Effective remediation of diazinon from spent sheep dip wash by disposal on land

Abstract

Spent sheep dip wash (about 3500 L) containing 59 mg diazinon/L was evenly distributed onto a 450-m² grassed, soil-bunded, sloping site near Cumnock in central New South Wales, Australia. The entire volume was contained within the bunded area but surface run-off created ponding in the lowest corner of the site. The mean concentration within the top 7 cm of soil was 2.32 mg/kg a day after application. By day 14, this had dropped to 0.4 mg/kg and by day 56, was below the limit of quantification (0.1 mg/kg). The half-life of diazinon in soil was estimated to be 7 days. Residues in the next 7 cm of soil depth were much lower and were below the limit of quantification in all samples collected at day 28 or later. This suggests that vertical leaching of diazinon within the soil profile did not occur despite more than 95 mm of rain during the trial interval. Throughout the 56-day trial interval, diazinon concentrations in the top 7 cm of soil 3 m downhill of the lowest corner of the dip disposal site were unchanged from background pre-treatment levels. No diazinon was detected in samples at 7–14 cm depth in the soil profile in this area. With neither vertical nor lateral movement of diazinon away from the initial treatment zone, we consider the disposal of spent diazinon sheep dips as described here, to be an acceptable and convenient option for Australian wool producers and dipping contractors. Suitable dip disposal sites should be situated away from sensitive locations in areas that have good grass cover over deep soil and that are contained by an effective bund. Stock and other animals should be excluded from these sensitive locations.