# Effect of Stockholm Convention Listing on Temporal Trends of Halogenated Flame Retardants in Herring Gull Eggs in Canada (2008–2023)

## TL;DR

This study examines how regulations under the Stockholm Convention have affected levels of flame retardants in herring gull eggs in Canada from 2008 to 2023.

## Contribution

The study provides new insights into the effectiveness of international regulations on flame retardants by analyzing long-term trends in herring gull eggs.

## Key findings

- Most colonies showed no significant changes in HFR concentrations over time.
- BDE-209 concentrations increased at one colony, while others showed declines in some comparisons.
- Regulations have had mixed or equivocal effects on reducing HFR exposure in gulls.

## Abstract

Halogenated flame retardants (HFRs) are chemical additives used in many household and commercial products. Due to their persistence, long-range transport, bioaccumulative potential, and toxicity, several HFRs were listed for elimination or restrictions under the international Stockholm Convention on Persistent Organic Pollutants (SC-POPs). To understand how levels of HFRs in the environment have changed since being listed under the SC-POPs, herring gull (Larus argentatus) eggs were collected from 17 colonies across Canada (Laurentian Great Lakes, Niagara and St. Lawrence rivers, and Atlantic and Arctic regions) from 2008–2023. Eggs were analyzed for SC-POPs-listed HFRs; total-α-hexabromocyclododecane (HBCDD), Σpolybrominated diphenyl ethers (PBDEs; sum concentration of 11 tri- to hepta-BDE congeners), BDE-209, and ΣDechlorane Plus (DP; sum concentration of syn- and anti-isomers). Overall, no significant temporal changes in concentrations of the four target classes of HFRs were found for most comparisons across colonies (75%, 51/68). Significant declines were found for 13% of class-colony comparisons while BDE-209 concentrations increased significantly at one colony. Evidence of a significant influence of the SC-POPs on concentrations was equivocal, with 6% of trends declining with the year of nomination, year of listing, or before the year of nomination, and 4% of trends showing increases. Despite more than a decade of regulation for some of these compounds, herring gulls continue to be exposed to HFRs, presumably from sources such as stockpiles, discarded products, or re-release from environmental reservoirs. Continued multi-site monitoring of HFRs is required to fully assess the effectiveness of regulations that may take several decades to show consistent evidence of reduced exposure in gulls.

The online version contains supplementary material available at 10.1007/s00244-025-01173-2.