Abstract
Tire-wear particles (TWPs) are being released into the environment by wearing down during car driving, and are considered an important microplastic pollution source. The chemical additive leaching from these polymer-based materials and its potential effects are likely temporally dynamic, since amounts of potentially toxic compounds can gradually increase with contact time of plastic particles with surrounding media. In the present study, we conducted soil toxicity tests using the soil nematode Caenorhabditis elegans with different soil pre-incubation (30 and 75 days) and exposure (short-term exposure, 2 days; lifetime exposure, 10 days) times. Soil pre-incubation increased toxicity of TWPs, and the effective concentrations after the pre-incubation were much lower than environmentally relevant concentrations. The lifetime of C. elegans was reduced faster in the TWP treatment groups, and the effective concentration for lifetime exposure tests were 100- to 1,000-fold lower than those of short-term exposure tests. Water-extractable metal concentrations (Cr, Cu, Ni, Pb, and Zn) in the TWP-soils showed no correlation with nominal TWP concentrations or pre-incubation times, and the incorporated metals in the TWPs may be not the main reason of toxicity in this study. Our results show that toxic effects of TWPs can be time-dependent, both in terms of the microplastic particles themselves and their interactions in the soil matrix, but also because of susceptibility of target organisms depending on developmental stage. It is vital that future works consider these aspects, since otherwise effects of microplastics and TWPs could be underestimated.
Highlights
Since the first car tire was produced in 1895, their global production has risen due to a steady increase of the motor vehicles market (Baensch-Baltruschat et al, 2020; Halle et al, 2020)
There was no effect on survival rate after the short-term exposure period (2 days, Figure 2A), but significant inhibition in growth started at 100 mg kg−1 of Tire-wear particles (TWPs) concentration (Figure 2B)
Other soil organisms have been shown to be negatively affected by TWPs: The growth of the earthworm (Eisenia fetida) was reduced in soil mixtures containing virgin crumb rubber (50:50) after a 33 days exposure period (Pochron et al, 2017), whereas no effect was observed in black worms (Lumbriculus variegatus) at
Summary
Since the first car tire was produced in 1895, their global production has risen due to a steady increase of the motor vehicles market (Baensch-Baltruschat et al, 2020; Halle et al, 2020). The first identification of tire rubbers in road dust was reported not before 1966 (Thompson et al, 1966), and they have been considered as a vehicle-derived pollutant (Bogdan and Albrechcinski, 1981). About 1.3 million tons of tire particles are generated annually in Europe (Wagner et al, 2018), and the global emission is estimated to be more than 3.3 megatons (Kole et al, 2017).
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