Hepatic metallothionein and total oxyradical scavenging capacity in Atlantic cod Gadus morhua caged in open sea contamination gradients.

Biological effects monitoring has seldom been undertaken in offshore pelagic environments. Cages containing hatchery-reared Atlantic cod Gadus morhua were deployed on expected contamination gradients, along a transect from the River Elbe in the German Bight, and in the vicinity of an oil field in the North Sea (Statfjord). Six weeks later, the cod were retrieved and samples taken for a range of biological effects techniques. In this study, metallothionein (MT) and total oxyradical scavenging capacity (TOSC) were measured in liver samples from the caged cod, together with metals (as a measure of bioaccumulation). Both MT and TOSC were highest in cod from the German Bight. In the Statfjord samples MT and TOSC decreased with distance from the oil platform indicating induction in response to anthropogenic sources. The bioavailability of metals appears to be a major factor in MT synthesis, and the measurement of MT and associated metals is shown to be a useful tool for biological exposure and effects monitoring in pelagic systems. There also appears to be a strong linkage between MT and TOSC levels, indicating overlapping capabilities as stress biomarkers. Results suggest that in addition to its role as a specific indicator of metal exposure, MT in cod could act as a more general biomarker of oxidative stress under certain conditions.