In ecotoxicology, the test using Daphnia magna immobilisation is a work‑horse for checking whether a water sample may be harmful to the aquatic environment. In parallel, researchers and regulators are asked to monitor water quality more often and with less effort and expenses. With evaluation of precious, low‑volume samples—think micro‑plastics leachates, nanomaterial suspensions, or field grabs from remote sites—the classic 100 mL test becomes impractical, expensive, and sometimes impossible. That gap sparked our curiosity and led us to check literature and evaluate a miniaturised version of the acute daphniaassay that still delivers the same reliable, reproducible results. By shrinking the test volume to just 1.5 mL per well and using a 24‑well plate format, we were able to run multiple replicates simultaneously, cut reagent use by 90 %, and dramatically reduce the amount of sample required. Our experiments showed that the concentration‑response curves, EC₅₀ values, and variability of the mini‑assay matched the standard protocol across a range of chemicals, proving that “small can be just as trustworthy as big”.

Why does this matter to UCL Open Environment readers? First, the assay opens the door for testing high‑value or hard‑to‑collect samples that were previously out of reach. Second, it aligns with the growing need for laboratory practices which cut down on waste, plastics, and chemicals. By writing this paper, we wanted to share literature data and a practical solution combining methodological rigor with real‑world challenges—something that interested researchers and monitoring authorities can establish quickly. Our main message is simple: one does not need 100 mL beakers full of water to get reliable ecotoxicity data; a compact, well‑validated mini‑assay can do the job, saving time, money, and sample material.

We chose to publish in UCL Open Environment because its open‑access ethos ensures that this low‑cost method reaches as many laboratories as possible, and because the journal’s interdisciplinary readership might appreciate methods that improve environmental testing while promoting sustainability. If you’re interested in the step‑by‑step protocol, validation data, and tips for implementation, read the full article and let’s start shrinking our tests—without shrinking our confidence in the results!

Miniaturisation of the Daphnia magna immobilisation assay for the reliable testing of low volume samples by Eberhard Küster (Helmholtz Centre for Environmental Research – UFZ, Leipzig, Germany), George Gyan Addo (Helmholtz Centre for Environmental Research – UFZ, Leipzig, Germany), Silke Aulhorn (Helmholtz Centre for Environmental Research – UFZ, Leipzig, Germany) and Dana Kühnel (Helmholtz Centre for Environmental Research – UFZ, Leipzig, Germany) is published in UCL Open Environment, volume 6.

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