SETAC Spotlight: Development of a higher-tier, indoor microcosm study using Chironomus riparius

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SETAC Spotlight: Development of a higher-tier, indoor microcosm study using Chironomus riparius

The larval stages of Chironomus riparius reside in the sediment of freshwater habitats such as ponds, rivers and lakes. They are considered as a key indicator species for ecosystem health and commonly utilised as a test species in standard, regulatory ecotoxicology studies for effect assessment of plant protection products (PPPs) and their active substances.

Standard (Tier I and Tier II) ecotoxicity tests are typically conducted under worst case conditions of exposure using axenic populations of determinate age. It is generally accepted that endpoints from these studies are conservative and lack a degree of environmental realism, and therefore context is required when extrapolating to real-world situations. For example, standard ecotoxicity studies do not consider species interactions, lifecycles and an organism’s ability to recover and/or recolonise following a perturbation to their environment. Higher tier ecotoxicological testing and bespoke study designs are able to take into account these factors, enabling refinement of effect endpoints to be used in environmental risk assessment. 

Here, we present our findings from the design and conduct of an indoor microcosm study with Chironomus riparius. The main objective of this work was to develop a method to evaluate the effects of an insecticide on multiple life-stages of C. riparius and to derive effects endpoints based on mortality, emergence and reproduction, including an assessment of recovery following short-term exposure.

The study was designed to incorporate several life-stages in an attempt to determine baseline mortality and emergence data in a microcosm setting. A representative insecticide was used to test the feasibility of the experimental design in a 28 day single pulsed exposure, focusing on the rate of emergence over time for this mixed-age-group population.

Based on our results, the design of the study was successful in determining a baseline level of mortality and emergence within the system and was eminently practical for determining organism recovery and assessment of population effects. As such, the system could be applicable for use with other sediment dwelling species and may prove to be an acceptable approach for higher tier ecotoxicity testing. Further work is needed using other representative toxicants and species.

To find out more about this work, please download our poster 'Development of a higher tier, indoor microcosm study using Chironomus riparius'.

In addition to this topic, CEA also presented six other posters at the SETAC virtual conference (SETAC SciCon, May 2021). These are available for download here.

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