Effects of PET microplastics on the physiology of Drosophila

Highlights

• The higher the concentration of PET-MPs was, the more obvious impact on flies became.

• PET-MPs increased the spontaneous activity of flies for 24 h.

• PET-MPs reduced egg production in female flies.

• PET-MPs decreased lipid, glucose content and starvation resistance in male flies.

Abstract

Microplastics, as a new type of pollution, have attracted global attention and have become a research focus in recent years. Given the small size of microplastics, they can be ingested by many organisms. In addition, microplastics can enter the human body through the food chain. So, the potential dangers of microplastics can't be ignored. This study took Drosophila as a model organism to delve the physiological effects of polyethylene terephthalate microplastics (PET-MPs). Here, we reported that the higher concentration of PET-MPs was, the more obvious the effect became. The amount of oviposition decreased in female flies exposed, indicating that microplastics affected reproduction. PET-MPs caused the decrease of triglyceride and glucose content in male flies, as well as the decrease of starvation resistance, suggesting the effect of microplastics on energy metabolism. In addition, the 24-h spontaneous activity of flies exposed to PET-MPs increased significantly. The experimental results can help understand the potential impact of microplastics on physiology.

Introduction

Microplastics are any polymeric matrix or synthetic solid particle, with size ranging from 1 μm to 5 mm and with regular or irregular shape (Frias and Nash, 2019). Plastic production is growing exponentially (Rochman et al., 2013). Since plastic is difficult to degrade, it will exist in the ecological environment in the form of microplastics for a long time after physical, chemical and biological actions. Microplastics pollution will become more and more serious. Tiny degradable plastic lurked in the oceans (Chubarenko et al., 2016), lakes (Xiong et al., 2018), soil (Rillig, 2012) and even in the air (Gasperi et al., 2018). Microplastics have also been found in drinking water (Koelmans et al., 2019), salt (Peixoto et al., 2019), seafood (Smith et al., 2018) and other foods. From plankton (Desforges et al., 2015) to earthworms (Rillig et al., 2017), from fish to humans, microplastics are consumed, causing a serious health threat to entire ecosystems.

Studies have shown that microplastics can be ingested by marine organisms, causing physical damage by blocking feeding auxiliary organs and digestive tracts. In addition, microplastics can also bring toxicological effects, such as oxidative damage (Lei et al., 2018b), increase of inflammation (Jin et al., 2018), decrease of immunity (Sharifinia et al., 2020), disorder in intestinal microorganism, hepatic metabolic disorders (Feng et al., 2021), fake fullness, decline in growth rate and increase in mortality (Jemec et al., 2016). Microplastics lead to decline in reproductive ability and has an impact on the production and development of offspring (Wang et al., 2019). In addition, the recent studies indicated that Polystyrene microplastics (PS-MPs) can cause inflammatory effects on human A549 lung cells and induce apoptosis in several human cell types, including human monocytic leukemia cell line (THP-1), human colon carcinoma cells (Caco-2), and human lung cancer cells (Calu-3) (Yee et al., 2021). Besides, microplastics have higher specific surface area than general plastics, and are easy to absorb organic pollutant such as perfluorinated compounds, fluorobenzene, aromatic hydrocarbons, polyfluorinated biphenyls, as well as substances such as heavy metals, bacteria and viruses, bringing mixed chemical pollution (Zhang et al., 2018; Verla et al., 2019). These contaminants are passed through the food chain and accumulate in living organisms, which may cause harmful effects on human health.

At present, the research on the harm of microplastics mostly focuses on two types, polyethylene (PE) or polystyrene (PS) (Lei et al., 2018a; Yin et al., 2018a; Enyoh et al., 2020; Malafaia et al., 2020; Matthews et al., 2021). There are few studies on other types of microplastics. In this experiment, Polyethylene terephthalate (PET) was chosen for research. PET is mainly used as packaging material and accounts for 7.1% of total plastic consumption in Europe. In addition, because of its high impact resistance, friction resistance and mechanical properties, it widely used in mineral water and carbonated beverage bottles. In the analysis of particles in the water, PET accounted for 84% in recyclable plastic bottles, and 31% in beverage bottles (Schymanski et al., 2018). An Austrian study shows that there are nine different types of microplastics found in human's feces, and the most common types are polyethylene terephthalate (PET) and polypropylene (PP) (Harvey and Watts, 2018). At the same time, 12 particles of microplastic were found in the placentas of 4 women (Ragusa et al., 2021). As a plastic type closely related to human life, the harm of the PET-MPs should not be overlooked.

In this experiment, Drosophila was selected as a biological model to explore whether PET-MPs would have an impact on physiology. The comparison of the genome sequences of Drosophila and human revealed a high degree of homology, which confirmed the feasibility and reliability of Drosophila as a model for the study of human diseases. It has been estimated that nearly 75% of human disease-related genes have functional direct-homologs in Drosophila. The results showed that PET-MPs increased the spontaneous activity of Drosophila (P < 0.01). PET-MPs decreased TG and glucose content in male flies (P < 0.05) and reduced the resistance to starvation in male flies (P < 0.05). PET-MPs reduced the amount of eggs laid (P < 0.05). In general, the experiment shows that the higher the concentration of PET-MPs was, the more obvious impact became on Drosophila.