Deep-ocean foraging northern elephant seals bioaccumulate persistent organic pollutants

Abstract

As top predators in the northeast Pacific Ocean, northern elephant seals (Mirounga angustirostris) are vulnerable to bioaccumulation of persistent organic pollutants (POPs). Our study examined a suite of POPs in blubber (inner and outer) and blood (serum) of free-ranging northern elephant seals. For adult females (N=24), we satellite tracked and sampled the same seals before and after their approximately seven month long foraging trip. For males, we sampled different adults and sub-adults before (N=14) and after (N=15) the same foraging trip. For females, we calculated blubber burdens for all compounds. The highest POP concentrations in males and females were found for ∑DDTs and ∑PCBs. In blubber and serum, males had significantly greater concentrations than females for almost all compounds. For males and females, ∑DDT and ∑PBDEs were highly correlated in blubber and serum. While ∑PCBs were highly correlated with ∑DDTs and ∑PBDEs in blubber and serum for males, ∑PCBs showed weaker correlations with both compounds in females. As females gained mass while foraging, concentrations of nearly all POPs in inner and outer blubber significantly decreased; however, the absolute burden in blubber significantly increased, indicating ingestion of contaminants while foraging. Additionally, we identified three clusters of seal foraging behavior, based on geography, diving behavior, and stable carbon and nitrogen isotopes, which corresponded with differences in ∑DDTs, ∑PBDEs, MeO-BDE 47, as well as the ratio of ∑DDTs to ∑PCBs, indicating the potential for behavior to heighten or mitigate contaminant exposure. The greatest concentrations of ∑DDTs and ∑PBDEs were observed in the cluster that foraged closer to the coast and had blood samples more enriched in (13)C. Bioaccumulation of POPs by elephant seals supports mesopelagic food webs as a sink for POPs and highlights elephant seals as a potential sentinel of contamination in deep ocean food webs.

Adipose Tissue as a Site of Toxin Accumulation

“…Highly lipid soluble POPs can disseminate through the food chain by collecting in body fat and biomagnifying, or increasing in concentration as they move from one organism to another. For example, the northern elephant seal is a “marine mammal predator” at the top of the food chain that contains massive concentrations of environmental contaminants that are primarily stored in AT (249) (99) (250) (318) (2). Measurements of bioaccumulation in fish and other aquatic organisms is often reported as the bioconcentration factor (BCF), which is defined as the extent to which a chemical concentration in an aquatic organism exceeds the chemical concentration in surrounding water (206).…”

Serum POP concentrations are highly predictive of inner blubber concentrations at two extremes of body condition in northern elephant seals

“…Serum, inner blubber, and outer blubber samples from all elephant seals had detectable concentrations of ΣDDTs, ΣPCBs, ΣCHLs, and ΣPBDEs. The concentrations of POPs used in this study for northern elephant seal serum, inner blubber, and outer blubber have been reported previously (Peterson et al 2015), although a summary of medians and ranges of POP concentrations can be found in Table 1. The specific equations to predict POP concentrations in one tissue from POPs concentrations in another tissue for all compounds are found in Table 2 and specific statistical results are found in Table 3.…”

“…We used standard procedures for chemical immobilization and collection of blubber and blood from northern elephant seals (Le Boeuf et al 2000, Robinson et al 2012, and these procedures have been described previously in Peterson et al (2015). In brief, a full-thickness blubber core was collected from the lateral pelvic area of each seal from a sterile scalpel incision with a 6 mm biopsy punch (Miltex, Inc., York, Pennsylvania, USA) and stored in aluminum foil.…”

“…Extraction, clean-up, and concentration measurement methods for blubber and serum followed protocols described in Vanden Berghe et al (2012) and Peterson et al (2015). In brief, for blubber analyses, the skin layer and hair (Schwarz et al 2015), was removed from the outer portion of the biopsy core, and the remaining blubber layer was cut into inner and outer segments of approximately equal mass.…”

“…Northern elephant seals (Mirounga angustirostris) are upper trophic level predators that bioaccumulate POPs as they forage in the northeastern Pacific Ocean (Peterson et al 2015). The life history of northern elephant seals includes two foraging migrations per year interspersed with fasting periods for breeding and molting on land, which makes them relatively accessible for study among marine mammals (Robinson et al 2012).…”