Clarifying relationships between persistent organic pollutant concentrations and age in wildlife biomonitoring: individuals, cross‐sections, and the roles of lifespan and sex

Abstract

Relationships between persistent organic pollutant (POP) levels and age in wildlife biomonitoring are often interpreted as changes in contaminant burden as organisms age. However, cross-sectional body burden-age trends (CBATs) obtained from biomonitoring studies, which sample individuals of different ages at the same time, should not be confused with longitudinal body burden-age trends (LBATs) obtained by sampling the same individuals repeatedly through time. To clarify how CBATs and LBATs for wildlife species deviate from each other, and describe any impact of lifespan and sex, we used mechanistic bioaccumulation models to estimate historic longitudinal exposures of polar cod, ringed seals, beluga whales, and bowhead whales to polychlorinated biphenyl congener 153. Cross-sectional body burden-age trends were then produced by sampling resultant LBATs of successive birth cohorts at specific time points. As found previously for humans, the year of sampling relative to the year of peak environmental contamination was a critical parameter in determining male CBAT shapes. However, a similar cohort effect was not apparent for reproductive females because efficient POP loss through lactation prevented their lipids from retaining a memory of past exposure levels. Thus, lactation loss was not only responsible for the large differences between the CBATs of males and females of the same species, but also the lack of female CBAT variability through time. Cross-sectional body burden-age trend shapes varied little between species by lifespan, as long as equivalent age scales were used. However, lifespan relative to the timescale of environmental contaminant level changes did determine the extent to which CBATs resembled LBATs for males. We suggest that accounting for birth cohort and sex effects is essential when interpreting age trends in POP biomonitoring studies of long-lived species.

Wandering Albatrosses Document Latitudinal Variations in the Transfer of Persistent Organic Pollutants and Mercury to Southern Ocean Predators

“…79,82 It must be noted, however, that the present work is a cross-sectional study, which does not necessarily reveal information on the contamination of individuals as they age. 91 However, similar contaminant concentrations have been reported in seabirds sampled repeatedly in different years. 41,70 Furthermore, POPs, Hg, and Cd did not affect mortality in the wandering albatross, 44 which excludes potential bias from differential survival of the most contaminated individuals.…”

Allee effect in polar bears: a potential consequence of polychlorinated biphenyl contamination

“…The reasons for the very high PCBs concentrations in the 10-14-year-old males and comparatively lower concentrations in older bears at that time are not known. It may be a reflection of the timing of the cross-sectional sampling of this population [37]. Thus, rather than representing a general threat to the reproductive capacity of Svalbard prime-aged males per se, PCBs may have acted against the reproductive success of a particular group of polar bears that experienced the highest doses of PCBs and subsequently carried these burdens throughout their lives.…”

ET&C Best Paper of 2014

“…Three external reviewers exceptionally praised the article written by Binnington and Wania . As mentioned by 1 reviewer, the work “sheds a new and interesting light on a phenomenon that has been reported many times in the wildlife monitoring literature.” In their article, the University of Toronto researchers aimed to improve understanding of age‐related changes in contaminant burdens.…”