Comparative Toxicity Assessment of Novel Brominated Flame-Retardant Tris (2,3-dibromopropyl) Isocyanurate in Standard and Native Earthworm Species.

Tris(2,3-dibromopropyl) isocyanurate (TDBP) is a novel brominated flame retardant. Its widespread application leads to environmental persistence and bioaccumulation. Although its toxic effects on aquatic organisms are documented, effects on terrestrial fauna, especially soil invertebrates, are not well studied. This study investigated the toxicological effects of TDBP on two earthworm species: Eisenia fetida (an Organisation for Economic Co-operation and Development-recommended model) and Perionyx ceylanensis (a native Indian species). Conventional endpoints (growth, survival, reproduction) and biochemical biomarkers were assessed, along with species sensitivity distributions, to compare interspecies sensitivity. Tris(2,3-dibromopropyl) isocyanurate exposure did not affect earthworm survival at 1,000 mg/kg for 28 days in both species. Similarly, long-term exposure to environmentally relevant concentrations (0.01-10 mg/kg) showed no significant effects on growth or reproduction. Exposure to TDBP increased reactive oxygen species levels and the activities of superoxide dismutase and glutathione-S-transferase, and lipid peroxidation at lower concentrations (0.01-0.1 mg/kg) in P. ceylanensis. On the other hand, threshold-dependent responses were noticed in E. fetida, with increased carboxylesterase activity only at 10 mg/kg, suggesting different cellular defence and tolerance mechanisms. Moreover, the integrated biomarker response version 2 (IBRv2) analysis also revealed significant physiological stress in both species, with values ranging from 3.69 to 11.94, despite the absence of organism-level effects. Species sensitivity distributions analysis has shown that P. ceylanensis is more sensitive than E. fetida towards TDBP exposure, with hazard quotient (HQ) values > 1 suggesting potential ecological risk to soil invertebrates. Collectively, this study demonstrates that TDBP is biologically active at environmentally relevant concentrations, and native earthworm species are 10-fold more sensitive than the standard test organism, E. fetida. These findings underscore the importance of a multi-species risk assessment approach for emerging contaminants in soil ecosystems.