Critical loads of trace metals in soils: a method of calculation

Critical load of trace metals in soils is a function of biological uptake, leaching by percolating water, input of the trace metals due to bedrock weathering, and the norms set to protect soils from metal pollution. The exceedance of the critical load is a difference between the calculated load and the measured input of the metals by atmospheric deposition and by application of agrochemicals. A critical time is the time when the concentration of a trace metal in soil, which is the result of all inputs and outputs of the metal in the soil, reaches the value of the norm. Data on biologically important trace metals in a small agricultural catchment in the Czech Republic indicate that the soil concentrations of As, Cd and Pb will reach the norms set for the soils after 4.5, 61, and 980 years, respectively. The present mass balances of Cu and Zn in the soils indicate that their steady-state concentrations will be below the norms so that the atmospheric and agricultural inputs will never overshoot the calculated critical load.