Effects of global treaties on commercial chemicals widely used as additives: a meta-analysis of historical measurements of polybrominated diphenyl ethers

Background

Commercial organic additives, many of which possess persistent, bioaccumulative, and toxic (PBT) features, are widely used in various products. Although some PBT chemicals have been restricted, the risks associated with long-term exposure remain. Polybrominated diphenyl ethers (PBDEs) are flame retardants in electronics, textiles, and many everyday products. They are a typical class of ubiquitous additive chemicals with PBT characteristics. PBDEs include three commercial formulations: penta-BDE, octa-BDE, and deca-BDE. Penta-BDE and octa-BDE were banned in most countries in the early 2000s and listed under the Stockholm Convention in 2009 with recycling exemptions. Deca-BDE was banned later, with the USA starting to phase it out in 2009, and was added to the Convention in 2017 only with exemption for inclusion in vehicle parts until 2036. We conducted a meta-analysis and systematic regression analysis to explore the impact of global policies and treaties on both internal (human) and external (environmental) exposure to PBDEs.

Methods

On Jan 4, 2023, we conducted a search of electronic databases including Web of Science, Scopus, Embase, and PubMed, along with grey literature. The search results were updated on March 21, 2025. The inclusion criteria focused on studies reporting PBDE concentrations in indoor dust (a major source of external exposure) and in the human body (internal exposure). We collated concentration data of major PBDE congeners, which are present in different formulations of flame retardants used in different products, including BDE-47, BDE-99, BDE-153, BDE-183, and BDE-209. We used a breakpoint regression model to analyse the temporal trends of PBDEs and compared these trends with the timeline of national and regional policies.

Findings

We identified 9782 studies, of which 343 were included, covering data from 94 countries worldwide. Marked differences were observed in PBDE internal and external exposure across countries. Using the EU, China, and the USA as examples, we summarised the general temporal patterns of large-scale indoor emissions (which dominate exposures of the general population) of different PBDE congeners and their effects on human exposure, correlating with treaty, production, and usage schedules. The results indicate that PBDE emissions in indoor environments have decreased following policy interventions, but reductions in human PBDE levels have been delayed and slow. Using breakpoint regression modelling, we identified a significant turning point in the concentrations of low-brominated PBDEs (BDE-47: 1996 [95% CI 1991–2001], p<0·0001; and BDE-99: 1997 [1992–2003], p<0·0001) in human milk in the EU. Significant decreases were observed in both China (BDE-47, p=0·0008; BDE-99, p=0·011) and the USA (BDE-47, p=0·0023; BDE-99, p=0·041). However, no decreasing trend over time was evident for BDE-153, nor for the higher-brominated BDE-183 (except in the EU: p=0·010) and BDE-209. In adult serum, PBDE concentrations showed minimal decreases, with only BDE-183 showing a significant decline in the EU (p=0·0099).

Interpretation

Long-term emissions from treated products with large stocks of these chemicals after bans, along with the bioaccumulation of PBDEs (especially BDE-153), have significantly delayed the effectiveness of treaties in eliminating human exposure and health risks. Moreover, regionally varied policy enforcement and consumption patterns have further reduced effectiveness of these treaties on a global scale. The chemical diversity of different PBDE congeners also affects the effectiveness of the bans. Currently, there is a paucity of systematic longitudinal studies to evaluate the effectiveness of monitoring at both global and national levels. This study highlights the need for more cautious and stringent chemical regulations and a unified global monitoring and management framework in the future, to better regulate commercial additives.