# Microplastic Pollution: Chemical Characterization and Impact on Wildlife
## 3 Microplastics and Wildlife
### Microplastics in Birds  
Microplastics are nowadays very extensive pollutants prevailing in seas that enter the plankton forages and zooplankton. The authors investigated 30 storm petrels (_Hydrobates pelagicus melitensis_) in the Mediterranean Sea which foraged with zooplankton, and they found 45% of the sampled storm petrels had previously ingested microplastics via food. They suggested that storm petrels could be used as an effective indicator for microplastic pollution/ingesion in the pelagic seabirds. Microplastic pollution in terrestrial ecosystem suggests that MPs transform from source to top predators by entering the food chain and soil is the great reservoir of MPs. [PERSON] et al., 2022 investigated the barn owl (_Tyto alba_) diet which is characterized by predation on synanthropic rodents. Pellets collected from owls contained MPs and were analyzed by micro-Fourier Transform Infrared Spectroscopy (\(\mu\)-FTIR). Authors found 33% of pellets were containing MPs, mainly macrofibers (88.2%) [81]. Microplastic pollution can cause myocardial dysplasia by the influence of endoplasmic reticulum (ER) stress-controlled autophagic pathways in terrestrial birds. [PERSON] et al. [82] developed an in vivo chick model for administering polystyrene microplastics (PS-MPs) in different concentrations (1 mg/10 mg/100 mg/1000 mg per liter of water) to chosen 12-day-old chicken embryos in vitro and then extracting primary cardiomyocytes for investigating the effect of PS-MPs on myocardial development. After a histopathological study, they found loose and irregular myocardial tissue arrangement with large cell gaps and damaged myocardial fiber bundles after PS-MP exposure, as observed in Figure 10. In addition, ER stress markers GRP78, PERK, eIF2\(\alpha\), IRE1, ATF4, ATF6, and CHOP were overexpressed, autophagy-related genes LC3, ATG5, Beclin1, and P62 were down-expressed, and TnnT2, Nkx2-5, Gata4, TBX5, and ACTN2 were downregulated after PS-MPs exposure. The TnnT2 gene expresses cardiac troponin T, a protein involved in the regulation of muscle contraction. Nkx2-5, TBX5, and Gata 4 have been shown to be crucial for the development of the heart in experimental animal models. ACTN2 is responsible for crosslinking filamentous actin molecules in tissues. In addition to the visually observed histopathological damage to the myocardium (Figure 10A), the highly significant, dose-dependent downregulation of the mRNA for these genes reported in Figure 10 suggests MPS administered to the chick embryos had substantial deleterious effects on the heart of the animals tested. So, the authors hypothesized that PS-MPs-induced myocardial dysplasia in birds is driven by the ER-stress-regulated autophagic pathway. Figure 10: Effects of PS-MPs exposure on myocardial development. (**A**) Histopathological damage to the myocardium at different concentrations of PS-MPs (objective magnification of 10\(\times\) and 20\(\times\)). (**B**) Relative mRNA expression level of TnnT2, Nkx2-5, Gata4, TBX5 and ACTN2. (**C**) Heat maps of relative mRNA expression. (**D**) Protein level of Gata4 and ACTN2. The results are presented as mean \(\pm\) standard deviation (SD), compared to the control group, ***\(p\) < 0.001. Figure reproduced from Ref. [82] with permission of publisher. Naturally aged polystyrene microplastics affect the different biomarkers of the small-sized terrestrial bird (_Coturnix Coturnix japonica_). [PERSON] et al. (2018) investigated birds that were assigned in two groups and fed with either 11 and 22 microplastic particles/day/bird, once a day for 9 days, and observed the effects in different organs. The groups were denoted by MP-I for 11 particles and MP-II for 22 particles of MP. The animals in the control group did not receive any type of plastic particles. Results found that significant reduction in body biomass in the MP ingested group and total reactive oxygen species (ROS) levels in muscle and liver in quails are higher in MP-I (average increase of 17.4%) and MP-II (average increase of 23.2%) groups.