For ATP and DHA, the ED 50 values calculated using both models were 3 or 4 orders of magnitude higher than the limit of Cd concentration in agricultural soils (3 mg/kg in alkaline soils) proposed by the EU directive (C.E.C. 1986). However, the values of Cd concentrations that produced a 10% or 5 % decrease (ED 10 and ED 5 ) in soil DHA and ATP content were closer to the maximum permissible concentration of Cd in soil.