Archived Stream Insects Show Microplastics Across the Schuylkill Watershed

October 5, 2026

Researchers went back to insect samples that had been sitting in a research archive for up to three decades, and found microplastics inside about a third of them. The study, published in the journal Insects (DOI: 10.3390/insects17040386), looked at aquatic macroinvertebrates collected in 1998, 2010 and 2019 from six headwater streams in Pennsylvania's Schuylkill River watershed. That watershed supplies drinking water to millions of people in the Philadelphia region. WHYY and The Allegheny Front reported on the work on October 1, 2026.

The team was led by Rachel McNeish (California State University, Bakersfield) and John Wallace (Millersville University), with John Jackson of the Stroud Water Research Center. Stroud has been collecting Schuylkill macroinvertebrates for water-quality monitoring since 1996.

What they found

The team examined 411 macroinvertebrates from 36 taxa, including mayflies, stoneflies, caddisflies, riffle beetles and midges. Microplastics turned up in 134 individuals (about 32.6%) from 24 taxa, at 0 to 6 particles per individual.
Every microplastic particle counted was a fibre. Blue, white and clear fibres were the most common colours.
Microplastics showed up at all six streams, whether the surrounding land was mostly forest, farmland or urban. Abundance was lowest in the farm-dominated streams. Forested and urban streams were not significantly different from each other.
Particle totals peaked in 2010 (251 particles, about 47% of the total) and were lowest in 2019 (15 particles, about 5%). Overall, the models showed abundance declining over time.
Collector-gatherers, insects that feed on fine particles and biofilm, held the most particles: 145, or 35.6%. Shredders held the fewest.

How the study worked

Archived specimens were rinsed, dried and digested with peroxide. The leftover particles were counted under a light microscope, using a minimum detectable fibre length of 125 µm. On a 10% subset, the team cross-checked counts with Rose Bengal dye, which stains natural material but leaves plastics unstained, and confirmed selected fibres with µ-FTIR spectroscopy. Light-microscopy counts came out about 17% lower than the dye method, so the authors describe their numbers as conservative.

The caveats

This study measured particles inside stream insects. It did not measure tap water or treated drinking water, and it makes no human-health finding. The authors note that archived samples can pick up contamination, and that preservation solutions may affect both particle brittleness and dye staining. Stroud's John Jackson told WHYY that the later decline does not necessarily mean less pollution. Water flow may have flushed particles out faster than new ones arrived. Only three sampling years were analysed.

What it means for readers

The study suggests that microplastics in a drinking-water watershed are not only an urban-stream issue: they turned up in forested headwaters too. It also shows how archived collections can help scientists reconstruct pollution trends over time. It is environmental research, not a measure of what comes out of anyone's tap.

A note on scope: this post summarises peer-reviewed research and news coverage. It is not medical advice or a drinking-water test result, and WaterVO was not involved in the research.

Sources

McNeish, R.E.; Macchia, M.D.; Lee, N.M.; Harrison, A.T.; Brown, A.J.; Jackson, J.K.; Wallace, J.R. “Archived Historical Aquatic Macroinvertebrate Specimens Suggest Connections Between Microplastic Abundance Patterns, Trophic Traits, and Land Use.” Insects 2026, 17(4), 386. DOI: 10.3390/insects17040386 · Article page
Zoë Read, “Researchers find microplastics in insects from Schuylkill River watershed,” The Allegheny Front / WHYY, October 1, 2026: alleghenyfront.org

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