Short- and long-term effects of heavy metals on phosphatase activity in soils: An ecological dose-response model approach

Summary The aim of this study was to provide manageable data to help establish permissible limits for the pollution of soil by heavy metals. Therefore the short-and long-term effects of heavy metal pollution on phosphatase activity was studied in five different soil types. The results are presented graphically as logistic dose-response curves. It was possible to construct a curve for sand and silty loam soil but it was more difficult to establish a curve for sandy loam and clay soil and nearly impossible (except for Cu) for peat. The toxicity of the various metals can be compared on the basis of mmol values. In clay soils, for Cd, Cr, Cu, and Zn, the 50% effective ecological dose (ED₅₀) values were comparable (approximately 45 mmol kg^–1), but the ED₁₀ values were very different, at 7.4, 41.4, 15.1, and 0.55, respectively. At the ED₅₀ value, toxicity did not decrease with time and, in sandy soils, was approximately 2.6 mmol kg ^–1 dry soil for Cd, Cu, and Zn. In four out of five soils, the Cd toxicity was higher 1.5 years after the addition of heavy metal salts than after 6 weeks. Toxicity was least in the sandy loam, silty loam, and clay soil, and varied in general between 12 and 88 mmol kg^–1. In setting limits, the criteria selected (no-effect level, ED₁₀ or ED₅₀) determine the concentration and also the toxicity of the sequence. It is suggested that the data presented here could be very useful in helping to set permissible limits for heavy metal soil pollution.