DEGRADATION OF THE PESTICIDES MECOPROP AND ATRAZINE IN UNPOLLUTED SANDY AQUIFERS

The potential for biodegradation of the pesticides mecoprop [(+/-)-2-(4-chloro-2-methyl-phenoxy)propionic acid] and atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine) in an aerobic aquifer was investigated in laboratory batch experiments. The experiments were performed with groundwater and suspensions of groundwater and aquifer sediment collected from a pristine sandy aquifer. Following a lag period of 35 to 40 d, mecoprop in a concentration of 100 mug/L was degraded in 30 d in groundwater at 10-degrees-C. New additions of 100 to 140 mug mecoprop/L were degraded within a week. In suspensions of groundwater and aquifer sediment, mecoprop in the concentration range 75 to 300 mug/L was degraded in 15 d, following a lag period of less than 7 d. Experiments performed with sediments taken from different depths indicate that there was a considerable variation in the degradation potential within the aquifer. Atrazine was not degraded during an incubation period of 539 d in groundwater and 174 d in suspensions of groundwater and aquifer sediment. The addition of nutrients, primary substrates (acetate and naphthalene), and a pH or temperature increase had not effect on the recalcitrance of atrazine.