Contribution of a medium-sized tropical river to the particulate heavy-metal load for the South Atlantic Ocean

The Paraíba do Sul River is a medium-sized river, 1145 km in length with a drainage basin of 55,400 km2. The riverine fluxes of particulate metals (Cu, Cr, Zn, Mn and Fe) were investigated over 24 months. Particulate matter samples were monthly collected from April 1994 to March 1996. The first 12-month period presented lower rainfall than the second, although both periods presented average precipitation lower than the regional average. The particulate matter flux in the second period (2,042,080 t) was 250% higher than the first period (821,489 t). The same trend was observed for the associated metals, which presented higher fluxes in the second period. This study highlights the strong dependence of the transported mass on the rainfall, and consequently with the river water discharge. The Paraiba do Sul River presents a low contribution to the world oceans, although the local contribution could be considered relevant.     

Mercury cycling between the water column and surface sediments in a contaminated area

Mercury cycling in the water column and upper sediments of a contaminated area, the Largo do Laranjo, Aveiro (Portugal), was evaluated after determination of reactive and non-reactive mercury concentrations in the water column and pore waters of sediments, collected in several places of this bay. In the water column, reactive mercury concentrations varied between 10 and 37 pmol dm(-3), the highest values being observed near the mercury anthropogenic source. However, reactive mercury was a narrowly constrained fraction of the total mercury, making up only 4-16% of the total, showing evidence of the importance of dissolved organic matter on mercury transport. In sediments, higher concentrations of mercury were also determined near industrial discharges. Results indicate the existence of an equilibrium between solid and liquid phases, determined by solid sediment/pore water distribution coefficients. Much of the mercury present in the solid fraction is associated with organic matter (r=0.837) and iron oxyhydroxides (r=0.919), but as oxides begin to dissolve in reduced sediments and organic matter decays, the adsorbed mercury is released. In fact, the mercury concentrations in pore waters of those contaminated sediments largely exceeded the values determined in the water column. As molecular diffusion may contribute to the dissolved mercury distribution in the overlying water column, this phenomenon was evaluated. However, the pore waters of Largo do Laranjo do not enrich the water column substantially in terms of reactive and non-reactive mercury. In fact, pore waters can contribute only to 0.2% and 0.5% of the reactive and non-reactive mercury present in the water column, respectively, showing that as long as mercury is being incorporated in sediments, it stays in stable forms.     

Contemporary and preindustrial mass budgets of mercury in the Hudson Bay Marine System: the role of sediment recycling

Based on extensive sampling of the rivers, troposphere, seawater and sediments, mercury (Hg) mass budgets are constructed for both contemporary and preindustrial times in the Hudson Bay Marine System (HBS) to probe sources and pathways of Hg and their responses to the projected climate change. The contemporary total Hg inventory in the HBS is estimated to be 98 t, about 1% of which is present in the biotic systems and the remainder in the abiotic systems. The total contemporary Hg influx and outflux, around 6.3 t/yr each, represent a 2-fold increase from the preindustrial fluxes. The most notable changes are in the atmospheric flux, which has gone from a nearly neutral (0.1 t/yr) to source term (1.5 t/yr), increased river inputs (which may also reflect increased atmospheric deposition to the HBS watershed) and in the sedimentary burial flux which has increased by 2.4 t/yr over preindustrial values, implying that much of the modern Hg loading entering this system is buried in the sediments. The capacity to drive increased Hg loading from the atmosphere to sediment burial may be supported by the resuspension of an extraordinarily large flux (120 Mt/yr) of shallow water glacigenic sediments uncontaminated by anthropogenic Hg, which could scavenge Hg from the water column before being transported to the deeper accumulative basins. Under the projected climate warming in the region, the rate of the sediment recycling pump will likely increase due to enhanced Hg scavenging by increasing biological productivity, and thus strengthen atmosphere-ocean Hg exchanges in the HBS.     

Mercury and methylmercury concentrations and loads in the Cache Creek watershed, California

Concentrations and loads of total mercury and methylmercury were measured in streams draining abandoned mercury mines and in the proximity of geothermal discharge in the Cache Creek watershed of California during a 17-month period from January 2000 through May 2001. Rainfall and runoff were lower than long-term averages during the study period. The greatest loading of mercury and methylmercury from upstream sources to downstream receiving waters, such as San Francisco Bay, generally occurred during or after winter rainfall events. During the study period, loads of mercury and methylmercury from geothermal sources tended to be greater than those from abandoned mining areas, a pattern attributable to the lack of large precipitation events capable of mobilizing significant amounts of either mercury-laden sediment or dissolved mercury and methylmercury from mine waste. Streambed sediments of Cache Creek are a significant source of mercury and methylmercury to downstream receiving bodies of water. Much of the mercury in these sediments is the result of deposition over the last 100-150 years by either storm-water runoff, from abandoned mines, or continuous discharges from geothermal areas. Several geochemical constituents were useful as natural tracers for mining and geothermal areas, including the aqueous concentrations of boron, chloride, lithium and sulfate, and the stable isotopes of hydrogen and oxygen in water. Stable isotopes of water in areas draining geothermal discharges showed a distinct trend toward enrichment of (18)O compared with meteoric waters, whereas much of the runoff from abandoned mines indicated a stable isotopic pattern more consistent with local meteoric water.     

Use of microbial and toxicant screening tests for priority site selection of degraded areas in water bodies

In this study, a new approach has been taken to evaluate Saint John River water and sediment conditions. A battery of biochemical, microbiological and bioassay tests were used to identify degraded or degrading sediments and waters. Data were obtained from waters and sediments at 38 sites within the Saint John River Basin. The data suggested that the following four sites had the highest priority concern: Little River No. 34, Grand Bay, Saint John River near Boars Head No. 33, Madawaska River below mill No. 7 and St Francois-de-Madawaska, mill stream No. 2. The data also indicated that microbial population, biochemical or bioassay tests performed independently do not provide realistic evaluations of priority concern areas and that the “battery of tests” approach is necessary to provide additional information.     

Distribution of total and methyl mercury in sediments along Steamboat Creek (Nevada, USA)

In the late 1800s, mills in the Washoe Lake area, Nevada, used elemental mercury to remove gold and silver from the ores of the Comstock deposit. Since that time, mercury contaminated waste has been distributed from Washoe Lake, down Steamboat Creek, and to the Truckee River. The creek has high mercury concentrations in both water and sediments, and continues to be a constant source of mercury to the Truckee River. The objective of this study was to determine concentrations of total and methyl mercury (MeHg) in surface sediments and characterize their spatial distribution in the Steamboat Creek watershed. Total mercury concentrations measured in channel and bank sediments did not decrease downstream, indicating that mercury contamination has been distributed along the creek's length. Total mercury concentrations in sediments (0.01-21.43 microg/g) were one to two orders of magnitude higher than those in pristine systems. At 14 out of 17 sites, MeHg concentrations in streambank sediments were higher than the concentrations in the channel, suggesting that low banks with wet sediments might be important sites of mercury methylation in this system. Both pond/wetland and channel sites exhibited high potential for mercury methylation (6.4-30.0 ng g(-1) day(-1)). Potential methylation rates were positively correlated with sulfate reduction rates, and decreased as a function of reduced sulfur and MeHg concentration in the sediments. Potential demethylation rate appeared not to be influenced by MeHg concentration, sulfur chemistry, DOC, sediment grain size or other parameters, and showed little variation across the sites (3.7-7.4 ng g(-1) day(-1)).     

Mercury in the river mersey, its estuary and tributaries during 1973 and 1974

Mercury levels found in waters and suspended matter from 53 stations, occupied four times at 3-monthly intervals, showed that most mercury was associated with particulates but the amount varied during the year. In the polluted region between Warrington and Runcorn, where fresh-water and sea-water converge, >80% of the mercury was associated with the particulates. Dissolved mercury concentrations and the mercury load on particulate matter were always greater in freshwater than in tidal waters, except during a flood. A model of partitioning of mercury between particulate and dissolved phases is presented. The River Weaver and the Manchester Ship Canal were grossly polluted with mercury throughout that year due to a Castner-Kelner plant at Runcorn. Dredge spoils and water flow transport 17 (range 8–138) and 1.55 ± 65% tonnes yr⁻¹ respectively of mercury into Liverpool Bay.     

The fate and transport of mercury, methylmercury, and other trace metals in Chesapeake Bay tributaries

Six tributaries to the Chesapeake Bay were analyzed for suspended particulate matter, dissolved organic carbon, particulate organic carbon, mercury, methylmercury, lead, nickel, zinc, cadmium, chromium, and copper. This study examined the importance of flow regime, suspended particulate concentration, and watershed characteristics on the transport of mercury, methylmercury, and other trace metals. Total mercury concentrations were higher under high flow conditions which is consistent with the tendency of this metal to bind strongly to particulate matter. Methylmercury showed less flow rate dependence. Nickel, lead, and zinc concentrations responded strongly to flow rate on the Potomac River, while weaker correlations were found on the other rivers sampled. Cadmium, copper, and chromium concentrations were the least influenced by flow. Partition coefficients calculated in this study were similar to those of other estuaries and overall decreased in the order of Hg > Ni-MMHg > Cr-Pb-Zn > Cd > Cu. Watershed yield estimates and associated retention factors were calculated for the various rivers. These calculations showed that for most of the rivers, mercury was the most strongly retained within the watershed.     

Mercury distribution, speciation and flux in the Sepetiba Bay tributaries, SE Brazil

Dissolved gaseous Hg, reactive Hg, total dissolved Hg and particulate Hg concentrations were measured in samples of majors tributaries of the Sepetiba Bay, SE Brazil (Itimirim, Itingu?u, Guarda, Guandu, S?o Francisco and Ita rivers), in dry and rainy seasons. The average Hg concentrations found varied from 0.02 to 0.18 ng L(-1) for dissolved gaseous Hg, from 0.1 to 18.1 ng L(-1) for reactive Hg, from 0.1 to 66.6 ng L(-1) for total dissolved Hg and from 0.3 to 250 ng L(-1) for particulate Hg. During the rainy season, a decrease in the dissolved Hg concentrations and an increase in the particulate Hg concentrations was observed. Positive correlations were found between the reactive Hg and the total dissolved Hg concentrations (r = 0.99), between the particulate Hg and TSS concentrations (r = 0.82) and between total Hg and particulate Hg concentrations (r = 0.95). The instantaneous Hg fluxes varied among rivers from 0.02 to 412 microgs(-1) for total dissolved Hg and from 0.03 to 12,572 microgs(-1) for particulate Hg. The log Kd varied from 3.76 to 6.43 and showed a significant increase in rainy season following an increase in particulate Hg and a decrease in dissolved Hg concentrations. These results suggest that erosion and runoff are the major pathways of Hg transport to rivers and eventually to Sepetiba Bay.     

The Almadén district (Spain): anatomy of one of the world's largest Hg-contaminated sites

We present data from an early reconnaissance survey (stream sediments, soil, and water Hg chemistry; plants and water crustaceans Hg intake) of the Almadén district (central Spain), that was carried out to establish the potential environmental hazards derived from the anomalous mercury concentrations measured in this realm. The Almadén mercury district (approximately 300 km2) can be regarded as the largest geochemical anomaly of mercury on Earth. The district includes a series of mercury mineral deposits, having in common a simple mineralogy (dominant cinnabar: HgS, and minor pyrite: FeS2). The ore deposits have been mined for more than 2000 years, and the main mine of the district (Almadén), has been active from Roman times to present day with almost no interruptions. The mercury distribution in soils of the district reveals the existence of high, and extremely high mercury values (up to 8889 microg g(-1)), whereas concentrations in stream sediments and waters reach exceptional values of up to 16,000 microg g(-1) and 11,200 ng l(-1) respectively. On the other hand, very high concentrations of methylmercury (MeHg) have been detected in calcines (up to 3100 ng g(-1)), sediments (0.32-82 ng g(-1)), and waters (0.040-30 ng l(-1)). Mercury gets incorporated to edible river crustaceans and plants. The red swamp crayfish Procambarus clarkii, has Hg concentrations of up to 9060 ng g(-1) (muscle) and 26,150 ng g(-1) (hepatopancreas). Regarding plants, the local wild asparagus (Asparagus acutifolius) yields values of up to 298 microg g(-1) Hg. Mercury also escapes to the atmosphere, and mineral deposits, together with metallurgical activities, generate strong anomalies of atmospheric Hg. The most important concentrations relate to the emissions from the Almadén metallurgical roaster, in the order of 14,000 ng Hg m(-3). Additionally, large open pit operations also contribute to the district atmospheric pool of mercury, with high concentrations above 1000 ng Hg m(-3). Thus, no system (rocks, soils, sediments, waters, atmosphere, biota) in the Almadén district is free from strong Hg contamination.     

Influence of intensive fishing on the partitioning of mercury and methylmercury in three lakes of Northern Québec

It has been demonstrated that intensive fishing, i.e., removing more than 25% of the fish biomass, can reduce mercury levels in predator fish in a lake. We test here the hypothesis that, by removing an important part of the fish biomass from a lake, a significant amount of methylmercury can be eliminated, therefore reducing the mercury available to the remaining biota, at least in the short term. A mass burden approach is used to evaluate the partitioning of total mercury and methylmercury in natural lake ecosystems. Three small natural lakes from the James Bay territory, in northern Québec, Canada, were selected for intensive fishing. Mercury (Hg) and methylmercury (MeHg) concentrations were evaluated for sediments, water column (dissolved fraction and suspended particulate matter), plankton, aquatic invertebrates, and fish. Biomasses were determined for fish, plankton, and aquatic invertebrates. Two case scenarios are presented using different mercury contributions from the sediment component (1 cm depth, and no sediment). Our results for the scenario including the sediment contribution show that lake sediments represent over 98% of the total mercury while the biotic components represent less than 0.1% of the same burden. For methylmercury, fish account for up to 5% of the burden, while sediments make up 84.6% to 93.1%. If we put aside the sediment contribution, the methylmercury in fish partitioning can represent up to 48%. As for invertebrates, they can account for up to 48% of the total MeHg burden. We do not observe any change in the partitionings or the quantities of Hg and MeHg before and after fishing in either of the two case scenarios even when we do not take into account dynamics of the ecosystems. This will be all the more the case when the dynamics of the system are included in the analyses. Therefore, biological parameters such as growth rates or fish diet must be considered.     

Elevated mercury concentrations in soils, sediments, water, and fish of the Madeira River basin, Brazilian Amazon: a function of natural enrichments?

Previous site-specific investigations have found that mercury concentrations in water, sediments, and biota of the Brazilian Amazon are elevated above global averages, and that these concentrations are a direct result of widespread mercury amalgamation mining operations conducted by non-organized prospectors. In order to assess the regional impacts of Hg contamination from these non-organized gold mining activities, water, sediments, and fish were systematically collected in 1997 along a 900-km reach of the Madeira River. The sampling program extended from the Amazon River upstream to Porto Velho, the site of historic and ongoing mercury amalgamation mining. Mercury concentrations were found to be elevated above global averages in all sampled media. However, the geochemical data suggest that the high mercury levels are due largely to natural sources and natural biogeochemical processes, and that the impacts of anthropogenically released mercury from mine sites is relatively localized.     

Mercury concentrations of fish, river water, and sediment in the Río Ramis-Lake Titicaca watershed, Peru

This study reports the first set of data on the concentration of mercury in muscle tissue of several varieties of fish from Lake Titicaca, including the pejerrey (Basilichthyes bonariensis), the carachi (Orestias), and 2 types of indigenous catfish (Trichomycterus). Approximately 27% of the pejerrey and 75% of the carachi exceeded the US EPA fish tissue-based water quality criterion level of 0.30 microg g(-1). Mercury levels of pejerrey increased with fish size, although this relationship was less apparent for the smaller carachi. The pejerrey and carachi are important food fish for local residents. A synoptic sampling of the Río Ramis--the largest tributary to Lake Titicaca--was conducted in an attempt to determine if mercury releases from artisanal gold mining could be an important source of Hg contamination to Lake Titicaca. Although highly elevated concentrations of Hg and other heavy metals were documented in headwater streams near the mining centers of La Rinconada and Cecilia, the quantity of Hg entering Lake Titicaca that could be attributed to mining in the Ramis watershed was below the quantifiable limit in our July 2002 study. This does not diminish the localized threat to mercury exposure for the artisanal gold miners themselves, as well as their families. Further studies of mercury dynamics in Lake Titicaca are recommended, as well as in the rivers draining into the lake. It is probable that most of the downgradient transport of Hg and other trace metals from the headwater mining centers occurs as suspended sediment during seasonal periods of high-flow.     

Mercury in different environmental compartments of the Pra River Basin, Ghana

Artisanal gold mining (AGM) with metallic mercury has a long history in Ghana. It is believed to be over 2,000 years old. Today, AGM has escalated in a new dimension consuming about half of the country where gold lode deposits exist along riverbanks or rivers are alluvial-gold rich. The Pra River in southwestern Ghana is a site of on going application of metallic mercury in prospecting gold, and this paper examines mercury (Hg) contamination in the different environmental compartments in its watershed. Samples of water, sediment, soil and biota (i.e., human hair and fish) were collected from locations along the course of the river during the rainy and dry seasons of 2002 and 2003, respectively. Besides the obvious Hg point sources along the Pra and its tributaries, the obtained results show that Hg levels and speciation in the studied aquatic system are controlled by precipitation, which drives the hydrology and differences in flow regimes versus seasons. The seasonal difference in Hg speciation suggests that methyl mercury (MeHg) found in the aqueous phase and riverine sediments is likely of terrestrial origin where its production is favored during the rainy season by high soil water and organic matter content. The use of the enrichment factor (EF) for the assessment of sediment quality indicated moderate to severe contamination of surface sediments in the rainy season, while in the dry season, the EF index indicates nearly no pollution of surface sediments. Accordingly, most of the Hg introduced into this river system is likely transported to depositional downstream terminal basins (e.g. the river delta and the Gulf of Guinea). With regard to biota, Hg measured in hair in the dry period was higher than data obtained on samples collected during the wet period. This could be explained at least in part by the shift in diet as a result of abundance of fish in the local markets and the concurrent increase and more active fishing during the dry season. Mercury data obtained on a very limited number of fish samples collected during the dry period only are also presented.     

Mercury in the environment and riverside population in the Madeira River Basin, Amazon, Brazil

This work presents quality control results on the mercury concentrations in different environmental (river sediments, forest soils, river suspended matter and fish) and human samples from the lower Madeira River, Amazon sampled between 2001 and 2003, about 15-20 years after the nearly cessation of gold mining activities in the region, which reached its peak in the late 1980s. The study aimed to compare mercury concentrations in these environmental samples with those reported by other authors during the gold rush of the Madeira River Basin. Today, in the Madeira River the releases of mercury register a sudden reduction due the gold price fall in the international trade. However, about 100 t of Hg were released to the atmosphere and to aquatic systems in the region during the gold rush. The present survey shows that notwithstanding the reduction of Hg emissions to the Madeira River Basin from gold mining proper, concentrations in fish and humans are similar to those measured during the gold rush. Reduction in Hg concentrations is restricted to areas close to old point sources and only for abiotic compartments (air and sediments). Remobilization of Hg from bottom sediments plus re-emission from soils due to land use changes are probably responsible for keeping high Hg concentrations in biological samples.     

Preliminary investigation of the mercury saturation in the Baltic Sea winter surface water

A new experimental measuring system for the total gaseous mercury saturation in the sea surface water has been developed. The technique applied to the system is based on equilibrating water-air mercury partial pressures at the air-sea interface. First data using this system were collected in the Baltic Sea on 13-22 January 2000. Measurements were completed from the research vessel 'Alexander von Humboldt' on the way from the Gotland Sea to the Mecklenburg Bight. In general the results showed domination of supersaturated winter sea surface waters with respect to gaseous mercury. Two areas with distinctly elevated mercury saturation were found: one in the east-west shipping route, south of Bornholm, where the equilibrated gaseous Hg content of water was approximately 9.2-fold higher, and another over the ammunition disposal region south-east of Hoburgs Bank, where the Hg content of water was approximately 3.8-fold higher than that in air. In general, the data indicate that the south-western Baltic Sea, and in particular both maritime areas identified with elevated mercury saturation, can emit gaseous mercury from surface waters into the atmosphere and contribute to long-range atmospheric transport.     

Mercury distribution and exchanges between the Amazon River and connected floodplain lakes

This work presents the distribution and the partition of mercury (Hg) in the Curuai floodplain lakes along the Amazon River. The maximum Total Filtered Hg (T-FHg) concentrations in the floodplain lakes (28 to 52 pmol L^− 1) coincide with the maximum T-FHg concentrations of the Amazon River and are measured during the flooding period. The lowest T-FHg values (3 to 5 pmol L^− 1) are observed during the flood peak of the mainstream, during the rainy season, when waters are diluted by the local rainfall. In this system, Hg is mainly transported in the particulate phase, confirmed by elevated values of the Hg partition coefficient (4.77 < K_d (Hg) < 5.83 L kg^− 1). The highest Total Particulate Hg (T-PHg) concentrations (47–478 pmol L^− 1) in the lakes are measured during the dry season when they are isolated from the mainstream. This enrichment is due to the elevated TSS content associated to the re-suspension of the bottom sediments by the wind action and the bioturbation in shallow water lakes.In the flooded system, the lakes show different geochemical characteristics that control the Hg distribution and partition. In the white water (WW) lakes, characterized by oxidative neutral waters and highest TSS contents (till 2041 mg L^− 1), the T-PHg is associated to the particulate organic matter mainly during the dry season, while the T-FHg and T-FMn concentrations are correlated. In the black water (BW) lakes that show reductive pH conditions and lowest TSS load (2 to 52 mg L^− 1), P-iron and T-PHg display a positive relationship whereas the redox conditions favor the desorption of Hg from the particulate to the filtered phase.The mercury mass budget estimated in this study confirms that the Curuai floodplain system acts as a particulate mercury trap, with a net storage of particulate Hg of 150 kg PHg year^− 1.     

Strategic environmental management: time for a new approach

We present a comprehensive analysis of the sensitivity of mercury (Hg) human exposure to environmental variables using a multimedia model of the fate and transport of Hg in the environment. The results of the analysis show that the Hg dose is most sensitive to the lake pH, the burial rate of Hg adsorbed to sediments, and the chemical speciation of Hg emissions to the atmosphere. The lake pH has a strong non-linear effect on the methylation rate and bioaccumulation of Hg in fish. The burial of sediments is a major pathway for removing Hg from the lake cycling. The speciation of Hg emissions is important because Hg(II) is deposited much more rapidly than Hg(0). These results highlight the importance of key variables that should be investigated through well-designed field programs, so that we can minimize the overall uncertainties associated with the modeling of mercury fate and transport.     

Mercury transport and bioaccumulation in riverbank communities of the Alvarado Lagoon System, Veracruz State, Mexico

The Alvarado Lagoon System (ALS) is located within the Papaloapan River Basin in southern Veracruz, Mexico. The ALS is a shallow system (2 m) connected to the Gulf of Mexico through a narrow sea channel. There are a large number of riverbank communities within the ALS that are dependent upon its biological productivity for comestible and economic subsistence. The purpose of this project was to determine the levels of mercury in water, sediment, fish, and hair samples from within the Papaloapan River Basin and to characterize the risk of Hg exposure to the individuals that reside in these communities. Water and fish samples were collected during the wet (September 2005) and dry (March 2003 and 2005) seasons. Hair samples, dietary surveys, and sediment samples were obtained during the wet and dry seasons of 2005. Total Hg in the water column ranged from 1.0 to 12.7 ng/L. A strong correlation (R(2)=0.82; p<0.001) between total Hg and total suspended solids in the water column suggests that particulate matter is a transport mechanism for Hg within the lagoon system. Total Hg in the sediments ranged from 27.5 to 90.5 ng Hg/g dry weight with no significant difference between the 2005 wet and dry seasons. There was a mild, but significant, correlation between total Hg and % carbon for the March 2005 sediment samples (R(2)=0.435; p=0.020), suggesting that Hg is associated with organic matter on the solid phase. Concentrations of total Hg in fish and shellfish harvested from the ALS ranged from 0.01 to 0.35 microg Hg/g wet. The levels of total Hg in hair ranged from 0.10 to 3.36 microg Hg/g (n=47) and 58% of the samples were above 1.00 microg Hg/g. The findings from this study suggest that individuals who frequently consume fish and shell fish containing low levels of Hg (<0.3 microg/g) can accumulate low to moderate body burdens of Hg, as indicated by hair Hg concentrations>1.0 microg/g, and may be at risk for experiencing low dose mercury toxicity.