AN ECOLOGICAL DOSE-RESPONSE MODEL APPROACH TO SHORT-TERM AND LONG-TERM EFFECTS OF HEAVY-METALS ON ARYLSULFATASE ACTIVITY IN SOIL

The aim of this study was to provide data to evaluate the short- and long-term effects of heavy metals on arylsulphatase activity in five soils. The effects are fitted on a logistic dose-response model and are presented graphically as the ecological dose (heavy metal concentration corresponding to 50% inhibition; ED50) and ecological dose range (heavy metal concentration range corresponding to 10-90% inhibition; EDR). In 7 out of 22 comparable soil-metal combinations the ED50 decreased significantly over 6 weeks to 18 months of incubation and in two cases the ED50 increased. Toxicity (defined as ED50) was highest in sand and sandy loam and lowest in sandy peat. Cd toxicity in sand, silty loam, and clay varied from 1.08 to 9.04 mmol kg-1. Both Cr and Ni toxicity varied strongly and decreased with time in some soils while increasing in others. The Cu toxicity ranged from 4.51 to 2 mmol kg-1 in sand and silty loam, respectively, but remained fairly constant over time. Pb was the least toxic element (14.5 to 59.9 mmol kg-1). The toxicity of Zn ranged from 5.73 to 148 mmol kg-1 in sand and sandy peat, respectively. At critical concentrations set by the Dutch Soil Protection Act, Cr, Cu, Ni, and Zn inhibited arylsulphatase by 53, 35, 48 and 97%, respectively.