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Effects of long-term exposure to tire wear particle leachate on life-cycle chronic toxicity and potential toxic mechanisms in the marine copepod Tigriopus japonicus
Summary
Researchers studied the long-term effects of tire wear particle chemicals on marine copepods across multiple generations and found severe impacts on survival, reproduction, and sex ratios. At the highest exposure level, no animals survived to the second generation, and females nearly disappeared from the population. The findings highlight that tire wear particles, a major source of microplastic pollution in coastal waters, can cause devastating multigenerational harm to marine organisms even through chemical leaching alone.
As a potential source of microplastic pollution, tire wear particles (TWPs) will persist for a long time and accumulate in coastal areas, which can lead to adverse effects to marine organisms. However, there is little information on the long-term toxicity of TWP constituents entering the ocean. In this study, the marine copepod Tigriopus japonicus was used as a model species to investigate the multigenerational toxicity and potential toxic mechanisms of TWPs. The results of the long-term chronic toxicity test showed that the TWP leachate could affect the growth, reproduction and sex ratio of copepods. Compared to the control group, after exposure to 0.85 g/L TWP leachate, the survival rates of T. japonicus were decreased to 73.3 % for F-1 generation and no animal of F-2 generation could survive. In addition, the average number of nauplii and the spawning frequency decreased by 60 % and 66 % for F-1 generation, respectively. As for sexual development, in the 0.85 g/L TWP leachate exposure group, the female proportion in the F-1 generation decreased to 22.6 %, and not a single female was even recorded in the F-2 generation. TWP caused significant differences in transcriptome and enzyme activity. A total of 3022 differential expressed genes were identified in T. japonicus exposed to the TWP leachate, among which 145 genes were up-regulated and 2877 genes were down-regulated. These genes were mainly related to oxidative stress, protein digestion and absorption, stratum corneum production, and oviposition ability. In addition, the decrease of estrogen and its receptor enzyme activity could affect the sex ratio of copepods. These toxic effects eventually resulted in a decrease of the intrinsic rate of increase (r) for T. japonicus. The r value decreased to 0 at the concentration of 0.868 g/L. The information obtained in this study filled the knowledge gap regarding the chronic toxicity of TWP leachate to T. japonicus and would be helpful to understand the potential mechanisms of toxicity.
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