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Microplastics and movement- exploring behavioural toxicity in Daphnia
Summary
Researchers investigated the behavioral toxicity of microplastics on Daphnia, moving beyond standard mortality and immobilization endpoints to capture subtler effects on movement. The study found that microplastic exposure alters locomotion in ways that standard tests would miss.
Microplastics toxicity in freshwater environments has been well explore, with an increasing number of plastics (polymer, morphology, size etc.) in addition to organisms studied. Toxicity endpoints are progressively more varied, moving beyond standardised endpoint such as mortality and immobilisation to include molecular endpoints such as reactive oxygen species production and behaviour such as increased heart rates or changes in feeding. In this study, we explored the impacts that microplastics (spheres, fragments and fibres) have on the movement of Daphnia magna. Daphnia are a well-established model organism for freshwater ecotoxicity assessments, and are keystones species within their ecosystems. Daphnia have previously been used to explore microplastic toxicity in a range of studies, with an increasingly diverse panel of particles and exposure conditions. Typically, the acute toxicity endpoint used to establish the effect concentration (EC) is immobilisation (as a proxy for mortality), which is outlined in the OECD 202 test guideline. Here, we explore the impact that physical toxicants can have on the movement of Daphnia. This was done by recording the Daphnia movement over a 48-hour period and assessing both the vertical migration in the test vessel, in addition to their movement in a 10mL well for stress indicators (i.e. more spins in the water are behavioural indicators of higher stress) in addition to any increase in immobilisation. Behavioural changes in organisms can provide a greater understanding of how populations may be impacted within these environments, and can link to ecosystem level impacts, for example a decrease in algal clearance rates. Here, we explored the Daphnia response to different microplastics (polymers and morphologies) to ascertain the scale of the impact across the panel of plastics. Through linking behavioural changes, population impacts and toxicant characteristics, we can create a more mechanistic understanding of the main drivers of toxicity in these environments. Also see: https://micro2024.sciencesconf.org/559740/document
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