THYROID-HORMONES AS BIOMARKERS IN GREY SEALS

Changes in grey seal (Halichoerus grypus) serum thyroid hormones with age, sex and during lactation were investigated. Concentrations were r elated to polychlorinated biphenyl (PCB) uptake and exposure in pups a nd females. There was no effect of sex or stage of lactation on either free or total thyroxine (T-4) and triiodothyronine (T-3), but signifi cant age-related variability was seen. Pups had significantly higher c oncentrations of total T-4 than adults (p < 0.0001) and serum levels d eclined with age. In general, there was no significant relationship be tween PCB exposure to pups through female milk or between PCB blubber concentrations and thyroid hormone levels, when the effect of age was controlled for. However, the ratio T-3:T-4 was significantly correlate d with the concentration of one congener, CB169 (p = 0.048), when stag e of lactation was used as a covariate, In conclusion, serum thyroid h ormone levels may be less useful biomarkers of contaminant exposure in seals than other biochemical measures. Although concentrations vary p redictably with age, other factors, such as condition and nutritional status, may compromise their usefulness in assessing contaminant-induc ed hormone disruption in pinnipeds, (C) 1998 Published by Elsevier Sci ence Ltd, All rights reserved.