Investigation of role of microplastics on mercury uptake using by manila clam (Ruditapes philippinarum)

Plastic pollution, which is one of the most important environmental problems at the present time, has been understood more recently and the effects of this pollution on the ecosystem and biota becoming a growing problem especially in the aquatic ecosystems. Microplastic is defined to be plastic particles in the range of the size between 1 μm – 5 mm which is originated from the various sources and found a large amount in the marine environment due to some mechanisms. Direct or indirect exposure to those particles leads to adverse effects on organisms. As well known plastic materials in the aquatic environment interact with the other pollutants such as metals, PAHs and PCBs, which can affect the uptake levels of those pollutants by organisms. Besides, as known that plastics can play a role as a matrix with vector potential by accumulating pollutants on their surfaces and transporting them to living organisms. In the present study, the clams Ruditapes philippinarum were exposed to polyethylene microbeads and mercury single, combined and incubated form envrinmentally relative concentrations for a week in controlled laboratory conditions. Afterwards, the uptake and tissue distribution of the stressors, as well as the microplastics' role on the transport of mercury to the organisms, were investigated. Moreover, filtration rates, biomarkers for immunomodulation and oxidative stress and histopathological alterations were evaluated. Additionally, the effects of microplastics and mercury on the levels of circulating cell free nucleic acids (ccf-DNA, ccf-RNA, ccf-miRNA) in clam tissues originating from various cellular pathways were discussed in the study. As a result, it was oberved that microplastics can be accumulated through filtering by Manila clams, translocated to various tissues and modulated uptake levels of mercury. However, it was seen that these particles have a vector role at low level on the transporting of mercury to the biota. Furthermore, the important effects in terms of filtration rates were observed in the clams that exposed to stressors at the aforementioned experimental scenarios. In the study, it was shown that both pollutants can affect the immunomodulation of organisms. While there was no differences among the treatment groups in terms of oxidative stress parameters, significant histopathological alterations were determined in gill and digestive gland tissue of clam. It was also observed that the microplastics and mercury did not lead to a significant alteration in terms of circulating cell-free nucleic acids levels.