Bioavailability Of Nano Mercury Sulfide In The Soil

Mercury is an important global heavy metal pollutant,which has received widespread attention due to strong toxicity,refractory degradability and high accumulation that will seriously affect people’s health.Mercury sulfide is an important form of mercury in the environment,widely present in ore,soil and sediment,which is generally considered to be the least bioavailable mercury-containing substance due to extremely low solubility.However,under certain circumstances in nature,mercury sulfide nanoparticles are formed,whose environmental risks are still to be studied.Therefore,exploring the bioavailability of nano-mercury sulfide in soil and analyzing its impact on soil organisms has practical significance for reducing the bioavailability of soil mercury,improving the soil ecological environment,and improving the quality of agricultural products.This paper uses earthworms as experimental organisms,and conducts exposure experiments under the environment with different mercury pollutions,earthworms lived for 35 days.We study what the effects of nano mercury sulfide on earthworms and soil properties after entering the soil through the detection of mercury in soil and earthworms and the analysis of soil p H,organic matter and microbial community.At the same time,the effects of earthworm activities on the bioavailability of micro and nano mercury sulfide in soil are also studied.We hope to provide some reference for the evaluation and treatment of soil mercury pollution and further study of the bioavailability of mercury in soil through these.In this study,two kinds of nano-mercury sulfide particles with a particle size of about10 nm were prepared by chemical synthesis for experiment.In this study,three kinds of mercury sulfide(micro-Hg S、nano-α-Hg S、nano-β-Hg S)at 80 mg/kg,mercuric chloride at 80 mg/kg and methylmercury at 8 mg/kg are exposed for following experiment where earthworms were used as exposed organisms.Total mercury has a significant accumulation effect in earthworm.The total mercury contents in earthworm exposed to mercury sulfide is 1.49～2.76 mg/kg,and the bioenrichment factor(BCF)is 0.024～0.038.The BCF of the mercuric chloride and methylmercury groups is over 20.To better analyze the effect of mercury sulfides on soil organisms such as earthworm,methylmercury is detected in the earthworms of the blank and three kinds of sulfide groups,and methylmercury accounts for 1.46～11.32% of the total mercury.In order to explore the source of methylmercury in earthworms,the study detectes methylmercury in the corresponding soil,and the concentrations were below the detection limit of the instrument.The methylmercury in earthworms may be produced by the methylation of mercury in earthworms..The study shows that the bioavailability of three mercury sulfides is as follows: micro-Hg S<nano-α-Hg S<nano-β-Hg S.To research the form of mercury in the soil,we use five-steps extraction method.It is found that mercury in natural soil mainly exists in residual form(F5).After exogenous mercury input,strongly bound(F4)will increase significantly,but the micro mercury sulfide exposure group is still dominated by F5.In mercuric chloride and methylmercury exposure groups,which have higher bioavailability,water-soluble form(F1)and gastric acid mimetic(F2)are significantly more than those in the mercury sulfide groups.Earthworm activities increase soil organic matter.During the period when earthworms active in the soil,soil p H first increases and then decreases with time.Changes in soil organic matter and soil environment lead to the activation of mercury sulfide in soil and increase the content of organically bound mercury(F3).The changes of environment can affect the diversity of soil microbial communities.In this experiment,mercury input increases soil microbial community diversity,while earthworm activity decreases it to a certain degree,that the mechanism needs further study.Changes in species richness before and after earthworm activity is positively correlated with mercury bioavailability.Firmicutes are the main phylum in the blank soil.The input of exogenous mercury greatly increases the content of proteobacteria.The presence of myxococcota is found in the methylmercury and mercuric chloride exposed group,and myxococcota and verrucomicrobiota are found in the mercury sulfide exposed groups.After earthworm activities,there is a substantial decrease in firmicutes but a substantial increase in bacteroidota.Research analysis shows that earthworm activities increase particulate matter aggregates and humic acid in soil,what promotes the accumulation of organic matter and increases the amount of organic matter that can bind to mercury.Meanwhile,what the accumulation of organic matter increases the contents of bacteroidota and proteobacteria,promoting the formation of organically bound(F3).So,it further increases the bioavailability of soil mercury.