Global occurrence and environmental behavior of novel brominated flame retardants in soils: Current knowledge and future perspectives

Since polybrominated diphenyl ethers (PBDEs) are on the list of regulated chemicals, novel brominated flame retardants (NBFRs) have been produced as alternatives and extensively used since the end of the 19th century. A comprehensive assessment of the environmental burden of NBFRs, which are emerging contaminants with biotoxic and carcinogenic properties, is urgently needed. Given that soil is a major sink for organic pollutants, this study systematically reviewed global data on NBFRs in soil for the period of 1990-2024 via a bibliometric analysis of 70 publications from the Web of Science Core Collection, reaching the following achievements. (1) NBFRs in soils have been reported in 17 countries or regions worldwide, ranging from not detected to 8.46 x 10(4) ng/g dw, showing an increasing trend over time, with severe contamination in Asia and Australia. (2) NBFR concentrations varied significantly across land use types: manufacturing land > electronic waste disposal areas > urban soil > farmland > forest > remote areas. (3) NBFRs with log KOA > 10 tend to settle from the air into the soil, where they may be absorbed by plant roots and bioaccumulate in the food chain. (4) Organism dietary habits and metabolism, along with the hydrophobicity and molecular weight of NBFRs, contribute to bioaccumulation differences. (5) Successive reductive debromination is the primary degradation pathway for NBFRs, and microorganisms such as the white-rot fungus P. ostreatus show potential for remediating NBFRcontaminated soil. This review clarifies the pollution status of soil NBFRs and provides a solid reference to develop management policies. Future research should focus on studying the transport mechanisms of NBFRs between soil and other media, and assessing the cumulative effects of high trophic level organisms on NBFRs.