Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2008
Publication Date: 10/9/2008
Citation: Chen, W., Li, L., Chang, A.C., Wu, L., Khosrivafard, M., Chaney, R.L. 2008. Characterizing the Solid-Solution Coefficient and Plant Uptake Factor of As, Cd and Pb in California Croplands. Agriculture, Ecosystems and Environment. 129:212-220.
Interpretive Summary: Concern about potential plant accumulation of potentially toxic elements from soils has encouraged evaluation of soil contamination and potential crop uptake of elements such as cadmium (Cd), arsenic (As), and lead (Pb), and development of limits on trace elements in fertilizer products. An extensive investigation of California soils was conducted by the University of California-Riverside in cooperation with the California Department of Food and Agriculture. Both soils and crops were sampled in different production regions of California and analyzed using modern methods with low detection limits. The values observed were reported in other manuscripts. In the present manuscript, the measured data from the survey were compared with model values being used by the Department of Food and Agriculture to model potential element uptake and determine if limits needed to be imposed on element levels in fertlizers, soils or crops of California. In the end, the objective results for the distribution coefficient (Kd) were found to vary much less than had been assumed in the CDFA modeling effort. Assumed statistical distributions for modeling need to correspond with field observed values so the models will predict potential problems that are real. On the other hand, the Department had used a narrower range of Plant Uptake Factor (PUF) estimates suggested by the University, and those estimates were verified by the new extensive field data.
Technical Abstract: In risk assessment models, the solid-solution partition coefficient (Kd), and plant uptake factor (PUF), are often employed to model the fate and transport of trace elements in soils. The trustworthiness of risk assessments depends on the reliability of the parameters used. In this study, we examined Kd and PUF for As, Cd and Pb based on soils and plant tissues obtained from 70 crop production fields in California. We also examined the California portion of a nationwide survey of trace elements in cropland soils conducted by the USDA, US-FDA and US-EPA. Results showed that the Kd and PUF for cropland soils are probabilistic in nature and follow log-normal distributions. The trace element concentration of the soil solution did not appear to be a more appropriate estimator of PUF than the total soil element content. The Kd used in the CDFA (California Department of Food and Agriculture) study had a much wider range than could occur in California croplands while the PUF used in the CDFA risk assessment were comparable to patterns observed in the field measurements.