1980 – 1981: Preston River (WA). Pesticides detected: Dieldrin, DDT, Aldrin and Heptachlor

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Organochlorine Pesticide Residues in the Preston River (Atkins 1982)

This study was conducted in 1980 and 1981 to monitor the possible effect of the use of organochlorine pesticides in the Preston River catchment on water, sediment and biota levels in the river and Leschenault Inlet.

Of the 88 samples of water taken, dieldrin was detected in 78. DDT, Aldrin and heptachlor were detected in 34, 25 and 5 samples respectively.

Between 22% and 67% of the dieldrin detections exceeded the EPA criterion depending on the site. DDT detection exceeded the EPA criterion between 11% and 33% of the time, depending on the sampling site. Aldrin and heptachlor detection were only occasionally above their respective EPA criteria.

The dieldrin levels were amongst the highest in rivers in the south west of WA, but were low when compared to other Australian rivers.

No organochlorines were detected in sediment samples, the limit of detection being 0.01 mg/kg.

Three specimens of fish were sampled from the lower reaches of the Collie River. Less than 0.001mg/kg of DDT were found in all three, and only in one did the dieldrin level equal 0.01 mg/kg.

This Report compared dieldrin levels with those found in the Preston River, by various other researchers, since 1974. The author concluded that no significant reduction in dieldrin levels in that time has occurred, even though the number of registered agricultural uses for dieldrin in the area had declined markedly. This could be due to the very high level of retention of dieldrin by soils, in which the slow “release” of this chemical, as soil is eroded into the river, masks the decline in dieldrin use. Alternatively, (and perhaps, additionally) dieldrin was continuing to be used illegally.

P50 Monitoring Pesticides – A Review – A Report to the Environmental Protection Authority by Peter A Rutherford. Environment Protection Authority. Perth Western Australia. Bulletin 407. December 1989.