Accumulation of chlorothalonil successively applied to soil and its effect on microbial activity in soil.

The effect of successive chlorothalonil applications on the persistence of chlorothalonil, soil respiration activity, and dehydrogenase activity (DHA) in soil was investigated under laboratory conditions. The persistence of chlorothalonil in soil was prolonged significantly with the increase in the concentration applied. Repeated applications of chlorothalonil at 25 mg kg⁻¹ led to its accumulation in soil. The effect of repeated chlorothalonil applications on soil respiration and DHA was found to be a concentration-dependent process. Soil respiration was permanently inhibited by the successive introductions of chlorothalonil at 25 mg kg⁻¹. DHA was reduced significantly on day 15 after four successive treatments of 10 mg kg⁻¹ and 25 mg kg⁻¹ of chlorothalonil, although a recovery trend could be found after the third and fourth treatments. Repeated chlorothalonil applications might increase the persistence of chlorothalonil in soil and thus alter soil microbial activity.