From the sea to the laboratory: Characterization of microplastic as prerequisite for the assessment of ecotoxicological impact
Key point 1: Understanding the environmental behavior of microplastic (MP) requires extensive knowledge about their physical-chemical characteristics; the relevance and implementation of an improved particle characterization for meaningful ecotoxicological testing is elaborated in theframe of this commentary. Key Point 2: MP in water bodies has to be perceived as a mixture of particles with diverse characteristics, and the importance of single parameters for assessing the environmental hazard of microplastic will be prospected. Key point 3: As MP in the environment is subject to changes due to weathering processes, the investigation of both pristine and weathered MP under controlled laboratory conditions are recommended, and challenges regarding the characteristics of weathered particles will be discussed. Key Point 4: An improved particle characterization of MP is the basis to understand the relevant differences between well-defined and weathered as well as environmental MP and hence, the key for interpretation of ecotoxicological data and finally improved hazard assessment. // The presence of microplastic (MP) in the aquatic environment is recognized as a global-scale pollution issue. Secondary MP particles result from an ongoing fragmentation process governed by various biotic and abiotic factors. For a reliable risk assessment of these MP particles, knowledge about interactions with biota is needed. However, extensive testing with standard organisms under reproducible laboratory conditions with well-characterized MP suspensions is not available yet. As MP in the environment represents a mixture of particles differing in properties (e.g., size, color, polymer type, surface characteristics), it is likely that only specific particle fractions pose a threat towards organisms. In order to assign hazardous effects to specific particle properties, these characteristics need to be analyzed. As shown by the testing of particles (e.g. nanoparticles), characteristics other than chemical properties are important for the emergence of toxicity in organisms, and parameters such as surface area or size distribution need consideration. Therefore, the use of ""well-defined"" particles for ecotoxicological testing (i.e., standard particles) facilitates the establishment of causal links between physical-chemical properties of MP particles and toxic effects in organisms. However, the benefits of well-defined particles under laboratory conditions are offset by the disadvantage of the unknown comparability with MP in the environment. Therefore, weathering effects caused by biological, chemical, physical or mechanical processes have to be considered. To date, the characterization of the progression of MP weathering based on powder and suspension characterization methods is in its infancy. The aim of this commentary is to illustrate the prerequisites for testing MP in the laboratory from 3 perspectives: (i) knowledge of particle properties; (ii) behavior of MP in test setups involving ecotoxicological test organisms; and (iii) accordingly, test conditions that may need adjustment. Only under those prerequisites will reliable hazard assessment of MP be feasible.