# Reality Check: Experimental Studies on Microplastics Lack Realism
## 6 Leached Chemicals  
### Aquatic Effects  
Plastics contain chemical additives such as phthalates and BPA (bisphenol a) that can leach out and cause toxicity ([PERSON] et al., 2019). In addition, contaminants, such as PCBs (polychlorinated biphenyls), metals, and pesticides, adsorb to plastic ([PERSON] et al., 2019). Many studies investigating the impacts of MPs use fresh (\"virgin\") plastic particles, but after weathering in the environment, particles acquire attached chemicals and are potentially more toxic than virgin particles. The use of pristine particles in many experimental studies could lead to an underestimation of the toxicological impacts. MPs could be considered \"vectors\" for moving contaminants into animals and up the food chain ([PERSON] et al., 2019; [PERSON] et al., 2019). The leaching of plastic additives as well as adsorbed chemicals makes MPs a \"cocktail\" of toxic contaminants ([PERSON] et al., 2019). Similar to other studies, most of the studies on chemical toxicity of MPs have used microbeads, not MFs, while studies comparing the two have suggested that MFs are more detrimental to organisms than microbeads (see earlier section), which could lead to further underestimation of MP impacts. A study of MFs from cigarette butts emphasized the concern about attached chemicals from tobacco as a source of ecotoxicity ([PERSON] et al., 2019). MFs are rarely studied for the toxicity of associated chemicals, even though dyes and hundreds of other chemicals used in the manufacture of textiles (e.g., antimicrobials, fire retardants, stain resistance chemicals) are toxic ([PERSON] et al., 2019; [PERSON] et al., 2019) (Figure 1). A key question is how tightly bound the chemicals are to the plastic versus how available they are to biota. The degree of availability depends on factors including the polymer, the chemical, and the surrounding environment. After ingestion, additives may leach and adsorbed chemicals may desorb ([PERSON] et al., 2019; [PERSON] et al., 2019; [PERSON] et al., 2019). Since ingestion is the most often studied type of exposure, it is important to study what proportion of the plastic additives and attached contaminants can be \"pulled off\" in the digestive system of different animals during the period of time that the MPs are going through the gut; this is likely to vary with the chemical, the type of MP (as seen in [69]), and the complexity, length, and chemistry of the gut (some invertebrates have alkaline stomachs rather than acidic stomachs similar to vertebrates). [PERSON] et al. (2014) investigated the potential for polyvinylchloride and polyethylene MPs to sorb and desorb various organic chemicals including \({}^{14}\)C-DDT, \({}^{14}\)C-phenanthrene,\({}^{14}\)C-perfluorocetanoic acid and \({}^{14}\)C-di-2-ethylhexyl phthalate [70]. Desorption was measured in seawater and under simulated gut conditions. Desorption was faster with gut surfactant and increased more in conditions simulating warm blooded organisms. [PERSON] et al. (2014) exposed amphipods (_Allorchestes compressa_) to MPs spiked with polybrominated diphenyl ethers (PBDEs) and found the amphipods assimilated the PBDEs [71]. Studies have found evidence for transfer of contaminants from MPs into organisms. Japanese medaka (_Oryza latipes_) were fed diets for ten weeks with 500, 1000, or 2000 \(\upmu\)g/g 10 \(\upmu\)m fluorescent spherical polystyrene MPs during maturation from juveniles to reproductive adults [72]. No changes in mortality, behavior, or growth were seen, and MPs were egested after 3-4 days. Nevertheless, females had dose-dependent decreases in number of eggs, and histological analysis showed changes in spleen and kidney. However, microscopic examination, histologic sections, and scanning electron microscopy found no MPs in any internal organs. Since MPs did not penetrate into tissues, toxic effects were attributed to the leaching of chemicals from the particles. [PERSON] et al. (2020) found abnormalities in MF-exposed medaka (_Oryza latipes_), including various pathologies in the gills [73].