Predicting copper phytotoxicity based on pore-water pCu.

The free ion activity and "biotic ligand" models predict that the free metal ion and other pore-water parameters describe terrestrial phytotoxicity. In this study, pore-water chemistry and measured Cu(2+) was used to describe phytotoxicity of cucumber (Cucumis sativa L) in 10 contrasting soils at different soil Cu loadings. Both soil solution Cu (Cu(pw)) and Cu(2+) successfully described the response variable for all ten soils with R(2) values of 0.73 and 0.66, respectively. Separation of soils as acid and alkaline and fitting separately showed that there was a strongly significant fit for both log Cu(2+) and log Cu(pw) in acidic soils (R(2) = 0.92 and 0.86, respectively) but weakly significant fit for alkaline soils. The pCu EC50 and EC10 values in all acidic soils for cucumber were 5.83 (6.03-5.63) and 7.53 (8.27-7.00), respectively. In our dataset alkaline soils need to be treated individually. In addition, pCu could be predicted based on pH and total concentration alone. Despite only 12 weeks 'ageing' there was quantitative agreement between pCu model from this study and predicted pCu from Sauvé et al. This agreement from studies performed independently indicates that, at least in the case of Cu(2+), the difference in an ageing period of ≥10 years appears minimal.