DTA downstream

In September last year the Direct Toxicity Assessment (DTA) Steering Group presented the recommendations from its three-year demonstration programme to the regulators, identifying "how DTA could be used to help drive environmental improvements in a cost-effective and practical manner". Kevin Long, Brixham Environmental Laboratory, on what it all means.

Currently, many effluent discharges are monitored and controlled based upon their chemical and physical parameters - used as surrogates in the prediction of their toxicity to the aquatic environment. These controls have enabled considerable improvements in water quality.

Further progress is required, however. Environmental regulators in Europe are considering the application of Direct Toxicity Assessment (DTA), originally developed in the US, to determine the likely effects of an effluent on organisms present in the receiving water, and the EU Water Framework Directive 2000/60/EC will provide a legislative tool to drive improved ecological quality.

Major consultation
In 1996 the UK Environment Agency (EA) undertook a major consultation exercise prior to its proposed introduction of DTA as a new method of controlling effluent discharges. This culminated in a workshop in Torquay in October 1996, organised jointly by the EA and Brixham Environmental Laboratory. The workshop, and associated consultation, resulted in two developments of the EA proposals: firstly, to include DTA as one of a range of diagnostic tools to identify areas where effluent improvement plans were needed, rather than applying DTA as a widespread compliance measure; and secondly to implement the scheme via a demonstration programme, jointly managed and funded by the regulatory and regulated communities, which would enable the draft protocol to be tested and optimised. This programme began in January 1997 and has now concluded.

In September 2000 the DTA Steering Group presented the recommendations from the programme to the regulators, identifying how DTA could be used to help drive environmental improvements in a cost-effective and practical manner. The methods manuals produced by the EA have already been adopted by the Irish EPA, and a DTA approach is now being used to monitor many aqueous effluents.

The principle learning points from the development of a DTA strategy were that:

  • DTA is time consuming and expensive, and thus needs to be used selectively.
  • DTA can demonstrate 'harmlessness' in IPC/IPPC applications.
  • DTA offers a cost-effective way of prioritising improvement plans to meet environmental objectives.
  • Current 'rapid' tests do not correlate well with conventional tests and thus have limited value.
  • Conventional tests can be miniaturised and are robust.

    Demonstration Programme output consisted of: a series of detailed technical reports of the work carried out on the three test sites; a DTA Best Practice Manual detailing the major learning points; and a report from the Steering Committee, addressed to the regulatory agencies, making recommendations as to how DTA should be used in the future.

    These documents were announced in September 2000, and it is expected that the EA and SEPA, in consultation with the DETR, will shortly produce proposals for the introduction of a DTA approach based on the recommendations.

    Several recommendations relate to the prioritisation of DTA application. The Steering Group confirms that the approach should be used "as a 'trigger' for action by industry to investigate and reduce ecotoxicity problems rather than applied as a pass/fail licence condition", and that operators will be encouraged in the voluntary use of a DTA approach, taking into account the regulator's judgment of their competence and performance. Furthermore, it is recommended that the decision to apply DTA should be based upon a consideration of cost-effectiveness in relation to the current chemical specific approach, and a methodology has been developed to provide guidance on this assessment. Once implemented, the procedure for the toxicity assessment should follow the guidance procedure developed to cover the generation and use of ecotoxicity data.

    Licence review
    Other recommendations cover:

  • The initial introduction of DTA, where the suggestion is that priority should be given to catchments with well defined water quality problems associated with point-source discharges causing impairment of the survival of aquatic organisms.
  • Reviewing all existing 'toxicity-based' conditions in licences to ensure consistency and efficiency savings in cases where such conditions are no longer required.
  • Requiring operators of all IPC/IPPC licensed processes with direct releases to receiving waters to provide data on the effects of their releases on the survival, growth and development of aquatic organisms, or to demonstrate why this is unnecessary, as a part of their licence review or application. This will make more ecologically relevant data available for environmental impact assessment.

    The DTA demonstration programme has been seen as a success in terms of the close collaboration between the regulators and the regulated, raising the profile of the UK DTA approach in Europe where similar applications of whole effluent assessment are being considered. This collaborative approach may be used as a model for the future development of DTA, possibly in considering broader applications. One suggestion is that DTA may be used in the assessment of the influence of effluent discharges on more subtle ecotoxicological endpoints such as the reproductive development of organisms exposed to complex mixtures of substances.

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