Atrazine degradation and transport in runoff on a Black Vertosol
D. J. Rattray A B D , J. Standley B , D. M. Silburn B , D. M. Freebairn B and K. P. Spann CA Queensland Department of Primary Industries and Fisheries, PO Box 102, Toowoomba, Qld 4350, Australia.
B Queensland Department of Natural Resources and Water, PO Box 318, Toowoomba, Qld 4350, Australia.
C K & D Aust. Pty Ltd, PO Box 27, Gatton, Qld 4343, Australia.
D Corresponding author. Email: danr@qmdc.org.au
Australian Journal of Soil Research 45(8) 598-606 https://doi.org/10.1071/SR07028
Submitted: 14 February 2007 Accepted: 30 October 2007 Published: 7 December 2007
Abstract
In Australia communities are concerned about atrazine being detected in drinking water supplies. It is important to understand mechanisms by which atrazine is transported from paddocks to waterways if we are to reduce movement of agricultural chemicals from the site of application. Two paddocks cropped with grain sorghum on a Black Vertosol were monitored for atrazine, potassium chloride (KCl) extractable atrazine, desethylatrazine (DEA), and desisopropylatrazine (DIA) at 4 soil depths (0–0.05, 0.05–0.10, 0.10–0.20, and 0.20–0.30 m) and in runoff water and runoff sediment. Atrazine + DEA + DIA (total atrazine) had a half-life in soil of 16–20 days, more rapid dissipation than in many earlier reports. Atrazine extracted in dilute potassium chloride, considered available for weed control, was initially 34% of the total and had a half-life of 15–20 days until day 30, after which it dissipated rapidly with a half life of 6 days. We conclude that, in this region, atrazine may not pose a risk for groundwater contamination, as only 0.5% of applied atrazine moved deeper than 0.20 m into the soil, where it dissipated rapidly. In runoff (including suspended sediment) atrazine concentrations were greatest during the first runoff event (57 days after application) (85 µg/L) and declined with time. After 160 days, the total atrazine lost in runoff was 0.4% of the initial application. The total atrazine concentration in runoff was strongly related to the total concentration in soil, as expected. Even after 98% of the KCl-extractable atrazine had dissipated (and no longer provided weed control), runoff concentrations still exceeded the human health guideline value of 40 µg/L. For total atrazine in soil (0–0.05 m), the range for coefficient of soil sorption (Kd) was 1.9–28.4 mL/g and for soil organic carbon sorption (KOC) was 100–2184 mL/g, increasing with time of contact with the soil and rapid dissipation of the more soluble, available phase. Partition coefficients in runoff for total atrazine were initially 3, increasing to 32 and 51 with time, values for DEA being half these. To minimise atrazine losses, cultural practices that maximise rain infiltration, and thereby minimise runoff, and minimise concentrations in the soil surface should be adopted.
Additional keywords: available atrazine, desethylatrazine, desisopropylatrazine, leaching, runoff, sorption.
Acknowledgments
The work was funded by the Grains Research and Development projects ‘Management options to minimise pesticide and nutrient transport in runoff from grain cropping areas’ and ‘Improving water quality in grain cropping farming catchments’. The authors thank farmer Julian Ridgway for his help and cooperation. Technical assistance with herbicide analyses by Alison Cockburn, and with field work by Brendan Power and Graeme Wockner, is gratefully acknowledged.
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