# Ecotoxicological Assessment of Microplastics in Freshwater Sources--A Review
## 5 Ecotoxicological Effects on Microplastics
### Ecotoxicological Effects on Fish  
MPs were detected in the intestine of fish caught in freshwater (urban areas [134], WWTPs down-streams [135]) and oceans (both: pelagic and demersal fish) [109]. PE, nylon, and polyamide [109; 136] were emphasized as the most abundant polymers. Exposure to MPs might have severe hazardous effects on fish including neurotoxicity [137], the reduction of predatory performance, growth, and reproduction [106], oxidative stress, and mortality [110]. Higher MPs concentration influenced mortality and length of larval fish in the case of European perch _Perca fluviatilis_[138]. Medaka fish _Oryzaias latipes_ was dietary exposed to the virgin and marine PE (<0.5 mm); the results showed bioaccumulation, liver stress, and even tumor formation [139]. _Oryzaias latipes_ embryos were also exposed to MPs with different CECs adsorbed (polycyclic aromatic hydrocarbons, polychlorinated biphenyl, polybrominated diphenyl ethers); MPs contributed to the transportation of CECs to embryos, negatively affecting juvenile growth and survival rate. MPs biomagnifications potential was studied as well [76; 140]. Once ingested, MPs come to the gastrointestinal tract; MPs < 150 \(\upmu\)m can pass through gut epithelium (i.e., it can penetrate into the organism), while those < 1.5 \(\upmu\)m can penetrate into organs. Yet, most MPs remain in the gastrointestinal tract. MPs ingestion can lead to increased biomagnification of MPs (and other contaminants, if adsorbed) in the food chains as toxins leach into tissue once present in the organism. Fish growth stage was correlated with the sensitivity to MPs exposure; results showed that embryos are much more sensitive than adults [106; 138]. [PERSON] et al. [126] investigated the presence of MPs in several freshwater species of fish (listed in Table 3); in 95.7% of subjected freshwater fish, MPs were found. The most abundant shape belonged to fibers, while cellophane followed by PET and polyester were the most abundant types. The most abundant shape of MPs found in the fishes from the Rio de la Plata also belonged to fibers (even 96%). The highest abundance of MP particles was found in the gut of fishes caught near sewage discharge as a sampling site [141]. On the other hand, the most abundant MPs shape found in fishes from the Amazon River estuary (97.4%) was detected as pellets and mostly pertained to polyamide [127]. Most of these MPs are found in stomachs (92.1%), while the rest was in the intestines. The ingestion of polyamide MP pellets is not surprising due to the high density of polyamide (1.13-1.15 g/m\({}^{3}\)) and the round shape of pellets, highly contributing to MPs accessibility to fishes. One of the freshwater organisms often used in ecotoxicological studies is zebrafish _Danio rerio_ (_D. rerio_). It has been proven that MPs can cause morphological deformations of _D. rerio_[125], as well as the changes of nervous (acetylcholinesteraseactive activity, AChE), visual [124] and immune system [142], oxidative stress (Reactive Oxygen Species -ROS) [125], reproductive toxicity [143], and damage of intestine [123], as shown in Figure 5.  
[PERSON] et al. [125] studied MPs (PS) accumulation in the adult _D. rerio_ over 7 days; 5 \(\upmu\)m particles were detected in gill, liver, and gut, while 20 \(\upmu\)m particles were not found in liver. [PERSON] et al. [144] exposed only male adult zebrafish to 5 \(\upmu\)m PS over 21 days and found a significant decrease of weight, influencing zebrafish condition and growth. Disruption of hepatic metabolism was noticed as well. [PERSON] et al. [124] exposed zebrafish larvae to micro- and nano-sized PS and found 22% inhibition of locomotor activity, including body length reduction for 6%, as well as neurotoxicity and genotoxicity. [PERSON] et al. [145] tested adverse effects of PS (50, 200, and 500 nm) on zebrafish's embryos; 50 nm particles passed through pores of chorion and penetrated into the body and were accumulated in tissues (brain, retina, blood vessels) and yolk. [PERSON] et al.