Are Microplastics Toxic? A Review from Eco-Toxicity to Effects on the Gut Microbiota

Abstract

Emerging studies have presented an initial picture of the toxic effects of exposure to environmental micro- and nanoplastics. They have indicated that micro- and nanoplastics may induce toxicity by leading to oxidative stress, energy metabolism disorders, gene damage, and so forth in environmental organisms, marine invertebrates and vertebrates, and laboratory mouse models. In recent years, micro- and nanoplastics have been discovered in human fecal samples, placentas, lung tissue, and even blood; thus, micro- and nanoplastics pose an alarming and ever-increasing threat to global public health. However, current research on the health effects of micro- and nanoplastics and the possible adverse outcomes in humans has only presented the tip of the iceberg. More robust clinical data and basic experiments are still warranted to elucidate the specific relationships and mechanisms. In this paper, we review studies on micro- and nanoplastic toxicity from the perspectives of eco-toxicity, the adverse effects on invertebrates and vertebrates, and the impact of micro- and nanoplastics on the gut microbiota and its metabolites. In addition, we evaluate the toxicological role of micro- and nanoplastic exposure and its potential implications in respect to human health. We also summarize studies regarding preventive strategies. Overall, this review provides insights on micro- and nanoplastic toxicity and its underlying mechanisms, opening up scientific avenues for future in-depth studies.

Keywords: gut microbiota; micro- and nanoplastics; microplastics; polystyrene; toxicity.

Figure 1

Advances in microplastic discovery. In recent years, scientists have gradually detected microplastics in human tissues.

Figure 2

Pathways of human exposure to microplastics mainly include ingestion, inhalation, and dermal contact. Ingestion is the most important route of exposure, and dermal contact is considered the least important route of exposure. For example, micro- and nanoplastics in salt, commercial fish, bottled water, and canned food can enter the human body through ingestion, those in floating fibers and dust in the air can enter the human body through inhalation, and those in toothpaste and skin-cleaning products can enter the human body through skin contact.

Figure 3

Normal gut microbiota versus micro- and nanoplastic-disturbed gut microbiota.