Seite - 168 - in Freshwater Microplastics - Emerging Environmental Contaminants?

in the gills (5 and 20 μm), gut (5 and 20 μm), and liver (5 μm) [38]. Indeed, histopathological analysis revealed an inflammatory response andaccumulationof lipids in the liver as well as oxidative stress. However, these findings were only significant at high concentrations (2mgL 1) of 0.07 and 5μmbeads. In compar- ison,Karamiet al. [37]observedhistological alterations in thegills (e.g., basal cell hyperplasia and necrosis in connective tissue) and blood biochemistry parameters (e.g., plasma cholesterol levels, bloodHDL levels) of theAfrican catfish (Clarias gariepinus) at lower concentrations ofHDPEfragments (50μgL 1).More severe changes (epithelial lifting, hyperplasia, extensivecell sloughing)were reported for higher particle concentration (500 μg L 1). Additionally, concentrations of 500μgL 1significantlyaffected thedegreeof tissuechange in the liverofexposed individuals. Overall, the authors point toward ethylenemonomers (released from HDPE) and internal as well as external abrasions (caused by sharp edges of the fragments) as possiblemechanisms for the changes in biomarker responses. It is well documented that suspended solids can damage organs in several fish species andcause adverse effects similar to thoseobserved forMPs.Highconcen- trations of SPMcan accumulate in the gills, disturb the respiratory function, and have been found to translocate into epithelial cells, cause lipid peroxidation, and reduce the tolerance of infection bypathogens [67, 68].Additionally, studieswith gill epithelial cells (rainbow trout, RTgill-W1) and fluvial fine sediment revealed translocation of fineminerals (<2 μm, 10–250mgL 1) into the cells as well as material-related cytotoxicity [69]. Here, quartz and feldspar only caused sporadic changes inbiomarker response, andexposure tomica (silicateminerals)andkaolin inducedcytotoxicityaswellas free radicalsandcellmembranedamage.Therefore, Michel et al. [69]conclude that theuptakeoffineparticlesbygill epithelial cells is a common natural event in aquatic species with the material, size, shape, and concentrationdetermining the impacts. 3.2 Chemical Impacts Sofar,MPsdetectedinfreshwaterenvironmentsrepresentarangeofmaterial types (e.g., PE,PS,PET,PVC,PA, andPP), originate fromvarious sources andapplica- tions, and represent a plethora ofmaterial characteristics. In general, plasticmate- rials are highly functional compounds of synthetic polymers and additives (e.g., plasticizers, flame retardants, colorants). Leachates from diverse plastic products were found to cause chemical toxicity [70, 71] induced bymonomers, residues of production processes (e.g., catalyzers, stabilizers), and additives. For instance, some leaching components were classified as endocrine disrupting chemicals 168 C.Scherer et al.