No one acts alone–unravelling the compositional influences of organic compounds in offshore produced water on zebrafish embryotoxicity

Offshore produced water (PW) is one of the largest and most chemically complex effluents of waste directly and intentionally discharged into the marine environment. Although it is well known that PW can be severely toxic to marine organisms, the mechanisms of toxicity remain poorly understood, contributed by the lack of comprehensive chemical characterization of the PW. In this study, we applied elements of effects-directed analysis with the aim to identify organic chemical drivers of toxicity in PW towards fish early life stages. A solvent extract of a PW was fractioned based on compound functionality and chemically characterized by a concert of techniques including high-resolution gas and liquid chromatography coupled with high-resolution mass spectrometry. The effect of PW and fractions on survival, development, and cardiotoxicity in zebrafish (Danio rerio) embryos was tested. It is evident that embryotoxicity of PW organics cannot be attributed to one compound class. In this study, the fractions primarily containing production chemicals were of low toxicity, whereas both fractions containing petroleum hydrocarbons, and fractions containing oxidation products of these, contributed to toxicity.