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26-6769-T Archived Freshwater Fishes Reveal Historical Microplastic Pollution
Summary
Scientists tested decades-old preserved fish from a Delaware River museum collection and found microplastics in every single specimen, showing that plastic pollution in fish has been building up for a long time, even fish collected back in 1985 already had it. This matters because these fish are a similar food source to the fish humans eat, and the study shows we can use old museum specimens to track how microplastic contamination has changed over time, especially near polluted sites like landfills.
Microplastics are pervasive contaminants in aquatic ecosystems, yet their historical occurrence in freshwater fishes remains poorly documented. Natural history collections provide an opportunity to reconstruct past exposure, but preserved specimens require validated methods for digestion, contamination control, and polymer identification. Here, we used formalin-fixed and ethanol-preserved freshwater fishes to assess historical microplastic contamination in the upper Delaware River. We validated an alkaline-oxidative digestion and Laser Direct Infrared (LDIR) chemical imaging workflow using a preserved Smallmouth Bass (Micropterus dolomieu) collected in 1985 and subsequently applied the method to archived Rock Bass (Ambloplites rupestris), Cutlips Minnow (Exoglossum maxillingua), and Tessellated Darter (Etheostoma olmstedi) collected upstream and downstream of the Cortese Landfill. Microplastics were detected in all examined specimens, with polypropylene the dominant polymer across species and sites, although elevated polypropylene counts in procedural blanks require cautious interpretation. Rock Bass exhibited a pronounced downstream shift in polymer composition despite similar non-polypropylene particle abundances. Tessellated Darter showed modest downstream increases in several polymers, and Cutlips Minnow contained higher non-polypropylene polymer counts upstream, suggesting that feeding ecology and prey availability influenced exposure pathways. Laboratory control samples showed polyethylene microsphere recoveries of 86% to 114%, while procedural blanks revealed polymer-specific background contamination that was incorporated into data interpretation. These findings demonstrate that archived freshwater fishes retain identifiable microplastic signatures and preserve ecologically interpretable patterns of historical exposure within a river system affected by legacy waste disposal.