Table 1. Maximum permissible concentrations which have been set in the U.K. for heavy metals in soil after application of sewage sludge (DOE, 1989)
Metal
Zinc Copper Nickel
Maximum permissible concentration of heavy metals in soil (mg kg-’ dry wt) PH” PH” PH pHb 5.0-5.5 5.5-6.0 6.0-7.0 > 7.0
200 250 300 450 80 100 135 200 50 60 75 110
For pH 5.0 and above
Cadmium 3 Lead 300 Mercury I Chromium 400 (provisional)
“For soils of pH in the ranges of 5.c5.5 and 5.5-6.0 the permitted concentrations of Zn, Co, Ni and Cd are provisional and will be reviewed when current research into their effects on certain crops and livestock is completed. bThe increased permissible heavy metal concentrations in soils of pH greater than 7.0 apply only to soils containing more than 5% calcium carbonate.
reported