Organochlorine pesticides (OCPs) in irrigated Vertosols of the Namoi Valley, north-western New South Wales

Abstract

Organochlorine pesticides (OCPs) such as DDT and DDE have been detected in the surface 0.2 m of Vertosols in the lower Namoi Valley of north western New South Wales even though they have not been applied to crops since 1982. However, their presence in the deeper soil horizons has not been investigated. The objective of this study was to determine if OCPs were present to a depth of 1.2 m in Vertosols under irrigated cotton farming systems in the lower Namoi Valley. Soil was sampled from the Australian Cotton Research Institute, near Narrabri, and two cotton farms near Wee Waa and Merah North in northern New South Wales. The OCPs and metabolites detected in order of concentration were: DDE > endosulfan sulphate >endrin > α-endosulfan > β-endosulfan >DDT and DDD. DDT was sprayed extensively in the lower Namoi Valley up to the early 1980’s and may explain the persistence of DDE, a metabolite of DDT, in the majority of soil samples. Dicofol and Dieldrin, previously undocumented in these soils were also detected. The movement of OCPs into the subsoil of Vertosols may occur when irrigation or rain transports soil colloids and organic matter via preferential flow systems into the deeper layers of a soil profile. The persistence in soil of OCP’s applied to cotton crops grown more than two decades ago suggests that they could enter the food chain. Their presence at depths of 1.2 m suggests that they could move into groundwater that may be used for domestic and stock consumption.