Temporal trends (1968-2019) of legacy persistent organic pollutants (POPs) in seabird eggs from the northeast Pacific: Is it finally twilight for old POPs?

Legacy persistent organic pollutants (POPs), such as organochlorine pesticides (OCs) and polychlorinated biphenyls (PCBs), are known to persist in the marine environment; however, whether concentrations of these POPs have decreased or stabilized from Canada's Pacific coast in recent years is unclear. Here, we examined temporal trends of various legacy POPs in the eggs of five seabird species; two cormorants (Nannopterum auritum and Urile pelagicus), an auklet (Cerorhinca monocerata), a murrelet (Synthliboramphus antiquus), anda storm-petrel (Hydrobates leucorhous), sampled 1968 to 2019 from 23 colonies along the Pacific coast of British Columbia, Canada. The contaminant profile in the eggs of all species and sampling years was dominated by sigma PCBs, followed by sigma DDT (mostly p,p'-DDE), sigma HCH (beta-HCH), sigma CHLOR (oxychlordane), and sigma CBz (HCB). sigma OC and sigma PCB concentrations were generally higher in double-crested cormorant eggs than in the other four species. The majority of legacy POPs are either significantly declining (e.g. p,p'-DDE, HCB, HE, oxychlordane, sigma PCBs) or showing no directional change over time (sigma Mirex) in the eggs of our monitoring species. Contaminants such as alpha-HCH, cis-and trans-chlordane, p,p'-DDT, dieldrin, and octachlorostyrene also showed evidence of downward trends, largely influenced by non-detect values during more recent sampling periods. Increasing trends were observed for beta-HCH in the eggs of some species; however, mean concentrations eventually returned to early 2000 levels by the end of the study period. Although bulk delta 15N and delta 13C egg values varied interannually, compound-specific amino acid analyses suggested no major changes in trophic position or baseline food web signature. Temporal trends observed here were comparable to those found in other seabird species and pelagic food webs. As most legacy POPs in our data set were at very low levels in recent years, we support the general consensus that it is indeed the twilight years for old POPs, and we attribute these declines largely to voluntary regulations and international restrictions on the production and use of these compounds, and thus their release into the marine environment.

Automated summary

This study investigated the temporal trends of legacy persistent organic pollutants (POPs) in the eggs of five seabird species along Canada's Pacific coast. The results showed that most legacy POPs have either significantly declined or stabilized in recent years, attributed to voluntary regulations and international restrictions on their production and use.