1988: Horsham (Vic) Wimmera River. Pesticide: DDT

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p576 “Residues of DDT and other organochlorines have been found in waterways in a recent survey in the Horsham district in the Wimmera (Bell, EPA, unpublished data). This study was initiated following reports of fish and yabby kills in the Horsham area in previous spraying seasons. Insecticide use is intensive in the area, particularly on legume crops (mainly field peas) to control budworm (Heliothis spp.) and pea weevil. Some 195,000 ha of legumes (139,000 ha of field peas) were grown in the Mallee and Wimmera in the 1989-90 season (ABS 1991).

The use of organochlorine insecticides is now prohibited and synthetic pyrethroids are largely the chemical of choice. Much spraying is done by aerial operations. Synthetic pyrethroids are very toxic to aquatic organisms but detection is difficult because these chemicals are non-persistent and break down rapidly in water and after ingestion.

Ten sites, including four dams (one private, three located at Government facilities), two irrigation channels, three sites on the Wimmera River and one wetland site, were selected to monitor the effects of pesticide spraying both before and during the 1988 field pea cropping season. Water and sediment samples were collected and monitored for organochlorine, organophosphate and pyrethroid pesticides. Results of the survey were inconclusive as to the effects of current agricultural management on pesticide levels, because too little data were obtained and wet weather conditions meant that pesticide spraying was less intensive than usual. However, the results did show that organochlorines at levels greater than the thresholds for harmful effects on aquatic ecosystems still persisted on occasion, in both water and sediment. Synthetic pyrethroid residues were detected in one site where yabby kills had occurred, but it was not possible to detect synthetic pyrethroid residues in dead yabbies.”

1991 State of the Environment Report. Agriculture and Victoria’s Environment. Office of the Commissioner for the Environment.