Elucidating the effects of naturally weathered aged-polypropylene microplastics and newly procured polypropylene microplastics on raw 264.7 macrophages

Abstract

Increasing worldwide plastic use, which leads to more plastic production along with inadequate recycling rates, is resulting in increased contamination of the environment. As plastics are ubiquitous in the environment, the aging and weathering process is inevitable and this leads to the formation of microplastics (MPs). Despite the fact that numerous studies have connected aged plastics to cellular toxicity, none of these studies have examined the effects of exposure to both newly obtained plastics, that is, not weathered, and aged plastics, that is, naturally weathered, on macrophage cells. We have collected weathered plastics from the environment, which are found to be naturally aged and weathered, and newly procured plastics as the purchased product. Both the plastic materials are of the same brand and size. In this study, we have compared the difference in cytotoxicity and intracellular damage caused by aged microplastics referred to as post-consumer microplastics (weathered aged-PPMPs) and pre-consumer microplastics mentioned as newly procured microplastics (NP-PPMPs) of size ≤450 nm prepared from in-house plastics and aged plastics, to which raw 264.7 macrophage cells were exposed. Microplastics in the environment may gain entry into the immune system through the food chain. Both types of PPMPs exhibited toxicity on cell viability; however, oxidative stress, membrane damage of mitochondria, apoptosis and detoxifying enzyme GST were higher in NP-PPMPs in comparison with aged-PPMPs. However, GST enzyme production was affected by both types of PPMPs, the aged-PPMPs induced higher effects than NP-PPMPs. Furthermore, NP-PPMPs (50 μg mL⁻¹ and 500 μg mL⁻¹) exhibited cytotoxicity after 48 h of treatment but aged-PPMPs remained non-toxic to the cells. This study provides information on the toxicity of aged-PPMPs and newly procured PPMPs to raw 264.7 macrophage cells, which is useful for determining the risk of PPMPs.