Scientists at the Naturalis Biodiversity Center in the Netherlands discovered long-term water contamination based on studying microplastics contained in caddisfly larval casings from the early 1970s. Published in Science of The Total Environment, their study confirms that freshwater ecosystems contain microplastic contamination for more than half a century, integrated into protective cases constructed by freshwater insect larvae. The study involved analyzing a sample of 549 caddisfly larval casings that were stored at the Naturalis museum. The caddisfly, a moth-like insect that inhabits water bodies, is renowned for its habit of using surrounding materials such as sand, twigs, and other trash to construct casings when it is in the larva phase. The casings act as defense mechanisms against predators while growing.

The research started when scientists noticed strange colored pieces in one of the museum larvae samples. Closer examination revealed that the pieces were pieces of microplastic. This led to a thorough examination of other samples, and several casings full of man-made material were discovered. One casing from 1986 had a range of blue plastic pieces and one from 1971 had yellow plastic. These samples prove that the pollution had occurred before in other water bodies in the Netherlands even decades ago. When the plastic samples were examined more closely, there was the discovery of the presence of additives such as lead, titanium, and zinc, which are usually added during industrial processing of plastic material.

These additives worsen the problems from the toxicological aspects to aquatic life, especially at early life stages such as larvae of insects. Reflective coloration and buoyancy of plastic debris were also mentioned as potential risk factors since the former could make the larvae more apparent to birds and fish, thus interfering with the natural survival mechanism. This study presents tangible historical data for the presence of microplastics in ecosystems much earlier than the problem came into the international arena.

Whereas most microplastic studies have centered on the last few decades and marine ecosystems, the current research aims at freshwater systems and stresses the extensive, chronic nature of the problem. Caddisflies, being globally distributed and having sole contact with aquatic substrate, are major bioindicators in studying the wider consequences of microplastic pollution on freshwater biodiversity. The findings of this study indicate freshwater environments were possibly more populated by microplastics than thought earlier and have had an influence on aquatic organisms over a longer time period than assumed.

It also calls for the re-examination of past ecological records and specimens in museum collections across the globe that could hold as-yet-untapped information regarding past environmental change. Re-examining past biological collections using contemporary analytical methods can provide useful information regarding the onset and development of pollution trends. Microplastics are plastic pieces less than 5mm in length, which have a multitude of sources such as consumer products, industrial by-products, and the breakdown of larger plastic items.

Microplastics have also been found to be environmentally persistent and the ability to be ingested by organisms in the food chain, causing bioaccumulation and the effect to spread across the ecosystem. The use of such materials in entomology, such as caddisfly case-making, shows how entrenched microplastic pollution has become in the natural process. The results indicate a broader environmental issue that needs to be incorporated into freshwater management and anti-pollution policy. It is important to know the long duration and extent of microplastic pollution in order to implement policy to prevent further environmental damage. Environmental museums and biological archives are also emphasized in the study as important resources to track long-term environmental change.

Through its detection of synthetic pollutants in bio-preserved biological samples that are more than half a century old, the study contributes to the literature lending credibility to the fact that microplastics are not new but have been a constant hazard for both freshwater and marine biota.

Future studies can use the same approach to other conserved species and locations and help establish a larger and more comprehensive corpus of data retrospectively commenting on the global and historical magnitude of microplastic pollution.

Source/Credits:Published by Phys.org, research from Naturalis Biodiversity Center | Published in Science of The Total Environment (2025) | DOI: 10.1016/j.scitotenv.2025.178947 | 2025 Science X Network.