Prediction of copper and zinc bioavailability in soil

Copper and zinc in soil are nutrients required for organisms to live, but they can also be phytotoxic or can accumulate to toxic levels in the food chain when soil-borne organisms are exposed to high doses. The toxic effects that occur due to copper and zinc can be predicted by the dose of metal. That dose cannot be predicted with reasonable accuracy through measurement of copper and zinc in soil extracts or digests, which are the current methods of choice. A method for better predicting plant doses of copper and zinc based on easily-measured soil parameters was developed.; Thirty-five field soils of international origins representing a wide range of copper and zinc concentrations, pH values, clay and organic matter contents were collected. These soils were characterized for physical and chemical characteristics implicated as having possible importance in determining copper and zinc bioavailability in soils. Three plant species, barley (Hordeum vulgare), lettuce (Lactuca sativa), and Indian mustard (Brassica juncea) were cultivated in these soils to determine Cu and Zn concentrations in plant roots and shoots. An artificial neural network model in combination with statistical analysis was used to determine the most important soil characteristics necessary for predicting Cu and Zn concentrations in plants. These soil measurements were used to develop predictive models for Cu and Zn concentrations in plant tissue. Models were tested using bioassay data from additional field soils and nutrient- and metal-amended soils. Models require measurement of metals and nutrients in soil extracts, pH, total carbon, nitrogen and sulfur, bulk density, and particle size distribution.; Previously published data from earthworm (Eisenia andrei) bioassays completed in 18 Dutch soils were used to develop a new model for predicting copper and zinc concentrations in earthworms based on the results of soil extractions at controlled pH-conditions. Earthworm exposure was modeled as originating through dermal or gut wall contact with soil. Results are comparable to previously published predictions, but include information about the relative importance of exposure routes: the dermal route of exposure dominates for Zn, and the gut wall exposure route dominates for Cu when soluble soil organic matter is considered.