Environmental risk assessment and monitoring of chlorinated seawater discharges on offshore oil and gas fields

Summary

This study examines potential water-column contamination on Norwegian offshore oil and gas fields by disinfection by-products (DBPs) from discharges of chlorinated seawater, an issue of growing regulatory concern. Despite decades of research on DBPs, major knowledge gaps remain. Though being globally small relative to natural fluxes, anthropogenic DBP inputs may still represent an ecotoxicological risk locally. Therefore, targeted monitoring and research on possible effects in marine biota is needed. Our study proposes a prioritised target set of 12 brominated DBPs; including bromoform, dibromoacetonitrile, dibromoacetic acid and 2,4,6-tribromophenol as priority 1, and a further eight compounds that give wider coverage of trihalomethanes, haloacetonitriles, haloacetic acids and bromophenols as priority 2. However, most of these DBPs have limited marine ecotoxicity data. Future research should therefore test realistic DBP mixtures on sentinel species such as blue mussels and fish early life stages, focussing both on exposure, uptake, tissue burdens and various DBP-relevant effects. We consider the proposed DBP set to be a realistic, analytically manageable first-line suite for exposure- and effectoriented monitoring and PEC/PNEC risk valuations, possibly within the existing offshore water column monitoring program.