Background Mercury Concentrations Research Articles

Содержание ртути в рыбе, выловленной ниже целлюлозно-бумажного комбината в Северной Двине

Subarctic Russian rivers tend to have swampy watersheds with a high content of hydro­gen ions and humic substances. These conditions are favourable for the formation of bioavail­able mercury. Thus, even background mercury concentrations can pose a danger to aquatic organisms. The Northern Dvina River attracts particular attention regarding mercury pollu­tion due to the presence of pulp and paper mills in the area. These mills have historically uti­lised mercury in their production processes. This study aims to analyse the mercury content in commercially important fish species living in the mouth of the Northern Dvina River. The content and distribution of mercury in tissue samples of various fish species were determined to provide insight into components of the mercury cycle in the study area. Lower mercury levels in pristine areas of the Russian subarctic showed the role of aquatic organisms as indicators of the biogeochemical cycle of mercury migration in northern freshwater areas. This study provides new scientific data on the levels of mercury found in fish from the Northern Dvina, particularly those in its estuary zone affected by the pulp and paper industry. The content and distribution of mercury were characterised using the most common fish species as an example. The difference was shown between mercury accumulation in different conditions and areas, with an analysis of relevant factors carried out.

Distribution of mercury concentrations in lichens, mosses and larch needles in Western Siberia (according to the 2019 data)

Abstract. This paper presents data on mercury concentrations in samples of lichen and moss, as well as needles of trees (larch, cedar and pine), taken in September 2019 along a rare sampling network on the meridional transect from the Novy Urengoy area in the north to Tobolsk in the south. The mean Hg concentration (ng/g) in samples of moss, lichen and larch needles was 26, 15 and 17, respectively. The Hg concentrations in samples of annual needles of pine and cedar were below the detection limit of the method (<10 ng/g). We discuss possible factors that affect the heterogeneity of the Hg distribution in biomonitors and the discrepancy between the Hg concentrations for samples taken at the same sites. There was a systematic increase in background mercury concentration near the Novy Urengoy city and the Gubkinsky town. We assume a possible decrease in the Hg concentration in the mosses of the middle part of Western Siberia compared to its northern part.

Air mercury monitoring in the Baikal area (2011-2021)

Abstract. We present long-term (2011 2021) data on air mercury monitoring that was started within the GMOS (Global Mercury Observation System) project (2011-2015) at the Listvyanka station located on the shore of Lake Baikal, Siberia. Monitoring shows an obvious seasonal variation in the background mercury concentration in the air, which increases in the cold season and decreases in the warm season. Short-term anomalies are associated with the wind carrying air from industrial areas where several large coal-fired power plants are located (Irkutsk and Angarsk). A positive correlation between mercury, SO2 and NO2 concentrations is observed both in short-term variations and in average monthly concentrations. The analysis of the forward and backward trajectories obtained with the HYSPLIT model demonstrates possible mercury emission sources. Concentration-weighted trajectory (CWT) analysis has revealed potential remote regions of mercury emissions from where mercury can be transported by air masses to the area of Lake Baikal, including the territories of Transbaikalia and Mongolia (Erdenet). During the 2018 cruise, the continuous air mercury survey above Lake Baikal covered 1800 km. The mean mercury concentration above Lake Baikal is significantly lower than the mean value obtained at the onshore Listvyanka station during the same days of the cruise. That can lead to the conclusion that Lake Baikal is a sink of atmospheric mercury.

Air Mercury Monitoring at the Baikal Area

The GMOS (Global Mercury Observation System) project has the overall goal to develop a coordinated observing system to monitor mercury on a global scale. Here we present the long-term (2011–2020) air mercury monitoring data obtained at the Listvyanka station located at a shore of Lake Baikal, Siberia. The long-term monitoring shows obvious seasonal variation of the background mercury concentration in air, which increases in the cold and decreases in the warm season. The short-term anomalies are associated with the wind carrying the air from the industrial areas where several big coal-fired power plants are located. A positive correlation between the mercury, SO2 and NO2 concentrations is observed both in the short-term variations and in the monthly average concentrations. The analysis of forward and backward trajectories obtained with the HYSPLIT model demonstrates revealing of the mercury emissions sources. During the cruise of 2018, the continuous air mercury survey over Lake Baikal covered 1800 km. The average mercury concentration over Baikal is notably less in comparison with the average value obtained at the onshore Listvyanka station during the same days of the cruise. That can lead to the conclusion that Baikal is a significant sink of the atmospheric mercury.

Background concentrations of mercury in Australian freshwater sediments: The effect of catchment characteristics on mercury deposition

Waterways in the Southern Hemisphere, including on the Australian continent, are facing increasing levels of mercury contamination due to industrialization, agricultural intensification, energy production, urbanization, and mining. Mercury contamination undermines the use of waterways as a source of potable water and also has a deleterious effect on aquatic organisms. When developing management strategies to reduce mercury levels in waterways, it is crucial to set appropriate targets for the mitigation of these contaminated waterways. These mitigation targets could be (1) trigger values or default guideline values provided by water and sediment quality guidelines or (2) background (pre-industrialization) levels of mercury in waterways or sediments. The aims of this study were to (1) quantify the differences between existing environmental guideline values for mercury in freshwater lakes and background mercury concentrations and (2) determine the key factors affecting the spatial differences in background mercury concentrations in freshwater lake systems in Australia. Mercury concentrations were measured in background sediments from 21 lakes in Australia. These data indicate that background mercury concentrations in lake sediments can vary significantly across the continent and are up to nine times lower than current sediment quality guidelines in Australia and New Zealand. This indicates that if waterway managers are aiming to restore systems to ‘pre-industrialization’ mercury levels, it is highly important to quantify the site-specific background mercury concentration. Organic matter and precipitation were the main factors correlating with background mercury concentrations in lake sediments. We also found that the geology of the lake catchment correlates to the background mercury concentration of lake sediments. The highest mercury background concentrations were found in lakes in igneous mafic intrusive regions and the lowest in areas underlain by regolith. Taking into account these findings, we provide a preliminary map of predicted background mercury sediment concentrations across Australia that could be used by waterway managers for determining management targets.

Technical and Physical Limitations in the Determination of Background Mercury Concentration

The optical schemes and characteristics of atomic absorption Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> analyzers based on the Zeeman effect and a low-pressure capillary mercury lamp, as well as on 190 fm linewidth UV dye laser systems have been studied in detail. The method of evaluating the limit of detection (LOD) of atomic absorption analyzers is proposed. The characteristics of modern ultra-narrowband sensors and sources of UV radiation are analyzed. The efficiency of using new thermal ultrasonic sensors as optical power detectors in the atomic absorption analyzer is discussed. Technical characteristics and reliability of such sensors are compared with all known thermal sensors. The main physical and technical limitations that have a negative effect on the sensitivity and miniaturization of thermal ultrasound sensors are presented. The study shows that such thermal sensors have low sensitivity and accuracy, which makes their use in portable express analyzers of background mercury impractical. The evaluation results prove that the analyzers which use a transverse magnetic field for splitting the lamp emission line also cannot register background mercury concentration. This fact is explained by the low signal-to-noise ratio (SNR) of the discharge low-pressure UV lamp operating in a continuous mode and by the absorption of forbidden oxygen lines by the reference optical signal. The estimation results shown that the portable Hg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> analyzers based on UV dye laser systems can reach the LOD <; 0.1 ng/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Thus, the main stage in the design of the portable express background mercury analyzers is a measurement of the SNR of UV sources and sensors.

Air Contamination by Mercury, Emissions and Transformations\u2014a Review

The present and future air contamination by mercury is and will continue to be a serious risk for human health. This publication presents a review of the literature dealing with the issues related to air contamination by mercury and its transformations as well as its natural and anthropogenic emissions. The assessment of mercury emissions into the air poses serious methodological problems. It is particularly difficult to distinguish between natural and anthropogenic emissions and re-emissions from lands and oceans, including past emissions. At present, the largest emission sources include fuel combustion, mainly that of coal, and “artisanal and small-scale gold mining” (ASGM). The distinctly highest emissions can be found in South and South-East Asia, accounting for 45% of the global emissions. The emissions of natural origin and re-emissions are estimated at 45–66% of the global emissions, with the largest part of emissions originating in the oceans. Forecasts on the future emission levels are not unambiguous; however, most forecasts do not provide for reductions in emissions. Ninety-five percent of mercury occurring in the air is Hg0—GEM, and its residence time in the air is estimated at 6 to 18 months. The residence times of its HgII—GOM and that in Hgp—TPM are estimated at hours and days. The highest mercury concentrations in the air can be found in the areas of mercury mines and those of ASGM. Since 1980 when it reached its maximum, the global background mercury concentration in the air has remained at a relatively constant level.

Critical perspectives on mercury toxicity reference values for protection of fish

Environmental management decisions at mercury-contaminated sediment sites are predicated on the understanding of risks to various receptors, including fish. Toxicity reference values (TRVs) for interpreting risks to fish have been developed to assess mercury concentrations in fish or fish prey. These TRVs were systematically evaluated based on several lines of evidence. First, their conceptual basis and specific derivation were evaluated, including a close review of underlying toxicity studies. Second, case studies were reviewed to investigate whether TRVs are predictive of effects on fish populations in the field. Third, TRVs were compared with available information regarding preindustrial and present-day background concentrations of mercury in fish. The findings show that existing TRVs are highly uncertain, because they were developed using limited data from studies not designed for TRV derivation. Although field studies also entail uncertainty, several case studies indicate no evidence of adverse effects despite mercury exposures that exceed the available TRVs. Some TRVs also fall within the range of background mercury concentrations in predatory or prey fish. Lack of information on the selenium status of mercury-exposed fish is a critical confounding factor, and the form of methylmercury used in toxicity testing may also contribute to differences between TRV-based predictions and field observations of mercury effects on fish. On balance, the available information indicates that several of the TRVs reviewed are lower than necessary to protect fish populations. The 20% effect concentration from a previously published dose-response analysis appears closer to an effect threshold, based on available laboratory data. Additional research is needed to provide a stronger basis to establish dose-response relationships for mercury effects on fish.

Correlation Analysis, Transportation Mode of Atmospheric Mercury and Criteria Air Pollutants, with Meteorological Parameters at Two Remote Sites of Mountain and Offshore Island in Asia

This study presents a comparison of trace (Hg) and criteria (CO, SO_2, NO_x, O_3 and PM_(10)) air pollutants monitored at two remote sites with the same latitude but different altitude: Mt. Lulin and the Penghu Islands, in Taiwan from 2011 to 2012. A filtering technique was comprehensively applied to distinguish the climatic characteristics of the two remote sites, as well as to determine their discriminant factor. The concentrations of air pollutants monitored at Mt. Lulin were generally lower than those at the Penghu Islands, with the exception of O_3 concentration. PM_(10) and NO_x were the important factors that can distinguish two clusters of measurement data at the two remote sites, and a criteria discriminant factor of atmospheric parameters derived from these two air pollutants. For both high- and low-frequency patterns, the concentrations of NO_x and PM_(10) exhibit significant differences between the two remote sites. However, O_3 concentrations showed almost no differences between these two remote sites, implying that the pattern for the formation and transportation of O_3 at these two sites resulted from similar mechanisms. Moreover, atmospheric mercury (TGM) had a very good linear correlation with CO. The diurnal variation of Hg concentration was dramatic at the Penghu Islands, while it appeared as low as the North Hemisphere background mercury concentration at Mt. Lulin, indicating that they were not formed via the mechanism modes. This study thus proposed ＂scenario mercury＂ and ＂background mercury＂ for interpreting this interesting phenomenon.

Sources and Dynamic Processes Controlling Background and Peak Concentrations of TGM in Nanjing, China

Total gaseous mercury (TGM) data from urban Nanjing, at the western edge of the Yangtze River Delta (YRD) region in China, over nine months, were analyzed for peak and background mercury concentrations. The background concentration of TGM was found to be 2.2 ng∙m−3. In examining episodic influences of free tropospheric air masses on the surface TGM concentrations in Nanjing, we hypothesize heterogeneity in the global distribution of TGM concentrations in the free troposphere. The nine-month averaged diurnal cycles of TGM indicate a strong co-emission with SO2 and an underestimation of greater than 80% TGM emissions in current inventories. Regular peak concentrations of mercury were investigated and the major causes were YRD emissions, transport from rural areas, and monsoonal transport. Transport of rural emissions is hypothesized to be from illegal artisanal small-scale gold mining that are currently missing in the emission inventories. Enhancement of TGM associated with summer monsoon contributed to a maximum TGM concentration in mid-May–early June, an inverse seasonality in comparison to most other observations in China, North America, and Europe.

Differential absorption lidar system employed for background atomic mercury vertical profiling in South China

A differential absorption lidar (DIAL) system based on a Nd:YAG laser pumped narrow-band dye laser is developed and employed to monitor the atmospheric background concentration of atomic mercury in Guangzhou, South China. Atmospheric oxygen is also studied by using neighboring wavelengths to the mercury absorption line (253.7nm), and is used to verify the operation of the DIAL system. A 24-hour continuous monitoring of background mercury concentration is performed and the average atomic mercury concentration below 330m is between 5ng/m3 and 12ng/m3.

Assessment of ambient mercury deposition fluxes by numerical air quality modeling

Since mercury monitoring activities are very limited in Japan and governmental monitoring data of mercury deposition fluxes are not available, it is necessary to choose some numerical models to protect and manage the local ambient air quality. Numerical models for mercury transportation and deposition should be developed to understand the scenario and pathway of atmospheric mercury concentration distributions and deposition fluxes in the local area of Japan. The ground-level mercury concentrations have to meet the environmental standards set by the Ministry of the Environment in Japan which is less than 40 mg m−3. The aim and scope of this research is to apply numerical models to forecast seasonal variation of ambient mercury concentrations and deposition fluxes in the local area of Japan. To estimate the ambient mercury concentrations in the local area, a dispersion model has been used, the National Institute of Advanced Science and Technology-Atmospheric Dispersion Model for Exposure and Risk Assessment (AIST-ADMER). The AIST-ADMER model calculated the yearly average concentration distributions of mercury in the Aichi Prefecture Japan, which serve as boundary and background concentrations of mercury for the mercury deposition model. Finally, the boundary and background concentrations of mercury calculated by the AIST-ADMER along with meteorological data were superposed in the mercury deposition model to calculate mercury deposition fluxes (dry and wet) in Isshiki Town of Aichi Prefecture. Maximum atmospheric concentrations of mercury were calculated as 2.89 ng m−3 by the AIST-ADMER model. In this study, total dry deposition fluxes and wet deposition fluxes were calculated to be 15.1 μg m−2 year−1 and 14.3 μg g m−2 year−1, respectively.

Influence of emissions on regional atmospheric mercury concentrations

Mercury is a global pollutant that is rapidly transported in the atmosphere. Unlike the majority of air pollutants the background concentrations of mercury play a major role for the atmospheric concentrations on a hemispheric scale. In this study the influence of regional anthropogenic emissions in comparison to the global emissions on mercury concentrations over Europe are investigated. For this purpose an advanced threedimensional model system is used that consists of three components. The emission model SMOKE-EU, the meteorological model COSMO-CLM, and the chemistry transport model (CTM) CMAQ. A variety of sensitivity runs is performed in order to determine the influence of different driving factors (i.e. boundary conditions, anthropogenic and natural emissions, emission factors, meteorological fields) on the atmoshperic concentrations of different mercury species. This study is part of the European FP7 project GMOS (Global Mercury Observation System). The aim is to identify the most important drivers for atmospheric mercury in order to optimize future regional modelling studies in the course of the GMOS project. Moreover, the model results are used to determine areas of interest for air-plane based in-situ measurements which are also part of GMOS.

Modeling of atmospheric dispersion of mercury from coal–fired power plants in Japan

The Air Quality Management Division of Ministry of the Environment in Japan selected the maximum level of annual mean air quality standard for mercury as 0.04μg/m3. The yearly average atmospheric emissions of mercury from two nearly located point sources, background concentrations of mercury in the atmosphere and one–year meteorological data was used to predict the ambient concentrations of mercury at ground level by atmospheric dispersion modeling. To estimate the mercury concentration in the air of the local area, two different models have been used. The first one is AIST–ADMER model that estimates regional atmospheric distribution of mercury concentration. The second one is METI–LIS model that estimates the atmospheric distribution of mercury concentration in the vicinity of industrial facilities. The annual mean concentration of mercury in the atmosphere was calculated for the central Honshu Island of Japan using the AIST–ADMER model, which served as a background data for the METI–LIS model to calculate atmospheric mercury concentration in the vicinity of industrial facilities. Maximum annual mean atmospheric concentrations of mercury in the vicinity of the two hypothetical coal–fired power plants were calculated as 0.0118μg/m3 that was lower than the Japanese annual mean air quality standard for mercury.

Evaluation of Potential for Mercury Volatilization from Natural and FGD Gypsum Products Using Flux-Chamber Tests

Synthetic gypsum produced by flue-gas desulfurization (FGD) in coal-fired power plants (FGD gypsum) is put to productive use in manufacturing wallboard. FGD gypsum wallboard is widely used, accounting for nearly 30% of wallboard sold in the United States. Mercury is captured in flue gas and thus is one of the trace metals present in FGD gypsum; raising questions about the potential for mercury exposure from wallboard. Mercury is also one of the trace metals present in "natural" mined gypsum used to make wall board. Data available in the literature were not adequate to assess whether mercury in wallboard from either FGD or natural gypsum could volatilize into indoor air. In this study, mercury volatilization was evaluated using small-scale (5 L) glass and Teflon flux chambers, with samples collected using both iodated carbon and gold-coated sand traps. Mercury flux measurements made using iodated carbon traps (n=6) were below the detection limit of 11.5 ng/m2-day for all natural and synthetic gypsum wallboard samples. Mercury flux measurements made using gold-coated sand traps (n=6) were 0.92 +/- 0.11 ng/m2-day for natural gypsum wallboard and 5.9 +/- 2.4 ng/m2-day for synthetic gypsum wallboard. Room air mercury concentrations between 0.028 and 0.28 ng/m3 and between 0.13 and 2.2 ng/m3 were estimated based on the flux-rate data for natural and synthetic gypsum wallboard samples, respectively, and were calculated assuming a 3 m x 4 m x 5 m room, and 10th and 90th percentile air exchange rates of 0.18/hour and 1.26/hour. The resulting concentration estimates are well below the U.S. Environmental Protection Agency (EPA) reference concentration for indoor air elemental mercury of 300 ng/m3 and the Agency for Toxic Substances and Disease Registry minimal risk level (MRL) of 200 ng/m3. Further, these estimates are below background mercury concentrations in indoor air and within or below the range of typical background mercury concentrations in outdoor air.

Atmospheric mercury at mediterranean coastal stations

Mercury in air has been measured at five coastal Mediterranean sites, involving measurements in Spain, France, Italy, Slovenia and Israel. Four two-weeks long measure- ments campaigns were performed at the five sites. The measurements were carried out during autumn 2003 and winter, spring and summer 2004. Total gaseous mercury/elemental gaseous mercury, particulate mercury and divalent gaseous mercury were measured in parallel at the five sites. The activities constituted a subtask of the EU funded MERCYMS research project, which also included Mediterranean Sea cruises where both mercury in air and water were measured. The result from an evaluation of all the coastal air data is presented. Mercury concentrations from the different sites are compared with similar data obtained in northern Europe and elsewhere. The result shows that the background concentration of mercury in Mediterranean coastal air is lower than earlier anticipated. Background concentrations of TGM, RGM and TPM corresponded to 1.75-1.80 ng m −3 , 1-13 and 3-23 pg m −3 , respec- tively. The measurements also showed that the mercury concentration occasionally can be

Mercury Contamination and Dynamics in the Sediment of the Second Songhua River, China

The Second Songhua River (SSR) was subjected to a large amount of mercury discharge from petrochemical industries in Jilin City from the 1960s to 1980s. The objectives of this study were to investigate the spatial and temporal change of mercury concentration in the sediments of the river and to assess Hg pollution in sediment employing enrichment ratio. Bottom sediments sampled in 2005 were digested with various acids followed by analysis by atomic fluorescence spectrometry for Hg, ICP-MS for Cd, Pb and Sc, and ICP-OES for Co, Cr, Cu, Zn, Mn, Ni, P, Pb, Sb, Ti, V, Al, Fe, Mg, Ca, Na, and K, in order to measure the total concentrations of these elements in the sediments. Results indicated that mercury concentrations in the sediments were strongly related with distance from the historic industrial point source, decreasing at an exponential rate from 1.27 mg kg−1 at Jilin City to 0.01 mg kg−1 at downstream Haerbin City. In addition, mercury concentration decreased from 16.8 mg kg− 1 y−1 in 1974 to 0.09 mg kg−1 y−1 in 2005 in the sediments at effluent discharge site, and from 0.006 mg kg−1 y−1in 1974 to 0.004 mg kg−1 y−1 in 2005 at Songyuan City 257 km downstream. In the sedimentary sections of the river, deeper sediments contained higher concentrations of mercury as compared to the surface sediments, suggesting discharges of higher levels of mercury in the past and its subsequent burial over the years by less polluted sediments. Background concentrations of mercury in the surface sediments, reconstructed by tracer Sc, were 0.011 to 0.018 mg kg−1. Enrichment ratios of Hg in the sediments of SSR was 5 to 75, indicating moderate to extreme pollution, while the sediment of Songhua River is less contaminated, with enrichment ratios of 0.9 to 1.5. At present, the previously accumulated and buried mercury in sediments may not significantly affect water quality of the SSR, but might pose a potential ecological risk to aquatic and amphibian animals. Natural attenuation seems to be an economic remedial choice for these sediments.

Bioaccumulation of Total Mercury and Monomethylmercury in the Earthworm Eisenia Fetida

Bioaccumulation factors (BAFs) for inorganic mercury in earthworms are usually < 1; however, factors up to ∼10 have been reported. Little information is available concerning the bioaccumulation of organic mercury in earthworms from actual contaminated soils and thus there has been uncertainty in the risk characterization phase of ecological risk assessments of mercury-contaminated sites. This study was initiated to determine the rate of uptake and bioaccumulation of total mercury (T-Hg) and monomethylmercury (MMHg) in Eisenia fetida from soils which have been contaminated with mercury for approximately 30 years. The study consisted of a 28-day uptake phase in three mercury-contaminated soils and one soil with background concentrations of mercury followed by a 14-day depuration phase in background soil only. Total mercury concentrations in the study soils ranged from 85 to 11,542 μg kg−1 dry weight soil; MMHg concentrations ranged from 1.12 to 7.35 μg kg−1 dry weight soil. Time to 90% steady states for T-Hg ranged from 36 to 42 days. A steady state did not occur for any of the MMHg exposures during the 42-day study; estimated time to 90% steady state varied from 97 to 192 days. BAFs for T-Hg ranged from 0.6 to 3.3. BAFs for MMHg ranged from 175 to 249. The BAFs for T-Hg and MMHg were larger in earthworms exposed to the lower contaminated soils and smaller in the higher mercury-contaminated soils. The absolute concentrations of T-Hg and MMHg bioaccumulated in E. fetida, however, were higher in the earthworms exposed to the higher mercury soils and lower in the less mercury-contaminated soils.

Mercury Emissions from Background and Altered Geologic Units Throughout Nevada

To date there have only been a few studies that measured mercury emissions from background substrate worldwide, and only a small amount of mercury flux data, from background substrate, exists for the Western United States. Because of this, the database of mercury emissions from background units < 0.1 mg kg-1 mercury) is incomplete. This study focused on the collection of in-situ mercury flux data from representative lithologic units in Nevada. Measured mercury fluxes from substrate with background mercury concentration throughout Nevada were low (mean 2.0 ± 4.1 ng m-2 hr-1), and ranged from –3.7 to 9.3 ng m-2 hr-1. The mean measured mercury flux is slightly higher than those measured from background substrate from various locations throughout the world. The mean mercury flux from in-situ mercury measurements from substrate located near altered geologic units across Nevada was 15.5 ± 24.2 ng m-2 hr-1. These mercury fluxes are higher than the values applied in published global models for naturally enriched geologic units.

Background mercury concentrations in river water in Maine, U.S.A.

Mercury concentrations in 58 rivers in Maine was measured to range from below detection up to 7.01 ng L(-1) and averaged 1.80 +/- 1.29 ng L(-1). The concentration gradient for mercury in rivers across the state was not uniform. Mercury strongly correlated with dissolved organic carbon (DOC) and aluminum, and less strongly with copper, lead, and zinc. Mercury exhibited significant differences in correlations with chemical variables and local geology when partitioned by flow state (high or low). Mercury concentrations were greatest in rivers flowing across either wacke-type bedrock at low metamorphic grade, or glacial-till deposits. Elevated concentrations of mercury formed a locus in northern Maine under both high and low-flow states while in southwestern Maine a locus formed only during high-flow states. These regional differences were statistically significant when compared by geographical location. We suggest that there is a bedrock source of mercury in northeastern Maine that is diluted during periods of high runoff. The elevated concentrations detected under high-flow states, as noted in southwestern Maine, may reflect mercury released from storage in association with DOC during periods of high runoff. The association of mercury with flow state indicates that watershed processes and local geology can modulate the concentration of mercury in rivers.