Chironomus sp. Acute Immobilization Test (OECD TG 235)
The Chironomus sp. Acute Immobilization Test according to OECD TG 235 is designed to evaluate the short-term toxic effects of substances on sediment-dwelling aquatic invertebrates, specifically larvae of Chironomus species (non-biting midges). These organisms are ecologically relevant and widely used as indicators of benthic toxicity in freshwater environments.
In this test, early instar larvae are exposed to a range of concentrations of the test substance under controlled laboratory conditions, typically via the aqueous phase, for a short exposure period (usually 48 hours).
The primary endpoint is immobilization, defined as the inability of the larvae to exhibit coordinated movement in response to external stimuli. Observations are made at defined intervals to assess the onset and extent of toxic effects.
The results are used to establish concentration–response relationships and to determine the median effective concentration (EC₅₀), representing the concentration at which 50% of the organisms are immobilized.
This test provides rapid and sensitive information on the acute toxicity of substances to benthic invertebrates and serves as a valuable screening tool within environmental risk assessment frameworks.
