Lessons learned from model species: Molecular markers for anthropogenic pollutant toxicity in cetaceans.

The planet is currently facing a triple crisis driven by climate change, biodiversity loss, and pollution. While the effects of environmental contaminants on reproduction, neurological function, and immune processes are well established in model species, far less is known about their impacts on marine sentinels such as cetaceans. Although contaminant burdens can be quantified, there is a lack of validated biomarkers that reliably capture molecular and cellular effects, limiting robust impact assessment and conservation strategies. Cetaceans exhibit unique physiological and metabolic adaptations, including specialised lipid dynamics and life-history traits, complicating direct extrapolation from model organisms. Here, we review current knowledge of biomarkers associated with three major contaminant classes: persistent organic pollutants (POPs), heavy metals, and microplastics. Candidate biomarkers such as cytochrome P4501A1, acetylcholinesterase, and metallothioneins are well characterised in experimental systems but show inconsistent responses in cetaceans, influenced by ecological, physiological, and methodological factors. Emerging evidence indicates that microplastics may drive gut inflammation, microbiome disruption, and systemic stress responses, although validated biomarkers remain scarce. Overall, we highlight the limitations of single-marker approaches and the need for integrative frameworks capturing complex, multi-stressor responses across biological scales. Future efforts should prioritise robust, early-warning biomarkers that account for species-specific physiology, trophic ecology, and cumulative exposure. Progress will require cross-disciplinary collaboration, integration of multi-omics tools, and improved standardisation of methods. Strengthening biomarker frameworks in cetaceans is essential for advancing marine conservation and understanding shared risks to ocean and human health.