Cd Accumulation In Soil Research Articles

Influence of Iron-Enriched Biochar on Cd Sorption, Its Ionic Concentration and Redox Regulation of Radish under Cadmium Toxicity

Cadmium (Cd), a potent heavy metal, causes a significant reduction in plant growth and its yield by interfering with the plant’s mineral nutrition and, primarily, by inducing Cd-induced oxidative damage. Cd mobilization at the soil–root interface is also very important in context of its bioavailability to plants. Therefore, an experiment was carried out to evaluate the mitigating role of iron-enriched biochar (Fe-BC) on Cd accumulation in soil and Cd toxicity in radish plants. Radish seeds were sown in pots, and two levels of Cd (0 and 0.75 mg kg−1) and two levels of Fe-BC (0 and 0.5%) were applied. Cd stress significantly reduced radish fresh and dry biomass production, which was due to high production of malondialdehyde (36%) and increase in cell membrane permeability (twofold) relative to control. Moreover, Cd stress considerably reduced chlorophyll concentrations and uptake of some essential nutrients, such as Ca, K, and Fe. Contrarily, Fe-BC application ameliorated Cd toxicity by triggering the activation of antioxidant enzymes (catalase and ascorbate peroxidase), primary and secondary metabolite accumulation (protein and phenolics concentrations), and by improving plant mineral nutrition under Cd treatment, compared with Cd treatment only. The ability of biosorbent material (Fe-BC) to adsorb the Cd ion on its surface and its immobilization from Cd-polluted soil to plant root was determined by using Langmuir and Freundlich isotherm models. Interestingly, Cd concentration was found in soil as diethylenetriamine (DTPA)-extractable soil Cd on radish root, but not reported in radish shoot with Cd+Fe-BC treatment, compared to Cd treatment; suggesting that Fe-BC treatment has a potential to provide extra strength to the root and shoot, and plays an important role in regulation ionic and redox homeostasis under Cd stress.

Cadmium accumulation in rice and its bioavailability in paddy soil with application of silicon fertilizer under different water management regimes

AbstractThe contamination agricultural soils and food by cadmium (cd) is one of the major concerns of the world. The field experiments were conducted to investigate the effects of silicon (Si) fertilizer on bioavailability and accumulation of Cd in soil, Cd chemical fractions, dynamic changes of soil pH, available Cd content and Cd content of various parts of rice plants. The results revealed that application of Si fertilizer and continuous flooding of soil have enhanced soil pH and diminished soil available Cd content. The application of Si fertilizer and continuous flooding have improved proportion of Fe‐Mn oxides bound and residual Cd in soil. The application of Si fertilizer has increased Cd content of rice roots, but reduced Cd content of rice stems and brown rice. The Cd content of brown rice in the treatment of SF was significantly declined by 38.80% compared to CK (p < .05). The biomass of rice root and brown rice was improved by 44.04% and 17.86%, respectively, with application of Si fertilizer under conventional irrigation compared with control. The significant variation in biomass of rice in treatment of continuous flooding was observed with application of Si fertilizer compared with control. The combined application of Si fertilizer with continuous flooding has effectively prevented Cd accumulation in rice.

Typical sources of Cd to paddy fields in different contaminated areas and their impacts on Cd accumulation in topsoil and rice in Changzhutan, China

Heavy metal pollution of soils has been worsening increasingly in China, which brings significant health risk to human, it is critical to investigate the sources of heavy metals in agricultural soils and explore the effects of heavy metal accumulation in crops. In this paper, the sources of cadmium (Cd) and their effects on Cd accumulation in soil and rice grown on urban farmland in Changzhutan were investigated. Among the main Cd sources (irrigation water, commercial fertilizer, and atmospheric deposition), the input flux of atmospheric deposition accounted for 76.36%–98.25% of total input flux, significantly higher than the input fluxes of irrigation water and commercial fertilizer. Manure fertilizer was also an important source of Cd in livestock breeding areas. The accumulation behaviors of Cd in soils and plants presented significant spatial variation among the study areas. Higher Cd input flux from atmospheric deposition resulted in higher Cd bioavailability in soil and more Cd accumulation in rice, and the newly deposited Cd contributed 7.35–41.23% in rice tissues. The use of manure fertilizer increased the soil pH and amount of available Cd in soil, as well as the accumulation of Cd in rice roots. Based on sequential extraction, acid-extractable Cd accounted for approximately 52.54%–61.88% of total Cd in atmospherically deposited particles in the study area, resulting in a high proportion of acid-extractable Cd in soil. This study provides useful reference data on the sources of Cd and its bioavailability in soil and rice.

Impact of Bio-Accumulated Cadmium in Bombyx mori L. Reared on Mulberry Plants Grown in Heavy Metal-Impregnated Soils in Faisalabad, Pakistan

Industries in Faisalabad are discharging their wastewater containing different kinds of heavy metals without treatment into sewerages. This wastewater is used to irrigate different crops and trees. This study was planned to observe the entry of Cd from inorganic to organic source and its effects on the lifecycle of Bombyx mori (L.). Mulberry plants were irrigated with Cd-containing synthetic effluents of different concentrations (25 to 200 mg/l) at pH 5, and different levels of pH (3 to 5) at 100 mg/l, to check against different instars of silkworm. The amount of Cd in the samples of soil, mulberry leaves, silkworm larvae, silkworm faeces and silk glands were determined by using atomic absorption spectrophotometry (AAS). The results showed that B. mori can be used as an indicator of Cd pollutants because its body weight, body length and mortality rate was directly related to Cd concentration. Greater toxicity to silkworms was observed at higher accumulation of Cd in mulberry leaves. Maximum accumulation of Cd in soil, mulberry plants, silkworm larvae, silk glands and silkworm faeces was observed at 200 mg/l Cd and pH 5. The maximum accumulations observed were 99.89 mg/kg, 95.67 mg/kg, 61.32 mg/kg, 58.97 mg/kg and 6.59 mg/kg, respectively. Silkworms can be successfully used as an indicator of heavy metal pollutants and their role can further be marked with changes in the development.

Effect of terrain gradient on cadmium accumulation in soils

Many studies have confirmed that terrain is an important factor affecting cadmium (Cd) accumulation in soil. However, the literature offers limited exploration on the effect mechanism of terrain on soil Cd accumulation. This study aims to explore the effect of terrain on the characteristics and influencing factors of soil Cd accumulation. A total of 182 soil samples are collected across the terrain gradient from soils in Dongguan City. Gradient boosting decision tree is implemented to identify the influencing factors of Cd accumulation in different terrain gradients. The goodness of fit of the models for low, median, and high terrains are 0.85, 0.80, and 0.84, respectively. Cd accumulation shows a significantly decreasing pattern in soils with an increase in terrain gradient (P < 0.001). Approximately 90.9% of Cd accumulation hot spots are observed in gentle terrain areas with a terrain niche index of <0.45, whereas 60.0% of cool spots are concentrated in low hilly areas with a terrain niche index in the range of 0.45–1.50. The influencing factors of Cd accumulation with the greatest relative contribution in low, median, and high terrains are agricultural practices (33.89% and 27.51%) and industrial production (41.32%), respectively. The relative contribution of influencing factors on Cd accumulation is affected by terrain gradient in the following order: agricultural practices (coefficient of variation (CV), 75.0%) > industrial production (CV, 74.6%) > soil properties (CV, 39.3%) > domestic wastes (CV, 26.1%) > traffic emission (CV, 17.9%) > mining (CV, 15.8%). When the terrain niche index is>1.50, the relative contribution of agricultural practices decreases sharply (24.26%) and that of industrial production shows a rapid increase (25.88%). The main reason for this phenomenon is that agricultural practices are more restricted by terrain gradient than industrial production. These findings imply that the differences of characteristics and influencing factors of Cd accumulation with terrain gradient must be considered in the formulation of targeted polices for controlling Cd contamination in soils.

Effects of long-term fertilization practices on heavy metal cadmium accumulation in the surface soil and rice plants of double-cropping rice system in Southern China.

Fertilizer regime is playing an important role in heavy metal cadmium (Cd) accumulation in paddy soils and crop plant. It is necessary to assess the Cd accumulation in soils and rice (Oryza sativa L.) plants under long-term fertilization managements, and the results which help to assess the environmental and food risk in Southern China. However, the effects of different organic manure and chemical fertilizers on Cd accumulation in soils and rice plant remain unclear under intensively cultivated rice conditions. Therefore, the objective was to explore Cd accumulation in paddy soils and rice plant at mature stage under different long-term fertilization managements in the double-cropping rice system. Cd accumulation in the surface soils (0-20cm) and rice plant with chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic matter and 70% chemical fertilizer (LOM), 60% organic matter and 40% chemical fertilizer (HOM), and without fertilizer input (CK) basis on 32years long-term fertilization experiment were analyzed. The results showed that the soil total Cd content was increased by 0.296 and 0.351mgkg-1 and 0.261 and 0.340mgkg-1 under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. And the soil available Cd content was increased by 0.073 and 0.137mgkg-1 and 0.102 and 0.160mgkg-1 under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. The bioconcentration factor of Cd across different parts of rice plant was the highest in root, followed by stem and grain, and the lowest in leaves. At early and late rice mature stages, the root Cd concentration of rice plant was increased by 0.689 and 0.608mgkg-1 with HOM treatment, the stem Cd concentration of rice plant was increased by 0.666 and 0.758mgkg-1 with RF treatment, and the leaf and grain Cd concentration of rice plant was increased 0.094 and 0.082mgkg-1 and 0.086 and 0.083mgkg-1 with LOM treatment, respectively, compared with the CK treatment. The soil Cd single-factor contaminant index (PCd) under different fertilization treatments was as the following HOM > LOM > RF > MF > CK. Meanwhile, the PCd with LOM and HOM treatments was higher than that of the MF, RF, and CK treatments, but there is no significant difference between that of MF and RF treatments. Therefore, long-term application of rice straw residue and chemical fertilizer had no obvious effect on the accumulation of Cd in paddy soils and grain, and soil Cd accumulation was increased as application of organic fertilizer.

Effects of continuous fertilization on bioavailability and fractionation of cadmium in soil and its uptake by rice (Oryza sativa L.)

A four-year field trial was conducted in a rice paddy in southern China to determine the effects of continuous phosphate fertilizer, pig manure, chicken manure, and sewage sludge application on soil Cd accumulation in soil and Cd uptake by rice. The results showed that continuous application of fertilizers with higher Cd levels caused Cd to accumulate and redistribute in various soil fractions. In turn, these effects influenced Cd bioavailability in rice plants. After four years of phosphate fertilizer, pig manure, chicken manure, and sewage sludge application, the annual soil Cd accumulation rates were 0.007–0.032 mg kg−1, 0.005–0.022 mg kg−1, 0.002–0.013 mg kg−1, and 0.032–0.087 mg kg−1, respectively. Relative to the control, the pig- and chicken manure treatments significantly increased soil pH and reduced DTPA-extractable Cd (DTPA-Cd) and the exchangeable Cd fraction (Exc-Cd). In contrast, sewage sludge application significantly increased DTPA-Cd and Cd in all soil fractions. Phosphate fertilization had no significant effect on soil pH, DTPA-Cd, or Exc-Cd. Pearson's correlation coefficients showed that the rice grain Cd levels varied directly with DTPA-Cd, and Exc-Cd but inversely with soil pH. Pig- or chicken manure decreased rice grain Cd content, but sewage sludge increased both soil Cd availability and rice grain Cd uptake. Application of phosphate fertilizer had no significant effect on rice grain Cd content. The continuous use of organic- or phosphate fertilizer with elevated Cd content at high application rates may induce soil Cd accumulation and influence rice grain Cd accumulation.

Soil cadmium and New Zealand dairy farms: Impact of whole-farm contaminant variability on environmental management

Two long-term dairy farms with different phosphorus (P) fertiliser application history in the North and South Island of New Zealand were studied to understand factors influencing the spatial distribution of soil cadmium (Cd). Intensive soil sampling within each farm showed that soil Cd concentrations (0–150 mm depth) were much greater and more variable in the Waikato (North Island) farm (mean: 1.04 mg kg−1, range: 0.48–1.64 mg kg−1) than the Canterbury (South Island) farm (mean: 0.34 mg kg−1, range: 0.15–0.64 mg kg−1). A significant (P < 0.001) relationship between total soil Cd and total P indicated the overriding influence of P fertiliser application history on soil Cd accumulation. However, within land management units (LMUs) of common P fertiliser history, soil type had a significant (P < 0.001) influence on soil Cd concentration. Slope class had no influence (P = 0.491) on soil Cd concentration within the range of 0−15°. There was no clear, consistent relationship between soil Cd and land-based effluent disposal on either farm. Given the large spatial variability in soil Cd concentration that was evident within the two farms of this study, it is recommended that sampling strategies used for the assessment of soil Cd (e.g. under environmental regulation/management frameworks) need to account for variation in land use, P fertilisation history, and soil type. Sampling individual paddocks based on predominant soil type will also allow areas to be identified where there is heightened risk of plant Cd accumulation.

Isotope Tracing of Long-Term Cadmium Fluxes in an Agricultural Soil.

Globally widespread phosphate fertilizer applications have resulted in long-term increases in the concentration of cadmium (Cd) in soils. The accumulation of this biotoxic, and bioaccumulative metal presents problems for the management of soil-plant-animal systems, because the magnitude and direction of removal fluxes (e.g., crop uptake, leaching) have been difficult to estimate. Here, Cd isotopic compositions (δ114/110Cd) of archived fertilizer and soil samples from a 66 year-long agricultural field trial in Winchmore, New Zealand, were used to constrain the Cd soil mass balance between 1959 and 2015 AD, informing future soil Cd accumulation trajectories. The isotopic partitioning of soil Cd sources in this system was aided by a change in phosphate source rocks in 1998 AD, and a corresponding shift in fertilizer isotope composition. The dominant influence of mixing between isotopically distinct Cd end-members was confirmed by a Bayesian modeling approach. Furthermore, isotope mass balance modeling revealed that Cd removal processes most likely increased in magnitude substantially between 2000 and 2015 AD, implying an increase in Cd bioaccumulation and/or leaching over that interval. Natural-abundance stable isotopes are introduced here as a powerful tool for tracing the fate of Cd in agricultural soils, and potentially the wider environment.

An assessment of the effect of contact time on cadmium phytoavailability in a pasture soil.

The length of time cadmium (Cd) is in contact with the soil has been recognised as a factor affecting phytoavailability, but the extent of this process is currently poorly understood. This study used isotopic dilution techniques (E and L values) to determine the effect of contact time on Cd phytoavailability from soil collected from a long-term phosphorus (P) fertiliser trial. Cadmium phytoavailability was determined in soil that was last fertilised with soluble Cd from P fertiliser 17years prior to sampling (residual plots) and soil that received annual applications of P fertiliser until sampling (continuous plots). It was found that both E values and L values increased with P fertiliser (viz Cd) inputs and were significantly related to each other (r 2=0.82 P<0.005). There was however no significant difference (P<0.05) in the percentage of total Cd that was phytoavailable calculated using E values (E%) between the continuous (mean 51%) and the residual plots (mean 51%). There was also no significant difference (P<0.05) in the percentage of total soil Cd that was phytoavailable calculated using L values (L%) between the continuous (mean 77%) and residual plots (mean 87%). These results suggest that despite Cd being in contact with the soil for 17years, there was no difference in the size of the phytoavailable Cd pool compared to recent Cd inputs. This study should be repeated for other soil types and factored into any analysis for the long-term implications of ongoing Cd accumulation in soil on future landuse.

Cadmium Accumulation Characteristic in a Soil-rice System in Zhejiang Province, China

Cadmium (Cd) pollution of rice grain or soil is of increasing concern. This study investigates the concentrations of Cd in soil-rice system in parts area of Zhejiang province and analysis the effects of soil pH and organic matter content on the available Cd concentration in soil and the Cd accumulation of rice grain. The results showed that Cd concentrations in 90 rice grain samples range from 0.01 to 0.31 mg/kg, with an average of 0.1 mg/kg. There is high Cd accumulation in soil that 40% of soil samples were polluted by Cd. The available Cd concentrations in soils had a range of 0.01-0.25 mg/kg, with an average of 0.10 mg/kg. The total Cd concentrations in soil were not the uniquely determined factor for the Cd accumulation of rice grain, Cd concentrations in rice grain were also significantly positive correlated with the available Cd concentrations in soil. The soil pH value and SOM also negatively correlated with available Cd concentrations in soils and Cd concentration in corresponding rice grain. The results indicated the variations of Cd concentration in rice grain were related to Cd concentrations in corresponding soils. Also, soil pH and organic matter content influence the Cd concentrations in soils and affected Cd absorption in rice.

Modelling cadmium contamination in paddy soils under long-term remediation measures: Model development and stochastic simulations

A pollutant accumulation model (PAM) based on the mass balance theory was developed to simulate long-term changes of heavy metal concentrations in soil. When combined with Monte Carlo simulation, the model can predict the probability distributions of heavy metals in a soil–water–plant system with fluctuating environmental parameters and inputs from multiple pathways. The model was used for evaluating different remediation measures to deal with Cd contamination of paddy soils in Youxian county (Hunan province), China, under five scenarios, namely the default scenario (A), not returning paddy straw to the soil (B), reducing the deposition of Cd (C), liming (D), and integrating several remediation measures (E). The model predicted that the Cd contents of soil can lowered significantly by (B) and those of the plants by (D). However, in the long run, (D) will increase soil Cd. The concentrations of Cd in both soils and rice grains can be effectively reduced by (E), although it will take decades of effort. The history of Cd pollution and the major causes of Cd accumulation in soil were studied by means of sensitivity analysis and retrospective simulation.

Phytoavailability of Cd and Pb in crop straw biochar-amended soil is related to the heavy metal content of both biochar and soil

Crop straw biochar incorporation may be a sustainable method of amending soil, but feedstock-related Cd and Pb content is a major concern. We investigated the effects of heavy metal-rich (RC) and -free biochar (FC) on the phytoavailability of Cd and Pb in two acidic metalliferous soils. Biochar significantly increased soil pH and improved plant growth. Pb in soil and plant tissues significantly decreased after biochar application, and a similar pattern was observed for Cd after FC application. RC significantly increased NH4NO3-extractable Cd in both lightly contaminated (YBS) and heavily contaminated soils (RS). The Cd content of plants grown on YBS increased, whereas it decreased on RS. The Cd and Pb input–output balance suggested that RC application to YBS might induce a soil Cd accumulation risk. Therefore, identifying heavy metal contamination in biochar is crucial before it is used as a soil amendment.

The influence of phosphate fertilizer application levels and cultivars on cadmium uptake by Komatsuna (Brassica rapa L. var. perviridis)

Cadmium (Cd) is a common impurity in phosphate fertilizers and application of phosphate fertilizer may contribute to soil Cd accumulation. Changes in Cd burdens to agricultural soils and the potential for plant Cd accumulation resulting from fertilizer input were investigated in this study. A field experiment was conducted on Haplaquept to investigate the influence of calcium superphosphate on extractable and total soil Cd and on growth and Cd uptake of different Komatsuna (Brassica rapa L. var. perviridis) cultivars. Four cultivars of Komatsuna were grown on the soil and harvested after 60 days. The superphosphate application increased total soil Cd from 2.51 to 2.75 mg kg−1, 0.1 mol L−1 hydrochloric acid (HCl) extractable Cd from 1.48 to 1.55 mg kg−1, 0.01 mol L−1 HCl extractable Cd from 0.043 to 0.046 mg kg−1 and water extractable Cd from 0.0057 to 0.0077 mg kg−1. Cd input reached 5.68 g ha–1 at a rate of 240 kg ha–1 superphosphate fertilizer application. Superphosphate affected dry-matter yield of leaves to different degrees in each cultivar. ‘Nakamachi’ produced the highest yield in 2008 and ‘Hamami No. 2’ in 2009. Compared with the control (no phosphate fertilizer), application of superphosphate at a rate of 240 kg ha–1 increased the Cd concentration in dry leaves by 0.14 mg kg−1 in ‘Maruha’, 1.03 mg kg−1 in ‘Nakamachi’, 0.63 mg kg−1 in ‘SC8-007’ in 2008, and by 0.19 mg kg−1 in Maruha’, 0.17 mg kg−1 in ‘Hamami No. 2’, while it decreased by 0.27 mg kg−1 in ‘Nakamachi’ in 2009. Field experiments in two years demonstrated that applications of different levels of calcium superphosphate did not influence Cd concentration in soil and Komatsuna significantly. However, there was a significant difference in Cd concentration of fresh and dry Komatsuna leaves among four cultivars in 2008 and 2009. The highest Cd concentration was found in the ‘Nakamachi’ cultivar (2.14 mg kg−1 in 2008 and 1.91 mg kg−1 in 2009). The lowest Cd concentration was observed in the ‘Maruha’ cultivar (1.51 mg kg−1 dry weight (DW)) in 2008 and in the ‘Hamami No. 2’ cultivar (1.56 mg kg−1 DW) in 2009. A decreasing trend in Cd concentration was found in ‘Nakamachi’, followed by ‘SC8-007’, ‘Hamami No. 2’ and ‘Maruha’ successively. It is necessary to consider a low-uptake cultivar for growing in a Cd polluted soil. In these two years’ results, ‘Maruha’ cultivar was the lowest Cd uptake cultivar compared to the others.

Availability of Cadmium and Zinc as Affected by the Use of Reactive Phosphate Rock, Lime, and Chicken Manure on an Indonesian Acidic Upland Soil under Field Conditions

We assessed cadmium (Cd) and zinc (Zn) availability when applying reactive phosphate rock (RPR) in combination with lime and chicken manure on Indonesian acidic upland soils. Maize plants were grown on unamended soil and soils treated with several combinations of 2 tons dolomite ha–1, 2 tons of chicken manure ha–1, 1 ton ha–1 of RPRL (reactive phosphate rock containing 4 mg Cd kg–1 and 224 mg Zn kg–1), and 1 ton ha–1 of RPRH (RPR containing 69 mg Cd kg–1 and 745 mg Zn kg–1). In addition to its positive effect on plant yield, application of RPR in combination with chicken manure did not result in toxic Cd concentrations. Although liming is effective to reduce plant Cd concentrations, it results in more soil Cd accumulation and more plant Zn deficiency. Cadmium and Zn concentrations in shoots and grains can be predicted well from amounts extracted from the soil by 0.5 M ammonium (NH4) acetate + 0.02 M ethylenediaminetetraacetic acid (EDTA) at pH 4.65.

Cadmium balance in soils under different fertilization managements including sewage sludge application

Simple balance of Cd input by different treatments and removal by agricultural crops was investigated in an ongoing precise long-term field experiment with application of sewage sludge (SS), farmyard manure (FYM), and mineral fertilizers (NPK). Potatoes, wheat and barley were grown in a rotation at 4 experimental sites of the Czech Republic with the aim to assess the risk of Cd accumulation in soil and plants under different soil and climate conditions. The results showed significant differences in Cd content of the input materials used, and in Cd inputs to soils under different fertilization managements. Three applications of sewage sludge during 1996–2005 resulted in total addition of 110 g Cd/ha into soil, which was by one order of magnitude higher than Cd addition in FYM or NPK treatments. From the total amount of sludge-borne Cd, only small portion was removed by harvests of crops (approximately 3.5%). Soil conditions significantly affected Cd input-removal balance. The highest Cd removals were obtained on soils with the lowest pH. The highest Cd removal was achieved by potato tubers followed by wheat and barley plants. The results showed that the risk of Cd accumulation in soils is high, especially with repeated sludge applications.

DGT estimates cadmium accumulation in wheat and potato from phosphate fertilizer applications

Cadmium is a common impurity in phosphatic fertilizers and may contribute to soil Cd accumulation. Changes in total and bioavailable Cd burdens to agricultural soils and the potential for plant Cd accumulation resulting from fertilizer input was investigated. Three year field studies were conducted using three dose levels of cadmium-rich, commercial, phosphate fertilizers applied at four agricultural sites. Labile Cd concentrations, measured using the passive sampling device Diffusive Gradients in Thin Films (Cd DGT), increased with increasing fertilizer application rates. Cd also accumulated in the edible portion of wheat and potato crops grown at the sites, and showed strong positive dose response with fertilizer treatment. Regression models were calculated for each site, year, and for individual crops. Model comparisons indicated that soil physical and chemical parameters in addition to soil Cd fractions, were important determinants of Cd DGT. Significant factors contributing to Cd DGT concentrations were Cd from fertilizer input (Cd fertilizer), pH, cation exchange capacity (CEC), and total recoverable Cd (Cd total). Important factors used to determine Cd concentrations in wheat grain (Cd wheat) and in potato (Cd potato) were as follows: Cd wheat:Cd fertilizer, and Cd DGT; and Cd potato:Cd fertilizer, Cd DGT, % O.M. The effective concentration, C E, calculated from DGT did not correlate well with Cd wheat or with Cd potato. Direct measurements of Cd DGT correlated better with Cd found in edible plant tissue. The modeling approach presented in this study helps to estimate Cd accumulation in plant tissue over multiple years and in distinct agricultural soil systems.

Monitoring of Cd pollution in soils and plants irrigated with untreated sewage water in some industrialized cities of Punjab, India

The disposal of industrial and sewage water is a problem of increasing importance throughout the world. In India, and most of the developing countries untreated sewage and industrial wastes are discharged on land or into the running water streams which is used for irrigating crops. These wastes often contain high amount of trace elements which may accumulate in soils in excessive quantities on long term use and enter the food chain through absorption by the plants. Among the trace metals, Cd has received the greater attention because of its easy absorption and accumulation in plants and animals to levels toxic for their health. The objective of this study conducted in three industrially different cities viz., Ludhiana, Jalandhar and Malerkotla was to monitor the extent of Cd accumulation in soils and plants receiving untreated sewage water. Plant and soil samples were collected from sewage and tubewell irrigated areas. Soil samples were analysed for texture, pH, EC, organic carbon (OC), CaCO(3), bioavailable DTPA-Cd and plant samples were analysed for total Cd. In sewage irrigated soils, the mean values of pH were lower but organic carbon and electrical conductivity were generally higher both in surface and sub-surface layers of all the three cities as compared to tubewell irrigated soils. The mean DTPA- extractable Cd in sewage irrigated soil was 6.3- and 4.36-fold in Ludhiana, 3.38- and 1.71-fold in Jalandhar and 3.35- and 6.67-fold in Malerkotla in 0-15 and 15-30 cm soil depth, respectively, compared with the values in tubewell irrigated soils. The accumulation of DTPA-Cd in sewage irrigated soils was restricted to 30 cm depth after which the values were generally close to values in tubewell irrigated soils. Soil pH, OC, CaCO(3), clay and silt collectively accounted for 37.1%, 65.1% and 53.9% DTPA-extractable bioavailable Cd in soils of Ludhiana, Jalandhar and Malerkotla, respectively. Lower R(2) values in Ludhiana suggest that factors other than the ones mentioned may be affecting Cd availability. At all sites plants receiving sewage irrigation had elevated levels of Cd as compared to the plants receiving tubewell irrigation. The mean Cd content of sewage irrigated plants irrespective of the city was 5.96 microg g(-1) dry matter as compared to 0.98 microg g(-1) dry matter in tubewell irrigated plants. The results suggest that the intake of Cd obtained from consumption of crops grown on sewage irrigated soils would be much higher than the tolerable limits set by WHO and may, therefore, prove potentially toxic leading to various health ailments to humans and animals.

RELEASE OF CADMIUM FROM A TRIPLE SUPERPHOSPHATE AND A PHOSPHATE ROCK IN SOIL

Although phosphorous fertilizers containing elevated amount of cadmium (Cd) could affect Cd accumulation in soils and crops, the extent of the effect may depend on the amount of Cd added and the rate of Cd release from those fertilizers. This study examined Cd forms of a triple superphosphate (TSP) and a western phosphate rock (PR) by sequential extractions and the rate of Cd release from the fertilizers by incubation in a silt loam and subsequent extraction with diethylenetriaminepentaacetic acid (DTPA). The lability of TSP Cd was high, as evidenced by its high solubility in water (36.0%) and 1 M HCl (57.8%). The lability of PR Cd, in contrast, was very low, with 0.1% soluble in water, 29.9% soluble in 1 M HCl, and 70.1% in the residual form. Although soil DTPA-Cd was substantially higher when the soil was treated with the TSP than with the PR at the same Cd rate, the difference narrowed as more PR Cd became extractable by DTPA with time, which reflected increased lability of PR Cd after incorporation into the soil. However, substantial amounts of the added TSP Cd (50%) and PR Cd (77.3%) remained not extractable by DTPA after 210 days of incubation. High correlation of DTPA-Cd with DTPA-zinc (Zn) in the TSP- or PR-treated soils suggested concurrent release of Zn with Cd from both P fertilizers. This should be beneficial, considering Zn can compete with Cd during bioaccumulation processes.

Modelling regional-scale mass balances of phosphorus, cadmium and zinc fluxes on arable and dairy farms

Accumulation of heavy metals in agricultural soils may cause serious problems for soil quality, groundwater and food chains. Based on the databases of the Swiss agricultural statistics and on data from experimental farms, we modelled regional-scale mass balances of phosphorus (P), cadmium (Cd) and zinc (Zn) and their uncertainties for a large number of arable and dairy farms in the northwest of Switzerland using the model PROTERRA-S. Large differences in P fertilization characteristics between these farm types were found. Crop demand for P on arable farms were primarily met through additions of inorganic fertilizers and sewage sludge, while on dairy farms the largest P input was provided by animal manure. Average model calculations predicted an enrichment between 0.8 and 1.9 g ha −1 per year for Cd and between 76 and 525 g ha −1 per year for Zn for soils of arable and dairy farms, respectively. Hence, according to our analyses, current agricultural land use is not sustainable in terms of soil quality standards. Predicted accumulation of Cd in soil was larger for arable crops than for grassland, while the opposite was true for Zn. Analyzing scenarios of changes in P fertilization management showed that Cd and Zn enrichment in soil was more sensitive to decreasing net P inputs to arable farms than to dairy farms. When uncertainty of input data was taken into account, large variances of the calculated accumulation rates were found. Coefficient of variation of the net fluxes ranged between 56 and 162% for Cd, and between 46 and 82% for Zn, and distribution functions of the net fluxes indicated that in some soils, particularly under grassland, also a depletion of Zn and Cd may occur. Hypothetical steady-state soil concentrations of Cd were estimated to exceed average soil threshold concentration on arable farms, while steady-state Zn concentrations in soils of dairy farms were on average below the corresponding threshold value. However, if the uncertainty of these Zn estimates was considered, a significant part of the distribution exceeded the threshold value. The results of our study demonstrate that information on variation in element balances is beneficial. Average flux balances alone do not provide sufficient information for an adequate assessment of sustainable land use.