Total Soil Cd Research Articles

Low-Cd wheat varieties and soil Cd safety thresholds for local soil health management in south Jiangsu province, east China

Wheat is the second most important staple food crop, therefore safe and environmentally friendly production of wheat is essential for human safety and health. Southern Jiangsu province is a very important wheat producing region that is highly industrialized with many soils polluted with potentially toxic metals, especially cadmium (Cd). Wheat varieties with low Cd bioconcentration factors (BCF) are often used to decrease Cd accumulation and increase the safety of products in field practice. In addition, the development of local soil safety thresholds, the main focus of soil health management, is also necessary to protect agricultural soil health and agricultural production. However, there is no published literature describing low-Cd-accumulating wheat varieties and soil safety thresholds in this region. Field plot experiments and field investigations at multiple experimental sites in southern Jiangsu province have therefore been conducted for several years to screen low-Cd-accumulating wheat varieties and to derive soil Cd safety thresholds. The varieties Yangmai 25, Zhengmai 12 and Yangmai 12 had stable and low Cd BCF. The deduced safe thresholds of total soil Cd concentrations for protecting 95 % of wheat varieties were 0.17, 0.18, and 0.31 mg kg−1 at 4.5 < pH ≤ 6.5, 6.5 < pH ≤ 7.5 and 7.5 < pH ≤ 9.0, stricter levels than the Chinese national risk screening values. The deduced thresholds were validated to increase the protection rates of wheat by field investigations. In conclusion, wheat varieties with low Cd BCF and soil thresholds can contribute to local soil health management and safe wheat production in southern Jiangsu province.

Prediction model for Cd accumulation of rice (Oryza sativa L.) based on extractable Cd in soils and prediction for high Cd-risk regions of southern Zhejiang Province, China.

Soil environmental quality in China for agricultural land always considers the effect of total cadmium (Cd) in soil, ignoring the bioavailability of soil Cd. The 139 paired rice (Oryza sativa L.) and soil samples were collected from the Cd-contaminated paddy fields of southern Zhejiang Province, China. The objectives of this study were to establish accurate prediction models for Cd accumulation in brown rice based on bioavailable Cd and physiochemical properties of soils and to evaluate the safety of rice production in Cd-contaminated paddy. The bioavailable Cd in soils was extracted and evaluated by using CaCl2, HNO3, diethylenetriamine pentaacetic acid (DTPA), diffusive gradients in thin-films technique (DGT), and sequential extraction method proposed by the European Community Bureau of Reference; 100 pairs of data were used as training sets, and the remaining 39 sets were used as validation sets. Stepwise multiple linear regression analysis and random forest analysis showed that total Cd in soil could roughly indicate the content of Cd in rice, while extractable Cd could better explain the accumulation of Cd in rice grain and DTPA and DGT extractive technologies are the most evaluative. The validation sets also showed that the prediction model has a good fit. Based on the prediction model for Cd in brown rice based on soil pH and DGT extractive Cd, the Monte Carlo simulation showed that 74.32% and 89.35% of the estimated brown rice hazard quotient (HQ) of the daily Cd intake of adults and children in safe utilization paddy sites could exceed the safe level of 1, respectively. Additionally, the threshold values for extractable Cd by DGT or DTPA for rice safe production were 3.4μg/kg or 0.13mg/kg when the pH in soils was below 5.5. The results further proved the threshold concentration of extractable Cd for predicting high-risk soils of Cd contamination in brown rice.

Effect of Citric Acid and Mowing on Enhancing the Remediation of Cadmium Contaminated Soil by Napier Grass (Pennisetum purpureum Schum)

A pot experiment was conducted to investigate the effects of citric acid application and mowing frequency on the remediation of cadmium (Cd) contaminated soil by napier grass (Pennisetum purpureum Schum). Three levels of citric acid were divided into three applications of 1.25, 2.5, and 5 mmol·kg-1. The mowing frequency of the plants was divided into no mowing, one mowing, and two mowing treatments. The results showed that:① 1.25 mmol·kg-1 citric acid increased the biomass of the upper part of the plant by 39.11% with one mowing, and multiple mowing treatments and high citric acid application were not beneficial to the biomass increase. ② Both citric acid application and mowing had the effect of increasing the Cd content in stems and leaves, and Cd content in stems harvested in the last mown crop was larger and increased by approximately six times under the 5 mmol·kg-1 citric acid application. ③ Citric acid application and mowing reduced the rhizosphere soil pH and organic matter and also reduced the total soil Cd content and TCLP-Cd content by a maximum of 14.29% and 10.17%, respectively. ④ Under the 1.25 mmol·kg-1citric acid application and one mowing treatment (L1), the best Cd extraction by Napier grass was achieved with 6.95 mg·plant-1 of above-ground parts, accounting for 9.38% of the total Cd content in the potted test soil. Therefore, the L1 treatment can be considered to improve the remediation efficiency when using napier grass to remediate Cd-contaminated soil in the future.

Redistribution and isotope fractionation of endogenous Cd in soil profiles with geogenic Cd enrichment

The concentration and speciation of endogenous cadmium (Cd) in soil systems derived from parent materials is continuously altered by rock-soil-plant interactions. Previous studies on the distribution of Cd primarily focused on surface soil at regional scale. However, it lacks a novel approach to provide a new perspective on dynamics and redistribution of Cd in soil profile. Therefore, this study tries to establish the linkage between isotope fractionation and environmental processes of Cd in soil profiles with geogenic Cd enrichment based on Cd isotopes. High Cd concentrations were observed in the profile from forest at accumulation zone and the one from farmland at ridge in a rural area, southwest China. Soil erosion and deposition substantially influence the vertical distribution of total Cd in soil from the accumulation zone. Accordingly, distinct Cd isotope compositions were observed in different layers (δ114/110Cd: −0.087 ‰ to −0.066 ‰ vs −0.325 ‰ to −0.056 ‰). Mineral transformation, pedogenesis and biological activities controlled the dynamics and redistribution of Cd. The mobility of Cd increased during weathering processes, with ~40 % to 60 % of Cd residing in exchangeable fraction in the surface layers. Biological activity is a vital factor that drives Cd isotope fractionation in soil, resulting in depletion of heavy Cd isotopes in surface layers of the studied farmland profile. Contrasting fractionation effects were observed in profiles from forest and farmland due to the variance in soil-plant Cd cycling. Our study revealed the processes that control dynamics and redistribution of endogenous Cd in soil profiles, and proved that Cd isotope is a useful tool to investigate the bio-geochemical processes of Cd in soil systems.

Application of chelate GLDA for remediating Cd-contaminated farmlands using Tagetes patula L.

In the present study, via a 180-day field trial, the indicators of soil total cadmium, DTPA-Cd, organic matter, and plant cadmium extraction were tested after the application of chelate tetrasodium glutamate diacetate (GLDA) to investigate the potential of GLDA combined with Tagetes patula L. to remediate cadmium-contaminated soil. To do so, five GLDA treatments (e.g., 0, 292.5, 585, 1170, and 2340kg hm-2) were practiced. For each treatment, the total GLDA was divided into two applications with 15-day intervals (0.25, 0.47, and 0.61mg·kg-1) under T. patula plantation. Compared with the control, our results showed that GLDA application significantly increased the biomass of aerial parts of T. patula by 21.9% (p < 0.05). Likewise, Cd content in aboveground and underground parts of T. patula increased by 94.7% and 60.5%, respectively, compared with the control (p < 0.05). GLDA application caused significant increases in Cd accumulations in cell soluble fraction and cell wall by 290% and 123%, respectively (p < 0.05); soil pH and DTPA-Cd content increased with the increase of total application of GLDA. Co-application of GLDA (2340kg hm-2) and T. patula reduced the total soil Cd content by 12.87% compared with the soil background. Altogether, our findings conclude on the efficacy of GLDA application for the remediation of Cd-contaminated farmlands under T. patula cultivation.

The determination of regulating thresholds of soil pH under different cadmium stresses using a predictive model for rice safe production.

Regulating soil pH becomes a crucial practice to alleviate cadmium (Cd) contamination. However, little is known about the threshold of soil pH for the safe production of rice at various soil Cd levels. In this paper, the relationships between soil pH values and the contents of available Cd extracted by calcium chloride (CaCl2-Cd) in neutral and acidic soils were studied by mandatory acidification with H+ addition or neutralization with lime at various soil Cd levels. The results showed that the soil CaCl2-Cd contents dramatically decreased with increasing soil pH, and a logarithmic function could well describe the relations of soil CaCl2-Cd contents and soil pH at constant total Cd (CaCl2-Cd model). The Cd contents in rice grain (grain-Cd) in relation to soil CaCl2-Cd was further established through modified rice pot experiments. A model for the prediction of Cd content in rice grains (grain-Cd model) was set up, though which the grain-Cd content could be predicted based on soil pH and total Cd content. 122 data pairs of rice grain-Cd contents obtained at various soil total Cd contents and pH were employed from the literature to verify the reliability of the established model, approximately 95.08% of those data favorably located within the 1:1 line ± 0.5 unit area of the grain-Cd model. Notably, this model can be applied to determine the thresholds of soil pH at a specific Cd pollution level. For instance, to achieve a rice grain-Cd contents matching the Chinese national food safety limit of 0.2mgkg-1, the soil pH thresholds were estimated to be 5.05, 5.70, and 6.02 at soil Cd contents of 0.3, 0.6, and 0.8mgkg-1, respectively. In addition, the established model can also be used to estimate the health risk from rice in broad regions with various soil pH values and Cd contents.

Effects of soil properties on heavy metal bioavailability and accumulation in crop grains under different farmland use patterns

Mining activities have increased the accumulation of heavy metals in farmland soil and in food crops. To identify the key soil properties influencing heavy metal bioavailability and accumulation in food crops, 81 crop samples and 81 corresponding agricultural soil samples were collected from rape, wheat, and paddy fields. Heavy metal (copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), iron (Fe), and manganese (Mn)) concentrations in soils and rape, wheat, rice grains were determined using inductively coupled plasma atomic emission spectroscopy, and soil physicochemical properties (pH, organic matter, total nitrogen, total phosphorus, available phosphorus, and available potassium (AK)) were analyzed. Soil extractable metals were extracted using various single extractants (DTPA, EDTA, NH4OAc, NH4NO3, and HCl). The average concentrations of Cu, Zn, Pb, Cd, and Mn in the soil samples all exceeded the local geochemical background value (background values of Cu, Zn, Pb, Cd, and Mn are 43.0, 81.0, 28.5, 0.196, and 616 mg/kg, respectively), and Cd over-standard rate was the highest, at 98%. Furthermore, soil total Cd concentrations (0.1–24.8 mg/kg) of more than 86% of the samples exceeded the soil pollution risk screening value (GB 15618-2018). The sources of Cu, Zn, Pb, Cd, and Mn in soils were mainly associated with mining activities. The key factors influencing heavy metal bioavailability were associated with the types of extractants (complexing agents or neutral salt extractants) and the metals. Cd and Pb concentrations in most wheat and rice grain samples exceeded the maximum allowable Cd and Pb levels in food, respectively, and Cd concentrations in approximately 10% of the rice grain samples exceeded 1.0 mg/kg. Furthermore, rice and wheat grains exhibited higher Cd accumulation capacity than rape grains, and despite the high soil Cd concentrations in the rape fields, the rape grains were safe for consumption. High soil pH and AK restricted Cd and Cu accumulation in wheat grains, respectively. Soil properties seemed to influence heavy metal accumulation in rice grains the most.

Comparison of Pb and Cd in wheat grains under air-soil-wheat system near lead-zinc smelters and total suspended particulate introduced modeling attempt

The excessive accumulation of wheat grain metals and metalloids caused by ambient air contamination has drawn an increasing concern. However, at present, the differences in the pathways of cadmium and lead accumulation in wheat grains in an air-soil-wheat system are not clear. In this study, wheat was grown around a lead‑zinc smelting area and exposed to different soil Pb and Cd levels and different ambient air Pb and Cd levels. Lead and Cd accumulation in wheat grains was examined in this study. Two models of wheat grain Pb and Cd concentrations were established based on the 3 variables including soil Pb and Cd concentration, ambient air Pb and Cd concentration, and soil pH. The results showed that total suspended particulate (TSP), soil, and wheat grains exhibited different degrees of Pb and Cd contamination in the study area, and the contamination of Cd is more serious than Pb contamination. The Pb in wheat grains was more likely to derive from ambient air than from soil, whereas the impact of ambient air on the accumulation of Cd in wheat grains might be very limited. This speculation was confirmed by the results of the predictor variable relative weight method based on the multiple regression analysis. Introduction of ambient air factor (TSP Pb and Cd) greatly improved the modeling effect of wheat grains Pb, while the modeling of grain Cd was more dependent on soil pH and total soil Cd. This research suggests that the reduction in wheat grain Pb is likely to be achieved by the control over ambient air Pb, whereas the reduction in the wheat grain Cd by the remediation of soil pollutants.

Remediation and Micro-Ecological Regulation of Cadmium and Arsenic Co-Contaminated Soils by Rotation of High-Biomass Crops and Sedum alfredii Hance: A Field Study

Rotation of high-biomass crops and hyperaccumulators is considered to be an effective, safe and economical method for the remediation of medium-mild heavy metal contaminated soil, but the present studies pay more attention to the removal efficiency rather than changes in soil micro-ecology. In order to explore the remediation effect of hyperaccumulators rotated with high-biomass crops on Cd and As co-contaminated soil, Cd hyperaccumulator ecotype (HE) Sedum alfredii Hance and crops were selected to construct a field experiment, five rotation modes including Sedum alfredii Hance-Oryza sativa L. (SP), Sedum alfredii Hance-Sorghum bicolor (L.) Moench (SS), Sedum alfredii Hance-Zea mays L. (SM), Sedum alfredii Hance-Hibiscus cannabinus L. (SK), Sedum alfredii Hance-Trichosanthes kirilowii Maxim. (ST), and investigated the effects of these modes on the removal efficiency, soil physiochemical properties and micro-ecological effects (soil nutrients, enzyme activities and microbial diversity) through a field experiment. The results showed that total soil Cd from the five rotation modes (SP, SS, SM, SK and ST) decreased by 25.1%, 20.3%, 34.5%, 6.3% and 74.3%, respectively, and total soil As decreased by 42.9%, 19.8%, 39.7%, 39.7% and 45.7%, respectively. The rotation significantly increased soil organic matter by 47.39–82.28%, effectively regulated soil pH value and cation exchange capacity. The rotation modes also significantly increased soil alkali-hydrolysable nitrogen by 9.09–50.91%, but decreased soil available phosphorus and rapidly available potassium. Except for urease, the soil enzyme activities increased overall. The Alpha diversity increased, and soil microbial structure optimized after rotation. ST mode was the most effective remediation mode, which not only reduces the content of Cd and As in the soil, but also effectively regulates the soil micro-ecology. The results from this study have shown that it is feasible to apply Sedum alfredii Hance and the high-biomass rotation method for the remediation of Cd and As co-contaminated soil.

Effects of soil aging conditions on distributions of cadmium distribution and phosphatase activity in different soil aggregates

Aging behaviors of metals in the field differ from those in a controlled laboratory environment. Whether aging conditions influence the fates of metals in soil remains unclear. In this study, distributions of cadmium (Cd) and phosphatase activity were compared in soil aggregates (i.e., >2, 1–2, 0.25–1, and <0.25 mm) along a profile (0–5, 5–10, and 10–15 cm) at the end of 500-day aging experiments under both controlled laboratory and field conditions. Cd concentration in the 0–5 cm layer was lower and Cd concentration in the 5–10 cm layer was higher in field-aged soil compared to laboratory-aged soil. 25.26–35.62% of soil Cd was loaded in >2 mm aggregates of field-aged soils, and 58.41–66.95% was in laboratory-aged soils. Higher loadings of Cd in 0.25–1 and <0.25 mm aggregates were found in field-aged soil. A higher proportion of exchangeable Cd fraction (20.93% of total soil Cd) was found in the 0–5 cm layer of field-aged soil than in laboratory-aged soil (17.63%), while the opposite tendency was found in deeper soil layers. Soil phosphatase activities in field-aged soils were 1.13–1.26 times higher than in laboratory-aged soils. Phosphatase loadings in the >2 mm aggregates were lower and loadings in both the 1–2 and 0.25–1 mm aggregates were higher in field-aged soils than in laboratory-aged soils. Furthermore, correlation analysis and principal component analysis indicated that available Cd fractions accounted for most of the variations in phosphatase activities. In summary, the fates of the exogenous metal Cd differed between field and controlled laboratory conditions. To better understand the behaviors of heavy metals in soil, especially in a seasonal freeze-thaw area, further field studies are needed.

Modeling Cadmium Contents in a Soil–Rice System and Identifying Potential Controls

Cadmium (Cd) pollution in a soil–rice system is closely related to widely concerning issues, such as food security and health risk due to exposure to heavy metals. Therefore, modeling the Cd content in a soil–rice system and identifying related controls could provide critical information for ensuring food security and reducing related health risks. To archive this goal, in this study, we collected 217 pairs of soil–rice samples from three subareas in Zhejiang Province in the Yangtze River Delta of China. All soil–rice samples were air-dried and conducted for chemical analysis. The Pearson’s correlation coefficient, ANOVA, co-occurrence network, multiple regression model, and nonlinear principal component analysis were then used to predict the Cd content in rice and identify potential controls for the accumulation of Cd in rice. Our results indicate that although the mean total concentration of Cd in soil samples was higher than that of the background value in Zhejiang Province, the mean concentration of Cd in rice was higher than that of the national regulation value. Furthermore, a significant difference was detected for Cd content in rice planted in different soil groups derived from different parental materials. In addition, soil organic matter and total Cd in the soil are essential factors for predicting Cd concentrations in rice. Additionally, specific dominant factors resulting in Cd accumulation in rice planted at different subareas were identified via nonlinear principal component analysis. Our study provides new insights and essential implications for policymakers to formulate specific prevention and control strategies for Cd pollution and related health risks.

Use of artificial neural network to evaluate cadmium contamination in farmland soils in a karst area with naturally high background values

In recent years, the naturally high background value region of Cd derived from the weathering of carbonate has received wide attention. Due to the significant difference in soil Cd content and bioavailability among different parent materials, the previous land classification scheme based on total soil Cd content as the classification standard, has certain shortcomings. This study aims to explore the factors influencing soil Cd bioavailability in typical karst areas of Guilin and to suggest a scientific and effective farmland use management plan based on the prediction model. A total of 9393 and 8883 topsoil samples were collected from karst and non-karst areas, respectively. Meanwhile, 149 and 145 rice samples were collected together with rhizosphere soil in karst and non-karst areas, respectively. The results showed that the higher CaO level in the karst area was a key factor leading to elevated soil pH value. Although Cd was highly enriched in karst soils, the higher pH value and adsorption of Mn oxidation inhibited Cd mobility in soils. Conversely, the Cd content in non-karst soils was lower, whereas the Cd level in rice grains was higher. To select the optimal prediction model based on the correlation between Cd bioaccumulation factors and geochemical parameters of soil, artificial neural network (ANN) and linear regression prediction models were established in this study. The ANN prediction model was more accurate than the traditional linear regression model according to the evaluation parameters of the test set. Furthermore, a new land classification scheme based on an ANN prediction model and soil Cd concentration is proposed in this study, making full use of the spatial resources of farmland to ensure safe rice consumption.

Drivers of cadmium accumulation in Theobroma cacao L. beans: A quantitative synthesis of soil-plant relationships across the Cacao Belt.

Elevated cadmium (Cd) concentrations in cacao and cocoa-based products (e.g., chocolate) present a potentially serious human health risk. While recent regulatory changes have established a threshold of 0.8 mg kg-1 for Cd content of cocoa-based products, the biophysical factors (e.g., climatic or edaphic conditions) that determine the amount of soil-derived Cd in the cacao bean are poorly understood and have yet to be quantitatively assessed across diverse production contexts. To determine the primary drivers of cacao bean Cd, we used the scientific literature to systematically compile a database of climatic, edaphic, and plant data from across the Cacao Belt, which is approximately 20 degrees latitude on either side of the equator. From this compiled dataset, we then used boosted regression trees to quantitatively synthesize and evaluate these drivers of cacao bean Cd. Total soil Cd concentration, soil pH, and leaf Cd were the best predictors of bean Cd content. Notably, we found that both available soil Cd and soil organic carbon (SOC) content had negligible effects on bean Cd. However, soil pH and SOC decreased the degree of bioconcentration of total soil Cd in the bean Cd concentration. Thus, given the difficulty in remediating soil Cd enriched soils, our results suggest that Cd mitigation strategies targeting plant physiology-based approaches (e.g., breeding, rootstocks) have a higher probability of success than soil-based strategies (e.g., remediation).

Effects of full inversion tillage during pasture renewal on soil and plant cadmium concentrations: a case study in New Zealand

Context Cadmium (Cd) accumulation is a concern in permanent pasture soils, as it can lead to increased Cd uptake by plants.Aims This study aimed to quantify the effect of full inversion tillage (FIT or ploughing deeper than 30cm), used during pasture renewal, on the redistribution of Cd within the soil profile and on plant Cd concentration.Methods Two field trials (Trial 1, Alfisol; Trial 2, Andisol) were established in New Zealand using contrasting tillage practices (FIT; SIT, shallow tillage; and NT, no tillage) to sow turnips as summer forage crops, followed by autumn re-sowing of perennial ryegrass/white clover pasture.Key results In the Alfisol, no measurable differences (P>0.05) in soil and plant Cd were detected among the tillage treatments. In the Andisol, FIT decreased (P<0.05) total (0.25mg/kg) and extractable soil Cd (0.013mg/kg) in the 0–5cm depth, compared to pre-tillage (0.42 and 0.031mg/kg, respectively). Moreover, at this soil depth, FIT achieved a 52% lower (P=0.034) extractable soil Cd concentration than the ST treatment. In addition, the subsequent new pasture had lower (P=0.007) average Cd concentration following FIT compared to ST (0.03 vs 0.05mg/kg).Conclusions We demonstrated that the use of FIT during pasture renewal is a potential solution to reduce topsoil Cd concentration.Implications The FIT is more effective in soil where total soil Cd concentration or its degree of vertical stratification with depth is relatively high.

Cadmium concentrations in Idaho wheat grain and soil

AbstractCurrent efforts to reduce the maximum allowable cadmium (Cd) concentrations in wheat (Triticum aestivum L.) for at‐risk populations such as infants require sourcing wheat with low concentrations of Cd. Since Idaho (USA) is a major wheat supplier, there is a need to understand which varieties and locations in Idaho produce wheat containing low Cd. Therefore, the main objective of this paper is to report on a survey of total Cd concentrations in 469 wheat grain samples and 216 soil samples from several varieties and locations throughout Idaho. Total Cd concentrations in wheat grain ranged from &lt;0.01 to 0.28 mg kg−1, varying by both wheat variety and location grown. Total soil Cd ranged from 0.450 to 1.85 mg kg−1. Bioaccumulation factor (BAF) was calculated by dividing the grain total Cd concentration by the soil total Cd concentration and ranged from 0.05 to 0.5. The variety ‘UI Sparrow’ had the lowest mean BAF (0.06), and several other varieties were also relatively low. Overall, almost all wheat varieties meet European Food Safety Authority (EFSA) requirements for Cd concentration for adult consumption. However, meeting the EFSA maximum allowable limit of Cd in infant food requires planting varieties noted for low Cd uptake, like UI Sparrow, and careful selection of growing regions with the lowest total soil Cd, such as northern, central, or western Idaho.

Environmental impact assessment of Egyptian Damietta governorate soils contamination with cadmium

Soil parental materials and anthropogenic activities are the sources of increasing Cd in soils and enrichment in edible parts of plants and creating hazards to animals and human. Thus, it is an important issue to estimate the levels of Cd in soils; straw and grains of rice and wheat plants grown in the soils contaminate with Cd and evaluates human health risk. In surface soil, total Cd (899±497µg kg-1) and Diethylene Triamine Penta Acetate (DTPA) extractable Cd (16.41±13.83µg kg-1) slightly higher by 1.02±0.20 and 1.31±0.45 folds than the subsurface layers, respectively. The DTPA extractable Cd concentration is significantly increased linearly with increasing total soil Cd (r=0.90). Positive significant correlation was found between soils DTPA extractable Cd and soil organic matter (OM) content (r=0.95), while significant negative correlation for both CaCO3 content (r=-0.92) and pH (r=-0.94). In rice Cd concentrations of straw (374±156µg kg-1) and grains (35±16µg kg-1) are significantly correlated with total soil Cd (r=0.89, r=0.86) and DTPA extractable Cd (r=0.84, r=0.74), respectively. Whereas, rice grains Cd is increased with increasing straw Cd (r=0.98). Wheat Cd concentrations of straw (194±71µg kg-1) and grains (18±13µg kg-1) are significantly correlated with total soil Cd (r=0.90, r=0.96) and DTPA extractable Cd (r = 0.91, r=0.95), respectively. Wheat grains Cd is increased with increasing straw Cd (r=0.95). The Cd Transfer factors (TF) as an average is higher in rice grains (0.04±0.014) than wheat grains (0.021±0.016). However, Cd concentrations in the wheat and rice grains are lower than the both EU and WHO/FAO permissible limits (0.24mg kg-1 and 0.4mg kg-1 dry wt., respectively) and so far no potential human health risk is concluded yet.

Predicting soil cadmium uptake by plants in a tailings reservoir during 48-year vegetation restoration

Plant uptake can reduce soil cadmium (Cd) pollution, while how to exactly predict plant Cd uptake in industrial or mining areas during vegetation restoration remains unexplored. Taking Heteropogon contortus as the object plant, we predicted plant Cd uptake in the Majiatian tailings reservoir during 48-year vegetation restoration by the methods of soil total Cd, DGT (diffusive gradients in thin films technique) and acetic acid (HAc) extraction. Meanwhile, we explored the effects of soil properties on the accuracy of the prediction. Total Cd concentrations in the soils exhibited a better prediction of plant Cd uptake relative to the methods of HAc extraction and DGT. However, the DGT method effectively predicted plant Cd uptake at low Cd supply (lower than 0.42 μg/L), probably because of the dominant diffusion limitation by plants. The prediction of plant Cd uptake by HAc extraction was improved when combined with soil pH. Our results indicate that with increasing external Cd inputs during the vegetation restoration, soil total Cd and traditional extraction method in combination with soil properties are effective ways to predict plant Cd uptake, especially when the Cd fractions cannot be measured by DGT. However, the DGT method works once plant Cd uptake dominated by diffusion limitation despite the interference in soil properties.

Cd Pollution and Safe Planting Zoning in Paddy Soils: A Case Study in a District of Chongqing

Rice has a strong ability to accumulate Cd in soil, and it is of great significance to study Cd pollution and safe planting zoning in paddy soils. In this work, 300 sets of paddy soil-rice samples were simultaneously collected in 22 towns in a District of Chongqing, and soil pH, soil total and available Cd contents, and brown rice Cd contents were determined. Soil Cd pollution was assessed using the geoaccumulation index, bioconcentration factor, and the single-factor pollution index. Based on the Cd pollution indices of soil and brown rice, safe planting zoning for rice was determined. The results showed that the paddy soils were generally acidic, and total Cd contents ranged from 0.09 mg·kg-1 to 1.60 mg·kg-1, with 35.0% of sites exceeding the risk screening value. The Cd contents of the brown rice ranged from 0.002 mg·kg-1 to 0.808 mg·kg-1 and exceeded the food safety limit in 13.7% of cases. Pearson correlation analysis showed that the Cd content of brown rice was significantly positively correlated with soil total and available Cd (P<0.01). The pollution evaluation indicated that significant Cd accumulation occurred in the paddy soils, with some areas showing light-to-moderate pollution levels. The enrichment coefficients of rice to soil Cd ranged from 0.004 to 1.72. Overall, the paddy soils in the studied area were considered generally safe with respect to Cd pollution, with low-risk areas distributed in the south, west, and east, whereas some medium-high risk areas were detected in eight towns.

Evaluation of the Effects of Cadmium in Soil on the LC50 of Soil Bacteria and Fungi for Environmental Monitoring

Contamination of soil with heavy metals by is currently of global concern. Cadmium (Cd) is one of the metals of concern. In the current study, LC50 of Cd to soil bacteria and fungi was used to assess the impact of anthropogenicactivity in development of Cd tolerance in soil microorganisms. Levels of Bio-physicochemical parameters in soil were determined. Results show that the concentration of Total Petroleum Hydrocarbon (TPH) and Cd in soil ranged between 5.09±0.33 to 9261.94±287.67, and 0.023±0.015 to 0.057±0.012 ppm respectively. There was significant difference (p = 0.001) in LC50 for fungi between the study and control samples. Pearson correlation showed that there was significant relationship (r = 0.30) between LC50 for bacteria and TPH. There was significant difference (p = 0.017) in LC50 values among the study and control samples for fungi. Anthropogenic activities influenced the concentrations of TPH soil but did not influence levels of Cd.

Factors affecting cadmium accumulation in the soil profiles in an urban agricultural area

Soil Cd pollution is a serious environmental issue associated with human activities. However, the factors determining exogenous Cd dynamics in the soil profile in a complex environment are not well understood. Based on regional observations from 169 soil profiles across the Chengdu Plain, this study explored the key factors controlling Cd accumulation in the soil profile under actual field conditions. Results showed that total soil Cd contents decreased from 0.377 to 0.196 mg kg−1 with increasing soil depth. The effects of phosphate fertilizer rates, road density and precipitation on the difference in total soil Cd content were only observed in topsoil, while agricultural land-use type and topography had no impact. In contrast, significant differences in the total soil Cd content among different parent material types were found in the 0–20, 40–60 and 60–100 cm soil depths. One sample t-tests showed that significant Cd accumulation occurred in the whole soil profile in soils formed from Q4 (Quaternary Holocene) grey alluvium, while soils formed from Q3 (Quaternary Pleistocene) old alluvium and Q4 grey-brown alluvium showed significant Cd accumulation only in the 0–40 cm soil layers. In the topsoil, acid soluble Cd accounted for the largest proportion of the total Cd in soils formed from Q4 grey alluvium, reducible Cd was the main fraction in soils formed from Q4 grey-brown alluvium, while reducible Cd and residual Cd contributed the largest proportion of the total soil Cd in soils formed from Q3 old alluvium. The above results indicated that parent material was the decisive factor determining the magnitudes and depths of exogenous Cd accumulation in the soil profile due to its impacts on the Cd fraction distributions. These findings suggested that the parent material-induced Cd fraction distributions and accumulation should be considered for effectively exploring targeted remediation strategies for Cd pollution.