Ecotoxicity of oilfield production chemicals and their mitigation by activated carbon adsorption and UV photolysis.

Produced water (PW) represents the largest wastewater stream in offshore oil and gas production, often containing chemical additives that cause significant ecological risks upon discharge. This study evaluated the acute and chronic toxicity of seven PW additives at operational dosages using Artemia sp. (acute) and embryos of the sea urchins Echinometra lucunter and Arbacia lixula (chronic). Furthermore, the effectiveness of activated carbon (AC) adsorption and UV photolysis in mitigating toxicity was investigated. The biocide (2,2-dibromo-3-nitrilopropionamide) was identified as the most hazardous additive, with an LC50 of 60.22 mg/L for Artemia sp. and IC15 values below 3 mg/L for sea urchins. Although the individual components were non-toxic, their mixture induced acute toxicity in Artemia sp., suggesting complex interactions. For A. lixula, mixture toxicity showed antagonistic effects with toxic additives but synergistic interactions when all seven substances were combined. Mitigation assays demonstrated that AC adsorption significantly reduced toxicity, achieving 98% removal efficiency for the biocide and 100% for the demulsifier. UV photolysis (19.6-172.8 kJ/m2) eliminated the biocide's acute toxicity and reduced its chronic toxicity by up to 98.2%, though its effectiveness varied among additives. Both treatment approaches are technically viable for offshore platforms due to their operational simplicity, compact footprints, and modular compatibility, with no secondary waste generation. These findings highlight the ecological risks posed by specific oilfield additives and confirm that AC adsorption and UV-based processes are effective strategies for mitigating toxicity prior to offshore discharge.