Heavy metal and Pb isotopic compositions of aquatic organisms in the Pearl River Estuary, South China

The accumulation of trace metals in aquatic organisms may lead to serious health problems through the food chain. The present research project aims to study the accumulation and potential sources of trace metals in aquatic organisms of the Pearl River Estuary (PRE). Four groups of aquatic organisms, including fish, crab, shrimp, and shellfish, were collected in the PRE for trace metal and Pb isotopic analyses. The trace metal concentrations in the aquatic organism samples ranged from 0.01 to 2.10 mg/kg Cd, 0.02 to 4.33 mg/kg Co, 0.08 to 4.27 mg/kg Cr, 0.15 to 77.8 mg/kg Cu, 0.17 to 31.0 mg/kg Ni, 0.04 to 30.7 mg/kg Pb, and 8.78 to 86.3 mg/kg Zn (wet weight). High concentrations of Cd were found in crab, shrimp and shellfish samples, while high concentration of Pb was found in fish. In comparison with the baseline reference values in other parts of the world, fish in the PRE had the highest elevated trace metals. The results of Pb isotopic compositions indicated that the bioaccumulation of Pb in fish come from a wide variety of food sources and/or exposure pathways, particularly the anthropogenic inputs.     

Mercury in sediment and fish from North Mississippi Lakes

Sediments and/or fish were collected from Sardis, Enid and Grenada Lakes, which are located in three different watersheds in North Mississippi, in order to assess mercury contamination. The mean total mercury concentration in sediments from Enid Lake in 1997 was 0.154 mg Hg/kg, while 1998 sediment concentrations in Sardis, Enid and Grenada Lakes were 0.112, 0.088 and 0.133 mg Hg/kg, respectively. Sediment mercury concentrations in 1999 were similar in all three lakes but, generally lower than 1998. Mean total mercury concentrations in edible fillets of fish collected from Enid Lake in 1998 were above the human health FDA action level (>1.0 mg Hg/kg) for bass (1.40), crappie (1.69) and gar (1.89); however, tissue concentrations were less than 1.0 mg Hg/kg in carp (0.63) and catfish (0.82). Human hazard indexes for each species was 1 for both adults and children, indicating that there is a potential for toxic effects to occur. In addition, calculated consumption limits indicate that adults may consume 4–12 oz. of fish per month, depending on the species consumed. For children, 2 oz. per month may be consumed. Further studies are needed to determine the exact environmental consequences and human health impacts associated with mercury contamination in North Mississippi and the Southeastern United States.     

Mercury Balance on a Large Pulverized Coal-Fired Furnace

This paper presents results of a survey of mercury concentrations in coal, ash, water, fly ash, and flue gas discharges from a 5.5 × 10⁶ Ib/hr steam generator serving a 775 MW (net) turbine-generator set. Representative composite or grab samples were obtained for inlet coal and outlet ash and water. Stack samples were obtained for fly ash and mercury vapor emissions while the unit was operated at 660 MW (net) (85% of full load). Samples were analyzed by anodic stripping voltammetry, plasma emission spectroscopy, and neutron activation analysis to determine mercury concentration entering the furnace in the coal and leaving the furnace in the flue gas, fly ash, bottom and hopper ash, and water. Method inter-comparisons are discussed. A material balance for mercury has been calculated from fuel, ash, and stack gas flow rates. About 90% of the mercury in the coal is released and appears as vapor discharged in the stack gas while 10% remains in the residual ash. For a 700 MW (net) unit, about 5 lb/day of mercury vapor is released to the atmosphere.     

Lake variability: key factors controlling mercury concentrations in New York State fish

A 4year study surveyed 131 lakes across New York State beginning in 2003 to improve our understanding of mercury and gather information from previously untested waters. Our study focused on largemouth and smallmouth bass, walleye and yellow perch, common piscivorous fish shown to accumulate high mercury concentrations and species important to local fisheries. Fish from Adirondack and Catskill Forest Preserve lakes generally had higher mercury concentrations than those from lakes in other areas of the state. Variability between nearby individual lakes was observed, and could be due to differences in water chemistry, lake productivity or the abundance of wetlands in the watershed. We found the following factors impact mercury bioaccumulation: fish length, lake pH, specific conductivity, chlorophyll a, mercury concentration in the water, presence of an outlet dam and amount of contiguous wetlands.     

The role of ammonia on mercury leaching from coal fly ash

The Federal Clean Air Interstate Rule issued in March 2005 will result in many power plants employing ammonia-based technologies to control NO(x) emission. The Clean Air Mercury Rule, issued at the same time, will encourage many power plants to use various technologies to remove mercury from flue gas, generating fly ashes that contain elevated concentrations of mercury. Ammonia forms relatively strong complexes with mercury compared to most other cationic elements and, therefore, may change the leaching characteristics of mercury. Understanding the impact of ammonia on the leaching of mercury from fly ash is critical in predicting the potential environmental impact of future fly ash. Batch methods were used to investigate the ammonia impact on mercury leaching from fly ash under different pH conditions. The results indicated that mercury leaching without external ammonia addition is not significant. However, ammonia addition increased mercury leaching in the alkaline pH range, due to the formation of less adsorbable mercury-ammonia complexes. Washed ash released more mercury than the raw ash if the ammonia concentration is the same, mainly due to the dissolution of some ash components during washing which exposed more mercury on ash surface. Mercury adsorption data indicated that more than 90% of available mercury was adsorbed by fly ash even in the presence of 1000 mg l(-1) ammonia addition.     

Bioaccumulation and elimination of tetrachlorobenzyltoluene (TCBT) by the rat and by fish

A comparative study has been made of the bioaccumulation and elimination by fish and the rat of (i) tetrachlorobenzyltoluene (TCBT), a substance recently proposed as a substitute for polychlorobiphenyl (PCB), and (ii) DP5, a pentachlorobiphenyl mixture (PCB-5 C1).

The study relating to fish (Brachydanio Rerio) comprised a 30-day accumulation period followed by a 30-day elimination period. Nominal concentrations of TCBT and PCB-5 C1, respectively, in the water, were 1mg/litre in both cases.

The study relating to the rat comprised a 90-day treatment period followed by a 30-day elimination period. The animals were exposed by oral (gavage) to doses of 0, 5, 30, and 200 mg/kg/day in the case of TCBT and to the single dose of 5 mg/kg/day in the case of PCB-5 Cl.

Concentrations of TCBT and PCB-5 Cl in rat liver and fats, in whole body tissues of fish and in water were measured by gas chromatography, using an electron capture detector.

Results showed a clear difference between TCBT and PCB-5 Cl: in fish, bioaccumulation of TCBT was relatively slight and the 50% depuration time was approximately 26 days; in rat liver and fats, TCBT was also only weakly accumulated and rapidly eliminated. This contrasted sharply with the findings for PCB-5 Cl, viz: high accumulation potential and slow elimination.

Observed rates of bioaccumulation and elimination of TCBT and PCB-5 Cl by the rat were in good agreement with the toxicological findings for the same species.     

Total mercury and methylmercury concentrations in native and invasive fish species in Shadegan International Wetland,Iran, and health risk assessment

Human exposure to mercury (Hg) mainly occurs through consumption of aquatics, especially fish. In aquatic systems, the bioaccumulation of Hg across trophic levels could be altered by invasive species through changing community composition. The present study is aimed at measuring total mercury (T-Hg) and methylmercury (MeHg) concentrations in non-native (redbelly tilapia (Tilapia zillii)) and native (Benni (Mesopotamichthys sharpeyi) and common carp (Cyprinus carpio)) fish species throughout Shadegan International Wetland and comparing health risk of their mercury contents to the local population. The concentrations were measured using a direct mercury analyzer (DMA 80). The average values of T-Hg and MeHg for native fishes were 19.8 and 10.49 μg/kg. These concentrations for the invasive fish were 28 and 14.62 μg/kg respectively. Despite having less length and weight than the native fish species, tilapia showed significantly higher T-Hg content, yet the lowest concentration of MeHg was observed in common carp with larger body length and weight. Concerning mercury health risk to consumers, tilapia demonstrated the highest estimated weekly intake (EWI) and percentages of tolerable weekly intake (%TWI) for both T-Hg and MeHg, while the highest hazard quotient (HQ) values were obtained for tilapia and Benni. Taken together, the mercury concentrations in the two native and non-native fishes were acceptable according to the international safety guidelines although the local people shall be warned for consumption of tilapia. Furthermore, the low calculated value of tissue residue criterion (TRC) for the wetland fishes sounds a warning.     

Arrested municipal solid waste incinerator fly ash as a source of heavy metals to the UK environment

Arrested fly ash samples from most currently operating municipal solid waste (MSW) incinerators in the UK have been analysed for a range of elements. Some of the more important heavy metals ranged in concentration as follows: Cd, 21-4646 (median = 271) mg kg(-1); Cu, 296-1307 (642) mg kg(-1); Cr, 44-1328 (574) mg kg(-1); Ni, 45-2204 (74) mg kg(-1); Pb, 447-9704 (4337) mg kg(-1); and Zn, 2285-13,500 (9232) mg kg(-1). These concentrations represent considerable enrichments relative to median UK soil concentrations. Enrichment ratios (defined as median fly ash: median UK soil) were as follows: Mn 1.6; Co 2.6; Ni 3.3; Ba 11; Sr 11; Cr 15; Cu 35; Pb 108; Zn 113; Cd 387. It is estimated that MSW incinerator ash contributes c. 15 t Cd and 241 t Pb to UK landfill sites per annum. These figures compare with previous studies by Hutton & Symon (Hutton, M. & Symon, C. (1986). The quantities of cadmium, lead, mercury and arsenic entering the UK environment from human activities. Sci. Total Environ., 57, 129-50.) which estimated that annual inputs to UK landfills from coal fly ash are c. 60 t Cd and 1270 t Pb. However, it is argued that metals associated with MSW ashes are potentially of greater environmental significance than in coal ashes, because they are much more available and present at much higher concentrations.     

Effect of point source removal on mercury bioaccumulation in an industrial pond

A one hectare pond on the headwaters of a mercury-contaminated creek in Oak Ridge, Tennessee acted as a biochemical reactor for the production of methylmercury, increasing waterborne methylmercury concentrations in the stream below the pond discharge. The flow of the creek was diverted around the pond in order to eliminate this input. Waterborne total mercury, methylmercury, and mercury in fish, were monitored in the pond and stream before and after bypass. Waterborne methylmercury concentration in the creek downstream from the pond decreased over 800% following diversion of streamflow around the pond, but mercury in redbreast sunfish in the pond tailwater did not decline similarly. Within the pond, now isolated from fresh waterborne mercury inputs from the stream, methylmercury concentrations in the water column remained similar to levels present before bypass. However, mercury concentrations in sunfish in the pond decreased approximately 75% following bypass, despite the continued presence of highly contaminated sediments (approximately 50 mg Hg/kg dry weight). We concluded that a decrease in the fraction of 'dissolved methylmercury' in the isolated pond relative to pre-bypass conditions explained the decrease in mercury in fish within the pond. That observation also indicates that mercury associated with pond sediments was relatively unavailable for eventual bioaccumulation when compared to 'fresh' mercury contributed by upstream sources. The lack of a post-bypass decrease in mercury concentrations in tailwater fish was also likely to be associated with the particle-associated nature of waterborne methylmercury exported from the pond.     

Spatial trends and impairment assessment of mercury in sport fish in the Sacramento–San Joaquin Delta watershed

A three-year study was conducted to examine mercury in sport fish from the Sacramento–San Joaquin Delta. More than 4000 fish from 31 species were collected and analyzed for total mercury in individual muscle filets. Largemouth bass and striped bass were the most contaminated, averaging 0.40 μg/g, while redear sunfish, bluegill and rainbow trout exhibited the lowest (<0.15 μg/g) concentrations. Spatial variation in mercury was evaluated with an analysis of covariance model, which accounted for variability due to fish size and regional hydrology. Significant regional differences in mercury were apparent in size-standardized largemouth bass, with concentrations on the Cosumnes and Mokelumne rivers significantly higher than the central and western Delta. Significant prey–predator mercury correlations were also apparent, which may explain a significant proportion of the spatial variation in the watershed.     

Insights into low fish mercury bioaccumulation in a mercury-contaminated reservoir, Guizhou, China

We examined Hg biogeochemistry in Baihua Reservoir, a system affected by industrial wastewater containing mercury (Hg). As expected, we found high levels of total Hg (THg, 664-7421 ng g(-1)) and monomethylmercury (MMHg, 3-21 ng g(-1)) in the surface sediments (0-10 cm). In the water column, both THg and MMHg showed strong vertical variations with higher concentrations in the anoxic layer (>4m) than in the oxic layer (0-4 m), which was most pronounced for the dissolved MMHg (p < 0.001). However, mercury levels in biota samples (mostly cyprinid fish) were one order of magnitude lower than common regulatory values (i.e. 0.3-0.5 mg kg(-1)) for human consumption. We identified three main reasons to explain the low fish Hg bioaccumulation: disconnection of the aquatic food web from the high MMHg zone, simple food web structures, and biodilution effect at the base of the food chain in this eutrophic reservoir.     

Mercury methylation in aquatic systems affected by acid deposition

Recently, it has been noted that fish in acidified lakes may contain elevated levels of mercury. While there is correlation among lakes between depressed pH and high mercury concentrations in fish, the cause of this problem is unknown. A number of hypotheses have been advanced in explanation, including increased mercury deposition, changes in mercury mobility due to acidification, pH dependent changes in mercury uptake by biota, and alterations in population size and/or structure which result in increased bioaccumulation in fish. Because fish accumulate mercury mainly in an organic form, methylmercury, changes in the biogeochemical cycling of this compound might account for elevated bioaccumulation. Mercury methylation is predominantly a microbial process which occurs in situ in lakes. This review focuses on microbiological and biogeochemical changes that may lead to increased levels of methylmercury in fresh waters impacted by acid-deposition. In particular, we focus on the hypothesis that sulfate-reducing bacteria are important mediators of metal methylation in aquatic systems and, moreover, that sulfate-deposition may stimulate methylmercury production by enhancing the activity of sulfate-reducing bacteria in sediments.     

Distribution of mercury in the combustion products from coal-fired power plants in Guizhou,southwest China

Method 30B and the Ontario Hydro Method (OHM) were used to sample the mercury in the flue gas discharged from the seven power plants in Guizhou Province, southwest China. In order to investigate the mercury migration and transformation during coal combustion and pollution control process, the contents of mercury in coal samples, bottom ash, fly ash, and gypsum were measured. The mercury in the flue gas released into the atmosphere mainly existed in the form of Hg°. The precipitator shows a superior ability to remove Hg^p (particulate mercury) from flue gas. The removal efficiency of Hg²⁺ by wet flue gas desulfurization (WFGD) was significantly higher than that for the other two forms of mercury. The synergistic removal efficiency of mercury by the air pollution control devices (APCDs) installed in the studied power plants is 66.69–97.56%. The Hg mass balance for the tested seven coal-fired power plants varied from 72.87% to 109.67% during the sampling time. After flue gas flowing through APCDs, most of the mercury in coal was enriched in fly ash and gypsum, with only a small portion released into the atmosphere with the flue gas. The maximum discharge source of Hg for power plants was fly ash and gypsum instead of Hg emitted with flue gas through the chimney into the atmosphere. With the continuous upgrading of APCDs, more and more mercury will be enriched in fly ash and gypsum. Extra attention should be paid to the re-release of mercury from the reutilization of by-products from APCDs.

Implications: Method 30B and the Ontario Hydro Method (OHM) were used to test the mercury concentration in the flue gas discharged from seven power plants in Guizhou Province, China. The concentrations of mercury in coal samples, bottom ash, fly ash, and gypsum were also measured. By comparison of the mercury content of different products, we found that the maximum discharge source of Hg for power plants was fly ash and gypsum, instead of Hg emitted with flue gas through the chimney into the atmosphere. With the continuous upgrading of APCDs, more and more mercury will be enriched in fly ash and gypsum. Extra attention should be paid to the re-release of mercury from the reutilization of by-products from APCDs.     

Air-surface exchange of mercury with soils amended with ash materials

Air-surface exchange of mercury (Hg) was measured from soil low in Hg (0.013 mg/kg) amended with four different ash materials: a wood ash containing -10% coal ash (0.070 mg/kg Hg), a mixture of two subbituminous coal fly ashes (0.075 mg/kg Hg), a subbituminous coal ash containing -10% petroleum coke ash (1.2 mg/kg Hg), and an ash from incinerated municipal sewage sludge (4.3 mg/kg Hg) using a dynamic flux chamber. Ash was added to soil to simulate agricultural supplements, soil stabilization, and pad layers used in livestock areas. For the agricultural amendment, -0.4% ash was well mixed into the soil. To make the stabilized soil that could be used for construction purposes, -20% ash was mixed into soil with water. The pad layer consisted of a wetted 1-cm layer of ash material on the soil surface. Diel trends of Hg flux were observed for all of the substrates with significantly higher Hg emissions during the day and negligible flux or deposition of Hg during the night. Hg fluxes, which were measured in the summer months, were best correlated with solar radiation, temperature, and air O3 concentrations. Mean Hg fluxes measured outdoors for unamended soils ranged from 19 to 140 ng/m2 day, whereas those for soil amended with ash to simulate an agricultural application ranged from 7.2 to 230 ng/m2 day. Fluxes for soil stabilized with ash ranged from 77 to 530 ng/m2 day and for soil with pads constructed of ash ranged from -50 to 90 ng/m2 day. Simple analytical tests (i.e., total Hg content, synthetic precipitation leaching procedure, heating, and indoor gas-exchange experiments) were performed to assess whether algorithms based on these tests could be used to predict Hg fluxes observed outdoors using the flux chamber. Based on this study, no consistent relationships could be developed. More work is needed to assess long-term and seasonal variations in Hg flux from (intact and disturbed) substrates before annual estimates of emissions can be developed.     

Recovery of mercury-contaminated fisheries

In this paper, we synthesize available information on the links between changes in ecosystem loading of inorganic mercury (Hg) and levels of methylmercury (MeHg) in fish. Although it is widely hypothesized that increased Hg load to aquatic ecosystems leads to increases in MeHg in fish, there is limited quantitative data to test this hypothesis. Here we examine the available evidence from a range of sources: studies of ecosystems contaminated by industrial discharges, observations of fish MeHg responses to changes in atmospheric load, studies over space and environmental gradients, and experimental manipulations. A summary of the current understanding of the main processes involved in the transport and transformation from Hg load to MeHg in fish is provided. The role of Hg loading is discussed in context with other factors affecting Hg cycling and bioaccumulation in relation to timing and magnitude of response in fish MeHg. The main conclusion drawn is that changes in Hg loading (increase or decrease) will yield a response in fish MeHg but that the timing and magnitude of the response will vary depending of ecosystem-specific variables and the form of the Hg loaded.     

Arsenic and mercury concentrations in major landscape components of an intensively cultivated watershed

To provide an understanding of arsenic (As) and mercury (Hg) concentrations in soil, sediment, water, and fish tissues, samples were collected from a Mississippi River alluvial floodplain located in northwest Mississippi. As concentrations increased approximately an order of magnitude from water (5.12 micrograms/l) to fish tissues (36.99 micrograms/kg) and an additional two orders of magnitude in soils, lake sediments, and wetland sediments (5728, 5614, and 6746 micrograms/kg), respectively. Average Hg concentrations in water, soils, lake sediments, and fish were 2.16 micrograms/l, 55.1, 14.5 and 125 micrograms/kg, respectively. As and Hg concentrations were within published ranges for uncontaminated soil, water, and sediments. As concentrations represented a low risk. Hg concentrations were also low but showed a greater tendency to concentrate in fish tissue. The dominant mode of entry of these materials into aquatic systems is through storm-generated runoff. Since both metals accompany sediments, agricultural conservation practices such as reduced tillage, buffer riparian strips, and bordering sediment ponds or drainage wetlands will minimize watershed input to aquatic systems.     

Speciation and mobility of cadmium in straw and wood combustion fly ash

Two fly ashes from biomass combustion have been analysed regarding cadmium speciation and mobility. A fly ash from straw combustion contained 10 mg Cd/kg dry matter, and around 50% of the cadmium was leachable in water. The possible main speciation of cadmium in this fly ash was CdCl2. When adding this fly ash to agricultural soil a threat for groundwater contamination and plant uptake is existing. A fly ash from wood chip combustion had 28.6 mg Cd/kg dry matter. In this fly ash, the cadmium was bound more heavily, with only small amounts of cadmium leached in mild extractants. A possible speciation of cadmium in this fly ash was as oxide or as CdSiO3. Long-term effects and accumulation of cadmium could be a problem when adding this fly ash to agricultural or forest soils.     

Geochemical investigations of metals release from submerged coal fly ash using extended elutriate tests

A storage pond dike failure occurred at the Tennessee Valley Authority Kingston Fossil Plant that resulted in the release of over 3.8 million cubic meters (5 million cubic yards) of fly ash. Approximately half of this material deposited in the main channel of the Emory River, 3.5 km upstream of the confluence of the Emory and Clinch Rivers, Tennessee, USA. Remediation efforts to date have focused on targeted removal of material from the channel through hydraulic dredging, as well as mechanical excavation in some areas. The agitation of the submerged fly ash during hydraulic dredging introduces river water into the fly ash material, which could alter the redox state of metals present in the fly ash and thereby change their sorption and mobility properties. A series of extended elutriate tests were used to determine the concentration and speciation of metals released from fly ash. Results indicated that arsenic and selenium species released from the fly ash materials during elutriate preparation were redox stable over the course of 10d, with dissolved arsenic being present as arsenate, and dissolved selenium being present as selenite. Concentrations of certain metals, such as arsenic, selenium, vanadium, and barium, increased in the elutriate waters over the 10d study, whereas manganese concentrations decreased, likely due to oxidation and precipitation reactions.     

Mercury exposure in the freshwater tilapia Oreochromis niloticus

Mercury (Hg) can be strongly accumulated and biomagnified along aquatic food chain, but the exposure pathway remains little studied. In this study, we quantified the uptake and elimination of both inorganic mercury [as Hg(II)] and methylmercury (as MeHg) in an important farmed freshwater fish, the tilapia Oreochromis niloticus, using ²⁰³Hg radiotracer technique. The dissolved uptake rates of both mercury species increased linearly with Hg concentration (tested at ng/L levels), and the uptake rate constant of MeHg was 4 times higher than that of Hg(II). Dissolved uptake of mercury was highly dependent on the water pH and dissolved organic carbon concentration. The dietborne assimilation efficiency of MeHg was 3.7-7.2 times higher than that of Hg(II), while the efflux rate constant of MeHg was 7.1 times lower. The biokinetic modeling results showed that MeHg was the greater contributor to the overall mercury bioaccumulation and dietary exposure was the predominant pathway.     

Triclosan in Fresh Water Fish Gibelion Catla from the Kaveri River,India, and Its Consumption Risk Assessment

Triclosan is a common antimicrobial agent that is found in significant levels in the aquatic environment and may elicit effects on aquatic organisms through unexpected modes of action. In this study, triclosan was quantified in fish from the Kaveri River, India, by using the gas chromatography and mass spectrometry technique and it was found in the range of 0.73–50 ng/g wet weight (ww). The mean bioaccumulation factor based on water (BAF_w 820) and sediment (BAF_s 2.12) in the Kaveri River showed that triclosan is accumulative in fish, and reflects its feeding behavior. The bioaccumulation indicates triclosan's persistence or prevalence throughout the river stretch. Human risk assessment through dietary intake demonstrated that the triclosan exposure is five orders of magnitude lower than the acceptable daily intake (50 μg/kg bw) and US EPA reference dose (300 μg/kg bw/day). This investigation is the first to report the bioaccumulation of triclosan in freshwater fish from India. Further, the results indicate that this fish acts as a biomarker of exposure for triclosan and thus shall be used to report triclosan pollution in the future.