Applied Geochemistry (v.26, #2)
Mercury biogeochemical cycling in mercury contaminated environments by Xinbin Feng; Gary N. Bigham (153).
Mercury contamination and its potential health effects in a lead–zinc mining area in the karst region of Guangxi, China by Chaobing Deng; Chaolan Zhang; Lihe Li; Zhongyi Li; Ning Li (154-159).
► Soil in the investigated area is severely contaminated by mercury. ► Contamination of T-Hg in paddy field soils is more severe than that in dry land soils. ► Vertical distributions of T-Hg are different in the paddy and dry land samples. ► T-Hg contents in the agricultural products exceed the Chinese tolerance value.Mercury contamination of the environment is of worldwide concern because of its global presence and its potent neurotoxicity. Mining, smelting and the electronics industry are the main sources of Hg pollution. However, few studies have been performed to investigate systemic Hg contamination in metal mining regions. In this study, concentrations of Hg in air, farmland soil, and crops were measured in a Pb–Zn mining area in the karst region of Guangxi, China. Key factors that could affect Hg distribution, such as the fate of waste ore and waste residue, were analyzed. Geo-statistical methods were adopted to analyze the characteristics of spatial structure and distribution of Hg. The results show that Hg contamination in this region is serious. The total mercury (T-Hg) content is far higher than the Level II Limit Value of Chinese Soil Standards of 0.30 mg kg−1, showing obvious directional characteristics from WNW to ESE. Highest Hg concentrations were found in the WNW portion of the study area. The contamination of paddy soil is higher than that in dry farmland soil. The vertical distribution of T-Hg and its decrease with depth suggest that the important sources are waste water irrigation and the improper disposal of the waste ore and waste rock. The T-Hg concentrations in the agricultural products examined exceed the Chinese tolerance value (0.02 mg kg−1 for rice and 0.01 mg kg−1 for vegetables), indicating the seriousness of the problem. The ecological environment and the safety of food grown in this mining area are being affected, with the result that human health is possibly being affected.
Mercury and other metal and metalloid soil contamination near a Pb/Zn smelter in east Hunan province, China by Zhonggen Li; Xinbin Feng; Guanghui Li; Xiangyang Bi; Guangyi Sun; Jianming Zhu; Haibo Qin; Jianxu Wang (160-166).
► The spatial distribution of metals (Hg, Cd, Pb, Zn, Cu) and a metalloid (As) in the agricultural soils around one of China largest Pb/Zn smelter was investigated. ► Pb and Zn smelting activities is the leading source to the soil metal(loid)s contamination. ► Contaminant concentrations decreased with distance from the smelter and the depth of the soil profile. ► Measures should be taken to safeguard the environment and human health.The spatial distributions of contaminant metals (Hg, Pb, Zn, Cd, Cu) and a metalloid (As) in vegetable plots and paddy fields located near a large scale Pb/Zn smelter in Hunan province, China, were investigated. Soil located 4 km from the smelter was severely contaminated, with maximum concentrations of Hg, Pb, Zn, Cd, Cu and As as high as 2.89, 1200, 3350, 41.1, 157 and 93 mg kg−1, respectively. Concentrations of soil metal and As decreased with distance in the dominant wind direction. Single-factor assessment indicated pollution levels of Hg, Pb, Zn and Cd were most severe, while pollution levels for Cu and As were less severe. Results from a potential ecological risk assessment indicated high risk associated with the soil within a 4 km radius, with the contribution for each contaminant calculated as follows: Cd (70.0%), Hg (19.4%), Pb (4.8%), As (3.0%), Cu (1.7%) and Zn (1.1%). The forest soil in the nearby city park was also affected by the atmospheric depositions from smelting activities. Soil profiles demonstrated the pollutants were mostly accumulated in the upper 20 cm layer. Contamination of the topsoil with Hg, Pb, Zn, Cd, Cu and As indicated remediation should be considered.
Potentially harmful elements in rice paddy fields in mercury hot spots in Guizhou, China by Marthe-Lise Søvik; Thorjørn Larssen; Rolf D. Vogt; Grethe Wibetoe; Xinbin Feng (167-173).
► Levels of Hg, Pb, Cd, Cu, Zn and As in soils from rice paddy fields were assessed. ► The two different regions were assessed, one impacted by mercury mining, one in a heavy industry area. ► In the mercury impacted regions soils had elevated levels of Zn and Cd in addition to Hg. ► In the coal impacted area soils had elevated levels of As and Hg.Levels of the chalcophile metals Hg, Pb, Cd, Cu and Zn and the metalloid As in soils from rice paddy fields were assessed in two regions impacted by different industrial activities in Guizhou province, China. The two study areas (Wanshan and Qingzhen) have previously received attention in the international literature due to heavy Hg pollution, though levels of other potentially harmful elements have not previously been reported. The regions were selected as representing two important, but categorically different metal(loid) contaminated areas in China: Wanshan has been a major region for Hg production while Qingzhen is an important region for a large range of various heavy industries based on coal as an energy source.Within a limited distance of the Hg mine tailings in Wanshan the rice paddy fields are heavily contaminated by Hg (median concentration 25 μg g−1, maximum 119 μg g−1) and moderately contaminated by Zn and Cd (median concentrations of 86 and 0.9 μg g−1, respectively). Zinc and Cd levels correlate well with Hg contamination, which indicates a similar source and mechanism of transport and accumulation. Other studies have concluded that the main sources of Hg contamination in Wanshan are the numerous Hg mine tailings. This is likely as these metals are all geochemically associated with the mineral cinnabar (HgS). The other chalcophile elements (Pb, Cu and As) are nevertheless found at background levels only. In Qingzhen the soils were found to contain elevated levels of As and Hg (median concentrations of 38 and 0.3 μg g−1, respectively). These are elements that are known to be more associated with coal and released during coal combustion.
Spatial variation of biological and pedological properties in an area affected by a metallurgical mercury plant: Almadenejos (Spain) by Rocio Millan; Thomas Schmid; Maria José Sierra; Sandra Carrasco-Gil; Maite Villadóniga; Celia Rico; Dolores María Sánchez Ledesma; Francisco Javier Díaz Puente (174-181).
► Mercury in soil. ► Mercury distribution in M. vulgare L. ► Physical-chemical soil parameters. ► Microbial biomass carbon. ► Soil microbiological activity.Almadén, Spain, has the most important known cinnabar deposits, which have provided a third of the entire world production of Hg, and has been the scene for numerous studies on Hg. This mining district includes several mines where cinnabar has been extracted in the past two millennia as well as facilities related to the production of primary Hg. The aim of the work is to evaluate the spatial distribution of Hg in the soil–plant system within an area where intense activity occurred over a long period. An abandoned metallurgical plant from the 17th–18th centuries was chosen as the study area, situated in Almadenejos a distance of 12 km from Almadén. Nowadays, this plot is covered with cinnabar mine tailings and it is used by village inhabitants for livestock grazing. The area has elevated Hg concentrations of natural origin and from human activities. Soil parameters are similar within the study area; however, data reveal high variability in total and available Hg concentrations in soils, making it difficult to establish a trend. Marrubium vulgare L. has been studied due to its abundance in the plot, and there is no evidence of phenological toxicity. In spite of elevated Hg concentrations, high biological activity is found in the sampled soils. All these characteristics, spatial variation, high Hg concentration, good biological activity, make this a particularly good area for studies involving Hg.
Multielemental contents of foodstuffs from the Wanshan (China) mercury mining area and the potential health risks by Xiaoyan Wang; Yu-Feng Li; Bai Li; Zeqin Dong; Liya Qu; Yuxi Gao; Zhifang Chai; Chunying Chen (182-187).
► Wanshan is the most important historical Hg mining area in China. ► Foodstuffs from Wanshan is collected and Hg, Pb, Cd, Mn and Se were determined. ► Cd and Hg were the most important contributors. ► Vegetables were the main source of potentially harmful element dietary intake. ► Consumption of local foodstuffs poses a potential health risk.Potentially harmful element contamination from mining and smelting raises concerns due to possible health risks. For most people, diet is the main route of exposure to potentially harmful elements, so determination of the concentrations of these elements in foodstuffs and assessment of their possible risk for humans via dietary intake is very important. This study was designed to investigate the concentrations of different elements, including Hg, Pb, Cd, Mn and Se in foodstuffs and to estimate the potential health risk of these elements via consumption of polluted foodstuffs in the Wanshan Hg mine area, Guizhou province, SW China. The multielemental concentrations were determined by inductively coupled plasma-mass spectrometry (ICP-MS). The target hazard quotient (THQ) and hazard index (HI) were calculated to evaluate the potential health risk from individual and combined potentially harmful elements due to dietary intake. The average contents of Hg, Pb, Cd, Mn and Se in the most frequently consumed foodstuffs were: 31, 248, 121, 1035 and 32 μg/kg respectively. Among them, Cd and Hg were the most important contributors to potentially harmful elements contamination in Wanshan. Eight of 10 kinds of vegetables were contaminated to various levels by different elements but the samples of rice, pork, radish and potato were below the stipulated limits for toxic elements. In this study, the average dietary intakes of Hg, Pb, Cd, Mn, Se by an adult man of 60 kg living in Wanshan were: 27, 167, 86, 1061, 42 μg/day, respectively. The HIs for multielement dietary intake was 3.11, with the relative contributions of Hg, Pb, Cd, Mn and Se being 22.3%, 24.3%, 45.0%, 3.9% and 4.4%, respectively, which indicated that consumption of food poses a potential health risk. Vegetables were found to be the main source of potentially harmful element dietary intake.
Mercury contamination due to zinc smelting and chlor-alkali production in NE China by Na Zheng; Jingshuang Liu; Qichao Wang; Zhongzhu Liang (188-193).
► Long-term Zn smelting and chlor-alkali production lead to Hg accumulation in the aquatic and terrestrial environment. ► A significant correlation is observed between T-Hg concentrations in the sediments and in Spirogyra. ► Although the environment of Huludao City is seriously contaminated with Hg, the health effect of Hg exposure to local inhabitants in Huludao is not serious.Zinc smelting and chlor-alkali production are major sources of Hg contamination to the environment, potentially leading to serious impacts on the health of the local population. Huludao, NE China has been heavily contaminated by Hg due to long-term Zn smelting and chlor-alkali production. The aim of this work was to determine Hg accumulation in the aquatic and terrestrial environment, as well as in the human population of Huludao. The investigation included: (a) Hg accumulation in sediments, Spirogyra algae, crucian carp and shrimp, (b) Hg distribution in soil, vegetables and corn, and (c) assessment of potential health effects of Hg exposure associated with total Hg (T-Hg) concentrations in human hair. Measured T-Hg concentrations in sediments of Wuli River ranged from 0.15 to 15.4 mg kg−1, with the maximum Hg concentration in sediment exceeding the background levels in Liaoning Province by 438 times. The maximum T-Hg levels in Spirogyra, crucian carp and shrimp were 13.6, 0.36, and 0.44 mg kg−1, respectively. Total-Hg concentrations in hair of the human population varied from 0.05 to 3.25 mg kg−1 (average 0.43 mg kg−1). However, the frequency of paraesthesia to most inhabitants in Huludao was estimated to be lower than 5%, with only one person rated at 50%. The results indicated minimal adverse health effects of Hg exposure to the inhabitants of Huludao, despite the serious Hg contamination of the environment.
Does anoxia affect mercury cycling at the sediment–water interface in the Gulf of Trieste (northern Adriatic Sea)? Incubation experiments using benthic flux chambers by Andrea Emili; Neža Koron; Stefano Covelli; Jadran Faganeli; Alessandro Acquavita; Sergio Predonzani; Cinzia De Vittor (194-204).
► Hypoxic and anoxic conditions play an important role in the remobilization of Hg species from sediment-water interface. ► Methylmercury fluxes were significantly high under anoxic conditions during incubation experiments. ► Re-oxygenation after anoxia determined a rapid decrease of methylmercury in the water column due to demethylation and/or scavenging by Fe/Mn oxyhydroxides.Coastal areas in the northernmost part of the Adriatic Sea (Gulf of Trieste and the adjacent Grado Lagoon) are characterized by high levels of Hg, both in sediments and in the water column, mainly originating from the suspended material inflowing through the Isonzo/Soča River system, draining the Idrija (NW Slovenia) mining district, into the Gulf of Trieste. Hypoxic and anoxic conditions at the sediment–water interface (SWI) are frequently observed in the Gulf of Trieste and in the lagoon, due to strong late summer water stratification and high organic matter input. Mercury mobility at the SWI was investigated at three sampling points located in the Gulf of Trieste (AA1, CZ) and in the Grado Lagoon (BAR). Experiments were conducted under laboratory conditions at in situ temperature, using a dark flux chamber simulating an oxic–anoxic transition. Temporal variations of dissolved Hg and methylmercury (MeHg) as well as O2, NH 4 + , NO 3 - + NO 2 - , PO 4 3 - , H2S, dissolved Fe and Mn, dissolved inorganic C (DIC) and dissolved organic C (DOC) were monitored simultaneously. Benthic Hg fluxes were higher under anoxic conditions than in the oxic phase of the experiment. Methyl Hg release was less noticeable (low or absent) in the oxic phase, probably due to similar methylation and demethylation rates, but high in the anoxic phase of the experiment. The MeHg flux was linked to SO4 reduction and dissolution of Fe (and Mn) oxyhydroxides, and formation of sulphides. Re-oxygenation was studied at sampling point CZ, where concentrations of MeHg and Hg dropped rapidly probably due to re-adsorption onto Fe (Mn) oxyhydroxides and enhanced demethylation. Sediments, especially during anoxic events, should be, hence, considered as a primary source of MeHg for the water column in the northern Adriatic coastal areas.
Distribution of Hg in mangrove trees and its implication for Hg enrichment in the mangrove ecosystem by Zhenhua Ding; Hao Wu; Xinbin Feng; Jinling Liu; Yang Liu; Yanting Yuan; Ling Zhang; Guanghui Lin; Pan Jiayong (205-212).
► Mangrove plants concentrate high contents of Hg and MeHg. ► Different distribution of Hg and MeHg in mangrove plants relates to their environmental and physiological properties. ► THg content of mature leaves was always higher than that in juvenile leaves, but MeHg showed a contrasting trend. ► The litterfall leads to high Hg content in mangrove ecosystem.The aim of this study was to evaluate Hg distribution in mangrove plants and changes of Hg content during leaf aging; the contribution of litterfall to Hg enrichment in mangrove ecosystems is also discussed. Contents of total Hg (THg) and methylmercury (MeHg) in mangrove plants and sediments were determined. Contents of THg and MeHg in the sediments were 225 ± 157 ng/g and 0.800 ± 0.600 ng/g. Concentrations of THg and MeHg in the mangrove plants were 1760 ± 1885 ng/g and 0.721 ± 0.470 ng/g (dry weight), respectively, which were much higher than those in terrestrial plants. Enrichment of THg in mangrove plants was different, following the order Rhizophra apiculata > Rhizophora stylosa > Kandelia candel > Aegiceras corniculatum > Avicennia marina; while MeHg contents in mangrove plants decreased in the order of R. stylosa > K. candel > A. corniculatum > R. apiculata > A. marina. There were obvious interspecies differences, regional differences, individual differences and tissue differences between THg and MeHg contents of mangrove plants, all of which were closely related to the environmental and the physiological characteristics of mangrove plants. In juvenile leaves, mature leaves and leaf litter, THg contents ranged 55.3–1760 ng/g, 204–1800 ng/g, and 385–2130 ng/g (dry weight), respectively; MeHg contents ranged 0.17–2.39 ng/g, 0.01–1.28 ng/g, and 0.13–1.47 ng/g (dry weight), respectively. Except for A. corniculatum and Bruguier gymnorrhiza, THg content of mature leaves was always higher than that in juvenile leaves, but MeHg showed a contrasting trend. THg content of litter leaves was between that of juvenile leaves and mature leaves, while MeHg content was generally lower than that of juvenile leaves and mature leaves. In the mangrove ecosystem, Hg enrichment contributed by the litterfall decreased in the order of K. candel > A. corniculatum > A. marina.
Mercury speciation and distribution in Aha Reservoir which was contaminated by coal mining activities in Guiyang, Guizhou, China by Xinbin Feng; Weiyang Bai; Lihai Shang; Tianrong He; Guangle Qiu; Haiyu Yan (213-221).
► We investigated mercury distribution in water column of a reservoir contaminated by coal mining. ► Mercury concentrations in water column in wet season were much higher than dry season. ► The contaminated sediment acts as a secondary contamination source for both inorganic mercury and methylmercury to the overlying water. ► The cycling of Mn in the sediment governs the diffusion process of inorganic mercury to water. ► High temperatures favor mercury methylation processes in sediment.Two sampling campaigns were carried out in March and August 2005 representing dry and wet seasons, respectively, to investigate the distribution patterns of Hg species in the water column and sediment profiles at two sampling stations in Aha Reservoir located in Guiyang, Southwestern China. Aha Reservoir has been contaminated by Hg due to small scale coal mining activities. Mercury concentrations in both water and sediment were elevated. A clearly seasonal variation of dissolved Hg (DHg), particulate Hg (PHg) and total Hg (THg) concentrations in the water column was observed. The concentrations of these Hg species in the wet season were significantly higher than in the dry season. Runoff input and diffusion of Hg from sediments could be the reasons for elevated concentrations of these Hg species in the wet season. The contaminated sediment is acting as a secondary contamination source for both inorganic Hg (IHg) and methylmercury (MeHg) to the overlying water. The cycling of Mn in the sediment governs the diffusion process of IHg to the water column. In the dry season (winter and spring), Mn occurs as MnO2 because the uppermost part of sediment is in an oxic condition and Hg ions are absorbed by MnO2. In the wet season (summer and fall), the uppermost part of the sediment profile is in a reduced condition because of stratification of the water column and MnO2 is reduced to Mn2+, which results in transformation of Hg2+ into porewater as Mn2+ became soluble. This causes a higher diffusive flux of IHg from sediment to overlying water in the wet season. Both sampling stations showed a consistent trend that THg concentrations decreased in the uppermost part of sediment cores. This demonstrated that the measures taken to reduce ADM contamination to Aha Reservoir also reduced Hg input to the reservoir. Methyl Hg diffusive fluxes from sediment to overlying water were higher in the wet season than the dry season demonstrating that high temperatures favor Hg methylation processes in sediment.
Methylmercury in tailings ponds of Amazonian gold mines (French Guiana): Field observations and an experimental flocculation method for in situ remediation by Stephane Guedron; Daniel Cossa; Michel Grimaldi; Laurent Charlet (222-229).
► Two tailings ponds of French Guiana Au mines were studied. ► High monomethylmercury (MMHg) production was found within water column and interstitial water. ► A laboratory experiment simulating tailings ponds was performed in oxic and anoxic conditions. ► Slaked lime addition decreased suspended particles but not MMHg concentrations. ► Remediation must consider decantation, ponds drainage and reforestation to limit Hg methylation.Sites of monomethylmercury (MMHg) production in Amazonian regions have been identified in hydraulic reservoirs, lake sediments and wetlands, but tailings ponds have not yet received sufficient attention for this purpose. This work evidenced high MMHg production within the water column and the interstitial water of two tailings ponds of French Guiana Au mines located; (i) in a small scale exploitation (Combat) where Hg was used for Au amalgamation, and (ii) in an industrial on-going Au mine (Yaoni) processing without Hg. The (MMHg)D maximum (2.5 ng L−1) occurred in the oxic water column above the sediment–water interface (SWI) of the most recent tailings pond (Combat), where the substrate was fresh, the redox transition was sharp and the pool of total Hg was large. In the Yaoni pond, the (MMHg)D maximum concentration (1.4 ng L−1) was located at the SWI where suboxic conditions prevailed. Using the (MMHg)D concentration as a proxy for Hg methylation rates, the present results show that Hg methylation may occur in various redox conditions in tailings ponds, and are favored in areas where the organic matter regeneration is more active.A 3-month long laboratory experiment was performed in oxic and anoxic boxes filled with high turbidity waters from the Combat Au mine to simulate tailings ponds. Slaked lime was added in an experimental set (2 mg L−1) and appeared to be very efficient for the reduction of suspended particulate matter (SPM) to environmentally acceptable concentrations. However, at the end of the experiment, large (MMHg)D concentrations were monitored under treated anoxic conditions with the (MMHg)D maximum located at the SWI above the Fe-reducing zones. No (MMHg)D was detected in oxic experiments. The use of slaked lime for SPM decantation appears to be an efficient and non-onerous process for Au miners to avoid Hg methylation in tailings ponds when it is combined with rapid drainage of the mine waters. A subsequent human intervention is however necessary for the recovery of soil structure through the cover of dried ponds with organic rich materials and reforestation to avoid the stagnation of rain waters and the occurrence of anoxia.
Mercury sources and bioavailability in lakes located in the mining district of Chibougamau, eastern Canada by Stéphane Petit; Marc Lucotte; Roman Teisserenc (230-241).
► Lake sediments near mine tailings in the Chibougamau region are enriched in mercury. ► Only small amounts of refractory organic matter are found in contaminated sediments. ► Only very small fraction of mercury can be methylated in these contaminated sediments. ► Logging activities correspond to higher mercury and refractory organic matter inputs. ► Highest fractions of methylmercury were observed in relatively pristine environments.The presence of Hg in the fish of the lakes from the Cu–Zn–Au mining region of Chibougamau (Canada) represents a serious source of concern for the health of local sports and subsistence fishers. This study focuses on identifying the origin of Hg present in the sediments of lakes with mine wastes stored in tailing facilities located on their shores. In addition to C/N ratios and determination of total Hg, Methyl Hg and other metals, a series of lignin biomarkers were used to contrast the history of the mining contamination with the nature and the intensity of terrigenous organic matter (TOM) inputs from the watersheds to the sampled lakes. It appears that sediments located nearest to mine tailings are as expected most enriched in total Hg and other metals (Cu, As, Al, Fe, Pb). Nevertheless, the presence of only small amounts of refractory TOM in these contaminated sediments could explain why only a very small fraction of Hg is found as Methyl Hg. In sediments with little or no impact by mining activities, a relationship was observed between logging activities in the lake watershed and increased TOM derived from inorganic gymnosperms soils horizons and increased Hg transport to the lakes. Nevertheless, it appears that the additional TOM transported to logged lakes is refractory enough not to promote high levels of Methyl Hg. The highest fractions of Methyl Hg relative to total Hg in lake sediments of the studied area were thus observed in relatively pristine environments where least degraded TOM is brought from the watersheds.
Seasonal and diel patterns of total gaseous mercury concentration in the atmosphere of the Central Valley of Costa Rica by Aylin Castillo; Juan Valdes; Jose Sibaja; Ilena Vega; Rosa Alfaro; José Morales; Germain Esquivel; Elisa Barrantes; Paleah Black; David Lean (242-248).
► Elevated seasonal and daily patterns of total gaseous mercury (TGM) were observed in the Central Valley of Costa Rica 27 km south-east of the Poas volcano. ► With the onset of the wet season TGM in late April, values increased from typical values near 10 to 905 ng m−3. ► During the day, TGM values increased until midday along with temperature and radiation but relative humidity showed a reciprocal pattern. ► We conclude that elemental mercury from the volcano may react with atmospheric oxidants especially during the dry season and the mercury would be deposited to the ground. ► With the onset of heavy rains, mercury in the soil is reduced and re-volatilized resulting in the high levels in atmospheric air at the end of April.Monitoring of Hg in the atmosphere near volcanoes is limited with no previous data for Costa Rica. Seasonal and daily patterns of total gaseous mercury (TGM) were observed at the main sampling location at the Universidad Nacional, Heredia, Costa Rica. The area (lat. 10.000230 long. −84.109499) is located in the Central Valley of Costa Rica and is 27 km SE of the Poas volcano (lat. 10.199486 long. −84.231388). Measurements were made from May 2008 to May 2009 at this location with some additional values obtained at other sites near the Poas volcano including San Luis and Grecia as well as near, Turrialba and Irazu volcanoes. Total gaseous Hg was determined in samples collected at a height of 2 m using the Tekran 2537A (Tekran Inc.) gas-phase Hg vapor analyzer. Meteorological data (temperature, relative humidity, wind speed, wind direction, radiation and precipitation) were obtained from the airport weather station located at Alajuela. Monthly precipitation is typically 85 mm during the dry season (December to April) with winds from the west. The wet season begins in late April and continues to December with monthly rainfall of 328 mm and winds from the NE. The annual mean temperature is 20 °C. With the onset of the wet season TGM increased from typical values near 10 to 905 ng m−3. Measurements made within 5 km of the Poas volcano were higher than at Heredia at that time. Diel values measured at the university site increased until midday along with temperature and radiation. Relative humidity showed a reciprocal pattern. It was found that high values of TGM were not related to wind velocity or direction. The strong diel pattern increased with sunrise, peaked at midday and was lowest during the night time. It would seem that Hg0 from the volcano is oxidized and is deposited to the soils during the dry season when winds are blowing from the volcano. With the onset of heavy rains in April, Hg in the soil is reduced and re-volatilized resulting in the high levels in the atmosphere. Values at other volcano sites were provided. The role of atmospheric pollutants such as H2O2 and O3 should be included in future studies as they may result in oxidation of reduced Hg. The instability in the air masses may also be a factor and local pollution sources may result in high levels that is emitted from the volcanoes of Hg being circulated to ground level as radiation intensity increases.
Mercury fluxes from air/surface interfaces in paddy field and dry land by Jinshan Zhu; Dingyong Wang; Xiao Liu; Yutong Zhang (249-255).
► It was found that agricultural fields are important local atmospheric Hg sources in the region. ► The Hg emissions from dry cornfield were higher than those from the flooded rice paddy, higher mercury emissions in the warm season than the cold season, and during daytime than at night. ► Mercury evasion is strongly related to solar radiation which is important in the emission of Hg at both sites.In order to provide insight into the characteristics of Hg exchange in soil/water–air surface from cropland (including paddy field and dry land), Hg fluxes were measured in Chengjiang. Mercury fluxes were measured using the dynamic flux chamber method, coupled with a Lumex® multifunctional Hg analyzer RA-915+ (Lumex Ltd., Russia). The Hg fluxes from paddy field and dry land were alternatively measured every 30 min. Data were collected for 24–48 h once per month for 5 months. Mercury fluxes in both fields were synchronously measured under the same conditions to compare Hg emissions between paddy field and dry land over diurnal and seasonal periods and find out what factors affect Hg emission on each surface. These results indicated that air Hg concentrations at the monitoring site was double the value observed at the global background sites in Europe and North America. The Hg release fluxes were 46.5 ± 22.8 ng m−2 h−1 in the warm season, 15.5 ± 18.8 ng m−2 h−1 in the cold season for dry land, and 23.8 ± 15.6 ng m−2 h−1 in the warm season, 6.3 ± 11.9 ng m−2 h−1 in the cold season for paddy field. Solar radiation is important in the emission of Hg over both sites. Hg exchange at the soil/air and water/air interfaces showed temporal variations. The amount of Hg emission from dry land was higher than that from the paddy field, and the emission in daytime was higher than that at night. Moreover, Hg emissions from land covered by crops, was lower than that for bare land.