Long-Term Adverse Effects of Chlorinated Saline Primary Sewage Effluent and Halo-Nitrophenolic Disinfection Byproducts on a Marine Polychaete

The practice of flushing toilets with seawater in coastal cities can result in bromide- and iodide-rich saline sewage effluent, which generates brominated and iodinated aromatic disinfection byproducts (DBPs) with relatively high developmental toxicity during chlorine disinfection. While the acute developmental effects of such DBPs are increasingly documented, their long-term impacts remain understudied. In this study, we investigated the developmental effects of saline primary sewage effluent on the marine polychaete Platynereis dumerilii (located at the bottom of the marine food chain) during a 25-day sub-chronic exposure. Although both non-chlorinated and chlorinated saline sewage effluents exhibited dose-dependent embryotoxic and teratogenic effects across effluent percentages (0%–33%), the chlorinated effluent induced such malformation effects at lower concentrations (1.3%–3.7%) than the non-chlorinated counterparts (4.8%–9.9%), which could be attributed to the presence of halogenated DBPs in the chlorinated sewage effluent. We then focused on 2,6-dihalo-4-nitrophenols, a group of aromatic DBPs that have been reported to exhibit acute developmental toxicity and persist in receiving seawater. Significant reductions in survival (p < 0.10) were observed for the sub-chronic and chronic exposure at environmentally relevant concentrations (3.4–340 nmol/L; equivalent to 1–100 μg/L as 2,6-dibromo-4-nitrophenol (DBNP)). Especially, the one-year chronic exposure to DBNP revealed significant concentration-dependent responses. Both survival rate and average body length of the polychaete were significantly decreased, and the overall maturation was delayed. Compared to seawater control with a natural balance gender, female-biased sex ratios (1.4–2.2) were observed in the worms exposed to 3.4–340 nmol/L of DBNP. This bias might result from the higher surface-area-to-volume ratio of male polychaete and the stronger binding affinity of DBNP toward the androgen receptor. This study is the first of its type that systematically recorded the long-term adverse effects of chlorinated saline sewage effluents and halogenated aromatic DBPs─at environmentally relevant concentrations─on the marine polychaete.