A serial dilution method for assessment of microplastic toxicity in suspension

Abstract

The occurrence of microplastic (MP) in the environment is of global concern. MP risk assessment, however, is currently hampered by lacking ecotoxicological methods due to conceptual and practical problems with particle exposure. Natural particles of similar size as MP, e.g., clay and cellulose, occur abundantly in the environment. For MP risk assessment and regulation it must be established whether the addition of MP to these particles represents an additional hazard. We present a novel approach employing a serial dilution of MP and reference particles, in mixtures, which allows the differentiation of MP effects from other particulates. We demonstrate the applicability of the method using an immobilisation test with Daphnia magna exposed to polyethylene terephthalate (MP) and kaolin clay (reference material). In the concentration range of 0.1 to 10000 mg L-1 of total suspended solids (TSS), with MP contributing 0-100 %, the LC50 values for MP-kaolin mixtures were significantly lower compared to the pure kaolin suspension. MP particles were thus more harmful to daphnids than the reference material. The estimated threshold for %MP contribution above which higher mortality was observed was 1 % MP at 36 mg TSS L-1. This approach has a potential for standardisation of MP ecotoxicological testing as well as other particulate material of anthropogenic origin.\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC=\"FIGDIR/small/401331_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (40K):\norg.highwire.dtl.DTLVardef@13e1153org.highwire.dtl.DTLVardef@1e37652org.highwire.dtl.DTLVardef@6d3efborg.highwire.dtl.DTLVardef@420d7a_HPS_FORMAT_FIGEXP M_FIG C_FIG