To the left: water flea (Daphnia magna) with visible plastic microbeads (green spots) in the gut. To the right: water flea that has ingested irregular plastic fragments, which, in contrast to microbeads, have formed clumps in the gut (red circle).

Effects of microplastics on aquatic organisms can vary depending on particle type and food availability shows a new study by researchers from ACES and colleagues from AquaBiota Research, Stockholm, published in journal PLOS One. Their results present a more complex picture of the effects of microplastics than previously thought.

“Microplastics are tiny particles that are less than 5mm in size and are released to the environment either as spherical microbeads from consumer care products or as irregular plastic fragments from degrading plastic litter. They are extremely diverse, varying in shape, size and chemical properties. The increasing amount of plastics in the environment has led to concerns about their effects on wildlife,” says Martin Ogonowski, postdoctoral researcher at ACES and lead author of the paper.

The scientists set out to understand how presence of microplastics, such as commercial microbeads and irregular plastic fragments, and naturally occurring microparticles, such as clay, affect water fleas (Daphnia magna). They found that at long exposure times and limited food, both microplastics and clay had a negative effect on growth but the opposite was true when food was more abundant. They also noted that different particle types affected food consumption and digestion differently.

“Microbeads behave like natural algal cells upon being eaten by microscopic animals, while irregular plastic fragments form clumps that slow down their elimination from the gut. In our study, reproduction and survival of water fleas were compromised by irregular plastic particles but only at extreme concentrations that normally cannot be found in the natural habitats of these animals. We found no negative effects of these particles at concentrations commonly reported in marine or freshwater environments,” says Martin Ogonowski.

Irregular plastic particles versus microbeads

Recently, a lot of media attention has been drawn to the potentially harmful effects of microbeads used in consumer care products. However, the scientists say that their findings paint “a more nuanced and complex picture” of the way microplastics affect the animals that eat them, one where their effects vary greatly depending on food availability and particle shape.

“Even though we could not detect any harmful effects of microplastics at environmentally relevant concentrations, our results demonstrate that irregular plastic particles may be more harmful than microbeads. Our findings also imply that different types of plastics should be studied under a variety of different environmental conditions before their exposure risks can be fully understood. For that, it may become challenging to make reliable assessments of the effects of microplastics in the future. In the meantime, a precautionary approach suggests that we should reduce the release of plastics to the environment,” says Martin Ogonowski.