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2I - High-tiered studies (MOP/115) Effects of hexachlorobenzene at various levels of biological organization in freshwater snails. Lagadic, L.1, Caquet, Th.1, 1 INRA EQHC, Rennes, France ABSTRACT- The fate and effects of the organochlorine fungicide hexachlorobenzene (HCB) were assessed in freshwater outdoor pond mesocosms (12 m3). Three nominal concentrations of HCB were used (0.5, 1.25 and 5 Key words: population density, growth-reproduction balance, sublethal effects |
g/L, respectively ; one replicate per treatment) and three untreated mesocosms were kept as the controls. A unique contamination was performed on May 5, and the fate and effects of the compound were studied for 8 months. HCB rapidly disappeared from the water (estimated half-life : 24.5 h) and accumulated in the sediments and the organisms. Analysis of the data on the benthic macroinvertebrate community using Principal Response Curve (PRC) showed a positive effect of HCB on populations of the freshwater snail Physella acuta (Draparnaud) at the two highest nominal concentrations. The analysis of population abundance data confirmed that this species was more abundant in the mesocosms contaminated with the two highest nominal concentrations of HCB. Although an indirect positive effect of HCB through food availability cannot be excluded, studies at the individual and population levels on a related model snail species, Lymnaea palustris (Müller), showed that HCB may have a direct effect on the performances of freshwater gastropods. HCB caused a decrease of growth and glycogen content and an increase of the fecundity and polysaccharide hydrolytic activity in caged L. palustris. These observations were confirmed in laboratory studies. The effects of HCB could be related to an impact on the neuro-endocrine control of the balance between growth and reproduction in exposed snails. This study confirms that mesocosms are suitable devices to study the propagation of toxic effects between various levels of biological organization, ranging from subindividual to community level, and to identify putative links between these effects.