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

Abstract

1. Juvenile white sturgeon (Acipenser transmontanus) and common carp (Cyprinus carpio) were exposed to 100 μg/1 [ring-¹⁴C]molinate in a flow-through metabolism system. Exposure was in three phases: acclimation (2h), uptake (24h), 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 < 0˙01) or that previously reported for striped bass (90˙5%, P < 0˙01). Differences in bioconcentration were not significant (P < 0˙05).

4. Common carp and white sturgeon oxidized molinate to form several products and hydrolysed, or conjugated with giutathione (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 < 0˙01) or striped bass (P < 0˙05).

6. The higher toxicity of molinate in common carp may be due to greater bioconcentration, slower depuration, and less efficient metabolic deactivation.