1998: Gwydir River Basin

1998: Gwydir River Basin: Pesticides Detected – Endosulfan, Atrazine, Amitraz, Chlorpyrifos, Profenofos, Diuron, Fluometuron, Metolachlor, Pendimethalin, Prometryn, Simazine & Trifluralin. Source of Contamination: Crops : Irrigated cotton, sorghum, maize
Where found: Rivers & streams. Reference: Muschal 1998.


Detections are less frequent in riverine environments than in irrigation drainage,
particularly in areas such as northern NSW where tailwater returns to the river are
tightly controlled. The Central and North West Regions Water Quality Program finds
chlorpyrifos in a very small number of samples (well below 1%) at concentrations
generally between 0.1 and 1μg/L. However, chlorpyrifos accumulated to quite
highlevels in passive samplers deployed during 1998. This could reflect accumulation from
background levels, or from occasional high pulses entering the river, with the latter
appearing more likely given that such pulses are detected from time to time. Such
detections, generally below 10μg/L but reaching as high as 26μg/L in one sample
from the Gwydir, may reflect non-agricultural uses such as termite protection of
bridges. However, predicted concentrations of this magnitude may also occur in
shallow water contaminated through excessive spray drift from higher rate uses, such
as for cotton. It seems likely that higher concentrations would occur in minor
tributaries where pesticide residues first enter the riverine system.
January 29 1998 Diuron 24ug/L
January 30 1998 Fluometuron 9ug/L
January 1998 Prometryn 9ug/L
*Cooperative Research Centre for Sustainable Cotton Production. Proceeding of the Cropping Systems Forum 2 & 3 December 1998 Narrabri NSW