Development and application of bioaccumulation models to assess persistent organic pollutant temporal trends in...

Individual- and population-based models were developed to simulate the bioaccumulation of persistent organic pollutants (POPs) over the lifetime of ringed seals (Phoca hispida) and account for the effects of age, growth, body condition and sex (including gestation, birth and lactation). Lactational transfer was described using a milk to blubber partition coefficient, which was shown to be a function of Kow (KMB=1/(1.676+1.293.10(-7).Kow) r2=0.60, n=32, p<0.001). Simulations showed that nursing mothers could transfer between 5% and 40% of their burden of low and high KMB contaminants, respectively, to their milk over 40 days of lactation. The models were calibrated using a POPs dataset for 50 seals (29 males, 21 females) from Arviat, Nunavut. They were initially calibrated for a group of eight highly recalcitrant PCB congeners (e.g. PCBs 153, 180) assuming a baseline elimination rate (ke) of about 0.03 year-1. For congeners more prone to biotransformation a satisfactory fit could only be reached by iteratively increasing ke to values ranging from 0.05 to 2.5 year-1 for PCBs 187 and 18, respectively; thus the models became a means for estimating ke. Estimated ke values were correlated with a calculated index of susceptibility to biotransformation (ke=0.0284/Rrelr2=0.98, n=20, p<0.001). This relationship was used to estimate ke values used in simulations to hind-cast temporal trends of SigmaPCB, SigmaDDT, SigmaCHL, alphaHCH, betaHCH in ringed seal populations and to predict potential future trends. Results of these simulations showed good agreement with measured concentrations in seals from two locations in the Canadian Arctic (Holman Island, NWT and Arctic Bay, Nunavut) collected between 1972 and 2001. The models show that the combined effects of rapid juvenile growth, a fast rate of population turnover and substantial capacity to eliminate many POPs result in fairly rapid responses to changes in contaminant loading, thus making ringed seals an effective choice for monitoring spatial and temporal trends of POPs in the Arctic marine ecosystem.