Applications of biological tools or biomarkers in aquatic biota: A case study of the Tamar estuary, South West England

•Biological tools used in the ecologically important Tamar estuary critically reviewed.•Studies suggest an increase in various detrimental responses in the upper estuary.•Future work using biological tools will benefit from an ecotoxicogenomic approach.•Integration of multiple tools essential for holistic environmental assessment. Biological systems are the ultimate recipients of pollutant-induced damage. Consequently, our traditional reliance on analytical tools is not enough to assess ecosystem health. Biological responses or biomarkers are therefore also considered to be important tools for environmental hazard and risk assessments. Due to historical mining, other anthropogenic activities, and its conservational importance (e.g. NATURA sites, SACs), the Tamar estuary in South West England is an ideal environment in which to examine applications of such biological tools. This review presents a thorough and critical evaluation of the different biological tools used in the Tamar estuary thus far, while also discussing future perspectives for biomarker studies from a global perspective. In particular, we focus on the challenges which hinder applications of biological tools from being more readily incorporated into regulatory frameworks, with the aim of enabling both policymakers and primary stakeholders to maximise the environmental relevance and regulatory usefulness of such tools.