Seite - 266 - in Freshwater Microplastics - Emerging Environmental Contaminants?

to formulate the right questions and to adapt or develop suitable test designs with adequate endpoints.This alsoapplies tobiomarkers used infield studies. Above all, scientists should consider that organisms are adapted to natural particles of differentmaterials (sand, clay, or similar), butwith similar properties asMP, in their natural habitats. It is crucial to perform tests onMP particles in comparisonwithsuchnaturalparticles.Thisappliesespecially totestsregardingthe “Trojan horse effect” – the transport of hydrophobic substances via MP into organisms (see [50]). Studies need to addresswhether there are differences in the sorption of chemicals to MP versus natural particles and, consequently, in the impact to organisms. In fact, there are regulations for priority substances bound to suspended matter – and MP particles are included in the suspended matter. Unfortunately,mostecotoxicologicalstudies lackadirectcomparisonofsuspended matter spikedwith chemicals toward spikedMPparticles.Knowledge about those aspects couldhelp to prioritize regulatory questions. 3.8 The InformationBase forRegulation:TooScarce?Too Much? Inapplicable? Even though scientists continuously provide new findings about MPs, it still provides a huge challenge for numerous scientific fields. The group of MPs comprises particleswith countless physicochemical properties determining their environmental fate and risk to organisms. It seems to be a playground for researchers to investigate open questions ranging from degradation process, uptakebyorganisms, and interactionwithchemicals to special surfaceproperties of aged plastics. Knowledge about those aspects is fundamental but in sum too complex to be considered for regulation. Wehave to formulatewhat information isneededfor regulationandwhatkind exceeds the scope of generalized regulation instruments.While the current lack of knowledge is obvious, this should not serve as a general excuse for delaying an implementation of regulation instruments for those persistent materials. To refer to the initial statements of this chapter, we have to ask ourselves which kind of knowledge is required to justify the need for regulation of highly persistentMP? Whilewe can clearly state that regulatory strategies for a reductionof environ- mental (micro)plastics are urgently needed,many questions about the implemen- tation ofmonitoring and regulatory strategies are still open: • How todefinemicroplastics? • Can we adopt existing regulative options or do we need to develop new strategies? • Which criteria can categorizeMPs for regulatory purpose? • Whichparticles have to be regulatedwith priority? • Whichmonitoringmethods can adequately answer regulatory questions? 266 N.Brennholt et al.