Microcosm study of the long term effect of endosulfan on enzyme and microbial activities on two agricultural soils of Yaounde-Cameroon

Abstract

Soil samples with different physical and chemical characteristics were taken from two sites, Minkoa-Meyos and Mendong, in Yaounde. These samples were treated with the insecticide endosulfan, using commercially recommended rates (1.5l ha-1), and incubated in the laboratory at 20°C in glass flask for 75 days in order to evaluate their toxic effects on enzyme activities, organic matter content and the availability of phosphorus in the soils studied. The enzyme activities studied included dehydrogenase, β-D glucosidase, acid and alkaline phosphatases. The results showed that, on one hand, endosulfan inhibits dehydrogenase, acid and alkaline phosphatase activities in both soils. β-D Glucosidase activity was inhibited in Mendong soil, but this activity seems not to be affected by endosulfan in Minkoa-Meyos soil. On the other hand, endosulfan appeared to have no measurable effect on the organic carbon content and on the availability of phosphorus in Minkoa-Meyos soil. However, these two functions were inhibited in the Mendong soil. Moreover, significant correlations in the Mendong soil at the highest concentration were obtained between acid phosphatase activity and the available phosphate (P = 0.024; r = 0.821), and between alkaline phosphatase activity and the available phosphate (P = 0.014; r = 0.858). Key words: Endosulfan, soil microcosm, enzyme and microbial activities, exposition time.