Collateral damage from the COVID-19 pandemic: Synergistic toxic effects of rapid antigen tests on the rotifer species Brachionus calyciflorus.

As the COVID-19 pandemic fades, its environmental impact is becoming clear. Beyond plastic pollution from masks and packaging, rapid COVID-19 test strips could add further impact through nanomaterial-based immunosensors containing gold nanoparticles (AuNPs), which, together with other nanomaterials, could cause lethal effects in the aquatic environment. We exposed the limnic rotifer Brachionus calyciflorus to the contents of a representative test strip to assess its potential impact. A dilution containing only 6.0 µl of the stock solution caused 100% lethality within 12 h and complete loss of reproduction, disrupting the species' key role in the zooplankton food web. However, AuNPs were internalized only in small amounts, and the diluted AuNP fraction was largely non-toxic, implicating that the toxicity derives from potential synergistic effects within the whole dilution. Given the growing use of rapid antigen tests commercially and nanomaterials in medicine, more attention is needed regarding their environmental risks and potential synergistic effects.