The research led by Dr Pourya Shahpoury and recently published in the international journal Environmental Pollution shows average pesticide levels found in sediments of streams running through the 15 South Island farms assessed were still within recommended thresholds.
Chlorpyrifos, the most frequently detected pesticide found in the stream beds is approved for use against pests. However, the study also found chemicals present that had been widely used many years ago before they were banned.
The team of researchers compared the presence of chlorinated pesticides at streams running through five sheep and beef farm clusters near Amberley, Akaroa, Outram, Owaka and Gore.
"While pesticide concentrations averaged across farm management types were below toxicity thresholds, up to 23% of the individual sediment samples contained concentrations above the toxicity thresholds"
Dr Pourya Shahpoury
In each of the five areas one property was farmed organically, a second was farmed using the integrated pest management (reduced pesticide use) farming method and a third was farmed conventionally.
Sediment samples were taken from the 15 different farmland streams during spring/early summer.
Shahpoury said chlorinated pesticides, within recommended thresholds, were found throughout the study areas regardless of the farming practices that took place on the farms eight to11 years before the study.
“Although the chemical chlorpyrifos was the most frequently detected in stream sediments, in contrast to our expectations, its concentrations were not highest in stream sediments from conventional farms and were found at similar levels across all three different farm types.
“This may have been due, at least in part, to its high potential to undergo vapour drift and re-distribution,” he said.
"While pesticide concentrations averaged across farm management types were below toxicity thresholds, up to 23% of the individual sediment samples contained concentrations above the toxicity thresholds.
“The presence of these toxic hotspots, although not common, may be partly responsible for the deterioration of macroinvertebrate communities in streams on conventional farms reported in an earlier Otago study.”
Shahpoury said the study shows that vapour drift from conventional or integrated farms might be an issue when it comes to the spread of pesticides to areas where they were not directly applied.
"We can minimise the environmental impact of farming by going 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."