Assessing the Effects of Alkaline Digestion on Micro- and Nanoplastics Derived from Consumer Biodegradable Plastics

Biodegradable plastics are designed to degrade under specific environmental conditions, such as in compost, soil, or marine environments. However, the same properties that enable their degradation may also cause them to break down during the procedures researchers use to detect and quantify them. As biodegradable plastics are increasingly adopted as alternatives to conventional plastics, it is essential to reliably quantify and identify the biological and environmental contamination associated with their derived micro- and nanoplastics (<5 mm, MNPs). Incubation with potassium hydroxide (KOH) is commonly used to isolate MPs from biological samples. However, the impact of alkaline digestion on consumer biodegradable plastics remains largely unknown. Therefore, the objective of this work is to evaluate the effects of alkaline digestion on MNP recovery by quantifying changes in mass and chemical signatures, thereby identifying potential biases and uncertainties in MNP quantification associated with the most common digestion protocol. It was found that plastics with ester linkages experienced >79% mass loss upon digestion. Additionally, spectral correlation (via FTIR) comparing biodegradable plastics pre- and post-digestion was poor (<65%). Finally, the thermal properties of the consumer plastics used in this study were characterized to provide context for digestion behavior, as processing history can produce substantial variability within a given polymer type. Ultimately, this research provides evidence that MNPs from consumer biodegradable plastics may become substantially altered during incubation with KOH. Therefore, the apparent absence or underrepresentation of biodegradable plastics in biological or environmental samples may reflect their susceptibility to alkaline hydrolysis rather than natural degradation, leading to bias and uncertainty in prevalence and health risk of these materials.