A tiered framework provides a structured approach to assess and manage risk and underpins much of the legislation concerning chemicals and environmental management. Management decisions regarding appropriate controls can have high cost implications to the regulated community. The risk framework provides an evidence-based approach to reduce uncertainty in decision making. Traditional assessment is heavily dependent on laboratory-generated toxicity test data and estimations of exposure and effect. Despite many well documented demonstrations of in situ methodologies, they are rarely used by regulators to help improve assessment or to validate risk. Emerging legislation puts greater emphasis on environmental outcomes and represents a significant shift from the reliance on chemical measures alone toward biological responses that improve assessment and demonstrate ecological benefit. Diagnostic methods, that could include in situ-based measures, will help assess and manage environments failing to achieve good status and it is likely that a weight of evidence approach will be needed to help inform management decisions. The potential application of such measures in the risk framework is reviewed in the context of current and emerging legislation concerning chemicals. Effect measures on the basis of in situ methods provide an alternative line of evidence and can help reduce uncertainty in decision making. Criteria are presented to help select appropriate methods in a multiple-line, weight of evidence approach.

This paper outlines the background, objectives, methodology, findings, outputs and recommendations from the Direct Toxicity Assessment (DTA) Demonstration Programme. This was a trial of a suite of bioassay methods and a seven-step protocol designed to deliver water quality improvements in catchments with well-defined water quality problems, where ecotoxicity from effluents was a contributing factor. The trial was run as a collaborative venture between the environmental regulators and water and manufacturing industries in the UK and was conducted at three project sites: -a reach of the river Aire near the city of Bradford in Yorkshire; -a reach of the River Esk near the town of Langholm on the border between Scotland and England; and -the lower Tees estuary on the north-east coast of England. The outcomes of each project are summarised in this paper. The learning points delivered by the programme were used to make recommendations to the regulators on how best to use bioassays for the assessment and control of complex effluents in the UK. Guidance was provided on how to carry out the bioassays and on how to use the data generated for regulatory decision-making. The programme also demonstrated how the regulators and the regulated can successfully work together to tackle environmental issues and deliver effective and workable solutions.

Whole sample toxicity assessment can help identify, diagnose and control impacts in the environment arising from the release of hazardous chemicals in complex mixtures. This role for direct toxicity assessment is considered against a background of increased international activity in the regulation of chemicals and reported improvements in the quality of surface waters in England and Wales. International legislation is largely focussed on the regulatory control of chemicals as individual substances although the majority of substances released to the environment enter in complex mixtures either as point source discharges or diffuse inputs. Whole sample measures of biological effect support the traditional substance by substance approach and provide a diagnostic capability to direct investigation into the likely chemicals or groups of chemicals of concern. Reported improvements in surface water quality in England and Wales are considered in the context of current impacts associated with hazardous substances.

The key findings to emerge from the successful Direct Toxicity Assessment Demonstration Programme are reviewed. At present, whole sample toxicity tests can identify and help control releases of complex mixtures that are likely to cause short-term toxic effects. Protection of aquatic organisms from the many hazardous chemicals that enter the environment, usually as complex mixtures, will require the introduction of new and improved techniques that are affordable and provide rapid turnaround of information. A number of bioassays were rigorously tested during the DTA programme. Further developments are suggested and other methods, including biosensors, biomarkers, and biological survey are briefly reviewed.

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