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It has been argued that the identification of the phytotoxic metal thresholds in soil should be based on field-collected soil rather than on artificially-contaminated soils. However, the use of field-collected soils presents several difficulties for interpretation because of mixed contamination and unavoidable covariance of metal contamination with other soil properties that affect plant growth. The objective of this study was to estimate thresholds of copper phytotoxicity in topsoils of 27 agricultural areas historically contaminated by mining activities in Chile. We performed emergence and early growth (21 days) tests (OECD 208 and ISO 11269-2) with perennial ryegrass ( Lolium perenne L.). The total Cu content in soils was the best predictor of plant growth and shoot Cu concentrations, while soluble Cu and pCu 2+ did not well correlate with these biological responses. The effects of Pb, Zn, and As on plant responses were not significant, suggesting that Cu is a metal of prime concern for plant growth in soils exposed to copper mining activities in Chile. The effects of soil nutrient availability and shoot nutrient concentrations on ryegrass response were not significant. It was possible to determine EC 10 , EC 25 and EC 50 of total Cu in the soil of 327 mg kg −1 , 735 mg kg −1 and 1144 mg kg −1 , respectively, using the shoot length as a response variable. However, the derived 95% confidence intervals for EC 10 , EC 25 and EC 50 values of total soil Cu were wide, and thus not allowing a robust assessment of metal toxicity for agricultural crops, based on total soil Cu concentrations. Thus, plant tests might need to be performed for metal toxicity assessment. This study suggests shoot length of ryegrass as a robust response variable for metal toxicity assessment in contaminated soils with different nutrient availability. [ABSTRACT FROM AUTHOR]

Abstract: The Puchuncaví Valley in central Chile has been exposed to atmospheric depositions from a copper smelter. Nowadays, soils in the surrounding area are acidic and contaminated with Cu and As. The objective of this study was to determine the effectiveness of lime and compost for in situ immobilization of trace elements in the soils of the Puchuncaví Valley by using earthworms as bioindicators of toxicity. The lime and compost treatments significantly increased soil pH and decreased the soluble and exchangeable Zn, exchangeable Cu, and free Cu2+ activity. However, the compost treatment increased soluble Cu, and soluble and exchangeable As. Lime application had no effect on earthworm reproduction in comparison with the unamended control, whereas the application of compost increased cocoon and juvenile production. There was a spatial variability of soil properties within treatments in the field plots. This allowed the identification of which soil properties were actually having an impact on earthworm reproduction. For both cocoon and juvenile production, soil organic matter (SOM) was a positive factor, i.e., more SOM increased cocoon or juvenile production. The toxicity (negative) factor was total soil As. However, total Cu and total As were well correlated (R 2=0.80, p<0.001), hence some of the trends could have been masked. In summary, compost treatment was effective in improving the quality of soils of Puchuncaví Valley, increasing earthworm reproduction. Future Chilean legislation on maximum permissible concentrations of trace elements in soils should consider SOM content due to its effect on trace element solubility and bioavailability. [Copyright &y& Elsevier]