Scanning electron microscopy and EDX spectroscopy of commercial swabs used for COVID-19 lateral flow testing

Abstract

The chemical composition of COVID test swabs has not been examined beyond the manufacturers' datasheets. Given the unprecedented demand for swabs to conduct rapid lateral flow tests and nucleic acid amplification tests, which led to mass production, including 3-D printing platforms, it is plausible that manufacturing impurities could be present in the swabs and, if so, could pose a risk for human health. We used scanning electron microscopy and energy dispersive X-ray (EDX) spectroscopy to examine the ultrastructure of five assorted brands of COVID test swabs, and to identify and quantify their chemical elements. We detected unexpected elements, including transition metals, such as titanium and zirconium, as well as aluminium, silicon, and fluorine. The amount of some of the detected elements is close to reported toxicological thresholds for inhalation routes. Experimental studies have shown that detrimental effects of the unexpected chemical elements include moderate to severe inflammatory states in the exposed epithelium as well as proliferative changes. Given the massive testing still being used in the context of the COVID pandemic, often as requisites for travelling, attending universities, or as mandatory work policies, we urge caution in continuing to recommend repeated and frequent testing, particularly of healthy, non-symptomatic, individuals.