Variation Of Atmospheric Mercury And Estimating The Mercury Exposure Dose In Residential Area Of City, China-Sweden

Mercury (Hg), a high toxic and unessential element, is regarded as potentially hazardous to the cells of living organisms. Since the outbreaks of Minamata Disease in Japan in the 1950s, the control of mercury pollution and study have roused great attention. Because of its unique physicochemical properties and potential for long-range transport, mercury is considered as a global pollutant via the atmospheric diffusion pathway and can be deposited in ecosystems remote from the original sources. It has been reported that coal combustion is one of the main anthropogenic sources of mercury and is also a major polluted source of acid deposition. Thus, there is a certain extent the same origin and cooperation between acid deposition and mercury deposition. Acid deposition has been endangering the environment, simultaneously it enhances the harm of mercury. Therefore, it is of great importance to conduct the studies of mercury pollution in the regions of serious acid deposition.Sweden and Chongqing, China are sufferring from serious acid deposition. However, the sources are different. In Chongqing, China, the main source of acid deposition is combustion of coal, while in Sweden, acid deposition was caused by the long-range transported pollutants originated from other developed countries. Concentrations of atmospheric mercury indoor and outdoor may display a big difference in the two regions. The exposure of mercury for human being might be also different. In such case, it is worth while to study the variation of atmospheric mercury indoor and outdoor in two regions and has a high comparability.Based on the reasons mentioned above, investigations were carried out in Gothenburg, Sweden and Chongqing, China. Atmospheric mercury indoor and outdoor was measured. Three-day back-trajectory model was used to identify the origin of atmospheric mercury during the sampling period. The simple box model was used to estimate the source strength of diffuse stationary emitters of mercury present in the interior environment. At the same time, the effect of outdoor and indoor atmospheric meteorologic paramete(?)s, pollutant species and the direct and indirect presence of individuals with amalgam fillings in a compartment on atmospheric mercury was studied and mercury exposure dose in residential area at lower concentration was discussed.Results showed that average concentrations of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (Hg-P) concentrations in 2005 in Nordstan were 1.96±0.38 ng.m^-3, 2 53±4.09 and 12.50±5.88 pg.m^-3 (mean±SD), respectively. On the average, the atmospheric mercury apportioned as follows: GEM (99.17%) > Hg-P (0.67%)>RGM (0.16%). GEM and Hg-P were frequently elevated compared to background site and the literature, respectively, while, RGM was decrease(?) compare to relevant literature.The mean concentrations of total gaseous mercury (TGM) for outdoor and indoor in residential area were 2.89±1.43 ng.m^-3 and 7.57±5.23 ng.m^-3 ng.m^-3 in Gothenberg, Sweden and 13±18 ng.m^-3 and 32±87 in summer and 9±5 ng.m^-3 and 62±354 ng.m^-3 in Chongqing China, respectively. TGM outdoor was higher than the background value of TGM concentration in Rorvik and in Nordstan measured in this study, and also greater than the background TGM concentration in Northen hemisphere. It was showed somewhat pollution in residential area in these two areas. TGM in indoor was lower than the TGM concentration (50-69 ng.m^-3) measured by Carpi et al in New York, US and also lower than the minimal risk levels (MRL) of 200 ng.m^-3 published by the Agency for Toxic Substances and Disease Registry (ATSDR) and the sanitatior standard for the design of industrial organization (300 ng.m^-3) of our country. However the TGM concentration in children' bedroom (1293 ng.m^-3) in Yu Bei district in summer and adults' bedroom (3494 ng.m^-3) in Dong Yan town of Bei Bei district were higher than these standards. Indoor TGM concentration was obviously higher than that of outdoor concentration because of the higher mercury background outside, mercury sources in indoor, the dynamic variation of people in indoor and atmospheric meteorological and pollutant species.Temporal variation of mercury species in Gothenberg showed RGM and Hg-P fluctuated bigger than GEM. Because RGM and Hg-P, which were removed rapidly from the atmosphere via both wet and dry depositions, were more influence by the local mercury sources and chemical conditions than GEM. There were some episodes of larger concentration for three mercury species. GEM was influenced by long term transported pollutants, local sources and natural sources in three episodes in Gothenberg. Three-day back trajectories showed the higher concentration came from southern highly industrialized regions. It was found that GEM were also elevated in RGM and Hg-P episodes of larger concentration and suggested the existence of local mercury sources during Feb. 21 to 25 within 0-45°wind sector.Temporal variation of outdoor TGM of residential areas in Gothenberg exhibited the biggest fluctuation in suburb, bigger in rural area, and then urban. Variation of indoor TGM in Gothenberg presented multi-peaks, and showed a similar tendency indoor. Nevertheless, variation of indoor and outdoor TGM in Chongqing presented multi-peaks, and showed a similar tendency within the indoor and outdoor. It indicated the mercury sources, atmospheric meteorological and pollutant species were similar.Outdoor TGM in suburb and rural area in Gothenberg accepted the long term transported pollutants, local sou(?)ces and natural sources, but the effect was local sources and natural sources in urban.The wind speed was very low (<1 m-s^-1) in Chongqing, China in sampling period, this limited the long- distance transportation for pollutants. Therefore the TGM were affected by local sources and natural sources.GEM (2.39 ng.m^-3) and RGM (2.96 pg.m^-3) concentration in Nordstan Gothenberg at wind speeds <1.5 m.s^-1 were higher than that at the wind speeds >1.5 m.s^-1 (1.93 ng.m^-3 and 2.49 pg.m^-3, respectively). GEM and RGM showed more random distribution in different wind directions when the wind speeds was less than 1.5 m·s^-1. The increased GEM and RGM suggested the influences of local sources, especially the emissions from oil combustion and emissions from natural sources. Lower wind speed promoted the form of a shallow nocturnal boundary layer, lead to a higher concentration and the present of the oxidation pathway. The difference among each wind directions of GEM and RGM was distinct at wind speeds≥1.5 m.s^-3. In southern sector, GEM was suggested to be impacted by long distance transport of mercury and local sources in 135°-180°(2.20 ng.m^-3) and 180°-225°(2.15 ng.m^-3) sector to get the highest concentration. 3-day back trajectories for GEM exhibited that all air masses have passed within the south developed country sector in two episodes of larger concentration. 0-45°sector was affected mostly by local anthropogenic sources showed the highest RGM concentration, especially during Feb. 21 to 25 there may be some high pollution episodes occurred; nevertheless, 45°-90°sector was the cleanest sector at least in the sampling period.Diurnal pattern of GEM in Gothenberg showed that maximum values occurred in the nighttime (2.13 ng.m^-3), whereas RGM concentration (4.39 pg.m^-3) was measured greater in the daytime along with the decrease of GEM. This result indicated the possibility of the transformation between GEM and RGM. Outdoor TGM in residential area exhibited the same tendence. The reasons may due to the formation of inversion, especially in the night; lower vertical mixing, high RH bounded the atmospheric oxidants and less available to oxidize Hg°to RGM. In addition, the RGM would be incorporated into water vapor which can be more efficient removal by wet deposition. During nighttime, thermal mixing increased the height of boundary layer, then lead to the dilution of Hg concentrations and the present of the oxidation pathway, and RGM increased in daytimeIndoor TGM exhibited high values in nighttime relative to daytime in Gothenberg. However, the trend for Chongqing was opposite. These were due to the effects of outdoor mercury polluted sources, indoor static state mercury sources, activity of indoor individuals; open-close the door and window and outdoor atmospheric meteorological and pollutant species.Introduced fresh air when open-close the door and window resulted in the same tendence for outdoor and indoor TGM.Indoor TGM increased obviously due to the present of individuals with amalgam fillings or higher mercury enrichment in a compartment. The difference reached to about 6.66 ng.m^-3 in Gothenberg; and 564 ng.m^-3 (was 8.5 times for empty room) in children' bedroom in summer inYu Bei and 2590 ng.m^-3 (was 67 times for empty room) in adults' bedroom in winter in Dong Yan town of Bei Bei district. The contribution from subjects with amalgam fillings or not present elsewhere in the flat was still exist. However the effect was diminished when individuals present in a cleanly room or individuals with lower mercury enrichment.An additional experiment performed in two assembly rooms showed TGM concentration within 1 h increased from a baseline concentration of 2.7-3.09 ng.m^-3 to 7.67ng.m^-3 by seven participants with amalgam fillings, about 2.5 times higher than the baseline concentration, and 26 ng.m^-3and 50 ng.m^-3, about 6⁸ and 2 times for outside concentration in Chongqing, respectively. These were undisputed examples exhibited he effect of individuals presence.Stationary emitters of mercury presented in the interior environment were an important factor influencing TGM inside the flat. It may be fit for using the logarithm equation for source strength, y= 3.7693+19815lnx, where x means accumulated emission time. A simple box model assuming a good mixing es(?)imated that the mean mercury release rate from the interior area of the flat with brick frame in Gothenberg closed to about 250 ng.m^-2.h^-1 The net concentration released from indoor mercury source (5.5 ng.m^-3) was greater than one person with amalgam fillings presence (0.01 ng.m^-3), but lower than two individuals with amalgam fillings presence in flat of Mell (6.66 ng.m^-3). Simultaneously it was speculated that the released source strength equalled the difference between the average indoor concentration of that flat and outdoor concentration.Except For2 and Axga in Gothenberg, which was influenced by outdoor meteorological conditions, the effect of a mospheric meteorological condition on indoor TGM was not obvious.Seasonal variation of outdoor TGM exhibited stronger fluctuation in summer than that in winter. Outdoor TGM concentration in summer was higher than that in winter. However outdoor TGM concentration in winter was greater than that in summer. These were due to the higher temperature and global radiation and lower relative humidity in summer.Spatial variation of outdoor TGM in Gothenberg followed the order of suburb (4.27ng.m^-3)> rural area (2.73 ng.m^-3) > urban (1.89 ng.m^-3), while indoor TGM exhibited urban concentration (7.79 ng.m^-3) > suburb concentration (5.54 ng.m^-3) > rural zone concentration (4.03 ng.m^-3). The reasons might be that Mell in suburb is located near the junction of arterial traffic and close to the coastline of Baltic Sea, which was impacted by oceanic condition. The lower concentration in urban was due to the lower wind speed (1.5 m.s^-1) and less anthropogenic polluted sources.Spatial variation of outdoor TGM in Chongqing followed the order of special industrial park (43 ng.m^-3)> commercial traffic and residential area (21 ng.m^-3)> urban residential area (9 ng.m^-3)>culture area (9 ng m^-3) > background area (4 ng.m^-3) in summer. It followed the order of Da Dukou district in urban residential area (15 ng.m^-3)>special industrial park (14 ng.m^-3)>commercial>traffic and residential area (9 ng.m^-3)>other urban residential area (9 ng.m^-3)>background area (9 ng.m^-3) >culture area (6 ng.m^-3) in winter. The reasons for the difference between summer and winter were related to atmospheric meteorological conditions and anthropogenic polluted sources. There are many heavy pollution industry plants located in Da Dukou district. The higher TGM in winter in Da Dukou district was due to poor dilution of pollutants under the condition of inversion and lower wind speed. The increased TGM concentration in background area in winter might come from the conducting architecture construction. Spatial variation of indoor TGM in Chongqing showed a descending order of Yu Bei district in urban residential area (187 ng.m^-3), special industrial park (49 ng.m^-3),commercial, traffic and residential area (23 ng.m^-3), other urban residential area (15 ng.m^-3), culture area (12 ng.m^-3) and background area (7 ng.m^-3) in summer; however a descending order of special industrial park (662 ng.m^-3), commercial, traffic and residential area (14 ng.m^-3), urban residential area (11 ng.m^-3), background area (8 ng.m^-3) and culture area (6 ng.m^-3) in winter.In Gothenberg, the exposure of mercury for an adult female, an adult male and a child (0-2 years) by inhalation indoor would be 49.4 -197 ng.day^-1, 66.4-265.0 ng.day^-1 and 19.7 - 119 ng.day^-1 respectively. In Chongqing, China, the exposure of mercury for an adult female, an adult male and a child (0-2 years) by inhalation indoor would be 49.4 -543 ng.day^-1, 66.4-730 ng.day^-1 and 19.7 - 327 ng.day^-1 respectively. This implied that individuals in Chongqing exposed more TGM than individuals in Gothenberg. The exposure of an adult female and a child by indoor inhalation in Chongqing would be exposed to approximately 12656 ng.day^-1 and 7611 ng.day^-1 calculated from the highest indoor TGM measured in this study, which was much higher than that of fish consumption (2900-3270 ng.day^-1). It is suggested that great attention be paid for inhalation exposure control to reduce the health risk of mercury in China.