An evaluation of cumulative risks from offshore produced water discharges in the Bass Strait

Highlights: • Detailed chemical and toxicity characterization of produced water (PW) from 12 Australian offshore platforms performed • Cumulative risks estimated using the multiple substance potentially affected fraction (msPAF) of species • msPAFs met 95% protection goal using either PW chemistry or toxicity data as complimentary lines of evidence • Hydrocarbons, sulphide and ammonia key PW constituents of concern • Tiered framework proposed for screening and refining PW cumulative risk assessment - Abstract: Chemical analyses and toxicity testing using six marine species were used to characterize the hazard of produced waters (PW) to marine life from twelve Australian offshore platforms. Hazard data were used in conjunction with platform-specific plume discharge dilution and species sensitivity distribution modeling to estimate cumulative risks by calculating the multiple substance potentially affected fraction of species in the local marine environment. Results provided two independent lines of evidence demonstrating that cumulative risks to marine life from these discharges meet intended 95% species protection goals at the edge of the mixing zone. A limited number of PW constituents (hydrocarbons, sulphide and ammonia) appeared to dictate risk thereby informing management and providing a rationale for more targeted analyses in future monitoring studies. Based on these findings a tiered framework is proposed to foster consistent screening and potential refinement of cumulative risk evaluations for PW discharges.