IMPACT OF PASTURE CONTAMINATION BY COPPER, CHROMIUM, ARSENIC TIMBER PRESERVATIVE ON SOIL BIOLOGICAL-ACTIVITY

Contamination of grazed pasture gave 0-5 cm soil contents of 19-835 mg kg(-1) Cu, 47-739 mg kg(-1) Cr, and 12-790 mg kg(-1) As. Soil Cu, Cr, As contents were correlated and declined with depth to 30 cm. In plot s with medium and high contamination buried cotton strips retained mos t of their original tensile strength, indicating repression of decompo sition processes. Lumbricus rubellus and Aporrectodea rosea were absen t in plots with medium and high contamination; there was no evidence o f heavy metal accumulation in earthworm tissue; soil bulk density was greater in the absence of lumbricids. Enchytraeids and nematodes were most abundant with low contamination. Nematode diversity was greater w ith low (0-5 cm) or medium (5-10 cm) contamination than in control plo ts or those with high contamination; the proportion of predators incre ased with contamination. Basal soil respiration was less sensitive tha n substrate-induced respiration to contamination. Although contaminati on reduced the nitrification rate, all mineral N was found as NO3- aft er 14 days. Sulphatase was the enzyme activity most sensitive to high contamination. Whereas contamination by 100 mg kg(-1) of Cu, Cr, and A s caused little depression of soil biological activity, there was some suppression at 400 mg kg(-1) and at 800 mg kg(-1) normal processes we re inhibited and herbage production was negligible. No single measurem ent adequately indicated the need for site remediation.