September 24, 2026 by Richard Maunder
I was pleased to see a paper that I co-authored, A Scientifically Robust and Regulatory Critical Fish (Pimephales promelas) Full Life Cycle Study with Ibuprofen: Fulfilling Chronic Toxicity Data Gaps to Support Informed Environmental Risk Assessment, was recently published in Environmental Toxicology and Chemistry. This study has particular significance for me as I conducted the GLP study it is based on while working as a Study Director at Scymaris Ltd. Ibuprofen is one of the most widely used and extensively studied pharmaceuticals in the aquatic environment, yet uncertainties remained about its potential long-term effects on fish and the suitability of the available evidence for regulatory environmental risk assessment.
The study followed fathead minnow (Pimephales promelas) exposed to ibuprofen at concentrations ranging from 0.01 to 1.0 mg L-1 throughout a comprehensive full life-cycle study. Beginning at egg fertilisation the fish grew through early life and juvenile stages before development into adults, where they reproduced to produce the subsequent generation. The ‘egg-to-egg’ exposure across two successive generations ensures that all life stages are exposed, providing the opportunity for effects occurring at any stage of the life cycle to be detected. At each key stage, we assessed a broad range of biologically and regulatory relevant endpoints to determine any effects of exposure on fish health, growth or reproduction. From the outset, the aim was to generate a scientifically robust dataset capable of addressing important gaps and uncertainties in the existing evidence base, rather than simply adding another study to the extensive literature on ibuprofen.
Overall, the study found no biologically meaningful adverse effects at concentrations up to 1.0 mg L-1. Although statistically significant effects were initially identified for survival of the first generation and hatching in the second generation, closer evaluation of the underlying data demonstrated the importance of considering biological relevance alongside statistical significance when interpreting complex chronic toxicity studies. It has been rewarding to revisit a study that the team at Scymaris and I worked so hard on, and to see the data contribute to the wider assessment of evidence for ibuprofen toxicity in fish, and ultimately to a publication that can support informed environmental risk assessment.
Designing and interpreting fish studies such as this requires careful consideration of study aims, experimental design, exposure concentrations, endpoint selection, statistical analysis and the biological relevance of observed effects. If you are planning or conducting fish toxicity or endocrine studies and would like support with study design, study monitoring or interpretation of the resulting data, or any other support with the environmental risk assessment of pharmaceuticals, please get in touch with the team at wca.