In 1992 (October) individual rice farms that were draining floodwater were monitored at the farm
drain exit. Pesticide concentrations determined in the drainage water were compared to the pesticide concentrations found in the nearest rice bay of the farm. The maximum concentrations of rice pesticides detected in the bays and drains are shown below:
Molinate: 1840ug/L Rice Bays. 1480ug/L Drains
Malathion: 25ug/L Rice Bays. 15ug/L Drains
Chlorpyrifos: 38ug/L Rice Bays. 7.1ug/L Drains
On at least one occasion (when a malathion concentration of 15μg/L was detected), aerial overspray of the drain with malathion impregnated rice was indicated.
In general if rice floodwater overflowed to the drain, as opposed to seeping through rice bay banks orleaking at control gates, the difference in concentration of pesticide residues detected in the bay
floodwater compared with the concentration in the drainage water, was minimal.
p69 PESTICIDE MONITORING IN THE IRRIGATION AREAS OF SOUTH-WESTERN NSW,
1990 – 1995 K H Bowmer, W Korth, A Scott, G McCorkelle, M Thomas CSIRO LAND & WATER
April 1998 TECHNICAL REPORT