# Microplastics in Water Resources: Threats and Challenges
## 2 Microplastics in the Aquatic Environment
### Threats Resulting from the Presence of MPs in Aquatic Ecosystems  
MPs introduce chemicals and organic compounds into water, which can negatively impact water quality [30]. A particular type of MPs in this regard are PVC particles. Figure 1: Main sources and transport pathways of microplastics to the aquatic environment. To improve the processing and utility properties of this material, additives are added including phthalates in amounts ranging from 10% to 70% [31]. According to research from the PlastChem report, more than 16,000 chemicals are known to be present in plastic materials and products, with less than 6% of them currently subject to global regulations. For nearly 4000 plastic chemicals, their annual production volumes exceed 1000 tons. Numerous studies have demonstrated the potential for these substances to enter the environment. The content of plasticizers is primarily significant, but so is the shape and structure of MPs. A larger surface area promotes leaching, which is highest in the outer layer of plastic particles [32]. According to [PERSON] et al. [33], for PVC particles smaller than 42 \(\upmu\)m, the release of plasticizers occurs almost instantly upon contact with water, indicating that contamination by fine micro- and nanoplastics in the environment can quickly affect water quality. The rate of this process is directly correlated with the particle size, and even small changes in size have a significant impact on the duration and characteristics of the leaching process. Since larger microplastics (e.g., >136 \(\upmu\)m) are transported and dispersed worldwide [34], and can release plasticizers for up to 60 days, their harmful reach is greater than that of small particles. [PERSON] et al. [33] also point out the acceleration of the process at higher temperatures, which, in correlation with rising sea and ocean temperatures [35], creates an environmentally hazardous phenomenon. The leaching of phthalates has potential consequences for the water resources used for drinking, agricultural, and industrial purposes. Once in the environment, phthalates persist in every component through biogeochemical processes and can accumulate in the food chain, subsequently causing serious health effects in mammals [36]. The impact may be related to its ability to act as so-called endocrine-disrupting substances, which means that they can disrupt hormonal functions in the body. Phthalates are suspected to affect the hormonal system, especially by mimicking sex hormones [37; 38]. Furthermore, laboratory studies in animals suggest that phthalates may have a negative impact on the development of the reproductive system and may be associated with certain diseases such as diabetes, cancer, obesity, and immune system problems [39; 40]. MPs have a wide capacity to absorb toxic chemicals. There are reports of heavy metal adsorption, pharmaceuticals, and other organic substances in plastic microparticles. In laboratory studies, [PERSON] et al. [41] demonstrated the absorption of pharmaceuticals in the presence of MPs. The particles in the undegraded plastic had a much lower absorption capacity than those subjected to aging. The absorption capacity also varied depending on the particle size. Smaller MPs particles (below 35 \(\upmu\)m) absorbed more substances than larger particles (59-157 \(\upmu\)m). Among the plastics, the highest absorption occurred in PP, PA, and PVC. In a study by [PERSON] et al. (2021) [42], the adsorptive properties of heavy metals in polystyrene (PS) MPs were examined, as well as the bioavailability and toxicity of MPs and heavy metals in an experiment with hydroponic wheat seedlings. The results showed that PS microplastics (0.5 \(\upmu\)m, 100 mg/L) had no significant impact on the growth of wheat seedlings, photosynthesis, and the content of reactive oxygen species (ROS). However, PS microplastics could adsorb copper and cadmium, mainly through chemisorption.