Soil physical and chemical property effects on toxicity and bioaccumulation of arsenic(V), cadmium, lead, and zinc by herbaceous plant receptors.

摘要

Soil properties can mitigate hazardous effects of environmental contaminants through soil chemical sequestration and should be considered when evaluating ecological risk from terrestrial contamination. The objective of this research was to identify predominant soil chemical/physical properties that modify phytoaccumulation and phytotoxicity of As (V), Cd, Pb, and Zn to the non-hyperaccumulating higher plants Alfalfa (Medicago sativa L.), Perennial ryegrass (Lolium perenne L.), and Japanese millet (Echinochloa crusgalli L.) and model effects with statistical prediction equations. Bioassays were conducted on five artificially contaminated experimental soils that ranged in selected chemical/physical properties. Soil properties selected for characterization included organic C (OC), pH, cation exchange capacity (CEC), clay content, and amorphous oxides of iron (Fe), aluminum (Al), and manganese (Mn). Phytotoxicity and phytoaccumulation parameters were estimated from dose-response experiments for each contaminant-plant-soil combination. Significant statistical associations were found between each endpoint and a subset of the selected soil properties for all four contaminants. However, significant intercorrelation was observed among soil property measurements which necessitated an alternative to conventional multiple regression commonly used by ecotoxicologists. Ridge regression, a technique that suppresses the effects of multicollinearity and enables prediction, was used to assess the marginal contributions of each mitigating soil property. In general, Ridge regression results suggested that OC, clay content, and soil pH, collectively, or CEC, individually, best described trends in phytoaccumulation and phytotoxicity for the cationic metals. Conversely, Ridge regression results suggested that soil pH and the Fe oxide fraction were usually the most important properties found to mitigate As phytoaccumulation and phytotoxicity. An additional objective was to evaluate differential contaminant sensitivities of the experimental plants that were used in the dose-response experiments as inter-species variability can limit the utility of statistical models used to predict the effects of soil properties on phytotoxicity of terrestrial contaminants. We, therefore, present a novel approach to toxicity estimation (the Plant Contaminant Sensitivity Index) that partitions the effect of differential sensitivities of test organisms from that of soil properties. The proposed normalization procedure is simply illustrated and is intended to be used as a means to integrate toxicity information from different studies with multiple test species.