Fourteen water samples put the Truckee's spring microplastic count ten times above fall

Divide the spring mean by the fall mean and the factor is 9.25 ^[17], which the study reports as nearly ten ^[4]. Both means come from grab samples, fourteen of them, six in fall 2022 and eight in spring 2023 ^[7][3]. The nine sites run from the headwaters at Lake Tahoe to points downstream of the Reno-Sparks metro area, picked to bracket population centers, wastewater treatment plants and river confluences ^[6]. With nine sites and fourteen visits, at least five sites were sampled in both seasons ^[18].

Season and year move together in that design. The low readings are from one autumn, the high ones from the following spring ^[3]. The study's explanation for the rise is hydrological: higher spring flows likely flush particles off the landscape and up from the river bottom ^[14].

Every particle in these counts was at least 50 micrometers across, the cutoff of the stainless steel mesh the samples were filtered through ^[8]. Anything smaller went through the filter and is not in the totals ^[25]. Composition came from Fourier transform infrared spectroscopy, which found polyethylene and polypropylene to be the dominant polymers ^[9][10]. The water was drawn from the top surface of the river ^[8].

Arienzo put the value of the work in terms of timing and place. "We hope our research helps water managers protect the Truckee River's water quality by offering more information about where and when microplastic concentrations are highest," she said ^[16]. The where, in this dataset, is the city reaches: the highest counts were at sites inside Reno and Sparks, and the lowest were upstream of the metro area and downstream of a river restoration site that may be holding particles in its meandering channel ^[11].

What the team measured was river water at nine points. The study did not measure treated or tap water, and it did not report any utility's sampling schedule ^[24]. One grab sample from this river can return anything between 0.1 and 10 particles per liter, a hundredfold spread, depending on when and where it is taken ^[5][20].

The Lake Tahoe comparison is the biggest number in the paper. Truckee concentrations ran three to four orders of magnitude above the headwater lake, a factor of 1,000 to 10,000 ^[12][19]. The plastic is joining the river below Tahoe. Levels in the Truckee are comparable to those reported in other Western rivers ^[12].

"The Truckee River is such a critical artery for northern Nevada," Lukasik said ^[15]. The river supplies drinking water to nearly half a million people around Reno and Sparks before it ends at Pyramid Lake ^[13][26].