Saturday 2 November 2013

Plastic contamination in Lake Garda, Italy.

Plastic contaminants are known to present a threat in many ecosystems, with particular concern being raised about the oceans, where large accumulations of plastic are known to be found on ocean gyres (large rotating currents) and where damage to wildlife from plastic ingestion is well documented. The effect of plastic contamination on freshwater ecosystems is less well documented, though studies of the Great Lakes of North America suggest that they may face similar problems to the oceans.

In a paper published in the journal Current Biology on 7 October 2013, a team of scientists led by Hannes Imhof of the Department of Animal Ecology at the University of Bayreuth, and the Department of Biology at Ludwig-Maximilians-University Munich, describe the results of an analysis of beach sediments at Lake Garda in northern Italy, and the implications of these.

Lake Garda is a subalpine lake split between the provinces of Verona, Brescia and Trentino. It is Italy's largest lake, and a popular tourist destination, as well as serving as a water supply for surrounding communities and an important natural habitat. Th critically endangered Carpione, Salmo carpio, (a type of Trout), is endemic to the lake.

Imhof et al. sampled beach sediments at two locations on the lake, one at Nago-Torbole on the north shore and one at Desenzano del Garda on the south. They found a significantly higher concentration of plastics at the northern site, with an average of 483 macroplastic particles and 1108 microplastic particles per square meter of shore, compared to 8.3 macroplastic particles and 108 microplastic particles at the southern site. This strongly suggests that the predominant local wind, the 'Ora', which blows from south to north, combined with a counter clockwise rotating eddy at the northern tip of Lake Garda, preferentially moves plastics in the lake to the northern tip of the elongate lake.

The location of Lake Garda, and map of the lake showing the two sample sites and the predominant winds in the region. Imhof et al. (2013).

They found that the plastics present were dominated by three low-density polymers, polystyrene (45.6% of the material present), polyethylene (43.1%) and polypropylene (9.8%), however polyamide and polyvinylchloride were also present as small microplastic particles. Polyvinylchloride is considered to be particularly hazardous to the environment, with a number of highly toxic breakdown products.

The ingestion of plastic particles by wildlife is known to be a particular problem in marine environments, but has not been well studied in freshwater ecosystems. Imhof et al. were able to demonstrate experimentally that a variety of freshwater invertebrates would ingest fluorescent polymethyl methacrylate microparticles, suggesting a mechanism by which plastics could enter the food chain in freshwater environments.

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