Andreas has been swimming with only occasional breaks for three hours. I try my best to guide him by keeping my kayak just ahead and to the left in his field of view. With each alternate breath he sees my boat. Between breaths he can just see his fingertips in the pea-green water of the Tennessee River as they execute another freestyle stroke. Except for a woman off to our left, we have separated ourselves from the pack of about one hundred swimmers taking part in this ten mile race. My job is easier. I have time to admire the ranks of trees blanketing the steep slopes to either side of us, the Turkey Vultures scribing circles in the sky high above, and the illuminated sandstone cliffs that form the upper cap of the Cumberland Plateau hundreds of feet above us.

I also have time to think about our swim of the entire 652-mile length of the river last year and the immense amount of water quality data we accumulated then. As it turns out the Tennessee is a fairly clean river. Its levels of pharmaceuticals are lower than what is found in the Rhine River. The heavy metals are low. The nitrates and phosphates are acceptable for a river flanked by extensive fertilizer-dependent agricultural areas. There was one big surprise, however – microplastics. These are pieces of plastic less than 5 mm in diameter that are either the broken down bits of larger plastic or small manufactured beads that are used in some toothpastes and soaps for their abrasive qualities. We analyzed for plastics by pumping 1000 liters of water (same as one cubic meter) through a filter that caught particles in the range of 0.025 mm to 0.5 mm. When we analyzed the first river sample we were so startled by the results that we analyzed it again. What we found was a staggering number: over 17,000 particles per cubic meter. This is the highest concentration of plastic particles ever detected in any river. Looking at the exact same size range a few years earlier in Europe’s Rhine River, Andreas only found 200 particles per cubic meter. The Rhine has ten times as many people living in its watershed compared to the Tennessee. How is this possible?

An answer may lie with another analysis we conducted that looked at the type of plastic found in our samples. Below is a diagram that shows the exact number of each plastic type found in Pickwick Lake, one of the nine reservoirs along the river:

Types of plastic particles found in a representative sample from Pickwick Lake. PE=polyethylene, PP=polypropylene, PA=polyamide.

This chart shows that almost half of the plastic found was polyethylene. Most polyethylene is used in light weight packaging and plastic grocery bags. The plastic wrap around produce and the plastic bag it is put into at the checkout counter are likely of this plastic. But how did all this polyethylene get into the river? Although we don’t know for certain, it is highly likely that the majority of it is derived from litter. The samples taken along the length of the Tennessee show roughly the same number of plastic particles from Knoxville, TN to Paducah, KY. Thus we are not dealing only with inputs from particular cities or industrial zones. We as a society are responsible for this plastic load in the river.

Why are microplastics in our waterways an issue? After all, plastic can be swallowed without negative side-effects by animals and people, right? This would be largely true if organisms consumed clean plastic. But plastic particles in a river have been exposed to a host of man-made chemicals that like to stick to their surfaces. Chemicals that include pharmaceuticals, PCBs and heavy metals. In addition to sampling for microplastics during the Tenneswim we also sampled for hundreds of man-made chemicals and heavy metals. What we found was a cocktail of chemicals like anti-seizure medications, blood pressure medications, over a dozen pesticides, pain killers, artificial sweeteners, contrast agents for x-ray and MRI procedures, caffeine, sunscreen ingredients, perfluorinated compounds (PFCs), and a host of other chemicals. That means that each plastic particle acts as a potential transport agent for some of these chemicals. We know that this has caused serious disruption of physiological processes in some river invertebrates (e.g., endocrine disruption), but we don’t yet know about the effects on fish – or humans that drink river water.

The American Paddlefish is a Tennessee River inhabitant that feeds on zooplankton. It is not known what impacts (if any) microplastics have on its physiology.

As I watch Andreas swim I realize that this means he is carving his way through thousands of plastic particles every few seconds. This also means that the Tennessee River is dumping 32 million plastic particles into the Ohio River every second.

As we emerge from a bend in the river I can see the big, orange buoy that marks the finish line off in the distance. Another 20 minutes and we reach it, Andreas coming in third out of a field of over 100 participants. We leave the water, but the microplastics continue on their journey to the Ohio, then the Mississippi, and ultimately the Gulf of Mexico. There they add to the 9 million tons of plastic entering the oceans annually. Estimates are that if things continue unabated, there will be more plastic particles in the ocean than fish by 2050.