Seite - 54 - in Freshwater Microplastics - Emerging Environmental Contaminants?

relatively comparable results due to the standardized sampling instrument [5].The applications of corers allows the determination ofmicroplastic depth profiles but results in small samplevolumes (25cm3)and is so faronly reported for themarine environment [6].Thedifferences betweenmicroplastic studies for the samplingof shore sediments start with the selection of the sampled area. Shore sediments are collectedparallel, perpendicular, or randomly selected indifferent distances to the shoreline. Themajority of the studies reports the collection of grid samples with samplingdepthsof2–5cmoftheuppersediment layer[7,8].Otherstudiesstate the sampling in relation to the lowest flotsam line of the waterbody [9, 10]. Sample collection is usually carried out with stainless steel spoons, trowels, or shovels [10,11]. Inaddition, thesamplingprocedureusedwillaffecthowthecorresponding results are reported. For example, studies that use grid samples usually report the results per surface sampled (e.g., m2), whereas studies based on aerial bulksamplesgive theresults referred to thevolumeormassof thecollectedsample (e.g.,m3or kg). During thesamplingand thesamplepreparation, it is important toavoidcontact with plastic equipment to keep the contamination by the method low. If plastic vessels are included for transportation, blank samples must be also analyzed to quantify theircontribution to themicroplastic loadof thesample[8,10]. Ingeneral, blank samples need to be regarded inmicroplastic studies to estimate the limit of quantification of eachmethodused, as the limit of quantification (LOQ) ismainly affected by the background contamination [12]. Especially studies dealing with fibersoftenneglectedtheanalysisofblanksamples; thus, theresultsobtainedmight be of limited validity. Moreover, the entire method starting from the sample preparation to the analytical detection must be critically evaluated. Therefore, a proper validation must be performed, which also allows a good comparability between different studies. This includes, for example, the determination of within-site variabilities for the sampling process or the determination of recovery rates for the separationmethods usedduring the sample preparation [10, 13, 14]. 1.2 SamplePreparation Even largemicroplastics like plastic pellets, especially aged and fouled ones, are difficult todistinguish fromnaturalmatter in surfacewater sampleswith thenaked eye. Various methods were developed that allow the mechanical separation of microplastics from the sediment and the removal or reduction of natural debris in thesampleprior toanalysisof the separatedparticles.Avarietyof techniqueshave beenusedduring the sample treatmentand themicroplastic identification.Because not all studies conducted extensivemethod validation including the determination of recoveryof themicroplasticparticlesordidnotprovideexperimentswithblank samples, the resulting data can lack comparability. 54 S.Klein et al.