Microplastic mud

Marine debris – the collection of discarded, man-made objects that accumulates in the world’s oceans – is a well-known environmental problem (NOAA even has a program dedicated to studying and ameliorating the issue). Ocean currents and wind patterns can gather marine debris into giant, floating masses of refuse, like the Great Pacific Garbage Patch, and encounters between wildlife and the litter can have devastating consequences.

Since it was published earlier this week, this paper from the journal PLoS ONE concerning the amount of plastic that humans have dumped into the world’s oceans has garnered a lot of media attention. One of the interesting findings in that paper was that, consistent with earlier studies, the researchers found a lot less of one type of plastic than they expected to find during their surveys – microplastic, or pieces smaller than five millimeters (that’s a little bit less than a quarter of an inch).

Another study published earlier this month offers another perspective on microplastic pollution – it appears to be ubiquitous in the sediment of at least one large river, the St. Lawrence River in eastern Canada. According to the scientists who conducted the study, other researchers have found microplastic floating in freshwater lakes and on their shorelines when they’ve looked for it (plastic debris have been much more extensively studied in marine than in freshwater environments), but, they write, “[n]o studies to date have addressed the presence of microplastics in North American freshwater sediments.” 

To address that deficiency, the researchers collected sediment from 10 sites on the St. Lawrence River, most between Quebec City and Montreal (two were below Montreal); they found microplastics at eight of the sites. The densities ranged from low (an average of seven pieces of plastic per square meter at the site with the lowest densities) to extraordinarily high – the single sample containing the most microplastic had 3,980 pieces per liter. Imagine a Nalgene water bottle full of mud from a riverbed, suffused with that many tiny bits of plastic.

Plastic pollution is a problem in the ocean, but it’s also a problem in freshwater environments, where it’s just beginning to be explored. If fish confuse morsels of microplastic for food, the effects on freshwater food webs could be devastating – and, as the authors of the paper note, this is an area ripe for future research: “[t]he extent to which microplastics have become incorporated into the St. Lawrence River food web – and the consequences for biotic communities – remain to be determined.”

Microplastic pollution is an environmental issue in both marine and freshwater environments. 

(Image by Wright via Wikimedia Commons)