Influência da variação de velocidade e pressão sobre Limnoperna fortunei Dunker, 1857 (Bivalvia, Mytilidae) e verificação dos efeitos da toxicidade do látex de Euphorbia Splendens var. hislopii N.E.B. (Euphorbiaceae) para esta espécie

Abstract

This work describes a study developed to evaluate the impact of Limnoperna fortunei in water closed conduits and test some mechanisms for reduction of its incrustation in industrial pipelines. The main goals of this study are to estimate the hydraulic head loss in closedconduits caused by the L. fortunei incrustation, to evaluate the efficiency of the molluscicides based on the latex extracted from the Euphorbia splendens var. hislopii to control L. fortunei infestation, to assess the effects of high pressure gradients on L. fortunei incrustation, and todetermine the minimum flow speed capable of pulling away the individuals of L. fortunei incrusted in steel pipelines. Several experimental tests are performed on closed conduits with diameters of 2in, 2 ½ in, 3in, and 4in, in which shells of death individuals have been fixed with Araldite®. The experimental results show that the infestation of L. fortunei provokes significant increases in the hydraulic loss for several levels of flow rate. In the evaluation of the latex toxicity, individuals are exposed in laboratory to concentration of 0.1 to 1000 ppm, at three temperatures (18C, 20C, and 22C), during 24 and 240 hours. The results show that theindividual size and the temperature affect the response of the L. fortunei to the latex toxicity. However, no latex concentration is able to kill 50% of the exposed individuals in 24 hours. The evaluation of the pressure gradient effects is carried out in field, by exposing individuals to pressure variations of 10 and 130 mca and instantaneous depressurizations. The results show that the pressure gradients are not harmful to the L. fortunei. The flow speed tests are also performed in field, using grid plates with incrusted individuals submersed during 5 and 13 months. In the experimental apparatus the flow rates are increased until all individuals are pulled away from the grids. The maximum flow speed for the L. fortunei release is about 2.87 m/s. At the end of this work, several recommendations and suggestions are presented aiming at the research continuity