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Responses of Hyalella azteca to acute and chronic microplastic exposures
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Researchers exposed the freshwater amphipod Hyalella azteca to polyethylene microplastics in both short-term and long-term laboratory tests. They found that chronic exposure over 10 days to high concentrations of the smallest microplastic particles reduced survival and reproduction. The study provides some of the first data on how microplastics affect freshwater invertebrates over extended periods, highlighting the importance of particle size and exposure duration.
Limited information is available on the presence of microplastics in freshwater systems, and even less is known about the toxicological implications of the exposure of aquatic organisms to plastic particles. The present study was conducted to evaluate the effects of microplastic ingestion on the freshwater amphipod, Hyalella azteca. Hyalella azteca was exposed to fluorescent polyethylene microplastic particles and polypropylene microplastic fibers in individual 250-mL chambers to determine 10-d mortality. In acute bioassays, polypropylene microplastic fibers were significantly more toxic than polyethylene microplastic particles; 10-d lethal concentration 50% values for polyethylene microplastic particles and polypropylene microplastic fibers were 4.64 × 10(4) microplastics/mL and 71.43 microplastics/mL, respectively. A 42-d chronic bioassay using polyethylene microplastic particles was conducted to quantify effects on reproduction, growth, and egestion. Chronic exposure to polyethylene microplastic particles significantly decreased growth and reproduction at the low and intermediate exposure concentrations. During acute exposures to polyethylene microplastic particles, the egestion times did not significantly differ from the egestion of normal food materials in the control; egestion times for polypropylene microplastic fibers were significantly slower than the egestion of food materials in the control. Amphipods exposed to polypropylene microplastic fibers also had significantly less growth. The greater toxicity of microplastic fibers than microplastic particles corresponded with longer residence times for the fibers in the gut. The difference in residence time might have affected the ability to process food, resulting in an energetic effect reflected in sublethal endpoints.
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A 42-day laboratory study found that polypropylene microplastic fibers caused significant reductions in growth and reproduction of freshwater amphipods at all tested concentrations, with no mating occurring at higher concentrations. The findings demonstrate that microplastic fibers—the most common form found in aquatic environments—are chronically toxic to small freshwater invertebrates at relatively low levels.
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Researchers exposed the freshwater amphipod Hyalella azteca to naturally aged polypropylene microplastics for up to 14 days followed by a 7-day recovery period. They found that the highest concentration caused significant mortality, while lower concentrations induced oxidative stress markers after 14 days of exposure. After the depuration period, biochemical damage levels were reduced, demonstrating that the organisms can partially recover once removed from the contaminated environment.
Exposure of the amphipod Hyalella azteca to microplastics. A study on subtoxic responses and particle biofragmentation
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Scientists exposed freshwater amphipods (Hyalella azteca) to polystyrene microplastics and observed subtle but measurable effects on the animals' behavior and biology even at concentrations below those causing visible harm. Importantly, the amphipods physically broke down the microplastics into much smaller fragments through ingestion and digestion. The study highlights that animals in the environment may be actively generating nanoplastics from microplastics, accelerating the fragmentation of plastic pollution.
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Researchers exposed the freshwater amphipod Hyalella azteca to realistic environmental concentrations of secondary PET microplastics generated from weathered plastic bottles, measuring biochemical stress responses to evaluate ecotoxicological effects on this benthic primary consumer. The study found significant biochemical alterations in exposed amphipods, indicating that environmentally relevant PET microplastic concentrations pose risks to freshwater invertebrate communities.
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