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PubMed2005

Quantitative and qualitative studies on the bacteriological quality of Indian white shrimp (Penaeus indicus) stored in dry ice.

Indian white shrimp (Penaeus indicus) stored in dry ice at the 1:1 ratio were found to be organoleptically suitable for consumption when they were stored for 24 h without reicing. Shrimp stored in water ice at the 1:1 ratio (as control) were acceptable up to 18 h. Shrimp stored in a combination of dry ice and water ice at the ratio of 1:0.2:0.5 were also found to be acceptable up to 24 h. Total bacterial load ranged from 10(6) to 10(9) cfu g(-1), while total psychrophiles ranged from 10(3) to 10(6) cfu g(-1). Total lactics were found in the levels of 10(2)-10(6) cfu g(-1). H(2)S producers were from 10(3) to 10(5) cfu g(-1). Lowest temperature of -4.8 degrees C was observed in shrimps stored in dry ice at 1:1 ratio. Bacterial flora associated with fresh raw shrimp were Aeromonas, Pseudomonas, Vibrio, Flavobacterium and Serratia. Aeromonas constituted 38% of the flora in raw shrimp. Flavobacterium (43%), Pseudomonas (47%) and Pseudomonas (38%) were the dominant bacterial flora in the shrimp stored in dry ice at 1:1 ratio, in the combination package, and in water ice at 1:1 ratio, respectively.

Animals↗

PubMed2005

Microbiological evaluation of bottled non-carbonated ("still") water from domestic brands in Greece.

The microbiological quality of 1,527 samples of bottled non-carbonated ('still') mineral water, purchased from retail outlets and derived from 10 manufacturing companies in Greece, was investigated during the period 1995-2003. Applying the membrane filter technique, the aliquots of water samples (250 ml) were analyzed for the presence and enumeration of total coliforms, Escherichia coli, Enterococcus spp. and Pseudomonas aeruginosa. Also, aerobic bacteria were counted as Heterotrophic Plate Count (HPC) ml(-1) at 22 and 37 degrees C. Positive samples for the parameters tested varied significantly among brands with an overall percentage of 13.95% bottled water samples noncompliant with the Greek water regulation. Microorganisms isolated from the samples tested were identified as species of Pseudomonas, Aeromonas, Pasteurella, Citrobacter, Flavobacterium, Providencia and Enterococcus. The most frequent isolated microorganism during the period of the study was P. aeruginosa. Generally, bacterial load of the samples tested ranged in low levels. The purpose of the current study was to evaluate the microbiological quality of the bottled water provided by domestic brands in the Greek market during the period 1995-2003.

Bacteria↗

PubMed2005

Effect of textile auxiliaries on the biodegradation of dyehouse effluent in activated sludge.

The textile industry is confronted with serious environmental problems associated with its immense wastewater discharge, substantial pollution load, extremely high salinity, and alkaline, heavily coloured effluent. Particular sources of recalcitrance and toxicity in dyehouse effluent are two frequently used textile auxiliaries; i.e. dye carriers and biocidal finishing agents. The present experimental work reports the observation of scientific and practical significance related with the effect of two commercially important textile dye carriers and two biocidal finishing agents on biological activated sludge treatment at a textile preparation, dyeing and finishing plant in Istanbul. Respirometric measurements of the dyehouse effluent spiked with the selected textile chemicals were carried out for the assessment of the "readily biodegradable COD fraction" of the wastewater. The respirometric data obtained to visualize the effect of the selected textile auxiliaries on biomass activity was evaluated by an adopted activated sludge model. Results have indicated that the tested biocides did not exert any significant inhibitory effect on the treatment performance of the activated sludge reactor at the concentrations usually encountered in the final, total dyehouse effluent. The situation with the dye carriers was inherently different; one dye carrier appeared to be highly toxic and caused serious inhibition of the microbial respirometric activity, whereas the other dye carrier, also known as the more ecological alternative, i.e. the "Eco-Carrier", appeared to be biodegradable. Finally, the respirometric profile obtained for the Eco-Carrier was described by a simplified respirometric model.

Biodegradation, Environmental↗

PubMed2001

Microbial treatment of a styrene-contaminated air stream in a biofilter with high elimination capacities.

A styrene-utilizing mixed microbial culture was isolated and utilized in a biofilter for the biological treatment of a contaminated air stream. Biofilter media consisted of composted wood bark and yard waste. The biofilters were acclimated at 120 s residence time and further evaluated at 60 and 30 s gas residence times. The biofilters received organic loading rates of up to 350 g/m(3) h. The styrene volumetric removal rate was a function of the organic loading rate and increased with increasing loading rates. Average volumetric removal rates of 69-118 g/m(3) h observed in our studies were higher than reported values for styrene biofilters. Average styrene removal efficiencies ranged from 65% to 75% (maximum 100%). Axial analysis of styrene concentration along the column indicated that the bulk of the styrene removal occurred in the first section of the biofilter. Analyses of the media indicated that the moisture content of the first section (50-55% w/w) was significantly lower than in the second and third sections (65-70% w/w). The pressure drops across the biofilter were low due to the high concentration of large media particles. The total pressure drops were 1-3, 4-6, and 10-16 mm for the 120-, 60-, and 30-s residence time periods, respectively.

Air↗

PubMed1996

[The effectiveness of using biohumus for growing plants under autonomous conditions].

There has been investigated the possibility of prolonging the useful time of the substrate on the basis of natural salt-loaded zeolite "Balkanin" used in space greenhouses to grow plants through introduction of an organic addition, i.e. biohumus, instead of regeneration. Biohumus has been applied into the substrate in amounts of 5.0-15.0 wt%. There has been grown tropical perennial plant Basella rubra L. used for food as a salad. It is found that the periodic introduction of biohumus in substrate enables a 4-19 time increase of its useful life without regeneration within more than 4 years and assures high and stable crop yield with high quality biomass. As compared to the control, the nitrates content of the plant biomass was, on the average, 3 times lower and decreased to the point of their total absence at the end of experiment. The results obtained allow us to recommend the above-mentioned technology of plant growing in space greenhouses both when included into closed environmental systems and in independent plant growth facilities aboard spacecraft. During space flights exceeding 2 years in length, additional supplies of biohumus will be required. This will be enough to stabilize the structure and the size of microbial community in substrate and provide a high crop yield.

Manure↗

PubMed1997

Pre-existence and emergence of drug resistance in HIV-1 infection.

Antiviral treatment of HIV-1 infection often fails because of the rapid emergence of resistant virus within weeks of the start of therapy. This raises the question of whether resistant viruses pre-exist in drug-naive patients or whether it is produced after the start of therapy. Here we compare the likelihood of pre-existence with the likelihood of production of resistant virus during therapy. We show that provided resistant virus pre-exists, then a stronger therapy may lead to a greater initial reduction of virus load, but will also cause a faster rise of resistant virus. In this case the total benefit of treatment is independent of the degree of inhibition of sensitive virus. If, on the other hand, resistant mutants do not pre-exist, then the emergence of resistance during treatment depends on the efficacy of the drug. If the drug is sufficiently potent to eradicate sensitive virus, then the probability that resistant mutants first appear during therapy is smaller than the probability that they existed before therapy. If the drug cannot eradicate the sensitive virus, then after sufficiently long time resistant mutants will appear. However, mutants that are unlikely to pre-exist may taken long time to appear.

Acquired Immunodeficiency Syndrome↗

PubMed2004

Novel pharmacokinetic-pharmacodynamic model for prediction of outcomes with an extended-release formulation of ciprofloxacin.

The pharmacokinetics of an extended-release (XR) formulation of ciprofloxacin has been compared to that of the immediate-release (IR) product in healthy volunteers. The only significant difference in pharmacokinetic parameters between the two formulations was seen in the rate constant of absorption, which was approximately 50% greater with the IR formulation. The geometric mean plasma ciprofloxacin concentrations were applied to an in vitro pharmacokinetic-pharmacodynamic model exposing three different clinical strains of Escherichia coli (MICs, 0.03, 0.5, and 2.0 mg/liter) to 24 h of simulated concentrations in plasma. A novel mathematical model was derived to describe the time course of bacterial CFU, including capacity-limited replication and first-order rate of bacterial clearance, and to model the effects of ciprofloxacin concentrations on these processes. A "mixture model" was employed which allowed as many as three bacterial subpopulations to describe the total bacterial load at any moment. Comparing the two formulations at equivalent daily doses, the rates and extents of bacterial killing were similar with the IR and XR formulations at MICs of 0.03 and 2.0 mg/liter. At an MIC of 0.5 mg/liter, however, the 1,000-mg/day XR formulation showed a moderate advantage in antibacterial effect: the area under the CFU-time curve was 45% higher for the IR regimen; the nadir log CFU and 24-h log CFU values for the IR regimen were 3.75 and 2.49, respectively; and those for XR were 4.54 and 3.13, respectively. The mathematical model explained the differences in bacterial killing rate for two regimens with identical AUC/MIC ratios.

Adult↗

PubMed2004

Female genital-tract HIV load correlates inversely with Lactobacillus species but positively with bacterial vaginosis and Mycoplasma hominis.

BACKGROUND: Bacterial vaginosis (BV) is associated with human immunodeficiency virus (HIV) acquisition. We examined the association between BV and BV-associated bacteria and expression of HIV in the female genital tract. METHODS: HIV RNA, lactobacilli, Gardnerella vaginalis, and Mycoplasma hominis in cervicovaginal lavage (CVL) samples were quantified by polymerase chain reaction (PCR). Gynecologic evaluation included Nugent score assessment, Amsel criteria assessment, detection of other genital-tract infections, and dysplasia grading. CD4 cell count, plasma HIV RNA level, and antiretroviral history were obtained. RESULTS: A total of 203 CVL samples from women with Nugent scores of 7-10 (BV group) and 203 samples from women with Nugent scores of 0-3 (no-BV group) were matched by plasma HIV RNA level and analyzed. After controlling for plasma HIV RNA level and Nugent score in univariate analyses, we found that G. vaginalis and M. hominis bacterial counts, Candida vaginitis, and herpes simplex virus (HSV) were positively associated with CVL HIV RNA levels. In multivariate analysis, only lactobacilli bacterial counts (P=.006; inverse association), M. hominis bacterial counts (P=.0001; positive association), Candida vaginitis (P=.007), and HSV (P=.03) were significantly associated with CVL HIV RNA levels. CONCLUSION: Bacteria associated with BV increase genital-tract HIV RNA levels. Quantitative bacterial counts for lactobacilli and M. hominis are better correlates of CVL HIV RNA than are Nugent score or Amsel criteria. Since plasma virus and CD4 cell levels did not differ between the BV and no-BV groups, these data suggest that the bacterial flora associated with BV influence genital-tract HIV shedding.

Adult↗

PubMed1994

Preparation, properties and the effects of free and liposomal tobramycin on siderophore production by Pseudomonas aeruginosa.

The in-vitro activities of encapsulated and free tobramycin were evaluated against Pseudomonas aeruginosa grown in iron-depleted chemically-defined culture medium (CDM-Fe). The liposomal formulations used for the efficacy studies of encapsulated tobramycin were based on the optimal loading and release patterns. The dehydration-rehydration (DRV) technique was used to prepare fluid phosphatidylcholine (PC) and solid, distearylphosphatidylcholine (DSPC), neutral, negatively charged phosphatidic acid (PA) and positively charged stearylamine (SA) liposomes containing tobramycin. The total charged phospholipid in each preparation was no more than 5% of the total phospholipid content. The effects of free and liposome-encapsulated tobramycin on siderophore production by P. aeruginosa were examined and involved using MIC and sub-MIC quantities of tobramycin: 0.25, 0.125, 0.0625 and 0.025 mg/L, corresponding to 1, 0.5, 0.25 and 0.1 times MIC, respectively, were used. Compared to free tobramycin, siderophore production was more effectively retarded in the presence of sub-MIC quantities of liposomal tobramycin, particularly at 0.5 MIC. Siderophore production was particularly reduced in the presence of positively charged PC liposomes.

Chemistry, Pharmaceutical↗

PubMed1999

Effects of organic pollutants on soil microbial activity: the influence of sorption, solubility, and speciation.

The Fe(III) reduction test was used to measure the toxicity of 12 organic chemicals [dichlorophenoxyacetic acid (2,4-D), trichlorophenoxyacetic acid (2,4,5-T), atrazine, picloram, 4-chlorobenzeneamine, pentachlorophenol (PCP), hexachlorobenzene (HCB), 1,1-bis-4-chlorophenyl-2,2,2-trichloroethane (DDT), trichloroethene, benzene, phenol, linear alkylbenzenesulfonate (LAS)]. The different inherent toxicity of the pollutants is strongly modified by interactions with the soils. The total amounts that cause 10, 50, and 90% inhibitions (effective doses, ED10, ED50, ED90) can be statistically related to soil parameters that control the sorption and solubility of the chemicals. Sorption experiments with 2,4-D, 2,4,5-T, PCP, and LAS confirm that the degree of sorption and the concentration in the soil solution are important for potential toxic effects. However, toxic solution concentrations of a chemical (effective concentrations, EC10, EC50, EC90) also vary considerably. For some chemicals the influence of soil pH on their speciation in the soil solution is mainly responsible for this, e.g., the transformation from anionic to nonionic species with decreasing pH. The nonionic species of 2,4-D, 2,4,5-T, and PCP formed under acidic conditions are more toxic than the anionic species. Thus, depending on the chemical parameters of the soils that determine the degree of sorption and the speciation of toxicants in the liquid phase, soils either can "buffer" high loads of toxicants or can be very sensitive toward contamination.

Dose-Response Relationship, Drug↗

PubMed1998

Vibrio splendidus biovar II as the causative agent of bacillary necrosis of Japanese oyster Crassostrea gigas larvae.

Recurrent outbreaks of a disease leading to mass mortalities in an oyster (Crassostrea gigas) hatchery located in western Japan were investigated. The disease occurred regularly in 2- to 8-d-old larvae and has been experimentally controlled in the hatchery by treating the larval rearing water with streptomycin, without ascertaining the etiological agent. The signs of the disease and the course of infection resembled bacillary necrosis reported in oysters and other bivalve molluscs in the USA and Europe. Quantitative and qualitative examinations of the bacterial flora of hatchery samples including source water, broodstock, larval feed and larvae revealed a very high total bacterial load and presumptive vibrios in diseased larvae. Further, the bacterial profile revealed that Vibrio spp. constituted approximately 60 to 95% of the bacteria isolated from infected larvae and most isolates were identified as V. splendidus biovar II and V. harveyi, suggesting their possible role in the disease. However, experimental challenges proved the pathogenicity of V. splendidus II. Several isolates of V. splendidus II from infected larvae were highly pathogenic, producing 100% mortality at levels of 10(5) cfu ml-1 in 24 h, while isolates from other sources demonstrated a low degree of virulence. Detection of V. splendidus II from broodstock, especially in the gonad of a few breeders, suggests the probability that broodstock could be the source and route of transmission of this pathogen.

Animals↗

PubMed2002

Efficacy of interferon monotherapy to 394 consecutive naive cases infected with hepatitis C virus genotype 2a in Japan: therapy efficacy as consequence of tripartite interaction of viral, host and interferon treatment-related factors.

BACKGROUND/AIMS: The mechanism of variable response to interferon (IFN) monotherapy in patients infected with HCV genotype 2a is still unclear. Here we investigated the response in a large group of patients infected with genotype 2a. METHODS: We evaluated 394 consecutive non-cirrhotic naive patients infected with genotype 2a who received IFN monotherapy for 24 weeks, including initial aggressive induction therapy. Of these, 97 were also evaluated for early viral kinetics in serum and treatment efficacy. RESULTS: The overall sustained response (SR) rate was 68.3% (viral load <1.0 Meq/ml (82.4%); >/=1.0 (52.4%)). Multivariate analysis identified five independent factors associated with SR; viral load <1.0 Meq/ml, total IFN dose > or =700 million units, hepatocyte steatosis none or mild, albumin > or =3.9 g/dl, and alanine aminotransferase > or =75 IU/l. The kinetic study showed that serum viral clearance at < or =1 week was the best predictor of SR, and persistence at > or = 4 weeks was a predictor of non-SR. CONCLUSIONS: Our study suggests that viral, host and IFN treatment-related factors determine the response to IFN monotherapy in patients infected with HCV genotype 2a. Further, we report that IFN monotherapy is very effective for patients with genotype 2a, especially for those with low viral load; and that early viral kinetics is useful as a predictor of the response.

Adolescent↗

PubMed2004

Morphological and phenotypical characterization of Bacillus sporothermodurans.

AIMS: Enumeration of resistant bacteria in ultra-high temperature (UHT) treated milk; morphological characterization and phenotyping of resistant strains by traditional and nontraditional methods and their identification by molecular biology. METHODS AND RESULTS: Modified standard plate count agar (PCA) and modified brain-heart infusion (BHI) agar were used for colony counts. Physiological culture traits were determined as suggested by Bergey's Manual of Systematic Bacteriology or in modified J-broth or in modified BHI agar. Scanning electron microscope (SEM) was used for microscopic examination. Strain identification was carried out by polymerase chain reaction (PCR). A total of 125 (62.81% of 199) samples were positive and the bacterial load was higher than 10(5) CFU ml(-1) in 46 samples (28.80% of 125). The 16S rRNA sequence of bacterial cultures obtained from UHT-treated milk was similar to that of Bacillus sporothermodurans M215 type strain((T)) and different biotypes were found by analysis of colony appearance, cell morphology and physiological traits. CONCLUSIONS: Bacillus sporothermodurans was the predominant sporigenous micro-organisms in UHT milk. SIGNIFICANCE AND IMPACT OF THE STUDY: BHI agar is more suitable than PCA for quality control of milk after UHT treatment. Modified J-broth medium is useful to determine selected physiological traits of B. sporothermodurans. The strains characterized and identified as B. sporothermodurans were significantly different compared with the type strain.

Animals↗

PubMed2006

Modelling salinity inhibition effects during biodegradation of perchlorate.

AIMS: To determine the mathematical kinetic rates and mechanisms of acclimated perchlorate (ClO)-reducing microbial cultures by incorporating a term to relate the inhibitory effect of high salinity during biological reduction of concentrated perchlorate solutions. METHODS AND RESULTS: Salt toxicity associated with the biodegradation of concentrated perchlorate (200, 500, 1100, 1700 and 2400 mg l(-1) as ClO) was investigated using two microbial cultures isolated from a domestic wastewater treatment plant [return activated sludge (RAS) and anaerobic digester sludge (ADS)]. Experiments were performed in wastewaters containing various sodium chloride concentrations, ranging from 0% to 4.0% (w/v) NaCl (ionic strength: 0.14-0.82 mol l(-1), total dissolved solids: 5.3-42.6 g l(-1)) at near-neutral values of pH (6.7-7.8). Perchlorate biodegradation was stimulated through stepwise acclimation to high salinity. The ADS culture was capable of reducing perchlorate at salinities up to 4% NaCl, while the RAS culture exhibited complete inhibition of perchlorate degradation at 4% NaCl, probably resulting from either a toxic effect or enzyme inactivation of the perchlorate-reducing microbes. Further, a kinetic growth model was developed based on experimental data in order to express an inhibition function to relate specific growth rate and salinity. CONCLUSIONS: Biological reduction of concentrated perchlorate wastewaters using either acclimated RAS or ADS cultures is feasible up to 3% or 4% NaCl, respectively. In addition, the kinetic model including a salinity inhibition term should be effective in many practical applications such as improving reactor design and management, furthering the understanding of high salinity inhibition, and enhancing bioremediation under high salinity loading conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Applications of these findings in water treatment practice where ion exchange or membrane technologies are used to remove perchlorate from water can have the potential to increase the overall attractiveness of these processes by eliminating the need to dispose of a concentrated perchlorate solution.

Bacteria↗

PubMed1999

An outbreak of nonflocculating catabolic populations caused the breakdown of a phenol-digesting activated-sludge process.

Activated sludge was fed phenol as the sole carbon source, and the phenol-loading rate was increased stepwise from 0.5 to 1.0 g liter-1 day-1 and then to 1.5 g liter-1 day-1. After the loading rate was increased to 1.5 g liter-1 day-1, nonflocculating bacteria outgrew the sludge, and the activated-sludge process broke down within 1 week. The bacterial population structure of the activated sludge was analyzed by temperature gradient gel electrophoresis (TGGE) of PCR-amplified 16S ribosomal DNA (rDNA) fragments. We found that the population diversity decreased as the phenol-loading rate increased and that two populations (designated populations R6 and R10) predominated in the sludge during the last several days before breakdown. The R6 population was present under the low-phenol-loading-rate conditions, while the R10 population was present only after the loading rate was increased to 1.5 g liter-1 day-1. A total of 41 bacterial strains with different repetitive extragenic palindromic sequence PCR patterns were isolated from the activated sludge under different phenol-loading conditions, and the 16S rDNA and gyrB fragments of these strains were PCR amplified and sequenced. Some bacterial isolates could be associated with major TGGE bands by comparing the 16S rDNA sequences. All of the bacterial strains affiliated with the R6 population had almost identical 16S rDNA sequences, while the gyrB phylogenetic analysis divided these strains into two physiologically divergent groups; both of these groups of strains could grow on phenol, while one group (designated the R6F group) flocculated in laboratory media and the other group (the R6T group) did not. A competitive PCR analysis in which specific gyrB sequences were used as the primers showed that a population shift from R6F to R6T occurred following the increase in the phenol-loading rate to 1.5 g liter-1 day-1. The R10 population corresponded to nonflocculating phenol-degrading bacteria. Our results suggest that an outbreak of nonflocculating catabolic populations caused the breakdown of the activated-sludge process. This study also demonstrated the usefulness of gyrB-targeted fine population analyses in microbial ecology.

Bacteria↗

PubMed1979

Cefaclor in the treatment of uncomplicated gonococcal urethritis.

Cefaclor is a cephalosporin antibiotic whose chemical structure is similar to that of cephalexin. The substitution of a chloro group for the methyl group of cephalexin has produced a compound with markedly improved antibacterial activity, while retaining the property of gastrointestinal absorption. Cefaclor has shown good in vitro activity against Neisseria gonorrhoeae. In a controlled clinical trial, 40 men with uncomplicated gonococcal urethritis received cefaclor given as a one gram loading dose, followed by 500 mg 4 times daily for 3 days, for a total dose of 7 g. All patients were re-evaluated at 3 to 7 days following completion of therapy. Two patients did not complete the entire course of therapy and were eventually treated with another regimen. Of 38 men who took the full course of therapy, 35 were clinically and bacteriologically cured. Two men were clinically infected but had negative pretreatment cultures. Of 19 men with beta-lactamase-positive gonococcal urethritis, 18 were cured, whereas among 17 men with penicillin-sensitive strains, all were cured. There were no adverse reactions to the drug, and all patients expressed a preference for the oral regimen. The success of cefaclor in this pilot study suggests that additional clinical trials should be performed.

Adult↗

PubMed2006

Spatial patterns of water quality in the Cuiabá River basin, Central Brazil.

This study evaluates the spatial patterns of land occupation and their relationship to water quality in the Cuiabá River watershed, one of the main affluents of the Pantanal floodplain. The impact of farming and other land occupation forms were studied using a three year time series. Monitoring included 15 parameters at 21 stations with a total of 1266 different samples. Ten stations along the Cuiabá River were ordinated by Principal Component Analysis (PCA). For an exploratory analysis in the spatial domain, sub-basins of the Cuiabá watershed were classified according to mean concentrations of selected water quality parameters. Supervised classification of digital Landsat ETM imagery and standard GIS techniques were applied to parameterize land use and occupation according to a watershed scale. Redundancy Analysis (RDA) was then used to evaluate impacts of environmental and socio-economic factors on water quality. A Cuiabá headwater station only shows slightly elevated total coliform counts and concentrations of nutrients in the river after it passes regions of extensive cattle farming. After the confluence with the Manso River, nutrient and COD concentrations increase significantly, receiving loads from sub-basins under intensive agricultural land use, with mean annual concentrations up to 1.74 mg/L of total nitrogen (Kjedahl). Sub-watersheds with intensive fishing culture activities were shown to have significant impact on nitrogen concentrations, reaching mean concentrations of 2.66 mg/L of total nitrogen in the affluents. Most serious biological and chemical water pollution can be observed at stream outlets in the urban agglomeration of Cuiabá/Várzea Grande. Affluent pollution is reflected in the water quality of the Cuiabá River: subsequent monitoring stations in the urban area are ordinated on a gradient of increasing degradation of chemical and biological water quality. The auto-depuration capacity of the Cuiabá River is intact, but elevated concentrations of Phosphorous and Chemical Oxygen Demand can be observed as far away as the Pantanal floodplain, about 120 km downstream from the urban agglomeration.

Agriculture↗

PubMed2005

Sources of methylmercury to a wetland-dominated lake in northern Wisconsin.

Several lines of evidence suggest that wetlands may be a major source of methylmercury (MeHg) to receiving waters, perhaps explaining the strong correlation between concentrations of waterborne MeHg and dissolved organic carbon (DOC) in regions such as northern Wisconsin. We evaluated the relative importance of wetland export in the MeHg budget of a wetland-dominated lake in northern Wisconsin using mass balance. Channelized runoff from a large headwater wetland was the major source of water and total mercury (HgT) to the lake during the study period. The wetland also exported MeHg in high concentrations (0.2-0.8 ng L(-1)), resulting in an export rate similar to those reported for other northern wetlands (ca. 0.3 microg MeHg m(-2) y(-1)). Yet, based on intensive sampling during 2002, the mass of MeHg that accumulated in the lake during summer was an order of magnitude greater than the export of MeHg from the wetland to the lake. Hence, a large in-lake source of MeHg is inferred from the mass balance. Most of the accumulated MeHg built-up in anoxic hypolimnetic waters; and the build-up was roughly balanced by losses of inorganic Hg (Hg(II)) implying a chemical transformation within the anoxic water column. An abundance of sulfate-reducing bacteria (SRB) in hypolimnetic waters, established by DNA analysis of the pelagic microbial community, along with a previous report documenting high methylation rates in the hypolimnion of this lake (ca. 10% d(-1)), suggest that this transformation was microbially mediated. These findings indicate that the direct effect of wetland runoff may be outweighed by indirect effects on the lacustrine MeHg cycle, enhancing the load of Hg(II), the activity of SRB, and the retention of MeHg, especially in northern lakes with flushing times longer than six months.

Ecosystem↗