River diversions for irrigations locks microplastics into catchments

Diverting streams and rivers to irrigate crops or provide drinking water may significantly extend the time microplastics spend in river catchments according to findings from a recent study.

The researchers found that irrigation diversions disperse microplastics across farmland from where they may be flushed back into other watercourses or neighbouring catchments.

The international group of scientists led by the University of Birmingham, studied the Boulder Creek river in Colorado, US and its less-urbanised tributary South Boulder Creek. The researchers found that microplastic concentration patterns in both rivers were related to the degree of catchment urbanisation.

They discovered that the magnitude of flow diversions from both streams resulted in large quantities of microplastics being removed from each stream and being transported out of their actual catchment. They reported that conservative estimates based on the >63 µm particle threshold of their study” showed some 41tr microplastic particles are being redistributed out of river networks into the terrestrial environment in North America every year, with about 459tr particles being redistributed globally.

Co-author and principal investigator, Professor Stefan Krause, from the University of Birmingham, said “Our current models may, therefore, underestimate the quantities and residence times of plastics held in river catchments and overestimate the speed with which microplastics are transported into our oceans.”

While toxicity was not a focus of the study, co-author, Professor Iseult Lynch from the University of Birmingham said the findings were “highly relevant for estimating ecotoxicological impacts on aquatic and terrestrial environments and ecosystems, with enhanced terrestrial residence times resulting in extended (chronic) exposures.”