The legacy of pesticides banned years ago remains in areas of rural South Island, according to research by a team from Otago's Departments of Chemistry and Zoology.
Researchers compared the presence of chlorinated pesticides in streams running through sheep and beef farm clusters near Amberley, Akaroa, Outram, Owaka and Gore. Each area comprised an organic, a conventional, and an integrated pest management (reduced pesticide use) property.
Dr Pourya Shahpoury says the pesticide chlorpyrifos (approved for current use) was the most frequently detected chemical in sediment samples, with similar concentrations throughout the study areas regardless of the farming method used during the past 11 years. This was contrary to expectations and may have been due, at least in part, to vapour drift from conventional or integrated farms, highlighting potential issues about the spread of pesticides to areas where they were not directly applied.
Signs of more toxic and now-banned pesticides such as DDT, endosulfan and dieldrin were also found. Degradation products of DDT and endosulfan were detected in up to 75 and 42 per cent of sediment samples respectively, with the highest levels from conventional farms, a likely result of increased pesticide run-off.
Although mean pesticide concentrations across all samples were below recommended toxicity thresholds for freshwater organisms, up to 23 per cent had residues of individual pesticides above these thresholds, Shahpoury says.
"We can minimise the environmental impact of farming by moving towards organic farming, but our study confirms that we can't eliminate the presence of pesticide residues from the environment – at least not for now."