Diazinon and diflubenzuron residues in soil following surface disposal of spent sheep dip wash

Abstract

Spent sheep dip wash (4000 L) containing 70 mg diazinon/L and sludge containing 320 mg diazinon/L were disposed onto a 450 m2 site designated for this purpose. After 14 days soil residues were less than 1 mg/kg. Diflubenzuron residues on a similar site following disposal of 5200 L of spent dip wash containing 370 mg/L remained at about 40 mg/kg for a month after disposal and were still about 6 mg/kg 12 months later. Results indicated that the half-lives in soil of diazinon and diflubenzuron from spent dip wash were about 9 and 117 days, respectively. We recommend disposing spent sheep dips on to bunded areas of flat, vegetated land isolated from sensitive areas such as watercourses and from which animals can be excluded. Area quarantine for up to 3 months might be adequate for diazinon-based products but we recommend excluding animals permanently from sites used for the disposal of diflubenzuron-based dips. Alternatively, more sophisticated methods of bioremediation of dip disposal sites may be preferred.