Page - 31 - in Freshwater Microplastics - Emerging Environmental Contaminants?

identification methods for microplastics in environmental samples. White and transparent fragments were identified through FT-IR, but not easily detected by microscopy, leading to underestimation of the actual concentrations of micro- plastics [29]. Incontrast,fibres, identifiedascottonfibresbyFT-IR,weremistaken for microplastics by stereomicroscopy, leading to overestimation of microplastic fibres using this technique [29]. The development of FT-IR combined withmicrospectroscopy (i.e. micro-FT- IR) greatly improved the spatial resolution, allowing the identification of particles downtoa fewμm[30,31].The techniqueallowsmeasurementof transmissionand reflectance.Thefirstgivesahigher-qualityspectrum,but is limited to thinsamples, while the latter can also be applied to thick and opaque particles [32]. However, irregular surface structures (e.g. of plastic fragments) can lead to refractive errors when using the reflectance mode [30]. In this case, attenuated total reflectance (ATR) micro-FT-IR can be used to improve the quality of the spectrum. The standardFT-IRtechniques relyonavisualpre-sortingofpotentialplasticparticles, which is time-consuming and prone to errors [30]. Therefore, the coupling of micro-FT-IR with focal plane array detectors is considered a promising method for high throughput analysis of microplastics in complex environmental samples [30, 31, 33]. Currently, however, the technique is limited to particles larger than 10–20μm, and sample preparation is labour-intensive.As formanyof the analyt- ical techniques used for engineered nanoparticles, FT-IR is particularly useful for controlled laboratory testswithmicroplasticsofknowncomposition.Thismaterial canbe included in the spectral library and is thendetected in samples.However, it can be difficult to use FT-IR to identify unknownplastics particles fromenviron- mental samples, as the spectra of polymers change due to the weathering and chemicalchangesof thesurfaceof theplastics [29].Ramanspectroscopyisanother commonly usedmethod to identify plastic particles. In combination with micro- scopy (i.e.micro-Raman), a resolution of less than 1 μmis achievable.However, the applicability ofmicro-Ramanwith automated spectral imaging for analysis of an entire sample is yet to be demonstrated for microplastics in environmental matrices [32]. Thedevelopmentofmethods todetect andcharacterisenano- andmicroplastics in environmental matrices with a higher resolution, lower time consumption and high throughput is ongoing, comparable to the developments being made for engineered nanomaterials. The requirements for ideal analytical techniques are similar for both groups of particles. As previously described byTiede et al. [26], such techniques should (a) cause minimal changes to the physical and chemical stateof theparticlesduring samplepreparation; (b)provide informationonseveral physicochemical parameters, such as chemical composition, size, shape, etc.; and (c) be able to handle complex, heterogeneous samples [26]. AquaticEcotoxicity ofMicroplastics andNanoplastics: LessonsLearned from. . . 31