**2. Pesticides in the marine environment**

Aquatic habitats are particularly subjected to contamination by pesticides, via run-off, leaching, spray drift or accidental spills. Pestices contamination of the marine environment has been and is monitored worldwide through analysis of water, sediment and marine species samples in order to elucidate the contamination status, distribution and possible pollution sources and to assess the risks on aquatic organisms and human.

Levels of pesticides measured in superficial waters generally range below lethal concentrations for aquatic species. However, sublethal adverse effects may result from exposure to these products at environmentally relevant concentrations.

Buisson et al. (2008) reported recently results about the monitoring of contamination levels in the Pacific cupped oyster, *Crassostrea gigas*, reared in Normandy (France). Six herbicides were detected in seawater for a total of 15 herbicides. Although the most estuarine sites showed

as residue on food, or are harmful to the environment because of their high toxicity, such as DDT (which is now banned in many countries). All pesticides act by interfering with the target species normal metabolism. Some inadvertently may affect other organisms in the environment, either directly by their toxic effects or via elimination of the target organism. By World War II, only about 30 pesticides existed. Dichloro-Diphenyl-Trichloro-ethane (DDT) was recognized as an insecticide until 1942. Other pesticides soon followed, such as chlordane and endrin. Poison gas research in Germany yielded the organophosphorus compounds, the best known of which is parathion. Further research yielded hundreds of organophosphorus compounds including malathion. The Environmental Protection Agency (EPA) estimates that the use of pesticides doubled between 1960 and 1980 with over 1.8 billion kilograms a year used today worldwide. In most countries, pesticides must be approved for sale and use by a government agency. However pesticide regulations differ from country to country. To deal with inconsistencies in regulations among countries, an International Code of Conduct on the Distribution and Use of Pesticides has been adopted in 1985 under the umbrella of the United Nations Food and Agriculture Organization and

Bivalves in culture may be affected by the presence of pesticides, potentially increasing their susceptibility to a wide range of infectious diseases. The effects of environmental contaminants may result from direct toxic actions on tissues or cells or from alterations of the homeostatic mechanisms including the immune system (Coles and Pipe, 1994; Carajaville et al., 1996). It has been suggested that bivalves may be weakened in relation to the presence of these pollutants. It has been shown in several vertebrates and invertebrates that pesticides are capable of diminishing immune defenses and/or of modifying genomes. They may render animals more vulnerable to infectious diseases (Ross et al., 1996; Gagnaire

Although pesticide effects on marine bivalves have been already studied in bivalves, a few of reviews summarizing their different effects are available. In this context, one of the major objectives of this chapter relies on summarizing existing body of data on pesticide detection in marine environments and their effects on bivalve physiology including genotoxicity and immunotoxicity. Moreover, another aim of the present chapter is to identify the topics on which scientific data are needed in order to better understand the complex interactions

Aquatic habitats are particularly subjected to contamination by pesticides, via run-off, leaching, spray drift or accidental spills. Pestices contamination of the marine environment has been and is monitored worldwide through analysis of water, sediment and marine species samples in order to elucidate the contamination status, distribution and possible

Levels of pesticides measured in superficial waters generally range below lethal concentrations for aquatic species. However, sublethal adverse effects may result from

Buisson et al. (2008) reported recently results about the monitoring of contamination levels in the Pacific cupped oyster, *Crassostrea gigas*, reared in Normandy (France). Six herbicides were detected in seawater for a total of 15 herbicides. Although the most estuarine sites showed

between pesticides, environment, marine bivalves and their infectious agents.

pollution sources and to assess the risks on aquatic organisms and human.

exposure to these products at environmentally relevant concentrations.

**2. Pesticides in the marine environment** 

then updated several times.

et al., 2007).

relatively high values in sea water samples, no pesticides were detected in the flesh of collected oysters (Buisson et al. 2008). At the contrary, Monirith et al. (2003) reported that all samples collected from all the sampling sites demonstrated the detection of organochlorines (OCs) with considerable residue levels of p,p(')-DDT and alpha-hexachlorocyclohexane (HCH) in mussels collected from coastal waters in the Asia-Pacific region.

Pandit et al. (2006) conducted a multi-compartment monitoring (sediment, water and marine species) of residue levels of pesticides in coastal marine environment of Mumbai in India. The total HCH concentration in sediment samples varied from 3.8 to 16.2 ng g-1 lindane (gamma-HCH) contributing almost 55% to the total HCH. The concentration of total HCHs in seawater ranged from 0.16 to 15.92 ng L-1 and concentrations of total DDT varied from 3.01 to 33.21 ng L-1.

The presence of herbicides, such as diuron, has been also detected in many aquatic ecosystems worldwide. For instance, in France, diuron has been detected in surface waters with concentrations ranging from 0.05 µg L-1 to 20.3 µg L-1 (Léonard, 2002). In Atlantic bays and estuaries, concentrations up to 0.7 and 1 µg L-1 have been reported (Munaron et al., 2006).

Due to its toxicity, the use of diuron has been forbidden by French policies since 2008. Diuron and isoproturon are also included in the list of priority to contaminants of the EU Water Framework Directive (European Comission, 2000). However, it is well-known that some herbicides may persist in the environment even if their use has been banned, e.g. atrazine (EEA, 2000). A recent study reported the presence of diuron on French aquatic environments, confirming its persistence despite restriction policies (Pesce et al., 2010).

Diuron metabolites such as DCPU (N-(3,4 dichlorophenyl)-urea), DCPMU (N-(3,4 dichlorophenyl)-N-(methyl)-urea) and DCA (3,4-dichloroaniline) have also been detected in aquatic environments (Munaron et al., 2006). Studies on biofilms have reported DCPMU to be more toxic than DCA (Pesce et al., 2010). However, the principal product of degradation of diuron reported in the literature is DCA, which has shown to be more toxic for various organisms of higher trophic levels, such as crustacean, insects and fish (Giacomazzi & Cochet, 2004). This product exhibits higher toxic effects than the parent diuron, and can affect organisms, such as crustacean with low concentrations (1 µg.-1, Giacomazzi and Cochet, 2004).

Different compounds including herbicides and their metabolites (Lanyi & Dinya, 2003; Sorensen et al., 2003; Vargha et al., 2005) are detected simultaneously in aquatic environments, suggesting that experimental approaches with toxicant mixtures are needed. Studies with diuron and its metabolites have shown additive, enhanced, antagonistic or independent effects (Knauert et al., 2008; Pesce et al., 2010; Neuwoehner et al., 2010). Thus, there is still a lack of data concerning the toxicity and effects of pesticide metabolites on bivalves, whether individually or in mixture with their parent compounds.
