Seite - 34 - in Freshwater Microplastics - Emerging Environmental Contaminants?

investigating the potential biological effects of nano- andmicroplastics. Thiswill enable a differentiation between effects caused by the particle itself and effects causedbyplastic additives. 5 BiologicalEffects Engineerednanomaterials areoftendesigned tohaveacertain reactivity, function- ality or biological effect. As discussed, nano- andmicroplastics often stem from unintentional anthropogenic rather than engineeredprocesses.Evenwhen theyare intentionally produced, they are not as such intended to be biologically active. Certain polymer additives may, however, have the purpose of, for example, preventing biotic or abiotic degradation. For both engineered nanomaterials and nano- andmicroplastics, it is therefore useful to consider their intended use and properties when evaluating their potential environmental risk. Engineered nano- materials that are intended to have biocidal effects are likely to bemore toxic to non-targetorganisms thanmaterials intended tobe inert.Similarly,plasticparticles A B C I IIIII IV Fig. 3 Illustration of the potential vector function of particles. (a) The interaction between the particles (orange,filled) and the co-pollutants (purple,open)will dependon theproperties of the particles, the pollutant and the surrounding medium. This will result in various degrees of absorption and/or adsorption. (b) Theparticles andpollutants are transported in the environment – individually and co-transported. This has been referred to as the ‘environmental vector effect’ [9]. (c)Theparticles andpollutants interactwithbiological organisms.This canbevia ‘indepen- dent action’whereby theparticle and thepollutant interactwith theorganisms individually (I). It can also be via desorption of the co-pollutant (or leaching of ions/additive),which subsequently interact with the organism (II). The pollutant can also be co-transported into the organisms and potentially further into cells (III). This has been referred to as an organismal and cellular vector effect, respectively [9]. Finally, the particles can act as a ‘trap’ for the pollutants, thereby decreasing the interactions between thepollutant and the organisms (IV) 34 S.Rist andN.B.Hartmann