Soil DTPA-extractable Cd Research Articles

Soil threshold values of total and available cadmium for vegetable growing based on field data in Guangdong province, South China

Human exposure to cadmium (Cd) is largely attributed to consumption of vegetables grown in polluted soils. In China, guidelines set for Cd in soils are uniform for different crops and diverse soil types, but not risk based. A high-density sampling of 711 paired soil and vegetables was carried out across Guangdong, South China. We aimed to model the transfer of Cd from soil to leafy, rootstalk and fruit vegetables, and to set regional guidelines of Cd [total and diethylenetriaminepentaacetic acid (DTPA) -extractable] in soil for vegetable safe production. Both total and DTPA-extractable Cd concentrations in soil were good predictors for Cd in vegetables. The transfer of Cd in soil to vegetables could be estimated by nonlinear models, with better fit when using DTPA-extractable Cd than total Cd in soil. The calculated thresholds of soil total Cd were 2.42, 0.94 and 1.57 mg kg(-1) whereas those of soil DTPA-extractable Cd were 1.08, 0.33 and 0.63 mg kg(-1) for leafy, rootstalk and fruit vegetable fields in Guangdong, respectively, all higher than the national soil Cd threshold. Cadmium-contaminated risk for vegetable production in Guangdong province might have been over-estimated according to the Chinese Environmental Quality Standard for Soil.

Phytoavailability and phytovariety codetermine the bioaccumulation risk of heavy metal from soils, focusing on Cd-contaminated vegetable farms around the Pearl River Delta, China

Five random vegetable farms were selected to investigate the bioaccumulation risk of heavy metals (HMs) by different type of vegetables around the Pearl River Delta (PRD), China. The concentration order of four major HMs in the surface soil samples was Cd<Cu<Pb<Zn, with only Cd concentrations (1.4–1.8mgkg−1) significantly higher than the permissible limit (≤0.3mgkg−1) for agricultural soils. Soil DTPA-extractable (phytoavailable) Cd concentrations differed markedly amongst the five farms, and varied within 0.017–0.17mgkg−1. Meanwhile, 28.0% of vegetable samples collected from these five farms were contaminated with Cd according to the permissible limit (≤0.05mgkg−1), and 71.4% of these polluted samples belonged to stem/leaf vegetables. The average bioaccumulation factors of Cd from cultivated soil to stem/leaf vegetables and melon/fruit/bean vegetables varied within 0.021–0.050 and 0.005–0.020 (soil total Cd basis), and 0.50–2.01 and 0.13–0.53 (soil DTPA-extractable Cd basis), respectively. Redundancy analysis (RDA) showed that DTPA-extractable Cd, which negatively but significantly correlated (P<0.05) to soil pH, was the key factor in influencing vegetable Cd accumulation, notably stem/leaf vegetables. The results show that Cd was the primary metal of risk in vegetable farms around the PRD region, and stem/leaf vegetables posed about 2.2 times higher health risks associated with exposure to Cd than melon/fruit/bean vegetables.

Spatial variability of soil total and DTPA-extractable cadmium caused by long-term application of phosphate fertilizers, crop rotation, and soil characteristics

Increasing cadmium (Cd) accumulation in agricultural soils is undesirable due to its hazardous influences on human health. Thus, having more information on spatial variability of Cd and factors effective to increase its content on the cultivated soils is very important. Phosphate fertilizers are main contamination source of cadmium (Cd) in cultivated soils. Also, crop rotation is a critical management practice which can alter soil Cd content. This study was conducted to evaluate the effects of long-term consumption of the phosphate fertilizers, crop rotations, and soil characteristics on spatial variability of two soil Cd species (i.e., total and diethylene triamine pentaacetic acid (DTPA) extractable) in agricultural soils. The study was conducted in wheat farms of Khuzestan Province, Iran. Long-term (27-year period (1980 to 2006)) data including the rate and the type of phosphate fertilizers application, the respective area, and the rotation type of different regions were used. Afterwards, soil Cd content (total or DTPA extractable) and its spatial variability in study area (400,000 ha) were determined by sampling from soils of 255 fields. The results showed that the consumption rate of di-ammonium phosphate fertilizer have been varied enormously in the period study. The application rate of phosphorus fertilizers was very high in some subregions with have extensive agricultural activities (more than 95 kg/ha). The average and maximum contents of total Cd in the study region were obtained as 1.47 and 2.19 mg/kg and DTPA-extractable Cd as 0.084 and 0.35 mg/kg, respectively. The spatial variability of Cd indicated that total and DTPA-extractable Cd contents were over 0.8 and 0.1 mg/kg in 95 and 25 % of samples, respectively. The spherical model enjoys the best fitting and lowest error rate to appraise the Cd content. Comparing the phosphate fertilizer consumption rate with spatial variability of the soil cadmium (both total and DTPA extractable) revealed the high correlation between the consumption rate of P fertilizers and soil Cd content. Rotation type was likely the main effective factor on variations of the soil DTPA-extractable Cd contents in some parts (eastern part of study region) and could explain some Cd variation. Total Cd concentrations had significant correlation with the total neutralizing value (p < 0.01), available P (p < 0.01), cation exchange capacity (p < 0.05), and organic carbon (p < 0.05) variables. The DTPA-extractable Cd had significant correlation with OC (p < 0.01), pH, and clay content (p < 0.05). Therefore, consumption rate of the phosphate fertilizers and crop rotation are important factors on solubility and hence spatial variability of Cd content in agricultural soils.

Cadmium distribution in rice plants grown in three different soils after application of pig manure with added cadmium

A glasshouse pot experiment was conducted to investigate Cd concentrations in the aboveground parts of two consecutive crops of rice and Cd availability in three different soils (loam, silt loam, and sandy loam) after application of pig manure with added Cd. Soil pH tended to increase with increasing application rate of pig manure from 1 to 3% (w/w, oven dry basis). Soil diethylene triamine pentaacetic acid (DTPA) extractable Cd showed a clear positive correlation with soil total Cd content and increased with increasing Cd amendment of the manure but showed no difference between the two manure application rates. Cd concentrations in the grain, husk, and straw were significantly and positively correlated with soil DTPA-extractable Cd (p < 0.001). Within each level of manure Cd, the higher rate (3%) of manure produced lower Cd concentrations in the grain, husk, and straw on all three soils than did the lower rate (1%) after the first crop, but this no longer occurred after the growth of the second crop. Grain Cd concentrations exceeded the Chinese National Food Quality Standard (0.2 mg kg(-1)) most often on the loam, with intermediate frequency on the silt loam, and least often on the sandy loam, the soil with the highest pH and lowest organic carbon content and cation exchange capacity.

Effects of EDTA, Sheep Manure Extract, and Their Application Time on Cd Uptake by Helianthus annuus from a Calcareous Mine Soil

Sunflower (Helianthus annuus L.), a potential phytoextraction plant, can accumulate high concentrations of Cd from metal-contaminated soils. Helianthus annuus was grown in a mine calcareous soil treated with increasing concentrations of EDTA (0, 0.5 and 2 g EDTA kg−1 soil) or sheep manure extract (0, 0.5 and 2 g SME kg−1 soil) 30 or 10 days before sowing (T1, T2) and 10 or 30 days after sowing (T3, T4). The EDTA application before seed germination reduced sunflower seedling emergence and dry weight. Cadmium concentrations in harvested shoots increased with EDTA concentration but the actual amount of phytoextracted Cd decreased at high EDTA concentrations, due to severe growth depression. Although application time of SME had no significant effect on shoot dry weight, it had significant effect on Cd uptake by Helianthus annuus. Applying 0.5 or 2 g SME kg−1 at T3 or T4 increased the DTPA-extractable Cd in soil and the metal concentrations accumulated in shoots and roots of sunflower. The results showed that the most efficient treatment for Cd phytoextraction by sunflower is application of 0.5 g SME per kg soil at 30 days after sowing. However, the removal efficiency of Cd from soil was very low (0.15%).