A novel method for assessing microplastic effect in suspension through mixing test and reference materials

Abstract

The occurrence of microplastic in the environment is of global concern. However, the microplastic hazard assessment is hampered by a lack of adequate ecotoxicological methods because of conceptual and practical problems with particle exposure. In the environment, suspended solids (e.g., clay and cellulose) in the same size range as microplastic, are ubiquitous. Therefore, it must be established whether the addition of microplastic to these background levels of particulate material represents a hazard. We present a novel approach employing a serial dilution of microplastic and reference particles, in mixtures, which allows disentangling the effect of the microplastic from that of the other particulates. We demonstrate the applicability of the method using an immobilization test with Daphnia magna exposed to polyethylene terephthalate (test microplastic; median particle diameter ~5 µm) and kaolin clay (reference material; ~3 µm). In the range of the suspended solids test concentrations (0–10 000 mg L −1 ), with microplastic contributing 0–100% of total mass, the LC 50 values for the plastic mixtures were significantly lower compared to the kaolin exposure. Hence, the exposure to polyethylene terephthalate was more harmful to the daphnids than to the reference material alone. The estimated threshold for the relative contribution of the test microplastic to suspended matter above which significantly higher mortality was observed was 2.4% at 32 mg of the solids L −1 . This approach has a potential for standardization of ecotoxicological testing of particulates, including microplastic.

Micro- and Nanoplastic Exposure Effects in Microalgae: A Meta-Analysis of Standard Growth Inhibition Tests

“…This should help to consolidate the search for convergent assays informing the risk assessment of plastic litter in aquatic ecosystems. Current standard toxicity testing is mostly developed for chemicals, not particulates with complex behavior resulting in particle aggregation and physical interactions with test organisms (Ogonowski et al, 2018;Gerdes et al, 2019). As a standard ecotoxicological endpoint, algal 2 | Practical recommendations for standardization of algal bioassays with micro-and nanoplastic and reporting routines based on the outcome of the meta-analysis.…”

Algal growth at environmentally relevant concentrations of suspended solids: implications for microplastic hazard assessment

“…Kaolin contains mainly the clay mineral kaolinite, a hydrous aluminosilicate, whereas cellulose is the primary substance in the walls of plant cells. Both materials occur globally in suspended particulates and have been used as reference material when assessing microplastic effects (Gerdes et al, 2019) and as a test material when assessing the effects of total suspended solids (Robinson et al, 2009;Ogonowski et al, 2018a). As a test microplastic, we used polyethylene terephthalate (PET, Goodfellow GmbH, product number ES306312) mixed with Milli-Q water passed through a 40-μm sieve to produce a size fraction similar to that of kaolin and cellulose.…”

Algal Growth at Environmentally Relevant Concentrations of Suspended Solids: Implications for Microplastic Hazard Assessment

“…Kaolin contains mainly the clay mineral kaolinite, a hydrous aluminosilicate, whereas cellulose is the primary substance in plant cell walls. Both materials occur globally in suspended particulates and have been used as reference material when assessing microplastic effects (Gerdes et al, 2019) and as a test material when assessing the effects of exposure to total suspended solids (Robinson et al, 2009;Ogonowski et al, 2018a,b).…”

“…However, plastic litter, including microplastic, is a new field in environmental pollution research with much-unsettled methodology, and standard methods for hazard assessment are not yet available (Adam et al, 2019). Current test methods in ecotoxicology are intended for soluble (at least partially) chemicals, whereas testing particle suspensions, such as microplastic, requires different approaches (Paul-Pont et al, 2018;Gerdes et al, 2019). Moreover, plastics are diverse: they represent different polymers and materials that include a broad array of chemical additives and come in many sizes, colors, and shapes (Rochman et al, 2019), which complicates comparisons between the effect studies (Reichelt and Gorokhova, 2020).…”