Physics World –
Tiny plastic particles are showing up in all sorts of places and have become a worldwide problem. Scientists are in the early stages of determining how microplastics, defined as particles smaller than 5 mm, enter the environment and are transported – often up to hundreds of kilometres – into previously pristine ecosystems. Researchers presented several observations on microplastic migration at the annual meeting of the American Geophysical Union (AGU) in San Francisco, California, in December.
Scientists group microplastics into three categories. The first are spherical microbeads, which typically come from facial cleansers and similar pharmaceutical products. The second are irregularly-shaped microfragments that have degraded from larger plastic objects. The third type are hair-like microfibres shed from synthetic fabrics.
Meredith Sutton, an undergraduate student at the University of Virginia, US, told researchers at the AGU meeting that microplastics are expected to be found downstream of urban centres. However, they are increasingly found downstream of agricultural areas as well. Sutton and her colleagues suspected that fertilizers made from sludge at wastewater treatment facilities might be a source, so they conducted a controlled experiment in the midwestern state of Nebraska. After rainfall, they found that much higher concentrations of microplastics (mainly fragments) ran into streams from fields treated with sludge-based fertilizers than from unfertilized control plots. The sludge treatment process does not screen for or filter out microplastics, Sutton said.