Characterizing kinetics of transport and transformation of selenium in water-sediment microcosm free from selenium contamination using a simple mathematical model

This study developed a seven-compartment model for predicting the fate of selenium (Se) in an aquatic environment containing a water-sediment boundary. Speciation of Se in water-sediment microcosms under microaerobic conditions was measured to evaluate first-order kinetics of Se transportation and transformation. The microcosm consisted of a 10-ml solution containing 1mM soluble Se as selenate (Se6+) or selenite (Se4+) and 8 g wet sediment that was free from Se contamination, sampled from the Senri, Yamato, or Yodo Rivers in Osaka, Japan. Stepwise reaction coefficients describing transportation and transformation were determined using an inverse method on this model which includes: selenate (Se(W)6+) and selenite (Se(W)4+) in ponded water; selenate (Se(S)6+) and selenite (Se(S)4+), elemental Se (Se0), organic Se (Se2-) in sediment; and gaseous Se (DMSe). During this 1-month experiment, soluble Se was transported from ponded water to the sediment and Se was transformed sequentially to other Se species through biochemical reactions. Experimental and kinetic analyses indicated quantitatively that the Yamato River microcosm, with its high organic matter content, had a high adsorption rate of soluble Se. The Yodo River microcosm had a low adsorption rate for Se6+ and a low Se reduction rate. The Senri River microcosm had an apparent high volatilization rate of DMSe. The model developed in this study is extremely useful for predicting fate of Se in aquatic environment in the field.     

Mercury in contaminated sediments and pore waters enriched in sulphate (Tagus Estuary,Portugal)

Three sediment cores, collected nearby the effluent of a chlor-alkali industry, were sliced in 0.5-cm layers and centrifuged for pore water extraction. Mercury, Fe and Mn were determined in the solids as total concentration, hydroxylamine extractable fraction and HCl extractable fraction. Sulphur was determined in the HCl extraction. Total and reactive mercury, chlorinity, S(2-), SO(4)(2-), total Fe, and total Mn were measured in pore waters. The solids contained 3.0-60 nmol g(-1) of total Hg and pore waters 70-5800 pM of total Hg and 1.8-76 pM of reactive mercury. Pore waters presented 2.3-94 times more sulphate than the overlying estuarine waters due to the input from the industry. In layers where hydroxylamine extractable Fe exhibited a broad maximum (precipitation of Fe-oxides) sulphate was reduced to S(2-). The competition between the high content of SO(4)(2-) and Fe(III) as electron acceptors, in chemical reactions occurring in the upper sediments, may explain the co-existence of S(2-) and Fe-oxides in the same layers. Mercury was detected in the hydroxylamine extracts (20-29 nmolg(-1)) in the layers where Fe-oxides were formed, and reactive dissolved Hg showed minimum concentrations. The excess of sulphate in pore waters favoured the abundant Fe-oxides in the upper solid sediments, which appear to work as a barrier limiting the escape of mercury to the water column.     

Impact of land use and physicochemical settings on aqueous methylmercury levels in the Mobile-Alabama River System

Mercury (Hg) concentrations above levels that could pose health risks have been measured recently in predatory fish from many aquatic systems in the southeastern region of the United States. Based on hypotheses derived from published experimental data on the aqueous geochemistry of Hg, we investigated the effect of certain natural and human-imposed conditions on in situ levels of methylmercury (MeHg) in the Mobile-Alabama River System (MARS). Water samples were collected from different types of environments, hypothesized to have contrasting levels of MeHg in the aqueous phase, and were analyzed for total-Hg (THg) and MeHg concentrations, as well as some key geochemical parameters. The results showed the following. i) Overall, total Hg concentrations in waters of the MARS are quite uniformly distributed and vary from 0.2 to 6 ng L(-1), suggesting that besides geological sources, atmospheric deposition is certainly the main source of Hg inputs in the studied system. ii) In locations with comparable THg levels, the Hg fraction present as MeHg was consistently higher in samples collected from the Coastal Plain portion of the MARS as compared to those from other geological provinces. iii) Our in situ observations confirmed conclusions derived from laboratory experiments, in that, MeHg abundance in aquatic systems correlates with sulfate (but only within a narrow range of concentrations); decreasing pH; and has no direct relationships with either nitrate or phosphate. iv) The investigation of Hg accumulation in biota at a single site showed that an aquatic system with low THg concentrations but a high MeHg:THg ratios, could have organisms with Hg content above safe levels. Therefore, potential health risks to fish eating populations can exist even when the aqueous phase does not show signs of significant Hg enrichment.     

Trace elements in striped dolphins (Stenella coeruleoalba) from the western Mediterranean

Tissues obtained from Stenella coeruleoalba stranded along the Spanish and Italian Mediterranean coasts from 1987 to 1994 were analysed for cadmium (Cd), copper (Cu), mercury (Hg), selenium (Se) and zinc (Zn). The age, length and weight of the dolphins were recorded. Hg levels were also assayed in skin biopsies from dolphins of the same species in the waters off northeastern Spain and in the Tyrrhenian and Ligurian Seas. Levels of all elements differed in muscle of stranded dolphins from the two areas. Hg was higher in tissues from animals stranded on the Italian coasts and in skin biopsies obtained in the Tyrrhenian and Ligurian Seas, than in the respective Spanish samples. This is probably related to Hg pollution from the natural weathering of cinnabar ores in central Italy. Se and Cd levels had similar accumulation patterns to those of Hg. Accumulation of Hg and Se is explained by the existence of a detoxification pathway involving both elements, however the reason for the similar Cd trend is unclear. Geographical differences in the accumulation pattern of these elements may reflect the existence of two different populations of Stenella coeruleoalba in the western Mediterranean.     

Correlates of mercury in fish from lakes near Clyde Forks, Ontario, Canada

Subsurface soils near Clyde Forks, Ontario, Canada, can have naturally high concentrations of mercury (Hg) from local geological sources. To investigate Hg in local aquatic food webs, Hg was measured in fish dorsal muscle (mainly yellow perch [YP] and pumpkinseed sunfish [PS]) and surface sediments from 10 regional lakes. Water chemistry, along with fork length, weight, and stable isotopes (delta15N, delta13C, delta34S) in fish were also measured. No lake sediments had elevated (>0.3microg/g dw) Hg, and average Hg concentrations in fish were not sufficiently high (<1microg/g dw) to be of concern for fish-eating wildlife. Variance in fish Hg was best explained by dietary carbon source (delta13C), and certain lake variables (e.g., pH for YP). PS with more pelagic feeding habits had higher delta34S and Hg than those with more littoral feeding habits. Potential biological linkages between fish Hg and delta34S, a parameter that may be related to the lake sulphate-reducing bacteria activity, requires further investigation.     

Effects of pH, organic acids, and competitive cations on mercury desorption in soils

The effects of pH, organic acids, and competitive cations on Hg(2+) desorption were studied. Three representative soils for rice production in China, locally referred to as a yellowish red soil (YRS), purplish clayey soil (PCS), and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were, respectively, collected from Jiaxin County, Deqing County, and Xiasha District of Hangzhou City, Zhejiang Province. Most of the added Hg(2+) was adsorbed at low initial concentrations (<2 mg l(-1)). Desorption of the adsorbed Hg(2+) in 0.01M KCl (simulating soil solution) was minimal, but was significantly enhanced by the change of pH, and the presence of organic acids or competitive cations. The desorption of Hg(2+) in the soils decreased with pH from 3.0 to 5.0, leveled off at pH 5.0-8.0, but increased with pH from 7.0 to 9.0. The presence of organic ligands enhanced Hg(2+) desorption in the soils except for YRS, in which the addition of tartaric, malic, or oxalic acid reduced Hg(2+) desorption at low concentrations (<10(-4)M), but Hg(2+) desorption generally increased with organic acid concentration. Citric acid was most effective in increasing Hg(2+) desorption, followed by tartaric acid and malic acid; and oxalic acid was the least effective. Desorption of adsorbed Hg(2+) increased with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Hg(2+) desorption more than Zn(2+) at the same loading rate. CAPSULE: The effects of organic acids and competitive cations on Hg desorption in soil-water system are related to their concentrations, basic chemical properties, and soil properties.     

Studies of mercury pollution in a lake due to a thermometer factory situated in a tourist resort: Kodaikkanal, India

Kodaikkanal, India, suffered mercury contamination due to emissions and waste from a thermometer factory. Kodai Lake is situated to the north of the factory. The present study determined mercury in waters, sediment and fish samples and compared the values with those from two other lakes, Berijam and Kukkal. Total mercury (Hg(T)) of 356-465 ng l(-1), and 50 ng l(-1) of mercury in methyl mercury form were seen in Kodai waters while Berijam and Kukkal waters showed significantly lower values. Kodai sediment showed 276-350 mg/kg Hg(T) with about 6% methyl mercury. Berijam and Kukkal sediments showed Hg(T) of 189-226 mg/kg and 85-91 mg/kg and lower methylation at 3-4% and 2%, respectively. Hg(T) in fish from Kodai lake ranged from 120 to 290 mg/kg. The results show that pollution of the lake has taken place due to mercury emissions by the factory.     

Metal bioavailability and toxicity to fish in low-alkalinity lakes: A critical review

Fish in low-alkalinity lakes having pH of 6.0-6.5 or less often have higher body or tissue burdens of mercury, cadmium, and lead than do fish in nearby lakes with higher pH. The greater bioaccumulation of these metals in such waters seems to result partly from the greater aqueous abundances of biologically available forms (CH(3) Hg(+), Cd(2+), and Pb(2+)) at low pH. In addition, the low concentrations of aqueous calcium in low-alkalinity lakes increase the permeability of biological membranes to these metals, which in fish may cause greater uptake from both water and food. Fish exposed to aqueous inorganic aluminum in the laboratory and field accumulate the metal in and on the epithelial cells of the gills; however, there is little accumulation of aluminum in the blood or internal organs. In low-pH water, both sublethal and lethal toxicity of aluminum has been clearly demonstrated in both laboratory and field studies at environmental concentrations. In contrast, recently measured aqueous concentrations of total mercury, methylmercury, cadmium, and lead in low-alkalinity lakes are much lower than the aqueous concentrations known to cause acute or chronic toxicity in fish, although the vast majority of toxicological research has involved waters with much higher ionic strength than that in low-alkalinity lakes. Additional work with fish is needed to better assess (1) the toxicity of aqueous metals in low-alkalinity waters, and (2) the toxicological significance of dietary methylmercury and cadmium.     

Cationic surfactant as a sensitizer for the spectrophotometric determination of hydrogen sulphide in air and evaluation of a new absorbing medium containing triethanolamine-zinc acetate-sodium hydroxide

An extractive spectrophotometric method for the determination of trace amounts of hydrogen sulphide after fixing the gas in triethanolamine (TEA)-zinc acetate-sodium hydroxide solution is described. The method is based on the reaction of iodate with hydrogen sulphide in the presence of acid and excess chloride ion leading to the formation of ICl2- species which is used to iodinate 2',7'-dichlorofluorescein to form 2',7'-dichloro-4',5'-diiodofluorescein. The iodinated product formed is extracted into an organic solvent and sensitized by equilibrating with a cationic surfactant, cetrimide, in the presence of acetate buffer (pH 5.9 +/- 0.1). The colour system obeys Beer's law over the range 0-1 microg of hydrogen sulphide and the relative standard deviation is 2.4% for 10 determinations at 0.75 microg of hydrogen sulphide. The effect of interfering gases on the determination is discussed. The proposed absorbing solution has been evaluated using a hydrogen sulphide permeation device. This absorbing solution has an absorption efficiency of > 93% at a flow rate of 1.5 litre min(-1) for a sampling period of 2 h. The fixed H2S is stable for 40 days. The method has been applied to determine residual H2S levels in a laboratory fume hood and in the vicinity of sewage pumping station. The method can be used to determine as little as 0.05 microg of hydrogen sulphide.     

Solubilization and methylation of HgS, PbS, and SnS by iodomethane, a model experiment for the aquatic environment

Iodomethane is produced in the marine environment by algae and plankton. Model experiments have shown that iodomethane can dissolve a series of metal sulphides, in agreement with some of the results mentioned in the relative literature. While no dissolution of SnS was observed, PbS and HgS were dissolved proportionally with the iodomethane concentration. The two forms of HgS (cinnabar and metacinnabar) behaved differently, with metacinnabar being more soluble than cinnabar. Moreover, iodomethane can methylate lead and tin and mercury can be methylated when methyllead and methyltin compounds are present in the model system. The methylated species were identified using gas chromatography, and there is evidence that lead and tin undergo the same methylation mechanism. Preliminary experiments with natural sediments were performed, but no dissolution of Pb, Sn or Hg was observed. CAPSULE: Iodomethane can solubilize Pb and Hg sulphides, and methylate Pb and Sn, and (indirectly) Hg.     

Stabilization and solidification of elemental mercury for safe disposal and/or long-term storage

A simple and highly effective stabilization/solidification (S/S) technology of elemental mercury using only sulfur with paraffin is introduced. First, elemental mercury is mixed with an excess of sulfur powder and heated to 60 degrees C for 30 min until elemental mercury is converted into mercuric sulfide (HgS black, metacinnabar) (Step 1). Then, metacinnabar with additional sulfur is poured into liquid paraffin (Step 2). Finally, the mixture is melted at 140 degrees C and settles to the bottom of the vessel where it cools and solidifies under the layer of liquid paraffin (Step 3). The proposed S/S method with sodium sulfide nonahydrate (Na2S x 9H2O) as an additive is also tested for comparison. The average toxicity characteristic leaching procedure test values are 6.72 microg/L (no additive) and 3.18 microg/L (with additive). Theses concentrations are well below the Universal Treatment Standard (25 microg/L). Effective diffusion coefficient evaluated from accelerated leach test and average headspace concentration of Hg vapor after 18 hr are 3.62 x 10(-15) cm2/sec, 0.55 mg/m3 (no additive) and 5.86 x 10(-13) cm2/sec, 0.25 mg/m3 (with additive).     

Effect of lead, mercury and cadmium on a sulphate-reducing bacterium

A sulphate-reducing bacterial strain isolated from the south-west coast of India resembling Desulfosarcina in its physiology was tested for its behaviour towards HgCl(2), CdSO(4) and Pb(NO(3))(2). The order of toxicity to growth of these metal salts in a lactate-based medium at 50 microg ml(-1) concentrations was Cd>Pb>Hg and to respiration Pb>Cd>Hg. Inhibitory concentrations (viz. 100 microg ml(-1) of HgCl(2) and 200 microg ml(-1) of Pb(NO(3)(2)) had a stimulatory effect when the substrate was changed to acetate. With sodium acetate at 0.1% concentration, Hg and Pb had maximum stimulatory effect for growth and sulphide production. Experiments conducted directly with sediment slurries amended with lactate showed that all three metals (at levels below their inhibitory concentrations, i.e. 50 microg ml(-1) of metal salt for Cd and Hg and 100 microg ml(-1) for Pb) inhibited sulphate-reducing activity (SRA) with Pb decreasing the peak production by 68%. The order of toxicity in both lactate and acetate-amended slurry was Pb>Cd>Hg and Pb>Hg>Cd, respectively. With acetate, SRA in the presence of Cd and Hg was stimulated 110% and 27%, respectively. Pb inhibited SRA by 11%. There is a general reduction in the inhibition of sulphide production in slurries as compared with pure culture of the isolate.     

Geothermal power plants at Mt. Amiata (Tuscany-Italy): mercury and hydrogen sulphide deposition revealed by vegetation

At Mt. Amiata (Italy) geothermal energy is used, since 1969, to generate electricity in five plants with a nominal capacity of 88 MW. Anomalous levels of mercury characterise geothermal fluids of Mt. Amiata, an area renowned for its vast cinnabar deposits and for the mercury production carried out in the past. Mercury emission rates range from 300 to 400 g/h, or 3-4 g/h per MW electrical installed capacity. These emissions are coupled with a release of 7-8 kg/(h MW) of hydrogen sulphide (H2S). Mercury is discharged as Hg0 gaseous species and reaches the atmosphere with the non-condensable gas fraction. In this fraction, CO, is the major component (94-98%), H2S is around 1% and mercury concentration is as high as 1-10 mg/Nm3. Leaves of a spontaneous grass (Avena sterilis), at the end of the vegetative cycle, were used as mercury bioconcentrators to map deposition near geothermal power plants and to calculate the corresponding average levels of Hg0 in the air. Direct measurements of mercury and hydrogen sulphide vapours in the air reached by power plant emissions showed a ratio of about 1-2000. This ratio was applied to calculate average levels of hydrogen sulphide starting from mercury deposition mapping: typical concentrations of mercury and hydrogen sulphide were of the order of 10-20 ng/m3 and 20-40 microg/m3, respectively.     

A preliminary risk assessment of trace elements accumulated in fish to the Indo-Pacific Humpback dolphin (Sousa chinensis) in the northwestern waters of Hong Kong

In order to assess the potential risks associated with consumption of contaminated prey items to the Indo-Pacific Humpback dolphin (Sousa chinensis), fish species (Collichthys lucida, Pseudosciaena crocea, Johnius sp., Thryssa sp., Mugil sp. and Trichiurus sp.) representing the main food items of the dolphin were collected from the northwestern waters of Hong Kong, including the Sha Chau and Lung Kwu Chau Marine Park, which form the main habitat of the dolphin in Hong Kong. Within these waters, there are several potential sources of pollution including significant inputs from the Pearl River catchment, several major sewage outfalls and a series of mud pits that receive contaminated dredged sediments. Concentrations of thirteen trace elements (Ag, As, Cd, Co, Cr, Cs, Cu, Hg, Mn, Ni, Se, V, and Zn) in the fish tissue were analyzed by inductively coupled plasma mass spectrometer (ICP-MS). An assessment of the risks of adverse effects on the dolphin due to consumption of tainted fish was undertaken using two toxic reference benchmarks, namely the reference dose (RfD) and toxicity reference value (TRV). The risk quotient (RQ) calculated for each element showed that the risks from consumption of fish were generally low and within safe limits. The risks associated with arsenic, cadmium and mercury were, however, elevated. The highest calculated RQ was associated with total arsenic; however, the majority of arsenic in marine organisms tends to be in the non-toxic organic form, and the actual risk to the dolphin due to this metalloid is likely to be lower.     

Exposure assessment for trace elements from consumption of marine fish in Southeast Asia

Concentrations of 20 trace elements were determined in muscle and liver of 34 species of marine fish collected from coastal areas of Cambodia, Indonesia, Malaysia and Thailand. Large regional difference was observed in the levels of trace elements in liver of one fish family (Carangidae): the highest mean concentration was observed in fish from the Malaysian coastal waters for V, Cr, Zn, Pb and Bi and those from the Java Sea side of Indonesia for Sn and Hg. To assess the health risk to the Southeast Asian populations from consumption of fish, intake rates of trace elements were estimated. Some marine fish showed Hg levels higher than the guideline values by U.S. Environmental Protection Agency and Joint FAO/WHO Expert Committee on Food Additives (JECFA). This suggests that consumption of these fish may be hazardous to the people.     

Degradation and decolorization of a biodegradable-resistant polymeric dye by chelator-mediated Fenton reactions

Chelator-mediated Fenton reactions (CMFRs) were used to decolorize a biodegradable-resistant polymeric dye (Poly R-478). Screening of different iron chelators was performed on Fe(3+)-reduction activity. All chelators showed Fe(3+)-reduction activity over a wide range of pH (2-7) and each mol of catecholate chelators (3,4-dihydroxiphenilacetic acid--DOPAC and 2,3-dihydroxibenzoic acid--DHBA) reduced about 5-6 moles of Fe(3+) whereas hydroxamate chelators (acetohydroxamic acid-AHA and desferrioxamine B-DFB) reduced Fe(3+) stoichiometrically. The most effective decolorization of Poly R-478 was achieved by CMFR using catecholate chelators. In addition, a 2(4) factorial design was performed with the aim of evaluating the effects of the variables considered in this study (pH, [DOPAC], [Fe(3+)] and [H(2)O(2)]) and optimizing the dye decolorization, using response surface methodology. Statistical analysis of results showed that, in the range studied, except for Fe(3+), all variables have a significant effect on dye decolorization. A second-order model is proposed to represent the Poly R-478 decolorization. At optimum conditions, complete decolorization of the dye (degradation of the chromophoric group) and also complete chemical degradation of the dye was observed.     

Sulphur isotopic investigation of a polluted raised bog and the uptake of pollutant sulphur by Sphagnum

The sulphur content and sulphur isotopic composition of Sphagnum as well as anionic compositions and sulphur isotope ratios of rainwater inputs and bog waters have been measured at Thorne Moors, a raised bog in eastern England. Rainwater sulphate isotopic composition shows the sulphur input at this site to be dominated by anthropogenic pollution from fossil fuel burning. Strong depletion of sulphate (low SO4(2-)/Cl-) and enrichment in 34S in sulphate occurs at depth in the bog porewaters due to bacterial sulphate reduction. Some surface waters have low SO4(2-)/Cl-) and are 34S enriched due to removal of sulphate by downward diffusion into a sulphate-reducing zone. Other sites have high SO4(2-)/Cl-) which appears to result from oxidation of organically bound sulphur in the peat. Sulphur is present in Sphagnum at around 0.2% by weight and is depleted by 0 to -9 per thousand in the heavier 34S isotope compared to sulphate. Comparison with similar data from pristine coastal sites shows that sulphur incorporation into Sphagnum is enhanced in the polluted site (as Sphagnum sulphur concentrations are higher at lower total sulphur inputs) and that sulphur incorporation is accompanied by a smaller isotopic shift than in the pristine sites. The data support a model of preferential incorporation of partially reduced sulphur species (probably HSO3-) into Sphagnum. In pristine sites these are only available as oxidation products of sulphide formed by sulphate reduction and are 32S depleted. In polluted sites this source is augmented by sulphur(IV) species in atmospheric inputs and the resultant mixture is less depleted in 32S. Thus, in the polluted sites more HSO3- is available for uptake and the isotopic shift between Sphagnum and aqueous sulphur species is smaller.     

Effect of a subchronic exposure to Simazine on energetic metabolism of common carp (Cyprinus carpio)

The energetic parameters, such as glycogen, glucose, proteins, lactate and adenosine triphosphate (ATP) content and lactate deshydrogenase (LDH) activity in tissues and blood of carps from simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) contaminated waters were investigated. In order to confirm the field results, a laboratory experiment was designed in which carps were exposed to simazine at the concentration level of 45 μ g. L^{? 1} (10-fold of the amount found in natural waters) for 90 days. Fish from a contaminated reservoir showed low glycogen concentrations in hepatopancreas and muscle, while fish in another contaminated reservoir showed high LDH activity together with an increase in lactate content in muscle. Laboratory findings did not confirm field results, and fish exposed to simazine did not show alterations in the parameters studied. The results suggest that carps were not stressed by the presence of the simazine at the concentration levels found in both studies and the mechanisms of defense covered the energetic demand.     

Survival of brown trout during spring flood in DOC-rich streams in northern Sweden: the effect of present acid deposition and modelled pre-industrial water quality

Mortality and physiological responses in brown trout (Salmo trutta) were studied during spring snow melt in six streams in northern Sweden that differed in concentrations of dissolved organic carbon (DOC) and pH declines. Data from these streams were used to create an empirical model for predicting fish responses (mortality and physiological disturbances) in DOC-rich streams using readily accessible water chemistry parameters. The results suggest that fish in these systems can tolerate higher acidity and inorganic aluminium levels than fish in low DOC streams. But even with the relatively low contemporary deposition load, anthropogenic deposition can cause fish mortality in the most acid-sensitive surface waters in northern Sweden during spring flood. However, the results suggests that it is only in streams with high levels of organically complexed aluminium in combination with a natural pH decline to below 5.0 during the spring where current sulphur deposition can cause irreversible damage to brown trout in the region. This study support earlier studies suggesting that DOC has an ameliorating effect on physiological disturbances in humic waters but the study also shows that surviving fish recover physiologically when the water quality returns to less toxic conditions following a toxic high flow period. The physiological response under natural, pre-industrial conditions was also estimated.     

Issues related to solution chemistry in mercury sampling impingers

Analysis of Hg speciation in combustion flue gases is often accomplished in standardized sampling trains in which the sample is passed sequentially through a series of aqueous solutions to capture and separate oxidized Hg (Hg2+) and elemental Hg (Hg0). Such methods include the Ontario Hydro (OH) and the Alkaline Mercury Speciation (AMS) methods, which were investigated in the laboratory to determine whether the presence of Cl2 and other common flue gas species can bias the partitioning of Hg0 to front impingers intended to isolate Hg2+ species. Using only a single impinger to represent the front three impingers for each method, it was found that as little as 1-ppm Cl2 in a simulated flue gas mixture led to a bias of approximately 10-20% of Hg0 misreported as Hg2+ for both the OH and the AMS methods. Experiments using 100-ppm Cl2 led to a similar bias in the OH method, but to a 30-60% bias in the AMS method. These false readings are shown to be due to liquid-phase chemistry in the impinger solutions, and not necessarily to the gas-phase reactions between Cl2 and Hg as previously proposed. The pertinent solution chemistry causing the interference involves the hypochlorite ion (OCl-), which oxidizes Hg0 to soluble Hg2+. Addition of sodium thiosulfate (Na2S2O3) to the front impinger solutions eliminates this false positive measurement of Hg2+ by selectively reacting with the OCl- ion. In general, the presence of SO2 also mitigates this interference in the same way, and so this bias is not likely to be a factor for Hg speciation measurements from actual coal combustion flue gases. It might, however, be a problem for those few combustor flue gas measurements and research studies where Cl2 is present without appreciable amounts of SO2.