Using Earthworm (Aporrectodea caliginosa) as Vital Soil Pollution Bio-indicator for Microplastic Toxicity

The present study investigates the toxicological effects of microplastics (MPs) on the earthworm species Aporrectodea caliginosa, a vital bio-indicator of soil health. Microplastics, resulting from the fragmentation of larger plastic debris, pose significant environmental threats due to their ability to transport harmful substances such as pesticides, heavy metals, and pathogenic microbes. This research focuses on three types of MPs: polyester, polyacrylic, and polyethylene, commonly found in the Egyptian environment. Earthworms were exposed to varying concentrations of these MPs. Acute toxicities and morphological abnormalities were assessed on A. caliginosa. Survival rates were recorded for five weeks. Additionally, soil physicochemical parameters were assessed at the end of the experiment. The obtained results revealed physical damage and morphological abnormalities induced by MPs. In addition, there was a dose-dependent decrease in earthworms' number and survival rates, with polyacrylic MPs showing the highest toxicity, followed by polyethylene and polyester. Furthermore, the introduction of MPs into soil increased soil pH and water holding capacity (WHC). Polyacrylic had no marked influence on soil nutrients, while polyester and polyethylene significantly decreased total N and available P contents. In conclusion, microplastics, particularly polyacrylic and polyethylene, were found to harm both the soil environment and Aporrectodea caliginosa. Overall, microplastics could trigger negative consequences for soil ecosystems. Therefore, this study emphasizes the need for urgent management of plastic waste, with the goal of substantially reducing the release of microplastics into the environment.