Investigations on the biotransformation capacity of organophosphates in the mollusc Dreissena polymorpha P.

Microsomes of Dreissena polymorpha were able to biotransform the organophosphates thiometon and disulfoton significantly after 1 h incubation at 10 °C. Contrarily to vertebrates, biotransformation with mussel microsomes occurred without the addition of reduction equivalents (NADPH), at a considerably lower extent however. Metabolites of thiometon and disulfoton were detected with gas chromatography/mass spectrometry (GC/MS) analysis. The P450 content of whole mussel tissue was 8 pmol mg−1 protein being two orders of magnitude lower than the amounts measured in mammal liver. Ethoxycoumarin deethylase (ECOD) activity could be measured at 10 °C in microsomes of Dreissena (22 pmol min−1 mg−1 protein) but not at 37 °C. ECOD activity was inhibited in the presence of NADPH (measured activity 3 pmol min−1 mg−1)

Organophosphates in the Zebra Mussel Dreissena polymorpha : Subacute Exposure, Body Burdens, and Organ Concentrations

Subacute exposures (10 d) of the freshwater mollusc Dreissena polymorpha to disulfoton (10 mg/L), thiometon (6 mg/L), and its activated oxygen analogue demeton-S-methyl (6 mg/L) corroborate earlier findings of organophosphate resistance and accumulation in the organism. Mortality occurred not before the ninth day of exposure. Mortality was induced at high ambient water concentrations and must be due to unknown specific organophosphate effects. Body burdens reached saturation levels within one week being around 40 mg/kg wet weight for thiometon and 60 mg/kg for disulfoton. Mussels dying during the tests showed lower tissue concentrations. Elimination of accumulated organophosphates was so low in the mussel, that an efficient metabolism of these compounds in the mussel was unlikely. Different organs of Dreissena previously acutely exposed (96 h) to the organophosphate thiometon (6, 12, 25, 50 mg/L) were analyzed for their thiometon content. Thiometon could be found in all organs, but were highest in the anterior part of the viscera (230 mg/kg), where it was accumulated either in the digestive gland and/or in the gonadal tissue

Esterases in the zebra mussel Dreissena polymorpha : activities, inhibition, and binding to organophosphates

Cholinesterase activities of Dreissena polymorpha were measured colorimetrically. In homogenates of whole control mussel, activities of 125 ± 29 μmol min -1 kg -1 were found (n = 6). Neither after exposure of Dreissena to organophosphates (thiometon, disulfoton, demeton-S-methyl) nor after addition of demeton-S-methyl (the activated oxygen analogue of thiometon) in vitro was the measured mussel esterase activity inhibited. Esterases of rat, mouse and human tissue showed a 90 100% inhibition. Radiolabelling of the active serine site of esterases in muscle homogenates with 3H-diisopropylfluorophosphate and subsequent separation on polyacrylamide gels revealed similarities as well as differences between rat and mussel esterases. Coomassie-stained muscle proteins of Dreissena showed a different distribution pattern than those of rat. Proteins of rat as well as proteins of mussel with molecular weights between 66 and 97 kDa showed best labelling (highest radioactivity). Proteins with molecular weights greater than 97 kDa were not labelled. Additionally, in Dreissena but not in rat, proteins of around 45 kDa were labelled. The results indicate that the esteratic enzymes in Dreissena were labelled but not inhibited by organophosphates