Bioaccumulative contaminants in New Hampshire Common Loon eggs indicate widespread exposure to persistent organic pollutants.

The Common Loon is a piscivorous bird whose populations have been impacted by human activities, including mortality and/or reduced productivity from lead fishing tackle, habitat loss, human disturbance, and elevated levels of mercury. In New Hampshire, the loon is listed as state threatened due to its slow recovery from historic population declines, current high rates of anthropogenic mortality, and declining productivity rates despite intensive management. The extent to which loons are exposed to persistent organic contaminants that could affect population health is not well understood. We quantified legacy contaminants (polychlorinated biphenyls [PCB], polychlorinated dibenzo-p-dioxins [PCDD], polychlorinated dibenzofurans [PCDF], organochlorine pesticides, trace elements) and contaminants of emerging concern (per- and polyfluoroalkyl substances [PFAS], brominated diphenyl ethers [BDE]) in 92 Common Loon eggs collected from 28 lakes between 1993-2021 in New Hampshire. We measured egg size and eggshell thickness to assess potential relationships with contaminant exposure. Egg burdens of 9PFAS ranged from 58.4-1,587.4 ng/g wet weight, 6BDE from 9.3-336.5 ng/g, 209PCB from 398-12,849 ng/g, PCDD/F from 5.4-55.5 pg/g toxic equivalency factor, total dichlorodiphenyltrichloroethane (DDT) from 132.8-974.0 ng/g, and total chlordane from 10.4-131.1 ng/g. Contaminant levels in 65% of eggs exceeded the lowest observed effects levels seen in other bird species for at least one contaminant class. Ordination and clustering analysis detected an inverse correlation between egg morphology and burdens of BDE, organochlorine pesticides, PCDD/F, and PCB. Further monitoring of contaminants in loon eggs is warranted to assess levels of contaminants in New Hampshire lakes, the relative contributions of spatial and temporal variation to exposure risk, and how co-exposure to multiple contaminant classes and other anthropogenic and environmental stressors could influence the health of loon populations.