly Gram positive bacteria and 6 fungal species which were identified. The total amount of microorganisms including bacteria and fungi increased after bioremediation of microbial agents combined with planting maize. On the contrary, fungi in rhizospheric soils were inhibited by adding microbial agents combined with planting soybean.

Can phosphate compounds be used to reduce the plant uptake of Pb and resist the Pb stress in Pb-contaminated soils?

The effects of different phosphate-amendments on lead （Pb） uptake, the activities of superoxide dismutase （SOD） and the level of malondialdehyde （MDA） in cauliflower （Brassica oleracea L.） in contaminated soils with 2500, or 5000 mg P2O5/kg soil of hydroxyapatite （HA）, phosphate rock （PR）, single-superphosphate （SSP） and the mix of HA/SSP （HASSP） were evaluated in pot experiments. Results showed that the Pb concentrations in shoots and roots decreased by 18.3%-51.6% and 16.8%-57.3% among the treatments respectively compared to the control samples. The efficiency order of these phosphate-amendments in reducing Pb uptake was as follows： HASSP= HA 〉 SSP ,= PR. With the addition of SSP, HA and the mix of HA/SSP, the SOD activity in shoot was reduced markedly （P 〈 0.05） compared with that in the control group. For example, the SOD activities in shoot by the treatments of HASSP, SSP, and HA in 5000 mg P2O5/kg were found to be only 51.3%, 56.2%, and 56.7%, respectively. Similar effects were also observed on the level of MDA in the shoots with a decrease in 24.5%-56.3%. The results verified the inference that phosphate compounds could be used to reduce the plant uptake of Pb and resist the Pb stress in the plant vegetated in Pb-contaminated soils.

Cu, Mn, Fe, and Zn Levels in Soils of Shika Area, Nigeria

Objective Heavy metals presented in toxic amounts can become injurious to human health. In areas where there is a high level of human activities on soils (such as agriculture and grazing) studies are therefore required from time to time to monitor levels of such metals in the soils in order to identify the point in time when toxicity problems become real. The objective of this paper is to determine the concentrations of some trace metals (Cu, Mn, Fe, and Zn) in soils under cultivation and grazing practices in Shika, a rural area of Kaduna state of Nigeria. Method In this study, soil samples collected from three different categories of locations (cultivated, grazed, and uncultivated/non- grazed serving as a control) across Shika area, Nigeria, were analysed for some trace metal levels (Cu, Mn, Fe, and Zn) using atomic absorption spectrophotometry. For each category, multiple sites were chosen to accommodate all possible intra-category variations, especially in terms of land use and management history and topographic characteristics. Topsoil (0-15 cm) and subsoil (20-30 cm) samples were collected from every site and analysed for the above metals. Averaged values of the metals for the three categories revealed that Zn is the most abundant metal, followed by Fe, then Mn and Cu the least. Results The results obtained indicate that the cultivation practices, and to a lesser extent grazing, in the area result in higher levels of all the metals than in the control, suggesting that crop immobilization of the metals from soils of the area is low, and that their systematic accumulation is taking place in cultivated soils of the area. Prospects of having elevated soil levels of the metals due to cultivation practices in the area therefore seem quite high. Conclusion On the basis of the results obtained, it was concluded that grazing and cultivation practices have in general caused some significant elevations in the bioavailable (i.e the plant available forms) levels of Zn, Fe, Mn, and Cu in soils of the area.

Comparison of properties of traditional and accelerated carbonated solidified/stabilized contaminated soils

The investigation of the long-term performance of solidified/stabilized （S/S） contaminated soils was carried out in a trial site in southeast UK. The soils were exposed to the maximum natural weathering for four years and sampled at various depths in a controlled manner. The chemical properties （e.g., degree of carbonation （DOC）, pH, electrical conductivity （EC）） and physical properties （e.g., moisture content （MC）, liquid limit CLL）, plastic limit （PL）, plasticity index （PI）） of the samples untreated and treated with the traditional and accelerated carbonated S/S processes were analyzed. Their variations on the depths of the soils were also studied. The result showed that the broad geotechnical properties of the soils, manifested in their PIs, were related to the concentration of the water soluble ions and in particular the free calcium ions. The samples treated with the accelerated carbonation technology （ACT）, and the untreated samples contained limited number of free calcium ions in solutions and consequently interacted with waters in a similar way. Compared with the traditional cement-based S/S technology, e.g., treatment with ordinary portland cement （OPC） or EnvirOceM, ACT caused the increase of the PI of the treated soil and made it more stable during long-term weathering. The PI values for the four soils ascended according to the order： the EnvirOceM soil, the OPC soil, the ACT soil, and the untreated soil while their pH and EC values descended according to the same order.

Heavy Metal/Metalloid Indexing and Balances in Agricultural Soils: Methodological Approach for Research

Heavy metal(loid)accumulation in agricultural soils is a threat to the soil capacity,quality,and productivity.It also increases human exposure to heavy metal(loid)s via consumption of contaminated plant-based foods.The detrimental effects of soil contamination also deteriorate the environment of plants and animals.For sustainable agriculture,therefore,the soil must be protected from toxic levels of heavy metal(loid)s.Studies on heavy metal(loid)balances in agricultural soils are important in predicting future risks to sustainable production from agro-ecological zones and human exposure to heavy metal(loid)s.The latest and continuous indexing of the problem seems a prerequisite for sustainable agriculture.This review provides some background information and then summarizes key methodological approaches for studies on indexing and balance of heavy metal(loid)s in agricultural soils.In the end,important soil and health indices are explained that may be useful in understanding the extent of the problem.The provided information would contribute to sustainable heavy metal(loid)management in the agricultural soils,high crop production,better soil protection,and ultimately to human health.

Effect of Heavy Metal Contamination on Soil Enzymes Activities

Several enzymes catalyze much of the processes that exist in the soil. Enzymes in polluted soils are usually less active due to their exposure to heavy metals. The main goal of this study was to see how bioavailable types of Cd affected the behavior of catalase, urease, and dehydrogenases, as well as to compare the findings from naturally and artificially polluted samples. An experiment was conducted on two types of farmland (garden) soil: natural soil and soil that had been chemically polluted with Cd. The total content of heavy metal graded these soils as very highly polluted with Cd. The experiment was repeated four times to test the effects of increasing concentration and days (time). Extracellular enzymes from farmland performed enzymatic activity tests that lasted 6 to 29 days after soil sampling. After 0, 5, 10, 20, 30, and 45 days of incubation, soil samples were taken for testing respectively. However, even though no nutrient was added, dehydrogenase and urease activity increased as Cd concentration increased from 0 to 5 mg/L as the days passed. This is a result of enzymes engaging in respiratory and other living activities because of the low cadmium concentration and respiratory soil properties. However, there were significant variations in enzyme activity between naturally polluted and artificially contaminated soils. Dehydrogenases, Urease, and Catalase all showed a common pattern of enzyme sensitivity, which could be ordered as Dehydrogenase > Urease > Catalase. Dehydrogenase enzyme activity has been discovered to be more Cd resistant.

Comparison of a Soil Vulnerability Map for Tetracycline Soil Contamination at a Global and Local Scale

Recently, de la Torre[1] provided an approach for assessing the vulnerability of European soils for tetracyclines, fluoroquinolones and sulfamides contamination using a spatial risk assessment. It allowed identifying areas where vulnerable soil more occur, providing useful information for policies designed to reduce contamination. In the current study, this approach was applied to a local level, the autonomous region of Castile and León (C&L), located in the north-west part of Spain. High accurate and reliable source data were employed to generate a soil vulnerability map for tetracyclines in the study area, attempting to improve the release and consequence risk prediction. More specifically, pig density, temperature and soil use risk estimators were improved using data from national or local databases. Result comparison between the European and the present approach showed a good agreement demonstrating the utility of the European vulnerability map to be employed not only at global level but also for deciding how to allocate limited resources on national or subnational environmental surveillance programs of antibiotics. The model application at local level using more accurate data from national or local sources, afforded a better understanding of the spatial distribution of the risk, mainly associated with the higher accuracy of the national land use database SIOSE. It could offer a useful tool for local management of the risk, such as the management of animal manures fertilization on soil.

Effect of soil properties and sample preparation on extractable and soluble Pb and Cd fractions in soils

The effect of soil extraction procedures and/or sample pretreatment (drying, freezing of the soil sample) on the extractability of cadmium and lead was tested in a model experiment, with an employment of optical emission and atomic ab- sorption spectrometry methods. In the first part, 6 extraction procedures were compared: 2 mol l-1 HNO3, 0.43 mol l-1 CH3COOH, 0.05 mol l-1 EDTA, Mehlich III extraction procedure (0.2 mol l-1 CH3COOH + 0.25 mol l-1 NH4NO3 + 0.013 mol.l-1 HNO3 + 0.015 mol.l-1 NH4F + 0.001 mol.l-1 EDTA), 0.01 mol.l-1 CaCl2, and deionised water. Addi-tionally, two methods of soil solution sampling were compared, and the centrifugation of satu-rated soil and the use of suction cups and dif-ferential pulse anodic stripping voltametry was applied to assess free and complexed metals portions. The results showed that different soil sample extraction methods and/or sample pre-treatments including soil solution sampling can lead to different absolute values of mobile cadmium and lead content in soils. However, the interpretation of the data can lead to similar conclusions as are apparent from the compari- son of the soil solution sampling methods where fairly good correlation was observed (for Cd r = 0.76, and for Pb r = 0.74). The ambiguous results were reported for voltammetric determinations of free and complex portions of Cd and Pb where a different behavior was observed for water extracts of soil and soil solution obtained using suction cups. Moreover, a changing extent of lead complexation was determined with prolonged storage of the samples. The results confirmed that soil and/or soil solution sampling under immediate soil conditions and limitations of pre-extraction operations are necessary.

Investigation of Pollution Level of Traces Metals Elements in Agricultural Soil of Oubritenga Province of Burkina Faso

The purpose of this study was to investigate the pollution level of trace metals As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se and Zn in agricultural soil around the water reservoir. A total of 36 soil samples were collected both during off-season agriculture and pluvial agriculture from April to October 2022. The samples were analyzed for trace metals according to the standard methods of the US EPA 2007 with a microwave plasma atomic emission spectrometer (MP-AES), Agilent Model 4210. The pollution level was assessed using contamination factor (Cf) and modified contamination degree (mCd). During the off-season, the concentration of trace metals followed in descending order as Mn > Cr > Cu > Pb > Zn. As, Cd, Co, Hg, Ni, Sb and Se were below the detectable limits. In pluvial season, the concentration of traces of metal follows the order Mn > Cr > Zn > Cu > Ni > Pb > Hg > As. Cd, Co, Sb and Se remain below the detectable limits. The concentrations of Cr, Mn and Zn were lower in the off-season agriculture than in pluvial agriculture. For Cu and Pb, the concentrations were higher in the off-season than in pluvial agriculture. The Cf ranges from 0.24 to 11.70 depending on the considered trace metal. The Cf values of As, Ni, Pb, Zn and Mn indicated that the agricultural study soil was lowery contaminated by these trace metals. The agricultural study soil was moderately contaminated by Cr and Cu, and highly contaminated by Hg. Globally the agricultural study soil presents a moderate degree of contamination (mCd 2.25) by the eight trace metals studied. This result provides information on understanding the risks of trace metal contamination of agricultural soil. It is important to anticipate the control of soil contamination through regular monitoring of toxic metals in agricultural soils, control the quality of chemicals used in agriculture and regulate their use.

Remediation of Cu Contaminated Soil by Fe_(78)Si_(9)B_(13)^(AP)Permeability Reaction Barrier Combined with Electrokinetic Method

Iron-based amorphous crystalline powder Fe_(78)Si_(9)B_(13)^(AP)is used as a permeability reaction barrier(PRB)combined with an electrokinetic method(EK-PRB)to study the removal rate of Cu in contaminated soil.After treating Cucontaminated soil for 5 days under different voltage gradients and soil water content,the soil pH is between 3.1 and 7.2.The increase of voltage gradient and soil water content can effectively promote the movement of Cu^(2+) to the cathode.The voltage gradient is 3 V/cm,and the water content of 40%is considered to be an optional experimental condition.Therefore,under this condition,the effects of Fe_(78)Si_(9)B_(13)^(AP)and zero-valent iron(ZVI)as PRB on the removal rate of total Cu in soil and the transformation of chemical forms of Cu are studied.Compared with ZVI,Fe_(78)Si_(9)B_(13)^(AP)as PRB has a better remediation effect.EK-Fe_(78)Si_(9)B_(13)^(AP)can remove 80.3%of total Cu in soil,and the biologically available Cu is reduced to 3.6%,which effectively reduces the environmental risk of contaminated soil.

A Preliminary Assessment of the Effect of Urban Waste Pollution in the Korle Lagoon Area of Accra, Ghana, on Nutrition and Growth of Maize (Zea mays L.) Plants

Disposal of domestic and industrial waste into the Odaw River and Korle Lagoon in Accra, Ghana, has led to pollution of the lagoon and surrounding soils. This study compared the elemental concentrations of heavy metals (lead and zinc) and essential plant macronutrients (nitrogen, phosphorus and potassium) in soils from the Korle Lagoon Area to those in baseline soils from the University of Ghana Agricultural Farm (UG Farm), also in Accra. A comparative pot experiment, using maize (Zea mays L.) as test plant, was conducted to assess the effect of each soil type on plant growth. Soil samples from the Korle Lagoon Area were significantly higher (P < 0.001) in lead (Pb), zinc (Zn), nitrogen (N) and potassium (K) concentrations than samples from the UG Farm. Mean plant height and mean leaf width of maize plants harvested 7 weeks after planting (WAP) were both significantly higher (P < 0.003) for samples from the Korle Lagoon Area soil compared to those from the UG Farm soil. Higher accumulation of Zn (448.3 ± 45.5) in maize shoot within 3 weeks of planting in the Korle Lagoon Area soil had phytotoxic effects on growth, resulting in shoot growth inhibition and reduced uptake of P and K in 11-week-old plants. The findings indicate that though nutrient enrichment due to sewage disposal into the lagoon may increase crop production, the nutritional quality of the crop produced could be compromised by heavy metal accumulation in the soil and subsequent uptake by the plant.

Regional assessment of cadmium pollution in agricultural lands and the potential health risk related to intensive mining activities: A case study in Chenzhou City, China

The purpose of this study was to assess the extent of cadmium （Cd） contamination in agricultural soil and its potential risk for people. Soils, rice, and vegetables from Chenzhou City, Southern China were sampled and analyzed. In the surface soils, the 95% confidence interval for the mean concentration of Cd varied between 2.72 and 4.83 mg/kg （P 〈 0.05） in the survey, with a geometric mean concentration of 1.45 mg/kg. Based on the GIS map, two hot spot areas of Cd in agricultural soils with high Cd concentrations were identified to be located around the Shizhuyuan, Jinshiling, and Yaogangxian mines, and the Baoshan and Huangshaping mines, in the center of the city. About 60% of the total investigated area, where the agricultural soil Cd concentration is above 1 mg/kg, is distributed in a central belt across the region. The critical distances, at which the soil Cd concentration were increased by the mining activities, from the mines of the soils were 23 km for the Baoshan mine, 46 km for the Huangshaping mine, and 63 km for the Shizhuyuan mine, respectively. These are distances calculated from models. The Cd concentrations in rice samples ranged from 0.01 to 4.43 mg/kg and the mean dietary Cd intake from rice for an adult was 191 μg/d. Results of risk indexes showed that soil Cd concentrations possessed risks to local residents whose intake of Cd from rice and vegetables grown in soils in the vicinity of the mine was 596 μg/d.

Soil enzymatic activities and microbial community structure with different application rates of Cd and Pb

This study focused on the changes of soil microbial diversity and potential inhibitory effects of heavy metals on soil enzymatic activities at different application rates of Cd and/or Pb. The soil used for experiments was collected from Beijing and classified as endoaquepts. Pots containing 500 g of the soil with different Cd and/or Pb application rates were incubated for a period of 0, 2, 9, 12 weeks in a glasshouse and the soil samples were analyzed for individual enzymes, including catalase, alkaline phosphatase and dehydrogenase, and the changes of microbial community structure. Results showed that heavy metals slightly inhibited the enzymatic activities in all the samples spiked with heavy metals. The extent of inhibition increased significantly with increasing level of heavy metals, and varied with the incubation periods. The soil bacterial community structure, as determined by polymerase chain reaction- denaturing gradient gel electrophoresis techniques, was different in the contaminated samples as compared to the control. The highest community change was observed in the samples amended with high level of Cd. Positive correlations were observed among the three enzymatic activities, but negative correlations were found between the amounts of the heavy metals and the enzymatic activities.

Removal of heavy metals from a contaminated soilusing tartaric acid

This study reports the feasibility of remediation of a heavy metal （HM） contaminated soil using tartaric acid, an environmentally-friendly extractant. Batch experiments were performed to test the factors influencing remediation of the HM contaminated soil. An empirical model was employed to describe the kinetics of riM dissolution/desorption and to predict equilibrium concentrations of HMs in soil leachate. The changes of HMs in different fractions before and after tartaric acid treatment were also investigated. Tartaric acid solution containing HMs was regenerated by chestnut shells. Results show that utilization of tartaric acid was effective for removal of riMs from the contaminated soil, attaining 50%-60% of Cd, 40%-50% of Pb, 40%-50% of Cu and 20%-30% of Zn in the pH range of 3.5-4.0 within 24 h. Mass transfer coefficients for cadmium （Cd） and lead （Pb） were much higher than those for copper （Cu） and zinc （Zn）. Sequential fractionations of treated and untreated soil samples showed that tartaric acid was effective in removing the exchangeable, carbonate fractions of Cd, Zn and Cu from the contaminated soil. The contents of Pb and Cu in Fe-Mn oxide fraciton were also significantly decreased by tartaric acid treatment. One hundred milliliters of tartaric acid solution containing HMs could be regenerated by 10 g chestnut shells in a batch reactor. Such a remediation procedure indicated that tartaric acid is a promising agent for remediation of HM contaminated soils. However, further research is needed before the method can be practically used for in situ remediation of contaminated sites.