Page - 30 - in Freshwater Microplastics - Emerging Environmental Contaminants?

read-across for regulatory purposes [24]. For example, if data exist on the toxicity of a certain nanomaterial, can these data then be used to assess the safety of a similar nanomaterial? Onwhat parameters should these two particles be similar: size, shape, surface chemistry?Andwhen is ‘similar’ similar enough tobeconsid- ered ‘the same’? This discussion will be relevant for nano- and microplastics, should legislative frameworks require regulatory data on their environmental safety. According to European legislation, polymers are currently exempted from registration under REACH [25]. However, thismay change in the future,making thediscussionof ‘sameness’also relevant forprimarynano-andmicroplastics.For secondary microplastics, sameness is likewise relevant to categorising particles occurring in the environment, as well as to comparing observed behaviour and effects of nano- andmicroplastic particles betweendifferent scientific studies. Thecharacteristicsandchemicalcompositionofparticleshaveconsequencesfor the feasibility of detection and quantification of particles, especially in environ- mental samples and biota. It is highly challenging to detect engineered nano- materials in the environment, especially due to their small size. Under controlled laboratory conditions, with known nanomaterials, techniques based on electron microscopy, mass spectrometry and spectroscopy can be applied to investigating the behaviour of the nanomaterials in the test system [26].However, applying the same techniques to the detection and quantification of nanomaterials in a natural environmental matrix is not straightforward – even when looking for a knownnanomaterial.For this reason,monitoringdata forengineerednanomaterials are practically non-existent. One of the main problems is that the nanomaterials maybemodified through samplepreparation (e.g., causingdissolutionor aggrega- tion),making it difficult to ‘extract’ theparticles fromthe sample in their naturally occurring state [26]. Electronmicroscopy, in combination with elemental ratios, has successfully been applied in detecting TiO2 nanoparticles released from sun- screen into lake surfacewaters [27].Comparing elemental ratioswas necessary in order todistinguishnaturalTi-bearingparticles fromtheirengineeredcounterparts. Even for engineered nanomaterials made of non-ubiquitous elements (e.g. Ag), detection is not straightforward due to complicated sample preparations, matrix interferences and analytical difficulties in distinguishing between different metal species [28]. Nano- andmicroplastics pose additional challenges due to their organic origin, affecting and limiting the analytical options when they are present in an organic matrix.While the larger-sized fractions can be collected or extracted fairly easily, for example, by filtering water samples or density-based fractionation of sand, it becomes increasingly difficult to distinguish smallermicroplastics, and especially nanoplastics, from the surrounding environmental matrix. At the same time, sec- ondary nano- andmicroplastics, which constitute themain environmental load of plastic particles, are irregular in shape, resulting from their formation through fragmentation rather than controlled production. Also, they are often transparent, semi-transparent or neutral in colour. A study has been carried out to compare stereomicroscopy and Fourier transform infrared spectroscopy (FT-IR) as 30 S.Rist andN.B.Hartmann