While research into the effects of microplastics has expanded greatly in the past decade, important questions about what concentrations are hazardous in water still remain unanswered. Moreover, water contains naturally occurring suspended particles, such as clay, that are of the same size as microplastic and may be equally harmful to aquatic life when present at high concentrations. With that in mind, what is the relative safe contribution of microplastics with regard to the total amount of suspended particles? To address this question, ACES scientists have developed a novel approach for assessing the effect of microplastics present in such mixtures. The study was published in Scientific Reports.

“The new approach builds on standard ecotoxicological methods but acknowledges the complexity of the natural environment where various suspended particles are present, including microplastic as a contaminant. We know, for example, that in turbid waters the feeding apparatus in animals filtering their food and gills in many fish and crustacean species become clogged with particulates suspended in the water, which may lead to decreased feeding and respiration, and, in severe cases, cause death,” says Zandra Gerdes, PhD student at ACES and lead author of the study.

The approach described in the paper was tested experimentally using an existing but modified ecotoxicological test that examined mortality of water fleas in response to suspended particle concentrations, mixed with different proportions of microplastics.

According to the authors, the new approach can provide answers to two important questions. The first question deals with defining what the hazardous levels of suspended particles would be. Specific test systems can be applied for regional waters, depending on the typical turbidity levels for this environment – taking into account seasonal and manmade variability in the levels of suspended particles. The second question, and focus of the article, is how much microplastics would be safe in that environment.

Current regulatory efforts require knowledge about what levels of microplastics in the water are harmful to aquatic life, and ecotoxicological studies seek to define these tolerable hazard thresholds.

“Defining these thresholds is hampered by methodological challenges, such as selecting environmentally relevant test concentrations of microplastics and taking into account effects of particles commonly present in water, such as clay, sand, and cellulose originating from decaying plant material. We hope that our approach will fuel the on-going discussions about standardising particle effect testing, including microplastic effects,” says Zandra Gerdes.

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