The herbicide/pesticide, monocrotophos exceeded the ADWG health-based guideline value during the 2011/12 reporting period. Westernport Water were not advised of this exceedence by their consultant laboratory and were therefore unable to take any remedial actions in response to the detection. It is important to note that this result was obtained in the raw water, and the health-based guideline values apply in the treated water.

Monocrotophos 0.02mg/L

The only positive pesticide detection for Westernport Water occurred on December 6 2011. The deregistered pesticide, Monocrotophos was detected at Candowie Reservoir at 0.02mg/L (20μg/L). Monocrotophos was last registered in Australia in 1999. This event is possibly the highest level of pesticide recorded in a Victorian domestic water supply since the early 1970’s. The source of the pollution was never investigated. Levels of insecticide this high, would suggest that high volumes would have to made their way into Candowie Reservoir. It also appears plausible that the detection may have been associated with an algal bloom which occurred in the Reservoir at the same time.

The major uses of Monocrotophos up to the end of the 1990’s were: are in cotton, lucerne, potato, sorghum, soybean, tobacco, tomatoes and commercial flower crops. (also used in Pome fruit, beans: French, millet, wheat, sorghum, sunflowers, non-crop areas, bananas, maize, panicum, soybeans, sweet corn, non-fruit bearing trees)

There is no Australian Drinking Water Guideline for Monocrotophos in the latest version of the Australian Drinking Water Guidelines. The level recorded at Candowie is 20 times higher than the “safe” level published in the 2004 version of the Australian Drinking Water Guidelines.