Technetium-99: Sources, transport, bioaccumulation, and trophic transfer in marine ecosystem

Technetium-99 (⁹⁹Tc) contamination in marine environment is garnering increasing global concern, primarily due to its increasing releases from nuclear-contaminated water and spent fuel reprocessing activities. ⁹⁹Tc with a long half-life predominantly exists as TcO₄⁻ in marine environment, having high solubility and strong mobility in seawater, posing a serious risk to marine ecosystems. Although pollution status and accumulation behaviors of ⁹⁹Tc in marine organisms have been reported, they have great limitations regarding the specific accumulation and transfer mechanisms within marine food chain. Herein, we critically synthesized the sources, geochemical distribution, transport behaviors, and biological transfer of ⁹⁹Tc in marine environments, with emphasis on the microbially mediated redox processes that regulate the fate and bioavailability of ⁹⁹Tc. We showed that the Irish Sea was among the ocean regions most impacted by ⁹⁹Tc contamination and its concentration was up to 550 mBq L⁻¹ . Additionally, we reviewed the research achievements on ⁹⁹Tc distribution in marine ecosystems, focusing on its bioaccumulation mechanisms in marine organisms like brown algae, which hold the highest distribution concentration of ⁹⁹Tc (19,700 Bq kg⁻¹). Notably, trophic transfer efficiency (TTE) and food chain transfer factor (FCTF) values were defined to evaluate the food-web transfer behaviors of ⁹⁹Tc across different marine species. The highest TTE value (31.65 %) was observed in the transfer from crustaceans to mollusks, while the highest FCTF value (49.86 %) was found in the transfer from brown algae to crustaceans. Future perspectives were also proposed for advancing the deep understanding of ⁹⁹Tc contamination in marine ecosystems.