1997 December – 1998 November: Imbil (Qld). Pesticides: Atrazine and metabolites.

Source: APVMA


The reconsideration of approvals of the active constituent atrazine,registrations of products containing atrazine, and their associated labels.

SECOND DRAFT FINAL REVIEW REPORT Including additional assessments
Timber Plantation Trials

p55 Surface Water Monitoring for Atrazine in Queensland Timber Plantations

Surface water monitoring in Queensland was conducted in a hoop pine plantation at
Imbil in the south-east corner of the State. The 8 ha study site was situated on silty clay
soils, at an elevation of 100-300 m with slopes of 5 to 30o. Atrazine was manually
applied along the tree row, by knapsack at 5 kg/ha (overall rate 2.25 kg/ha) on six
occasions over a 2 year period. The subtropical climate demanded more frequent
treatments in order to achievesatisfactory weed control, but also leads to a shorter half-
life for atrazine in soil. Summer rainfall is dominant at this subtropical location, and
was near average at 1130 mm in year 1 and well above at 1703 mm in year 2, with a
correspondingly high number of flood events (19 at the upstream station and 21
downstream). One large storm in February of the second year delivered 540 mm over a
3 day period and caused a major flood event.
Atrazine was applied four times in the first year, in December 1997 and April, August
and November 1998. Flood events occurred 2, 34 and 53 days after the first treatment,
1 and 9 days after the second, 27 and 91 days after the third, and 2, 29 and 43 days after
the fourth in the high CAR (94%). Atrazine concentrations at the upstream station
remained in the low ppb range for the first and last treatments, but reached 109μg/L for the second treatment (in the second event) and 127.7μg/L for the third (first event). Atrazine was accompanied by significant amounts (in the order of 10%) of the dealkylated metabolites DEA and DIA, the former being predominant. Peak concentrations at the low CAR (4.4%) downstream station, after each application were 7.6, 18.2, 105.5 and 25.6μg/L (note not always in the first flood event, and that the duration of the peaks was brief).
Previous experience with hoop pine plantation establishment had indicated that surface
runoff is much more likely to be generated from point sources than from the general
plantation area, the high infiltration capacity of which is enhanced by slash retention and contoured windrows which pond runoff water. Direct contamination of watercourses was discounted as these were protected and chemical was applied manually.
Road areas (including access tracks and snig tracks within the plantation) were suspected as the main source of contamination because of their high rainfall runoff coefficient. Drainage outlets compounded the problem as they flowed directly to watercourses via roadside drains, rather than being directed back into the general plantation area via water
spreading structures.
A number of procedural changes were introduced in late 1998 to minimise the risk of
contamination. Roadside transfer of herbicide mix from tanker to knapsacks was

restricted to areas where drainage was directed back into the plantation, with staff
instructed to minimise the possibility of spillage during transfer and test the spray units
only within the plantation area. Application to potential point sources in the general
plantation area, such as access tracks and snig tracks, was to be avoided.
Treatments in 1999 occurred in February and October, with flood events at the high CAR station 11, 77, 126, 189 and 234 days after the first treatment and 1 and 13 days after the second. Atrazine concentrations, at the upstream stations, were elevated after the first treatment, reaching 41.8μg/L in the first of two events 11 days after treatment, and 50.4μg/L in the second. Concentrations remained in the low ppb range after the second treatment. At the downstream station, concentrations did not exceed 2.3μ g/L…”