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Plastics in Open Channel Drains

September 16, 2016

I’m a firm believer that an area that looks like a garbage dump,  acts as a garbage dump. By that I mean people are more apt to dump a candy wrapper,  a bag from chips, etc. in an area that looks nasty – versus a pristine,  manicured,  well kept up spot.

We live in a society where plastic is all around us in everyday life.  It’s no coincidence it gets into our open channel stormwater drains. The Red Run has 54 MILES of open drainage. 

Now add in the Clinton River tributaries,  as it all flows into Lake St.Clair. Washing Machine discharge contains synthetic fiber fragments from our clothing.  A combined sewer overflow event dumps them into the waterways. 

EXCERPTS from study

The physical properties of different plastics and the hydraulics of the different water bodies played a role in the study.

Micro-plastic particles are eaten by fish,  birds,  and other wildlife.  It is often mistaken for real food.  

Negatively buoyant fibers made of polymers such as polyester, rayon, nylon, and cellulose acetate may remain in suspension in the turbulent flow of a stormwater drain.

In contrast, many foams, films, and pellets/beads are made of positively buoyant polymers such as polystyrene, polyethylene,and polypropylene, which likely remain afloat in the lakes for some time, until biofouling or adsorption of minerals increases their density and causes them to sink.

The fibers enter the lakes but likely settle and accumulate in the lakebed sediments rather than at the surface.

This accumulation of microplastics in lakebed sediments may have important effects on benthic organisms as well as organisms at higher trophic levels that are reliant on benthic organisms.

https://www.epa.gov/national-aquatic-resource-surveys/indicators-benthic-macroinvertebrates

This study characterized the quantity and morphology of floating micro- and macroplastics in 29 Great Lakes tributaries in six states under different land covers, wastewater effluent contributions, population densities, and hydrologic conditions. Tributaries were sampled three or four times each using a 333 μm mesh neuston net. Plastic particles were sorted by size, counted, and categorized fibers/lines, pellets/beads, foams, films, and fragments.

Plastics were found in all 107 samples, with a maximum concentration of 32 particles/m3 and a median of 1.9 particles/m3

Ninety-eight percent of sampled plastic particles were less than 4.75 mm in diameter and therefore considered microplastics.

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