Toxicity of the effluents from shrimp ponds: outlook for risk analysis and decision-making

Abstract

Shrimp farming, has grown worldwide above the average of agricultural activities over the last decade and, like  any human enterprise, it has also altered in different ways the place of its installation. Little scientific research has been  produced aiming at their mitigation, especially as to the evaluation of the impacts caused by the activity’s effluents. The  objectives of this study were to evaluate the toxicity of shrimp ponds effluents while being drained to enable the shrimp  harvest, and to ascertain the existence of differences in water quality between the various layers of the water column. Tests  were performed with embryos of the mangrove oyster  Crassostrea rhizophorae , trying to relate possible abnormalities  with the measured values of physical-chemical parameters in effluent samples. The bioassays with embryos proved the  occurrence of effluent toxicity in the organisms and, applied together with the analysis of physico-chemical parameters,  have been found to contribute to a better assessment of the water’s quality in ponds. The results also showed the existence  of a quality gradient along the water column of shrimp ponds, where the surface layer showed a better quality than the  bottom substrate.