The oil and gas industries contaminate the environment through the generation of waste products known as produced water (PW). Globally, large volumes of treated PW, originating from offshore oil and gas installations are discharged into the sea, potentially affecting the marine environment. The substances most commonly present in PW are corrosion (CIs) and scale (SIs) inhibitors. These are chemical compounds comprised of quaternary ammonium salts (QUATs), imidazoline, phosphate esters (PEs) and other chemical substances, and are commonly used in the oil and gas industry to prevent corrosion problems arising during both exploration and production operations (E&P).
The present study evaluates the effects of QUATs, imidazoline, PEs and all components of PW on the marine environment, using a range of biomarker indices. The Comet assay was used to investigate DNA damage, expressed as% tail DNA, in individual haemocytes and gill cells derived from marine mussels Mytilus edulis that had been exposed to environmental concentrations of QUATs, imidazoline, PEs and PW. DNA damage is often an indirect effect of the oxidative radicals generated by a chemical or its metabolites. The oxidative stress assay employed was superoxide dismutase (SOD), and the associated lipid peroxidation was determined using the thiobarbituric acid reactive substances (TBARS) assay. Lysosomal membrane instability, a measure of cytotoxicity, was assessed using the neutral red retention (NRR) assay found in haemocytes cells. Bioaccumulation of the QUATs, imidazoline, PEs and PW were also determined. The results of the study show a significant increase in DNA damage in the haemocytes and gills taken from adult mussels exposed to QUATs, imidazoline, PEs and PW within a concentration range of 0.001, 0.01, 0.1, 0.5 and 1 mg/L, when compared to control groups. Oxidative stress was measured, showing that QUATs, imidazoline, PEs and PW increased SOD activity and lipid peroxidation in a concentration-dependent manner (≥ 0.5, 0.001, 0.1 and 0.001 mg/L and 0.1, 0.1, 0.5, 0.001 mg/L, respectively). Lysosomal membrane stability was affected at concentrations of ≥ 0.1 mg/L for QUATs, imidazoline and PW. Moreover, it was affected by PEs at concentrations ≥ 0.5 mg/L. In addition, QUATs and imidazoline were found to have accumulated in mussel tissues at concentrations of ≥ 0.1 and 0.001 mg/L, respectively, but PEs were not found in tissues.
This work suggests that very low concentrations of QUATs, imidazoline, PEs and PW may be harmful to marine organisms and the biomarkers described could be further developed as tools for monitoring and regulating the disposal of PW at sea
