Abstract
The extent until which plastics are present in our surrounding environment completely exceeds our expectations. Plastic materials in the form of microplastics have been found in terrestrial, freshwater and marine environments and are transported through the atmosphere even to remote locations. However, we are still far from understanding the effects that they may have caused and are causing to biota. In the present study, we investigated the alterations in the expression of twelve genes in the aquatic insect Chironomus riparius after 36 h exposures to polystyrene and tire rubber microplastics at nominal concentrations of 1 and 10 mg L−1. The results indicated that several genes encoding for heat shock proteins (hsp90, Glycoprotein 93 (Gp93), hsc70, hsp60, hsp40, and the small HSP hsp17) were overexpressed respect to the control. In addition, the genes coding for manganese superoxide dismutase (SOD Mn, related to alleviation of oxidative stress) and for the FK506-binding protein of 39 kDa. (FKBP39, related to development and pupation) showed altered expression. Most of the alterations on gene expression level occurred at a concentration of 10 mg L−1 of tire rubber microplastics, although specific modifications arose at other concentrations of both rubber and polystyrene. On the contrary, one hsp gene (hsp10) and genes related to biotransformation and detoxification (Cyp9f2, Cyp12a2, and ABCB6) did not alter their expression in any of the treatments. Overall, the results of the gene expression indicated that microplastics (especially tire rubber) or their additives caused cellular stress that led to some alterations in the normal gene expression but did not cause any mortality after 36 h. These results highlight the need for more studies that describe the alterations caused by microplastics at the molecular level. Additionally, it opens questions about the effects caused to aquatic fauna in environmental realistic situations, especially in hot spots of microplastic contamination (e.g., tire rubber released in storm water runoff discharge points).
Highlights
The contamination of waters with plastics and microplastics is one of the most important and distressing water risks and chemical pollution episodes that has ever existed during the history of humankind
The potential toxicity may be caused by very complex mixture of chemicals, very recently a quinone transformation product of a tire rubber antioxidant was identified as the sole chemical inducing high toxicity in coho salmon (Tian et al, 2021)
The observed results indicate a strong stress response in Chironomus riparius at the conditions studied, involving the overexpression of several HSPs and SOD Mn and aimed at the reduction of the effects derived from oxidative stress
Summary
The contamination of waters with plastics and microplastics is one of the most important and distressing water risks and chemical pollution episodes that has ever existed during the history of humankind. The main reason is that the extent until what microplastics are present in the planet is still not fully understood, as we are likely underestimating the amount of plastic in the water environment (Lindeque et al, 2020). Despite the myriad of articles reporting toxic effects of microplastics, the reported concentrations Worldwide are not high enough to cause toxic effects on organisms (Burns & Boxall, 2018). There is a need to conduct more studies at all levels of biological organization to achieve results that show realistic effects for the protection of our environment
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