新疆准东矿区土壤与降尘重金属空间分布及关联性分析

土壤重金属与大气降尘重金属之间的关联性可以反映重金属污染的来源、土壤-大气系统中重金属的传输、迁移和扩散特征。为了研究矿区表层土壤的污染状况及与降尘重金属质量分数间的关联性,该研究以新疆维吾尔自治区准东矿区为研究靶区,利用2014年采集的51个表层土壤和大气降尘样品的室内实测重金属质量分数数据,并基于此分析了样品中6种重金属(As、Cu、Cr、Hg、Pb、Zn)的空间分布特征、地积累指数以及潜在生态风险;利用Pearson相关性分析矩阵和灰色关联法对表层土壤与大气降尘中重金属浓度的相关性和关联度进行探讨。结果表明:1)准东矿区表层土壤重金属的分布状况存在着明显的空间差异,其中Hg的污染程度最严重,处于强-极强度污染,其潜在生态危害指数达到了较高生态风险;Zn和Cu基本处于无污染状态,属于轻微生态风险;2)大气降尘重金属空间分布存在着明显差异,降尘中的Zn处于极强度污染,Hg处于无污染状态;3)Pearson相关分析与灰色关联分析表明,准东地区表层土壤与大气降尘中6种重金属的相关系数大小顺序与关联度排序结果一致,其中Hg和As元素具有较强的一致性,且具有相同的来源,说明大气降尘对表层土壤中重金属的质量分数有一定影响。但因不同重金属元素沉降特性不同,导致各元素之间的关联度有所差异。     

基于PMF模型的准东煤矿周围土壤重金属污染及来源解析

为了解准东煤矿区周围土壤的污染状况及来源,在准东露天矿区采集47个表层土壤样本,测定其中Zn、Cu、Pb、Cr、Hg和As 6种重金属元素的含量。运用统计学方法、地累计指数(geoaccumulation index,I_(geo))和潜在风险指数(potential ecological risk index,PER)对研究区土壤重金属污染程度和生态风险态势进行评价,采用正矩阵分解模型(positive matrix factorization,PMF)解析重金属污染源。结果表明:1)研究区土壤Zn、Cu、Pb、Cr、Hg和As含量均超出新疆土壤环境质量背景值,超标率分别为2.1%、14.9%、4.3%、68.1%、68.1%和95.8%,其中As含量的均值分别超过国家土壤质量Ⅰ级和Ⅱ级标准(GB15618-1995)的2.1和1.3倍;2)Hg的地累积指数和潜在生态风险指数呈极高污染和高风险态势,Zn、Cu和Pb处于未污染和低风险状态。研究区综合潜在生态风险指数介于50.09～1 038.47之间,差异明显,均值为180.22,21%和11%土壤采样点呈现出较高和高风险水平;3)PMF模型结果显示:研究区土壤Hg主要受到燃煤活动的影响;Pb的积累主要与交通运输有关,As的积累主要与大气沉降和工业排放有关,工业排放是Cr的主要污染源,Zn和Cu的积累主要与土壤成土母质等自然因素有关。燃煤、交通运输、大气降尘、工业排放和自然因素5种来源的贡献率分别为20.79%,16.83%,16.83%和27.72%和17.82%。     

宝鸡燃煤电厂周围土壤环境Hg污染及其评价

通过对宝鸡燃煤电厂周围土壤环境的调查、采样,研究了土壤汞的污染状况。结果表明,电厂周围土壤中Hg的含量为0.137~2.105mg kg-1,平均值为0.606mg kg-1,高于陕西、全国和世界土壤中Hg的平均含量。单因子污染指数、地质累积指数和潜在生态危害系数评价结果表明,电厂周围土壤出现不同程度汞的污染。     

强烈人为作用下城镇周围汞的空间变异及其积累迁移规律

研究土壤中汞(Hg)元素积累的空间变异和迁移转化规律对土壤利用、环境评价和污染修复具有重要参考价值。本研究选择经济发展迅速的苏南某地为研究区域,对土壤、水稻和大气降尘中的Hg进行了详细分析。结果表明,该区域土壤全汞平均含量达1 345μg kg-1,有效汞(HC l-Hg)平均含量51μg kg-1,水稻Hg平均含量20μg kg-1,大气Hg沉降量为5.13 g km-230 d-1。土壤和水稻高含量Hg主要积聚于城镇周边,随着与城镇距离的增加其含量逐渐减少。大气Hg沉降量在空间上变化不大。进入土壤中的Hg主要在土壤表层0~20 cm范围内富集,但直至60 cm深处依然存在积累现象,整个剖面土壤活性态汞和半活性态汞含量占全汞的比例变化不大。研究区土壤出现了明显Hg积累,导致水稻Hg吸收明显增加,不少样点超过了国家土壤环境质量二级标准(300μg kg-1)和国家食品污染物限量标准(20μg kg-1),可能对环境和人体健康产生危害。较低的大气Hg沉降量和土壤积累的Hg已与土壤条件达到平衡的事实表明,目前Hg的积累已明显减少。今后应采取措施修复污染土壤或者通过改变作物种类来减少土壤Hg含量或抑制作物对Hg的吸收,达到环境治理的目的。     

大气沉降对土壤和作物中重金属富集的影响及其研究进展

以我国农田土壤-作物-大气系统为研究对象,综述了近年来大气沉降中重金属的来源及时空分布规律以及大气沉降对农田土壤和作物中重金属富集的影响及其研究进展。人为活动产生的重金属进入大气后,受多种自然和人为因素及环境保护政策等综合因素的影响,导致大气沉降中的重金属具有明显的时空分异特征:从时间分异来看,大气重金属含量呈现出冬季高于其他季节,供暖期高于非供暖期的特点;从空间分异来看,工业发达地区较高,燃煤为主的城市高于其他城市,城区高于郊区及远郊地区。大气沉降不仅会使土壤重金属含量上升,也会对农作物造成直接和间接的影响。大气中的重金属会通过气孔进入作物细胞,在细胞壁、液泡中积累,当含量过高时会影响作物正常生长或引起作物重金属超标风险,不利于农业安全生产。未来的研究应将传统分析方法与空间和地统计技术、多元同位素示踪技术、数学模型模拟等多种技术手段相结合,在区域尺度和田间自然条件下开展土壤-作物-大气系统重金属循环过程的研究,为区域农田重金属污染防控和环境管理提供科学依据和决策支撑。     

太原市污灌区土壤重金属污染现状评价

对太原市污灌区土壤重金属分布特征进行了分析评价,结果表明重金属Pb、Zn、Cu、Ni、Mn、Cr、As、Hg、Cd含量均值均未超过土壤环境质量标准（GB15618—1995）,但其平均值均显著高于太原市土壤背景值。各重金属间的相关分析表明,Pb、Zn、Cu、Ni、Mn、Cr、As、Cd之间呈极显著相关,说明这8种元素污染源可能相同。Hg是本区表层土壤重金属污染的主要因子,重金属元素的污染程度依次为Hg〉Cd〉Pb〉As〉Cu〉Zn〉Cr〉Mn〉Ni。土壤重金属单项污染指数均值均大于1,综合污染指数为2.81,总体上,污染水平为中度及其以上。各种重金属单因子污染指数和综合指数在研究区有相似的空间分布格局,总体分布趋势为东南部小店地区和中南部晋源区相对较高,南部清徐县相对较小;通过因子分析并结合污灌区污染源调查,表明Hg除受污水灌溉的影响外,燃煤释放的Hg可能是重要来源之一,Cd、Zn、Pb和Cu可能来自污水灌溉和大气沉降,以污水灌溉的贡献为主,Ni、Mn、As、Cr来自污水灌溉。Hg、Cd是太原市污灌区土壤中需要优先控制的重金属。     

污灌区土壤重金属累积影响因素研究

本文研究了大气沉降、化学肥料施用、污水灌溉3个外源因素对污灌区土壤中重金属Hg、Cd、Pb累积的影响,结果表明:污灌区大气干湿沉降和施肥输入土壤中3种重金属元素的数量顺序为Pb>Cd>Hg。污灌水中重金属Hg、Cd、Pb含量的高低与相对应的灌区土壤中重金属的累积量的多少基本一致,对土壤Cd累积影响最大的是污水灌溉,对土壤Hg累积影响最大的是大气沉降,污灌与大气沉降对土壤Pb累积影响作用相近,施肥对3种重金属元素累积影响最小。     

燃煤烟气对土壤-小麦系统中汞累积及分布的影响

为研究燃煤烟气对土壤-小麦系统中汞积累和分布的影响,在小麦苗期和成熟期采集河南省商丘市某燃煤电厂周围农田土壤和小麦植株样品,用ZYG-Ⅱ型智能冷原子荧光测汞仪测量样品中的汞含量。结果表明,小麦苗期和成熟期,土壤样品中汞含量没有超过土壤环境质量标准（GB15618—1995）二级标准的限值。燃煤电厂周围表层土中汞含量要明显高于深层土,呈表层富集现象,苗期小麦根的汞含量高于茎叶,其根、茎叶的汞含量与表层土的汞含量呈显著正相关。小麦从苗期到收获期,表层土、小麦根和茎叶的汞浓度升高。小麦从苗期到收获期,茎叶面积迅速增加,小麦叶片直接从大气中吸收燃煤烟气中的汞,使小麦茎叶通过叶面吸收的汞浓度增加,收获期燃煤电厂周围小麦各器官汞含量为茎叶〉根〉颖壳〉籽粒。成熟期小麦根的汞含量与表层土的汞含量呈显著正相关,而茎叶汞含量与表层土的汞含量无相关性。因此,燃煤烟气中汞沉降影响燃煤电厂周围种植的小麦各器官对汞的吸收和累积。     

防止土壤污染的迫切问题

作者建立了污染物随大气沉降到土壤根系分布中的等式方程;探讨了方程中各项的主要因素;提出了污染物质流入土壤并随地面水、地下水和植物吸收而流失的情况下,方程中时间函数的解法。最后讨论了为取得具体参数所必须进行的田间和实验室实验。从大气沉降到土壤表面和植被的污染物,参与生物地球化学循环,并在土壤中向     

拉林河流域土壤重金属污染特征及来源解析

该文选取拉林河流域表层土壤为研究对象,通过对土壤重金属的含量和空间分布分析、污染评价、以及潜在生态风险评价,了解土壤重金属的分布特征和污染现状,并利用正定矩阵因子分解法（PMF）探索土壤重金属污染的来源。结果表明,表层土壤中Cr、As、Pb、Cu、Zn、Ni、Mn、V的平均含量均低于背景值,Co和Se略微高于背景值,部分土壤样点Cd和Ni超过国家土壤环境质量标准的二级标准。研究区土壤污染的主要金属元素为Cd和Hg,地累积指数表明受到污染的样品比例分别达到45.1%和37.0%,其潜在生态危害指数平均值分别为49.83和70.29。根据PMF计算结果,拉林河流域表层土壤重金属累积主要受自然源、农药肥料源、工业排放源的影响。其中,自然本底对研究区土壤中重金属的影响最大,贡献率为38.0%,其次是农药和肥料施用,贡献率为32.6%,燃煤和工业排放源的贡献率稍低,为29.4%。     

The biogeochemical cycling of Hg in forests: Alternative methods for quantifying total deposition and soil emission

A biogeochemical cycling approach to the Hg cycle is explored using existing data from the literature in order to begin to identify important processes that might be studied in detail and extrapolated to a regional scale. If it is assumed that all foliar Hg is taken up from the atmosphere, then estimates of total Hg deposition are rather easily made from measurements of leaf litterfall and throughfall. This assumption needs absolute verification before such an extrapolation can be made, however, because litterfall is a major Hg flux to the forest floor. Hg⁰ evolution from soils can be an important process and needs to be measured in more ecosystems. The diffusion model for soil gaseous efflux may be useful in this regard and deserves testing. There is a critical need for a systematic analysis of Hg cycles using common protocols so as to minimize artifacts associated with sampling methodology (i.e., soil Hg efflux). This should be done in several soil and forest types, given the high degree to which Hg transformations in and emissions from soils are dependent upon soil organic matter content, redox potential, and temperature.     

Mercury in the Swedish environment — Recent research on causes,consequences and corrective methods

During the last decade a new pattern of Hg pollution has been discerned, mostly in Scandinavia and North America. Fish from low productive lakes, even in remote areas, have been found to have a high Hg content. This pollution problem cannot be connected to single Hg discharges but is due to more widespread air pollution and long-range transport of pollutants. A large number of waters are affected and the problem is of a regional character. The national limits for Hg in fish are exceeded in a large number of lakes. In Sweden alone, it has been estimated that the total number of lakes exceeding the blacklisting limit of 1 mg Hg kg-1 in 1-kg pike is about 10 000. The content of Hg in fish has markedly increased in a large part of Sweden, exceeding the estimate background level by about a factor of 2 to 6. Only in the northernmost part of the country is the content in fish close to natural values. There is, however, a large variation of Hg content in fish within the same region, which is basically due to natural conditions such as the geological and hydrological properties of the drainage area. Higher concentrations in fish are mostly found in smaller lakes and in waters with a higher content of humic matter. Since only a small percentage of the total flow of Hg through a lake basin is transferred into the biological system, the bioavailability and the accumulation pattern of Hg in the food web is of importance for the Hg concentrations in top predators like pike. Especially, the transfer of Hg to low trophic levels seems to be a very important factor in determining the concentration in the food web. The fluxes of biomass through the fish community appear to be dominated by fluxes in the pelagic food web. The Hg in the lake water is therefore probably more important as a secondary source of Hg in pike than is the sediment via the benthic food chain. Different remedy actions to reduce Hg in fish have been tested. Improvements have been obtained by measures designed to reduce the transport of Hg to the lakes from the catchment area, eg. wetland liming and drainage area liming, to reduce the Hg flow via the pelagic nutrient chains, eg. intensive fishing, and to reduce the biologically available proportion of the total lake dose of Hg, eg. lake liming with different types of lime and additions of selenium. The length of time necessary before the remedy gives result is a central question, due to the long half-time of Hg in pike. In general it has been possible to reduce the Hg content in perch by 20 to 30% two years after treatments like lake liming, wetland liming, drainage area liming and intensive fishing. Selenium treatment is also effective, but before this method can be recommended, dosing problems and questions concerning the effects of selenium on other species must be evaluated. Regardless how essential these kind of remedial measures may be in a short-term perspective, the only satisfactory long-term alternative is to minimize the Hg contamination in air, soil and water. Internationally, the major sources of Hg emissions to the atmosphere are chlor-alkali factories, waste incineration plants, coal and peat combustion units and metal smelter industries. In the combustion processes without flue gas cleaning systems, probably about 20 to 60% of the Hg is emitted in divalent forms. In Sweden, large amounts of Hg were emitted to the atmosphere during the 50s and 60s, mainly from chlor-alkali plants and from metal production. In those years, the discharges from point sources were about 20 to 30 t yr 1. Since the end of the 60s, the emission of Hg has been reduced dramatically due to better emission control legislation, improved technology, and reduction of polluting industrial production. At present, the annual emissions of Hg to air are about 3.5 t from point sources in Sweden. In air, more than 95% of Hg is present as the elemental Hg form, HgO⁰. The remaining non-elemental (oxidized) form is partly associated to particles with a high wash-out ratio, and therefore more easily deposited to soils and surface waters by precipitation. The total Hg concentration in air is normally in the range 1 to 4 ng m-3. In oceanic regions in the southern hemisphere, the concentration is generally about 1 ng m^?3, while the corresponding figure for the northern hemisphere is about 2 ng m-3. In remote continental regions, the concentrations are mainly about 2 to 4 ng m^?3. In precipitation, Hg concentrations are generally found in the range 1 to 100 ng L^?1. In the Nordic countries, yearly mean values in rural areas are about 20 to 40 ng L^?1 in the southern and central parts, and about 10 ng L^?1 in the northern part. Accordingly, wet deposition is about 20 (10 to 35) g km^?2 yr^?1 in southern Scandinavia and 5 (2 to 7) in the northern part. Calculations of Hg deposition based on forest moss mapping techniques give similar values. The general pattern of atmospheric deposition of Hg with decreasing values from the southwest part of the country towards the north, strongly suggests that the deposition over Sweden is dominated by sources in other European countries. This conclusion is supported by analyses of air parcel back trajectories and findings of significant covariations between Hg and other long range transported pollutants in the precipitation. Apart from the long range transport of anthropogenic Hg, the deposition over Sweden may also be affected by an oxidation of elemental Hg in the atmosphere. Atmospheric Hg deposited on podzolic soils, the most common type of forest soil in Sweden, is effectively bound in the humus-rich upper parts of the forest soil. In the Tiveden area in southern Sweden, about 75 to 80% of the yearly deposition is retained in the humus layer, chemically bound to S or Se atoms in the humic structure. The amount of Hg found in the B horizon of the soils is probably only slightly influenced by anthropogenic emissions. In the deeper layers of the soil, hardly any accumulation of Hg takes place. The dominating horizontal flow in the soils takes place in the uppermost soil layers (0 to 20 cm) during periods of high precipitation and high groun water level in the soils. The yearly transport of Hg within the soils has been calculated to be about 5 to 6 g km^?2. The specific transport of total Hg from the soil system to running waters and lakes in Sweden is about 1 to 6 g km^?2 yr¹. The transport of Hg is closely related to the transport of humic matter in the water. The main factors influencing the Hg content and the transport of Hg in run-off waters from soils are therefore the Hg content in soils, the transport of humic matter from the soils and the humus content of the water. Other factors, for example acidification of soils and waters, are of secondary importance. Large peatlands and major lake basins in the catchment area reduce the out-transport of Hg from such areas. About 25 to 75% of the total load of Hg of lakes in southern and central Sweden originates from run-off from the catchment area. In lakes where the total load is high, the transport from run-off is the dominating pathway. The total Hg concentrations in soil solution are usually in the range 1 to 50, in ground water 0.5 to 15 and in run-off and lake water 2 to 12 ng L^?1, respectively. The variation is largely due to differences in the humus content of the waters. In deep ground water with a low content of humic substances, the Hg concentration is usually below 1 ng L^?1. The present amount and concentrations of Hg in the mor layer of forest soils are affected by the total anthropogenic emissions of Hg to the atmosphere, mainly during this century. Especially in the southern part of Sweden and in the central part along the Bothnian coast, the concentrations in the mor layer are markedly high. In southern areas the anthropogenic part of the total Hg content is about 70 to 90%. Here, the increased content in these soils is mainly caused by long-range transport and emissions from other European countries, while high level areas in the central parts are markedly affected by local historical emissions, mainly from the chlor-alkali industry. When comparing the input/output fluxes to watersheds it is evident that the present atmospheric deposition is much higher than the output via run-off waters, on average about 3 to 10 times higher, with the highest ration in the southern parts of Sweden. Obviously, Hg is accumulating in forest soils in Sweden at the present atmospheric deposition rate and, accordingly, the concentrations in forest soils are still increasing despite the fact that the emissions of Hg have drastically been reduced in Sweden during the last decades. The increased content of Hg in forest soils may have an effect on the organisms and the biological processes in the soils. Hg is by far the most toxic metal to microorganisms. In some regions in Sweden, the content of Hg in soils is already today at a level that has been proposed as a critical concentration. To obtain a general decrease in the Hg content in fish and in forest soils, the atmospheric deposition of Hg has to be reduced. The critical atmospheric load of Hg can be defined as the load where the input to the forest soils is less than the output and, consequently, where the Hg content in the top soil layers and the transport of Hg to the surface waters start to decrease. A reduction by about 80% of the present atmospheric wet deposition has to be obtained to reach the critical load for Scandinavia.     

Mercury distribution in tephra soil layers in Hokkaido, Japan, with reference to 34,000-year stratification

Tephra from volcanic eruptions contains only small amounts of mercury (Hg) right after the eruption because the high temperature at eruption evaporates Hg in volcanic ash. Thus, accumulation of Hg in tephra soil layers during the dormant periods of the volcano may reflect Hg deposition while the layer was exposed to the atmosphere. To estimate sequential changes in Hg deposition, we measured the Hg content and accumulation in tephra layers from 6 sites in Hokkaido known to have many tephra layers derived from volcanic eruptions over a 34,000-year period. Mercury content and accumulation rate in the soil profiles varied widely depending on the tephra. In each tephra layer, the Hg content and accumulation rates increased principally at the upper soil horizons and decreased at the lower depths. The Hg deposition rates calculated from the amount of Hg accumulated in the tephra layers were similar within the same tephra. These characteristics of Hg distribution indicate that Hg deposition accumulated on the surface of each tephra layer during the period the tephra layer was exposed to the atmosphere. Although physicochemical processes such as leaching out, wind erosion, and volatilization might lead to over- and/or underestimation of the deposition rates, our estimated amounts of Hg were markedly higher in the tephra soils after 1,600 year BP than before that time. The results of this study suggest that tephra layers in Hokkaido offer important implications for understanding of the historical changes in atmospheric Hg deposition.     

Mercury distribution in tephra soil layers in Hokkaido,Japan, with reference to 34,000-year stratification

Abstract

Tephra from volcanic eruptions contains only small amounts of mercury (Hg) right after the eruption because the high temperature at eruption evaporates Hg in volcanic ash. Thus, accumulation of Hg in tephra soil layers during the dormant periods of the volcano may reflect Hg deposition while the layer was exposed to the atmosphere. To estimate sequential changes in Hg deposition, we measured the Hg content and accumulation in tephra layers from 6 sites in Hokkaido known to have many tephra layers derived from volcanic eruptions over a 34,000-year period. Mercury content and accumulation rate in the soil profiles varied widely depending on the tephra. In each tephra layer, the Hg content and accumulation rates increased principally at the upper soil horizons and decreased at the lower depths. The Hg deposition rates calculated from the amount of Hg accumulated in the tephra layers were similar within the same tephra. These characteristics of Hg distribution indicate that Hg deposition accumulated on the surface of each tephra layer during the period the tephra layer was exposed to the atmosphere. Although physicochemical processes such as leaching out, wind erosion, and volatilization might lead to over- and/or underestimation of the deposition rates, our estimated amounts of Hg were markedly higher in the tephra soils after 1,600?year?BP than before that time. The results of this study suggest that tephra layers in Hokkaido offer important implications for understanding of the historical changes in atmospheric Hg deposition.     

Source and selectivity in the accumulation of mercury and other metals by the plants of Mt. Etna

The air Hg content at and near the summit of Mt. Etna is approximately 500- to 2000-fold lower than it is in the atmospheres around Antarctic, Hawaiian and Icelandic volcanoes. In contrast, the soils and plants on Mt. Etna show only 10- to 30-fold reductions in Hg content; in other words, there is at least a ten-fold enrichment relative to air. This disparity called into question the source of Hg in the vegetation and upper soil layers. Soils and a variety of plant species were analyzed for Hg, Fe, Cu, and Mn content at a number of stations on Mt. Etna including several also sampled for air Hg, and compared with the data for plants and soils from other volcanic and non-volcanic locations, especially Hawaii, Africa and Iceland. Etna vascular plants do not accumulate Hg, and lichens do so only to a moderate extent. Relative to their Fe content, however, all the Etna soils are enriched in Hg, but the reverse is true for Cu relative to Hg. The plants, on the other hand, when compared with their soils, are enriched in Hg relative to Cu. By comparing Fe/Hg atomic ratios for plants and soil, we calculated an Enrichment Factor (EF) for Hg. This value ranged from 19 to 102 for Etna, and 19 to 184 for all subtropical plants discussed here. The Hg EF for Icelandic samples was ca. 823, reflecting other environmental/geochemical determinants. No net surface deposition of Hg takes place on Etna from plant or atmospheric sources, and the relative Hg contents of soils and plants do not show a consistent relation to air Hg concenctration. Nevertheless, the plant/soil Cu and Hg ratios (CR) vary similarly as do the atomic ratio (AR) values for Fe and Hg. We conclude from these relationships that the atmosphere is not a major source of plant (or soil) Hg and that the likely alternatives are: release at some relatively remote point in time, but not to any significant degree since; release into the atmosphere as Hg = species other than Hg⁰; or movement from very deep subsurface compartments. These alternatives are not mutually exclusive. It is highly improbable that summit emissions constitute a significant source of Hg in the Mediterrean Basin.     

Mercury from Combustion Sources: A Review of the Chemical Species Emitted and Their Transport in the Atmosphere

Different species of mercury have different physical/chemical properties and thus behave quite differently in air pollution control equipment and in the atmosphere. In general, emissions of mercury from coal combustion sources are approximately 20–50% elemental mercury (Hg°) and 50–80% divalent mercury (Hg(II)), which may be predominantly HgCl₂. Emissions of mercury from waste incinerators are approximately 10–20% Hg° and 75–85% Hg(II). The partitioning of mercury in flue gas between the elemental and divalent forms may be dependent on the concentration of particulate carbon, HCl and other pollutants in the stack emissions. The emission of mercury from combustion facilities depends on the species in the exhaust stream and the type of air pollution control equipment used at the source. Air pollution control equipment for mercury removal at combustion facilities includes activated carbon injection, sodium sulfide infection and wet lime/limestone flue gas desulfurization. While Hg(II) is water-soluble and may be removed from the atmosphere by wet and dry deposition close to combustion sources, the combination of a high vapor pressure and low water-solubility facilitate the long-range transport of Hg° in the atmosphere. Background mercury in the atmosphere is predominantly Hg°. Elemental mercury is eventually removed from the atmosphere by dry deposition onto surfaces and by wet deposition after oxidation to water-soluble, divalent mercury.     

Fluxes,pools, and turnover of mercury in Swedish forest lakes

In boreal forest lakes, high Hg concentrations in fish are common, even in remote areas. In this paper, the effects of atmospheric Hg pollution in Sweden are synthesized and related to a concept based on the strong interaction of Hg with biogenic matter (Hg/B). Based on this concept, a compartment model is developed to predict concentrations, pool sizes, flux rates and turnover times of Hg along the biogeochemical cycle, including atmosphere, forest soils, surface runoff, lake waters, and aquatic biota. The aim is to provide a conceptual framework, both for a comprehensive mechanistic model, and for predictions from readily available information, such as regional data on acid deposition, air temperature and surface runoff, and local data on the trophic status of lakes with respect to humus and nutrient concentrations. The model is in good agreement with observations from recent Swedish field studies in all compartments. It suggests a strong influence of climate on the susceptibility of soil and lake ecosystems in the boreal region to Hg contamination. The high Hg concentrations in fish from forest lakes can be largely attributed to the low productivity of both terrestrial and aquatic biota. The impact of historical point sources of Hg is considered, as well as the slow turnover of Hg in forest soils, both resulting in elevated fish Hg levels in humic lakes for centuries following atmospheric deposition.     

Mercury pathways in municipal wastewater treatment plants

A nine-week sampling and analysis program was completed at a large municipal wastewater treatment plant to characterize the fate of Hg entering the plant. Mercury removal in primary treatment averaged 79%, and the average Hg removal across the entire plant was approximately 96%. Mercury loadings on the secondary (activated sludge) treatment process were elevated to near plant influent levels due to the recycle of spent scrubber water from sewage sludge incinerator emissions control equipment. This internal recycle of spent incinerator scrubber water resulted in elevated Hg loadings to the incinerators, and effectively reduced the Hg control efficiency of the emissions control equipment to near zero. Measurements indicate that approximately 95% of the Hg mass entering the plant is discharged to the atmosphere via sludge incinerator emissions. These results indicate that municipal wastewater treatment facilities can remove Hg from wastewater quite effectively; however, where wastewater sludge is incinerated, almost the entire mass of Hg removed from the wastewater can be discharged to the atmosphere.     

The coupling of mercury and organic matter in the biogeochemical cycle — towards a mechanistic model for the boreal forest zone

In boreal forest lakes, high Hg concentrations in fish are common, even in remote areas. In this paper, the effects of atmospheric Hg pollution in Sweden are synthesized and related to a concept based on the strong interaction of Hg with biogenic matter (Hg/B). Based on this concept, a compartment model is developed to predict concentrations, pool sizes, flux rates and turnover times of Hg along the biogeochemical cycle, including atmosphere, forest soils, surface runoff, lake waters, and aquatic biota. The aim is to provide a conceptual framework, both for a comprehensive mechanistic model, and for predictions from readily available information, such as regional data on acid deposition, air temperature and surface runoff, and local data on the trophic status of lakes with respect to humus and nutrient concentrations. The model is in good agreement with observations from recent Swedish field studies in all compartments. It suggests a strong influence of climate on the susceptibility of soil and lake ecosystems in the boreal region to Hg contamination. The high Hg concentrations in fish from forest lakes can be largely attributed to the low productivity of both terrestrial and aquatic biota. The impact of historical point sources of Hg is considered, as well as the slow turnover of Hg in forest soils, both resulting in elevated fish Hg levels in humic lakes for centuries following atmospheric deposition.     

Long-term changes in concentration and deposition of atmospheric mercury over Scandinavia

Samples for measurements of total gaseous mercury (Hg) in air have been collected since 1980 in south-western part of Scandinavia. A collection program for precipitation samples used to determine changes in depositional fluxes of total Hg has been in operation since 1987. A comparison of today's total gaseous Hg levels in air and the total Hg concentrations in precipitation with the ones found earlier, shows a clear decrease with time. At the Swedish west-coast, yearly average air concentrations and median levels of 3.3 and 3.1 (1980–1984), 3.2 and 2.8 (1985–1989), and 2.7 and 2.6 ng Hg/m³ (1990–1992), respectively, were found. Increased average and median winter concentrations were always found, with levels at 3.7 and 3.4, 3.7 and 3.3, and 3.0 and 2.7 ng Hg/m³ for the respective time period. Higher winter values were expected due to increased anthropogenic emissions and changes in the mixing height of the atmosphere. The corresponding total wet deposition rates decreased from 27 (1987–1989) to 10 μg Hg/m² yr. (1990–1992). A finding of special interest was the decreased number of episodic events of high total gaseous Hg levels in air, from 1990 and further on. In addition, the frequency distribution of the concentrations of Hg in air seems to be different for these years compared to the other two time periods. A frequency distribution of air concentrations of Hg more resembling a normal distribution was found for the years 1990 to 1992. The decrease of the atmospheric burden of total gaseous Hg and deposition of total Hg are most probably connected to lower emissions in source areas on the European continent. It seems logical to state that the problem of high Hg depositional fluxes to Scandinavia, is best solved by abatement strategies on the regional scale.