08. October 2024, Topic: Aquatic Ecotoxicology Risk Assessment

International workshop on sampling frequency

On 19-20 September 2024, the Ecotox Centre organised a workshop of the EU Working Group Chemicals on the topic of sampling frequency, in which around 25 experts participated online or live. The aim of this working group is to develop a guideline on the sampling frequency for priority substances whose entry into the environment can fluctuate greatly over time.

In the EU Member States, monitoring of priority substances under the Water Framework Directive is focussed on larger rivers, which are monitored via monthly grab samples. However, the concentrations of plant protection products and other substances with temporally fluctuating concentration patterns are not correctly recorded in this way, meaning that good chemical status cannot be assessed. The use and concentration of plant protection products fluctuate with the season and the substances enter water bodies in high peak concentrations during rain events.

In Switzerland, the risk of plant protection products is determined by taking two-week composite samples throughout the year. The average concentration over two weeks is compared with the chronic environmental quality criterion, as this period corresponds to the average test duration of the ecotoxicological tests for the derivation of the chronic environmental quality criteria and thus the period in which chronic effects can already occur in water bodies.

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