# Toxicological Effects and Potential Therapeutics of Chronic Exposure to Polyurethane Nanoplastics in Caenorhabditis elegans

## TL;DR

This study shows that chronic exposure to polyurethane nanoplastics harms the worm C. elegans, but cinnamon essential oil may help reduce the damage.

## Contribution

The first study to demonstrate toxic effects of polyurethane nanoplastics at environmentally relevant concentrations and identify cinnamon essential oil as a potential antidote.

## Key findings

- Chronic exposure to polyurethane nanoplastics at 10 μg/L reduced worm reproduction and movement, while higher concentrations caused shorter lifespan and increased mortality.
- Cinnamon essential oil enhanced antioxidant responses at low nanoplastic concentrations and reduced toxicity at high concentrations by interacting with key stress response genes.
- Molecular docking revealed that cinnamaldehyde, a compound in cinnamon oil, strongly binds to a key stress response protein in worms.

## Abstract

Despite growing concerns about the ecological and health risks of nanoplastics at environmentally relevant concentrations (ERCs), the effects of polyurethane nanoplastics (PU NPs) on environmental organisms remain unclear. This study assessed the toxicity of PU NPs in the μg/L range in Caenorhabditis elegans (C. elegans) through chronic exposure. Our results showed that 10 μg/L PU NP exposure significantly reduced brood size, head thrashes, and body bends, while 100 μg/L PU NP exposure decreased lifespan, and 1000 μg/L PU NP exposure increased mortality in wild-type C. elegans. Analysis of oxidative stress showed that both 10 and 1000 μg/L PU NP exposures elevated reactive oxygen species (ROS), SKN-1::GFP, and GST-4::GFP levels. Notably, while ROS production rose at 1000 μg/L, SKN-1::GFP and GST-4::GFP expression decreased compared to the 10 μg/L group, suggesting a compensatory response in C. elegans at lower exposure levels. The expression of oxidative stress-related genes and phenotype of differentially expressed genes indicated that C. elegans was in a compensatory phase when exposed to 10 μg/L of PU NPs, participating in the protective response of C. elegans to PU NPs. However, when exposed to 1000 μg/L of PU NPs, C. elegans was in a decompensatory phase, participating in the toxic regulation of PU NPs. In addition, under 10 μg/L PU NP exposure, cinnamon essential oil (CIEO) can enhance the expression of more antioxidant enzymes, thereby increasing the protective effect. Under 1000 μg/L PU NP exposure, CIEO could alleviate the toxic response of C. elegans to PU NPs exposure by promoting the expression of skn-1. Molecular docking analysis showed that the main active component of CIEO, cinnamaldehyde (CID), has a strong affinity with SKN-1/Nrf2. Our study is the first to emphasize the toxic effects of PU NPs on environmental organisms at ERCs and that CIEO might serve as a potential antidote for nanoplastic poisoning.