Accumulation Characteristics And Health Risk Assessment Of Different Species Of Atmospheric Mercury In Leaf Vegetables

Mercury is a toxic heavy metal.The combustion of fossil fuels and other human activities resulted in a large amount of mercury discharging into the environment in the forms of waste gas and waste water.Mercury can migrate and transform in different environmental media including atmosphere,soil,water and plants.Vegetables are one of the important components of dietary structure,which can not only absorb mercury from soils through the root system,but also absorb mercury in the particulate or gaseous species from atmosphere.Mercury is easy to be enriched in organisms,which produces bio-amplification effect through the food chain.After being accumulated in human body,mercury would have a serious impact on human health.Therefore,it is very important to comprehensive study on the accumulation characteristics of various species of mercury in vegetables and health risk assessment,which will provide scientific basis for ensuring the safety of vegetable food and the health of residents.Thanks to the support of the National Natural Science Foundation of China(No.41271472).Shanghai suburbs was selected as the study areas and four common leaf vegetables(water spinach,amaranth,Shanghai Green cabbage and leaf lettuce)were selected as the main research objects.The planting of vegetables were conducted in the greenhouse of the biological station on campus of East China Normal University(Minhang district).Through the integrated application of field investigation,potted simulation experiment and hydroponics exposure experiment,we try to systematically investigate the mercury levels in different species in PM2.5,air and atmosphere wet deposition samples,to analyze the accumulation characteristics of mercury in different species in vegetable leaves,to study the absorption ability of mercury in different species by vegetables through air-leaf pathway,to discuss the dynamic accumulation characteristics of mercury in vegetables,then to reveal the pollution effects of mercury on different types of vegetables exposed to different species of mercury,and further to evaluate the possible health risks caused by contaminated vegetables.The main conclusions are as follows:(1)The concentrations of particulate mercury in PM2.5 were 0.13 ± 0.04 ng·m-3 in Shanghai in autumn and winter,and the concentrations of mercury in atmospheric wet deposition in winter were between 0.08~0.28 ?g·L-1.The average concentrations of gaseous mercury in the atmosphere was 2.48 ng·m-3 in winter.In general,the air quality was generally good in winter of 2018 in Shanghai,and mercury concentrations in all species were at a low level due to frequent rainfall.There were significant positive correlations between the three species of mercury and AQI.Particulate mercury in PM2.5 might mainly come from the oxidation of gaseous elemental mercury in the atmosphere and the emission from coal combustion.Upwind traffic emissions to the sampling sites might be an important source of pollutants in wet deposition.Gaseous mercury concentrations were significantly affected by meteorological conditions,and the long-distance transport of coal combustion might be an important source of gaseous mercury.(2)The result of exposure experiments to soil-cultured leaf lettuce showed that,after particulate mercury exposure,the mercury content in edible part and root of leaf lettuce increased significantly,but decreased when it came to the mature period due to the growth dilution effect.Only at high concentrations did the concentrations increased.The effect of liquid mercury exposure on leaf lettuce was weak,and the mercury content was at a low level.When exposed to gaseous mercury,the mercury concentration in edible part and root of leaf lettuce increased significantly,but the content of lettuce also decreased at the end of growth due to the effect of growth dilution.The analysis of bioconcentration factors showed that with low concentration the ability of mercury transfer from soil to root of leaf lettuce was weak,and the accumulation of gaseous mercury in soil-cultured vegetables was affected by exposure time,vegetable species and other factors.(3)In the exposure experiments on hydroponic vegetable,there was an obvious accumulation of mercury in leaves after the exposure of particulate mercury.The concentration and bioconcentration factors of mercury in green cabbage were higher than those of water spinach and amaranth because of its larger leaf area.Liquid mercury exposure can increase the concentraction of mercury in three vegetables in a short time,but with the maturation of vegetables,the growth dilution effect causes the mercury content in water spinach and amaranth decreased to the level of the control group,while in green cabbage increased relatively.After the exposure of gaseous mercury,the mercury content in vegetables increased significantly,and the mercury accumulation ability in edible part was greater than that in root.Mercury in the root of hydroponic vegetables may come from the gaseous mercury absorbed by the root and the transfer of mercury in the vegetable.Although the mercury content in vegetables was increased by three different exposure experiments to different extent,the effective mercury content was very low.The exposure experiment affected the normal growth of the three vegetables to a certain extent.Exposure experiments all led to the accumulation of mercury in vegetables.The mercury content in vegetables growing slowly in autumn was higher,but the total accumulation of mercury in a single plant was lower than that in vegetables growing normally in summer.(4)The health risk assessment results of vegetables after exposure experiment showed that the non-carcinogenic health risk caused by mercury in vegetables was greater for children than for adults,and the non-carcinogenic risk for women was greater than that for men.The non-carcinogenic risks of vegetables exposed to simulated particulate and liquid mercury were of safe range.The health risks of vegetables exposed to gaseous mercury do not pose non-carcinogenic risk,which is already at very high levels.Off-season vegetables grow slowly and mercury has a higher noncarcinogenic risk.The non-carcinogenic risk of mercury in green cabbage and leaf lettuce was higher than amaranth and cabbage due to the influence of their own characteristics.