SETAC Spotlight: The importance of confidence limits for ecotoxicological endpoints

In Europe, Tier I ecotoxicity tests using standard species are a regulatory risk assessment requirement for all chemicals prior to commercial use. The most common statistical endpoints used in acute and chronic ecotoxicological studies are Effect Concentration (ECx) values. These describe the concentration at which ‘x’ percent of the test organisms are affected, for any given parameter. For example, an EC50 value for mortality would be the calculated concentration where 50% of all test organisms had died.

In recent years, there has been a requirement for the provision of both EC10 and EC20 values in addition to the traditional EC50 values. Therefore, older study data is routinely re-analysed to generate these values to be submitted to the regulatory authorities for current environmental risk assessments.

These re-analyses should also include an assessment of the reliability of each endpoint. This is usually carried out by investigating the corresponding confidence limits. Although confidence limits are a key indicator of the reliability of the data, they can sometimes be overlooked, or their importance misunderstood.

Here, we provide an overview on the current guidance for calculating ECx values, and their confidence limits, to provide an insight on how confidence limits can be used to identify a reliable ECx endpoint. We will also highlight the standard species accepted endpoints detailed in the OECD test guidelines.

The poster is available for free download.

You can find all of the other posters that CEA presented at SETAC Dublin here. You can also find all of our publications from previous conferences and links to journal articles we have authored on our library page.

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