Pacific oyster (Crassostrea gigas) hemocyte are not affected by a mixture of pesticides in short-term in vitro assays

Abstract

Pesticides are frequently detected in estuaries among the pollutants found in estuarine and coastal areas and may have major ecological consequences. They could endanger organism growth, reproduction, or survival. In the context of high-mortality outbreaks affecting Pacific oysters, Crassostrea gigas, in France since 2008, it appears of importance to determine the putative effects of pesticides on oyster susceptibility to infectious agents. Massive mortality outbreaks reported in this species, mainly in spring and summer, may suggest an important role played by the seasonal use of pesticides and freshwater input in estuarine areas where oyster farms are frequently located. To understand the impact of some pesticides detected in French waters, their effects on Pacific oyster hemocytes were studied through short-term in vitro experiments. Bivalve immunity is mainly supported by hemocytes eliminating pathogens by phagocytosis and producing compounds including lysosomal enzymes and antimicrobial molecules. In this study, oyster hemocytes were incubated with a mixture of 14 pesticides and metaldehyde alone, a molecule used to eliminate land mollusks. Hemocyte parameters including dead/alive cells, nonspecific esterase activities, intracytoplasmic calcium, lysosome number and activity, and phagocytosis were monitored by flow cytometry. No significant effect of pesticides tested at different concentrations was reported on oyster hemocytes maintained in vitro for short-term periods in the present study. It could be assumed that these oyster cells were resistant to pesticide exposure in tested conditions and developing in vivo assays appears as necessary to better understand the effects of pollutants on immune system in mollusks.

Pesticides and Ostreid Herpesvirus 1 Infection in the Pacific Oyster, Crassostrea gigas

“…Fourteen pesticides belonging to 4 pesticide groups (herbicides, fongicides, insecticides and molluscicides) were selected based on their detection in the aquatic environment in Britany and Charente Maritime [ 20 ] and their immunotoxic potential for invertebrates. The mixture of the 14 selected pesticides consisted of carbaryl, fosetyl aluminium, alachlor, métolachlor, glyphosate, atrazine, terbuthylazine, diuron, AMPA, bentazon, tebuconazol, imidacloprid, mancozeb and metaldehyde [ 21 ] ( Table 1 ). Solvents were used as recommended by manufacturers ( Table 1 ) and final solvent concentration was less than 0.5% in order to avoid effects of the solvent.…”

“…Assays were carried out to study the effect of the pesticide mixture in vitro on viral (OsHV-1) suspension [ 22 ]. Three concentrations of pesticide mixture were tested (1X, 10X and 200X) [ 21 ] with a 24 hour exposition at 15°C in the dark.…”

The cell cultures and the use of haemocytes from marine molluscs for ecotoxicology assessment

“…Molluscan haemocytes are known to synthesize MT after Cd exposure as a protection mechanism against metal toxicity (Roesijadi et al 1997;Langston and Bebianno 1998). Another study carried out with pesticides showed no significant effect of a mixture of 14 pesticides and methaldehyde alone tested at different concentrations (according to flow cytometry) on Pacific oyster haemocytes maintained in vitro for short-term periods (2, 4 and 21 h) (Moreau et al 2014). Gagnaire et al (2003) reported no effect on cell viability in Pacific cupped oyster haemocytes exposed to atrazine in vitro.…”

“…Katsumiti et al (2014) showed that phagocytosis was not modified in M. galloprovincialis haemocytes exposed to ionic Cd. Similarly, no significant effect of a mixture of 14 pesticides, tested at different concentrations, on the phagocytic activity of C. gigas haemocytes was observed (Moreau et al 2014). Thus, for a given contaminant, the responses of immunological biomarkers like phagocytosis are sometimes contradictory since the effects can range from almost total immunodepression to immunostimulation, including no effect .…”

Crop protection: new strategies for sustainable development

“…Aquatic organisms are generally very sensitive to pesticides, and it is therefore important to study the impact of molecule alone or in combination to detect possible synergistic action. Moreau et al (2013) from the Institut Français pour la Recherche et l'Exploitation de la Mer (Ifremer) of La Tremblade and Nantes showed that Pacific oyster (Crassostrea gigas) hemocytes are not affected by a mixture of 14 pesticides or metaldehyde alone in shortterm in vitro assays. They conclude that it could be assumed that these oyster cells were resistant to pesticide exposure in tested conditions, and developing in vivo assays appears necessary to better understand the effects of pollutants on immune system in mollusks.…”