# Microplastic Pollution: Chemical Characterization and Impact on Wildlife
## 3 Microplastics and Wildlife
### Microplastics in Aquatic Animals
Total food intake ratios in zebrafish were reduced by 64.3-69.6% after exposure to PS + BSA at the five observation timepoints (1-5 min), indicating that total food intake was approximately only 30% of that of controls at the 5 min timepoint for the corona complex. As a result, when zebrafish were exposed to PS + BSA, their food intake was significantly reduced compared to the control, BSA, and PS groups. PS + BSA exposure contributed to lower Keap1-Nrf2-ARE antioxidant signaling pathway transcript and protein levels as opposed to PS exposure alone. Figure 9 reports that exposure to PS + BSA deteriorated the potent antioxidant action of related enzymes and led to the formation of reactive oxygen species (ROS), potentially causing significantly more gastrointestinal damage than PS exposure alone. Consider Figure 9a which demonstrates a significant change in the level of catalase after exposure to MPs. Catalase is crucial for the bioregulation of hydrogen peroxide in organisms, and alteration of the enzyme's activity suggests MPs may play a role in altering levels of reactive oxygen species (ROS). Figure 9b is even more concerning, as it illustrates a significant decline in superoxide dismutase (SOD) activity after exposure to MPs. Superoxide (O\({}_{2}\)\({}^{-}\)) is highly reactive and must be regulated in organisms through the action of SOD or it will cause massive cellular damage. The large decline in SOD activity observed by the investigators is of significant concern as it implies that MPs may cause significant cellular level disruption via oxidative chemistry. The authors also found levels of reactive oxygen species (ROS) more than doubled when MPs were administered--confirming suspicions that MPs affect cellular-level oxidative balance. The results presented in Figure 9 are quite troubling since they suggest MPs cause seismic shifts in cellular chemistry within the zebrafish model. Such changes would be expected to exert substantial impacts on the lifeform. Microphatics (MPs) may make it easier for organic contaminants like hydrocarbons present in oil to reach organisms by adsorbing onto MP surfaces. [PERSON] et al. investigated mussels that were exposed for 21 days to 4.5 \(\upmu\)m polystyrene microplastics alone or with sorbed water accommodated fraction (WAF) of crude oil in two dilutions (25% termed MP25, and 100% termed MP100) [75]. Microplastic exposure was found to alter glutathione transferase and isocitrate dehydrogenase enzymatic activity in the mussels' body, caused genotoxicity, increased oocyte atresia and basophilic cell volume in digestive tubules, and decreased absorption efficiency. Aquatic animals like mussels are exposed to mixtures of microplastics and polycyclic aromatic hydrocarbons (PAHs) particles that enhance the bioaccumulation and biotransformation of MPs which can enter the food chain of humans and animals that can lead to health hazards to the top predators. PAHs concentrations in control mussels and mussels exposed to MPs alone were close to detection limits and were comparable to PAHs concentrations measured in mussels exposed to MP25 and MP100. The total amount of PAHs measured ranged from \(142\pm 39.27\) to \(188\pm 40.29\) ng/g dry weight (control group and MP100, respectively) on day 7 and from 156 \(\pm\) 11.42 to 247 \(\pm\) 59.39 ng/g dry weight (MP and control group, respectively) on day 21. Naphthalene was the most common PAH in all cases. Mussels exposed to WAF bioaccumulated many PAHs, particularly on day 7. Total PAH values were higher on day 7. Figure 9: CAT activity (**a**), SOD activity (**b**), and ROS content (**c**) in zebrafish intestines after 14- and 21-day exposures to BSA, PS, or PS + BSA. * \(p\) < 0.05 and ** \(p\) < 0.01 indicate significant differences between the treatment groups and the control group. # \(p\) < 0.05 indicates significant differences between the two groups indicated. Figure reproduced from [PERSON] et al. [74] with permission.