Development of guidance for assessing the impact of mixtures of chemicals in the aquatic environment

mixtures minibiodiversity miniMixtures and co-exposure /
Biodiversity and ecosystems

Environmental Sciences Manager Malyka Galay Burgos

Administrative Assistant Christine Yannakas

The findings of the task force were published in October 2011 as ECETOC Technical Report No.111; “Development of guidance for assessing the impact of mixtures of chemicals in the aquatic environment”

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ECETOC member company experts, an expert EU regulator and leading scientists reviewed recent developments in assessing the effects of mixtures at a two-day scoping meeting in October, 2008. Key aims were to identify which concepts and data are available to support scientifically valid environmental assessments of mixtures, consider how mixtures are assessed in different legal settings and to identify research needs. The outcome from that meeting is summarised below.

The theory of mixture toxicity has become more sophisticated over recent years but the long held principles of concentration addition still seem to provide a generally reliable, rough and conservative, estimate of toxicity. This means we can usually predict the toxicity of mixtures, for risk assessment purposes, when we know roughly the properties (e.g. via summary parameters) or chemical components of a mixture. However, we do not tend to consider interaction of specific chemicals or chemical mixtures with other, unknown, chemicals present in the environment, i.e. we do not ask; what is the potential impact of all chemicals present in the environment? This leaves industry vulnerable to criticism, in particular, for not determining whether chemicals present in the environment, including those at concentrations below their respective PNECs, act additively to cause an overall effect. Current European monitoring programmes such as the NORMAN project continue to feed this type of criticism through highlighting the presence of hazardous chemicals. In addition, as the WFD is implemented and water quality is perceived to be below good ecological status, we can expect chemicals and mixtures of chemicals to be considered as suspected agents causing adverse effects. REACH does not address this question directly since it is driven by prospective risk assessment or simple hazard profiling, neither of which properly consider the combined action of unknown mixtures in the environment.

Considering that it is not possible to consider, or even predict, all the potential combinations of chemicals in the environment, prospective risk assessment of mixtures, as currently used in regulation of individual chemicals is not possible. However, a retrospective approach comparing actual with expected (or desired) biological quality, e.g. diversity and/or function, can provide integrated assessments of whether environmental mixtures really cause impacts. A key advantage of retrospective assessment is that actual ecosystems are assessed rather than extrapolates to them. A retrospective approach can also provide a reality check on the identification of priority concerns identified by the WFD. However, this is not a simple activity and requires development of methods to discriminate impacts of chemicals (or other stressors) from natural environmental variation.

Retrospective assessments can also inform the debate over the apparent loss of biodiversity – is chemicals management inadequate and therefore unsustainable? Since both the chemical industry and the water industry have stakes in ensuring good water quality, this approach may facilitate future co-operation, i.e. a wider multi sector involvement in understanding the true impact of chemicals and the effectiveness of treatment infrastructure.

Terms of reference

  • Review field based comparative approaches for assessing impacts on the aquatic environment and develop guidance on suitable methods.
  • Using case studies, identify research needs, including how methods can be implemented, what diagnostic tools are required.
  • Consider the value of retrospective assessment in assessing the capacity of aquatic communities for tolerating man made discharges.

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