Aquatic Toxicity Bioassays and Gesamp-Based Hazard Profiling of Oil Field Chemical Additives: Acute, Chronic, and Sub-Lethal Effects on Freshwater and Marine Organisms

Abstract

Oilfield chemical additives (OFCAs) played a critical role in petroleum exploration and production, particularly in corrosion control, demulsification, scale control, and microbial management. Although they were important for industrial processes, their discharge into water bodies via runoff and accidental losses posed ecological and human health risks. Traditional environmental risk analyses were heavily based on acute toxicity measures, particularly 96-hour lethal concentration (LC)50 values, which did not sufficiently reflect the ecological significance of chronic and low-level exposures. The use of acute toxicity categorizations as indicators of sublethal biological impairment and overall environmental risk was therefore not fully addressed. This paper presented a critical synthesis of existing bioassay data to assess the relationship between acute toxicity categories and chronic and sublethal biological outcomes of OFCAs, with the objective of improving hazard characterization beyond LC50-centric regulatory frameworks. A systematic review of published aquatic toxicity studies from 1992 to 2018 was conducted using the Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) hazard profiling framework. Bioassay data were compiled for major classes of OFCAs using Oreochromis niloticus, a freshwater teleost model, and Palaemonetes africanus, a crustacean sentinel species. Key toxicity endpoints were compared and analyzed, including LC50, No-Observed Effect Concentration (NOEC), Lowest Observed Effect Concentration (LOEC), and various sublethal endpoints such as growth, reproduction, and developmental impairment. The GESAMP hazard classifications (A1, D3) were applied. The synthesis indicated that marine and crustacean species were consistently more sensitive than freshwater fish. High acute hazards were commonly associated with biocides and demulsifiers, while chronic toxicity thresholds were often one or two orders of magnitude lower than lethal concentrations. Extensive sublethal effects, including growth inhibition, reproductive impairment, and developmental abnormalities, were observed. The substantial difference between acute lethality and chronic toxicity classifications indicated a major underestimation of long-term ecological risk when LC50 values were used alone. These findings demonstrated that environmental risks associated with OFCAs were predominantly chronic and sublethal rather than exclusively acute and lethal. This supported the adoption of precautionary, species-sensitive, and multi-endpoint hazard assessment frameworks that incorporated chronic toxicity measures into regulatory decision-making processes. Moving beyond LC50-based approaches enhanced ecological risk characterization and strengthened environmental protection strategies in oil-producing regions, particularly in vulnerable aquatic ecosystems such as those in the Niger Delta.