Effects of Pesticides on Marine Bivalves: What Do We Know and What Do We Need to Know?

Abstract

Estuaries are among the most productive environments in the world, by serving as feeding grounds, as nurseries for juvenile economically important fish and invertebrate larvae, and by providing shelter for many types of benthic organisms. However, they also rank among the most contaminated areas. Among pollutants, pesticides have become more common in estuarine areas. They are mainly introduced into rivers via run-off and then may enter marine areas, particularly estuarine and coastal zones. These pollutants may have major ecological consequences and could endanger organismal growth, reproduction or survival (Banerjee et al., 1996). Among important organisms inhabiting estuarine zones, bivalves are sessile and filterfeeder species, able to accumulate contaminants in their tissues. Moreover, bivalve farming is an ancestral activity all around the world. It has been expanded and intensified in the last century and represents a major economic activity in various countries. In the majority of cases, bivalve species are reared in estuaryine zones, continually impacted by pollutants including pesticides. Natural and man-made toxicants enter marine ecosystems by various routes, including direct discharge, land run-off, atmospheric deposition, in situ production, abiotic and biotic movements and food-chain transfer. Pollutant run-off into the ocean represents a potential threat to marine organisms, especially bivalves living in coastal environments. In this context, bivalve molluscs such as mussels and oysters have been postulated as ideal indicator organisms because of their wide geographical distribution, and sensitivity to environmental pollutants. They filter large volumes of seawater and may therefore accumulate and concentrate contaminants within their tissues (Ramu et al., 2007; Bernal-Hernandez et al., 2010). As an example, the level and extent of organic contaminants along the Korean coast has been estimated through a mussel watch program (Choi et al., 2010). Moreover, development of techniques allowing effect analysis of pollutant on bivalve biology may lead to the development of diagnosis tools adapted to analyze pollutant transfer towards estuarine areas. A pesticide is defined as a chemical substance used for killing pests, as insects, weeds or rodents. Pesticids are often classified by the type of organism: fungicides, herbicides, insecticides, nematocides and rodenticides. They are used especially in agriculture and around areas where humans live. Some are harmful to humans, either from direct contact or