T. Renault

*Ifremer/Laboratoire de Génétique et Pathologie, Ronce-les-Bains, France* 

#### **1. Introduction**

226 Pesticides in the Modern World - Risks and Benefits

Zou, E & Stueben, B (2006) Acute exposure to naphthalene reduces oxyregulating capacity

Zou, E; Nanshan, D. & Wei, L (1992). The effects of acute progressive hypoxia on the

*Biology*, 149, pp.1411-1415, ISSN (printed): 0025-316.

334, ISSN: 0254-5853 .

of the brown shrimp, *Penaeus aztecus*, subjected to progressive hypoxia. *Marine* 

respiration rate of the Chinese crab *Eriocher sinensis. Zoological Research*, 14, pp.327-

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

Effects of Pesticides on Marine Bivalves: What Do We Know and What Do We Need to Know? 229

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)

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

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.,

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

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

Several studies have been conducted in various marine bivalve species in order to define

Chung et al. (2007) evaluated the sensitivity of the juvenile hard clam, *Mercenaria mercenaria*, to DDT (organochlorine pesticide) by exposure to contaminated sediments (10 day) and seawater (24-h). The aqueous LC50 (24h) value was defined at 0.61 mg L-1 DDT. and the LC50 (10 day) value for sediment toxicity tests was 5.8 mg kg-1 DDT. The authors concluded that

bivalves, whether individually or in mixture with their parent compounds.

LC50 for different pesticides including DDT, diuron, atrazine or lindane.

**3. Lethal effect of pesticides on marine bivalves** 

in mussels collected from coastal waters in the Asia-Pacific region.

from 3.01 to 33.21 ng L-1.

2006).

Cochet, 2004).

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 then updated several times.

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 et al., 2007).

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