Comparative biotransformation of molinate (Ordram) in the white sturgeon (Acipenser transmontanus) and common carp (Cyprinus carpio).

1. Juvenile white sturgeon (Acipenser transmontanus) and common carp (Cyprinus carpio) were exposed to 100 micrograms/l [ring-14C]molinate in a flow-through metabolism system. Exposure was in three phases: acclimation (2 h), uptake (24 h), and depuration (24 h). 2. Excreted metabolites were collected on a macroreticular resin, and retained metabolites were extracted from homogenized fish tissue. Identification and quantification was by h.p.l.c. cochromatography (gradient conditions) and determination of 14C, and confirmation was by t.l.c. 3. 14C depuration (elimination) by common carp (77.8%) was significantly slower than that by white sturgeon (96.0%, P less than 0.01) or that previously reported for striped bass (90.5%, P less than 0.01). Differences in bioconcentration were not significant (P less than 0.05). 4. Common carp and white sturgeon oxidized molinate to form several products and hydrolysed, or conjugated with glutathione (GSH), the sulphoxide or sulphone; both fish also formed a D-glucuronic acid conjugate. 5. Common carp were significantly less capable of molinate sulphoxidation and GSH conjugation than either white sturgeon (P less than 0.01) or striped bass (P less than 0.05). 6. The higher toxicity of molinate in common carp may be due to greater bioconcentration, slower depuration, and less efficient metabolic deactivation.