1985 December – 1986 May: Preston River (WA). Pesticides: Dieldrin, DDT, Heptachlor, Chlordane

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Organochlorine Pesticide Residues in the Preston River (Klemm 1988 – (unpublished)

This is a follow-up to the previous study by Atkins (1982). The main objective of this study was to monitor the predicted reduction of dieldrin residues reaching the Preston River. In addition, the study aimed to detect any increase in other residues, and to detect any accumulation of organochlorines in Leschenault Inlet.

The study area, as in the previous one, extended from Glen Mervyn Dam to the Glen Iris Road Bridge, a 60km section of Preston River. Then ten sampling sites used by Atkins (1982) were again used in this study, Sampling took place between December 1985 and May 1986.

It was found that organochlorine residues in the Preston River had decreased. Dieldrin was still the predominant pesticide, but the mean level had fallen from 0.006 to 0.003 ug/L since the Atkins (1982) study. In addition, the percentage of recordings that exceeded the EPA crtiterion of 0.003ug/L had declined from 58% in the 1982 study to 13% in this study.

DDT levels had also fallen from a mean of 0.004 to 0.002 ug/L, with a fall from 46% to 8% of the recordings exceeding the EPA criterion.

Heptachlor, and for the first time, chlordane were found more frequently, and the proportion of heptachlor readings that exceeded the EPA criterion increased from 8% to 13% (chlordane from nil to 12%).

These changes have reflected the change in use-pattern of the chemicals. Dieldrin lost all agricultural registration in 1982, with heptachlor replacing dieldrin for potato production and in some orchards.

No organophosphorus residues were detected in the samples.

Levels of organochlorines in the twenty samples of freshwater mussel did not exceed the limit of detection (0.001 mg/kg) and therefore do not indicate bioaccumulation.

Organochlorine residues in the Preston River are now generally comparable with other river systems. The range of dieldrin residues is similar to the Swan and Serpentine River’s systems, but levels are still higher than other South West Rivers.

P51 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.