The photodegradation kinetics of atrazine (2-chloro-6-(ethylamino)-4-isopropylamino-1,3,5-triazine) and ametryne (2-methylthio-4-ethylamino-6-isopropylamino-s-triazine), in fresh and coastal salt water from Barbados, were measured under irradiation with artificial solar and UV254-radiation. The first-order rate constants were greater for ametryne than for atrazine, and the rates were reduced in seawater relative to fresh water, and in soil slurries relative to fresh water. However, rates were accelerated in the presence of iron(III) at pH 3 due to photo-Fenton type processes. This rate enhancement was reduced at ambient pH values (pH 7-7.5) representative of surface water in Barbados. These results have important implications for the relative persistence of these contaminants in aquatic environments in tropical areas.
The triazine herbicides atrazine (AT) and ametryne (AMET) are used extensively in Barbados to control weeds in sugar cane fields. These pesticides were monitored in groundwater (the primary source of potable water on the island) for the dry seasons July -December, 1992. Residues of either AT or AMET were detected in all 277 groundwater samples collected from 23 wells in three major groundwater catchments underlying heavily cultivated sugar cane fields. The concentration of AT and the metabolite deethylatrazine (DEAT) were in the range 0.11 -2.61 mg/l with the highest occurrence in the most heavily cultivated sugar cane area, the Hampton catchment. These measured levels of atrazine in the groundwater, represent a relatively small fraction that may have leached from the annual application, and was estimated to be 0.12, 0.17 and 0.19% of the total amount applied to the Belle, Hampton and Western catchments respectively. These levels, however, are in general higher than those reported for related studies and lower application rates of atrazine in sugar cane plantations should be considered to help preserve the quality of potable water on the island.
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