Abstract
The toxicity of produced water (PW) discharges has been repeatedly demonstrated. However, the causative mechanisms of toxicity remain poorly understood. While PW composition is very complex, regular monitoring of effluent composition still only focuses on a limited set of chemical classes, most of them petrogenic compounds. Early life stages (ELS) of fish have been shown to be particularly sensitive to pollution and are expected to be vulnerable also to PW compounds. In the current study, we apply a novel functionality-based fractionation method to separate twelve discrete fractions of a PW collected at the point-of-release from a North Sea oil production facility. A battery of standard, non-standard and high-resolution chemical characterization techniques are applied to each fraction to allow the to date most comprehensive investigation of PW composition described. The toxicity of the PW and its fractions to ELS of the model fish species zebrafish (Danio rerio), as well as to Atlantic cod (Gadus morhua) is seen in light of the chemical composition of each fraction. The bulk composition of the PW in question comprised aliphatic and aromatic hydrocarbons, while phenols and organic acids also constituted a significant part of the total. A range of production chemicals were identified in separate fractions of the PW. In terms of toxicity, the produced water extract caused effects on hatching success, cardiac function and development of the embryos. No individual fraction was able to provoke the same level of effects as the total PW, but the 'hydrocarbon' fractions in combinations (oil constituents) were considered the most potent mixture. The potential for synergistic and antagonistic effects between different produced water fractions is currently being investigated.