Patterns of variability of retinol levels in a harbour porpoise populationfrom an unpolluted environment

Organochlorine compounds (OC) are known to induce vitamin A (retinoids) def iciency in mammals, which may be associated with impairment of immunocompet ence, reproduction and growth. This makes retinoids a potentially useful bi omarker of organochlorine impact on marine mammals. However, use of retinoi ds as a biomarker requires knowledge about its intrapopulation patterns of variation in natural conditions, information which is not currently availab le. We investigated these patterns in a cetacean population living in an un polluted environment. 100 harbour porpoises Phocoena phocoena from West Gre enland were sampled during the 1995 hunting season. Sex, age, morphometrics , nutritive condition, and retinol (following saponification) and OC levels in blubber were determined for each individual. OC levels found were extre mely low and therefore considered unlikely to affect the population adverse ly: mean blubber concentrations, expressed on an extractable basis, were 2. 04 (SD = 1.1) ppm for PCBs and 2.76 (SD = 1.66) ppm for tDDT. The mean blub ber retinol concentration for the overall population was 59.66 (SD = 45.26) mu g g(-1). Taking into account the high contribution of blubber to body m ass, blubber constitutes a significant body site for retinoid deposition in harbour porpoises. Retinol concentrations did not differ significantly bet ween geographical regions or sexes, but they did correlate significantly (p < 0.001) with age. Body condition, measured by determining the lipid conte nt of the blubber, did not have a significant effect on retinol levels but the individuals examined were considered to be in an overall good nutritive condition. It is concluded that measurement of retinol concentrations in b lubber samples is feasible and has a potential for use as a biomarker of or ganochlorine exposure in cetaceans. However, in order to do so, biological information, particularly age, is critical for the correct assessment of ph ysiological impact.