Effects of Endosulfan (Thiodan 35 EC®) on Meiofauna Community Through a Microcosm Approach

A microcosm experiment with natural community of meiofauna was performed to test the effects of the organochlorine pesticide Thiodan 35 EC (35% endosulfan) at concentrations more likely to reach the estuaries by the sugar cane crops runoff. A methodological proposal for microcosms was tested for tropical estuaries. The nominal concentrations (0.001, 0.005, 0.01, 0.05, 0.10, 0.20, 0.35 and 0.55 μg.g-1 + control) and experimental times (0, 1, 4, 8 and 16 days) were adopted. Nominal and measured endosulfan concentrations in Thiodan showed highly significant correlation with losses below 60%. Significant differences were detected for meiofauna structure between experimental days and concentrations tested. The organochlorine Thiodan measured as endosulfan concentrations had affected the Kinorhyncha group on Day 8 and the Simple Linear Regression explained part of densities variation. There were no significant concentration effects on microphytobenthos and its concentration was not related to groups’ feeding. Despite the moderate to high volatilization rate of the endosufan observed in the end of the experiment, it is suggested the absence of mortality patterns due to pesticide bioavailability related to both sedimentary factors and the presence of microalgae. Possible replacement of sensitive by tolerant species or predominance of resistant species in each meiofauna group throughout the experiment is another hypothesis to be discussed. Keywords: meiofauna, microcosm, pesticide, endosulfan, Thiodan, sugar cane, microphytobenthos.