Investigation Of Microbial Uptake Of Mercury Sulfide Nanoparticles And Its Effect On Mercury Methylation

Mercury,mainly released from all kinds of chemical manufacturing process,is a highly toxic and global contaminant.It can be transported by long range and finally accumulated in sediment through dry-wet deposition.The anaerobic microorganisms,thriving in anoxic zones can transform inorganic mercury to highly toxic methylmercury by microbial methylation.Methylmercury can cause health threats to the human due to its bioaccumulative nature in food chain.Mercury sulfide nanoparticles(HgS_NP)isan important“newly discovered”Hg species.Numerous studies demonstrated that HgS_NP can be found in various chemical process such as the whole petroleum and natural gas industrial chain and industrial wastewater treatment process.At the same time,HgS_NP have been found to be widespread in various enviromental compartments.It is reported that HgS_NP can be methylated to MeHg which is a threat to human health.Therefore,the impact of HgS_NP released from chemical process to enviroment need to be further monitored and evaluated.This study aims to assess the bioavailability of HgS_NP,focusing on the effects of methylation and microbial uptake,by employing an array of methods,including isotope tracing technique,single cell inductively coupled plasma mass spectrometry?ICP-MS?,size exclusion chromatography?SEC?-ICP-MS,and transmission electron microscopy?TEM?.For demonstrating the contribution of HgS_NP for microbial methylation in simulated natural environment which include other dominant mercury species?such as Hg?II?-DOM?,an isotope tracing system for measuring methylmercury content was conducted involving ethylation derivatization-purging-Tenax trapping-thermal desorption-ICP-MS.When¹⁹⁹Hg?II?-DOM and ^NHgS_NPP were exposed together in bacteria culture medium,the highest transformation rate was 12.99±0.47%for Hg?II?-DOM and 8.86±0.11%for HgS_NP,,the difference is 4.13%.It is implied that Hg?II?-DOM has a higher bioavailability of mercury methylation in natural environment than HgS_NP?However,the contribution of HgS_NPfor mercury methylation can not be ignored.At the same time,cell slice and TEM verified the existence of direct microbial uptake of HgS_NP.It was found that the uptake content of HgS_NP was obviously higher than that of Hg?II?-DOM by SEC-ICP-MS and other technique.By optimizing the instrument parameter and data processing methods,it was found that the content of HgS_NP increased by the time in single cell and it is potential for analyzing HgS_NP uptake in single cell using single cell-ICP-MS.In this study,the methylation effect,microbial uptake process,and bioavailability of HgS_NP were estimated and analyzed.Meanwhile,this study provided important implications for the impact of HgS_NP formed in chemical process to global methylation and the biosecurity of HgS_NP.