Biomedical subjects

David L Sedlak

Publications and source records attributed to David L Sedlak.

18 recordsLinked to original sources

PubMed2006

The fate of wastewater-derived NDMA precursors in the aquatic environment.

To assess the stability of precursors of the chloramine disinfection byproduct N-nitrosodimethylamine (NDMA) under conditions expected in effluent-dominated surface waters, effluent samples from four municipal wastewater treatment plants were subjected to chlorination and chloramination followed by incubation in the presence of inocula derived from activated sludge. Samples subjected to free chlorine disinfection showed lower initial concentrations of NDMA precursors than those that were not chlorinated or were disinfected with pre-formed chloramines. For chloraminated and control (unchlorinated) treatments, the concentration of NDMA precursors decreased by an average of 24% over the 30-day incubation in samples from three of the four facilities. At the fourth facility, where samples were collected on three different days, NDMA precursor concentrations decreased by approximately 80% in one sample and decreased by less than 20% in the other two samples. In contrast to the low reactivity of the NDMA precursors, NDMA disappeared within 30 days under the conditions employed in these experiments. These results and measurements made in an effluent-dominated river suggest that although NDMA may be removed after wastewater effluent is discharged, wastewater-derived NDMA precursors could persist long enough to form significant concentrations of NDMA in drinking water treatment plants that use water originating from sources that are subjected to wastewater effluent discharges.

Biodegradation, Environmental↗

PubMed2005

Formation of nitrosodimethylamine (NDMA) during chlorine disinfection of wastewater effluents prior to use in irrigation systems.

The probable human carcinogen nitrosodimethylamine (NDMA) is produced when wastewater effluent is disinfected with chlorine. In systems where wastewater effluent is used for landscape or crop irrigation, relatively high chlorine doses (i.e., up to 2,000,mg-min/L) are often used to ensure adequate disinfection and to minimize biofouling in the irrigation system. To assess the formation of NDMA in such systems, samples were collected from several locations in full-scale wastewater treatment systems and their associated irrigation systems. Up to 460 ng/L of NDMA was produced in full-scale systems in which chloramines were formed when wastewater effluent was disinfected with chlorine in the presence of ammonia. Less than 20 ng/L of NDMA was produced in systems that used free chlorine (i.e., HOCl/OCl(-)) for disinfection in the absence of ammonia. The production of NDMA in ammonia-containing systems was correlated with the concentration of NDMA precursors in the wastewater effluent and the overall dose of chlorine applied. Much of the NDMA formation occurred in chlorine contact basins or in storage basins where water that contained chloramines was held after disinfection. When landscape or crop irrigation is practiced with ammonia-containing wastewater effluent, NDMA production can be controlled by use of lower chlorine doses or by application of alternative disinfectants.

Agriculture↗

PubMed2005

Use of the chiral pharmaceutical propranolol to identify sewage discharges into surface waters.

The discharge of relatively small volumes of untreated sewage is a source of wastewater-derived contaminants in surface waters that is often ignored because it is difficult to discriminate from wastewater effluent. To identify raw sewage discharges, we analyzed the two enantiomers of the popular chiral pharmaceutical, propranolol, after derivitization to convert the enantiomers to diastereomers. The enantiomeric fraction (the ratio of the concentration of one of its isomers to the total concentration) of propranolol in the influent of five wastewater treatment plants was 0.50 +/- 0.02, while after secondary treatment it was 0.42 or less. In a laboratory study designed to simulate an activated sludge municipal wastewater treatment system, the enantiomeric fraction of propranolol decreased from 0.5 to 0.43 as the compound underwent biotransformation. In a similar system designed to simulate an effluent-dominanted surface water, the enantiomeric fraction of propranolol remained constant as it underwent biotransformation. Analysis of samples from surface waters with known or suspected discharges of untreated sewage contained propranolol with an enantiomeric fraction of approximately 0.50 whereas surface waters with large discharges of wastewater effluent contained propranolol with enantiomeric fractions similar to those observed in wastewater effluent. Measurement of enantiomers of propranolol may be useful in detecting and documenting contaminants related to leaking sewers and combined sewer overflows.

Chromatography, Gas↗

PubMed2005

Similarities between inorganic sulfide and the strong Hg(II)-complexing ligands in municipal wastewater effluent.

Municipal wastewater effluent contains ligands that form Hg(II) complexes that are inert in the presence of glutathione (GSH) during competitive ligand exchange experiments. In this study, the strong ligands in wastewater effluent were further characterized by comparing their behavior with sulfide-containing ligands in model solutions and by measuring their concentration after exposing them to oxidants. The strong Hg(II) complexes in wastewater effluent and the complexes formed when Hg(II) was added to S(-II) were retained during C18 solid-phase extraction (SPE) and did not dissociate in the presence of up to 100 microM GSH. In contrast, Hg(II) complexes with dissolved humic acid were hydrophilic and dissociated in the presence of GSH. The combination of sulfide and humic acid resulted in formation of Hg(II) complexes that were inert to GSH and were only partially retained by C18-SPE, indicating that NOM interacted with the Hg-sulfide complexes. When wastewater effluent samples and model solutions of free sulfide, Zn-sulfide, and Fe-sulfide were exposed to 0.14 mM NaOCl for 1 h (to mimic conditions encountered during chlorine disinfection), the strong Hg(II)-complexing ligands were completely removed. Exposure of the wastewater effluent and the model ligands to oxygen for 2 weeks resulted in approximately 60% to 75% loss of strong ligands. The strong ligands that remained in the oxygen-oxidized samples were resistant to further oxidation by chlorine, indicating that oxidation of S(-II) results in the formation of other sulfur-containing ligands such as S8 that form strong complexes with Hg(II).

Cations, Divalent↗

PubMed2005

Decrease in net mercury methylation rates following iron amendment to anoxic wetland sediment slurries.

The rate of mercury methylation in anoxic wetland sediments is affected by the concentration of bioavailable complexes between Hg and sulfide. Previous research with pure bacterial cultures has shown that addition of ferrous iron reduces the net rate of mercury methylation by decreasing the concentration of dissolved sulfide. To assess the possibility of using this approach to decrease net mercury methylation in restored and constructed wetlands, laboratory experiments were conducted by adding Hg(II) and Fe(II) to sediments collected from six sites in five estuarine wetlands. Addition of 30 mM (0.07 mmol g(-1) or 3.9 mg g(-1)) Fe(II) decreased net mercury methylation relative to that of unamended controls by a factor of 2.1-6.6. In all cases, the observed decrease in net mercury methylation was accompanied by a decrease in the concentrations of sulfide and filterable mercury in the water overlying the sediments. When iron was added to one of the sediment samples at doses that were small relative to the concentration of sulfide present, net mercury methylation either increased slightly or was unaffected. Comparison of the results to speciation model predictions suggests that dissolved reduced sulfur-containing species play a role in the formation of uncharged, bioavailable Hg complexes. Although further research is needed to determine the long-term effect of iron amendment, these results suggest that iron addition decreases mercury methylation in authentic wetland sediments.

Anaerobiosis↗

PubMed2005

Quantification of the oxidizing capacity of nanoparticulate zero-valent iron.

Addition of nanoparticulate zero-valent iron (nZVI) to oxygen-containing water results in oxidation of organic compounds. To assess the potential application of nZVI for oxidative transformation of organic contaminants, the conversion of benzoic acid (BA) to p-hydroxybenzoic acid (p-HBA) was used as a probe reaction. When nZVI was added to BA-containing water, an initial pulse of p-HBA was detected during the first 30 min, followed by the slow generation of additional p-HBA over periods of at least 24 h. The yield of p-HBA increased with increasing BA concentration, presumably due to the increasing 'ability of BA to compete with alternate oxidant sinks, such as ferrous iron. At pH 3, maximum yields of p-HBA during the initial phase of the reaction of up to 25% were observed. The initial rate of nZVI-mediated oxidation of BA exhibited a marked reduction at pH values above 3. Despite the decrease in oxidant production rate, p-HBA was observed during the initial reaction phase at pH values up to 8. Competition experiments with probe compounds expected to exhibit different affinities for the nZVI surface (phenol, aniline, o-hydroxybenzoic acid, and synthetic humic acids) indicated relative rates of reaction that were similar to those observed in competition experiments in which hydroxyl radicals were generated in solution. Examination of the oxidizing capacity of a range of Fe0 particles reveals a capacity in all cases to induce oxidative transformation of benzoic acid, but the high surface areas that can be achieved with nanosized particles renders such particles particularly effective oxidants.

Hydrogen-Ion Concentration↗

PubMed2004

Dairy wastewater, aquaculture, and spawning fish as sources of steroid hormones in the aquatic environment.

A suite of androgens, estrogens, and progestins were measured in samples from dairy farms, aquaculture facilities, and surface waters with actively spawning fish using gas chromatography-tandem mass spectrometry (GC/MS/ MS) to assess the potential importance of these sources of steroid hormones to surface waters. In a dairywaste lagoon, the endogenous estrogens 17beta-estradiol and estrone and the androgens testosterone and androstenedione were detected at concentrations as high as 650 ng/L. Samples from nearby groundwater monitoring wells demonstrated removal of steroid hormones in the subsurface. Samples from nearby surface waters and tile drains likely impacted by animal wastes demonstrated the sporadic presence of the steroids 17beta-estradiol, estrone, testosterone, and medroxyprogesterone, usually at concentrations near or below 1 ng/L. The endogenous steroids estrone,testosterone, and androstenedione were detected in the raceways and effluents of three fish hatcheries at concentrations near 1 ng/L. Similar concentrations were detected in a river containing spawning adult Chinook salmon. These results indicate that dairy wastewater, aquaculture effluents, and even spawning fish can lead to detectable concentrations of steroid hormones in surface waters and that the concentrations of these compounds exhibit considerable temporal and spatial variation.

Androgens↗

PubMed2004

Transformation of aromatic ether- and amine-containing pharmaceuticals during chlorine disinfection.

Many of the human pharmaceuticals detected in municipal wastewater effluent, surface water, and groundwater contain functional groups that could undergo transformation reactions during chlorine disinfection. To assess the potential importance of these reactions to the environmental fate of pharmaceuticals, the rate of transformation of a group of compounds was measured over a pH range of 5-10. Several of the pharmaceuticals reacted rapidly with free chlorine (i.e., HOCl/OCl-) and would be expected to undergo transformation under the conditions typically encountered in many chlorine disinfection systems. For compounds containing aromatic ether functional groups, the rate of transformation was strongly affected bythe other substituents on the ring. The amine-containing pharmaceuticals underwent a rapid reaction with hypochlorous acid to form chlorinated amines, which could be converted back into the parent compound by reaction with thiosulfate. In the absence of thiosulfate, the chlorinated amines slowly decomposed to form species that could not be converted back into the parent compound. The reaction rates of the pharmaceuticals with combined chlorine (i.e., chloramines) were significantly slower, and transformation of the compounds would not be expected under the conditions encountered during chloramination.

Amines↗

PubMed2004

Characterization and fate of N-nitrosodimethylamine precursors in municipal wastewater treatment plants.

The potent carcinogen, N-nitrosodimethylamine (NDMA), is produced during disinfection of municipal wastewater effluent from the reaction of monochloramine and organic nitrogen-containing precursors. To delineate the sources and fate of NDMA precursors during municipal wastewater treatment, NDMA formation was measured after extended chloramination of both model precursors and samples from conventional and advanced wastewater treatment plants. Of the model precursors, only dimethylamine, tertiary amines with dimethylamine functional groups, and dimethylamides formed significant NDMA concentrations upon chloramination. In samples from municipal wastewater treatment plants, dissolved NDMA precursors always were present in primary and secondary effluents. Biological treatment effectively removed the known NDMA precursor dimethylamine, lowering its concentration to levels that could not produce significant quantities of NDMA upon chlorine disinfection. However, biological treatment was less effective at removing other dissolved NDMA precursors, even after extended biological treatment. Significant concentrations of particle-associated NDMA precursors only were detected in secondary effluent at treatment plants that recycled water from sludge thickening operations in which dimethylamine-based synthetic polymers were used. Effective strategies for the prevention of NDMA formation during wastewater chlorination include ammonia removal by nitrification to preclude chloramine formation during chlorine disinfection, elimination of dimethylamine-based polymers, and use of filtration and reverse osmosis to remove particle-associated precursors and dissolved precursors, respectively.

Bioreactors↗

PubMed2004

Effect of ferric chloride addition on the removal of Cu and Zn complexes with EDTA during municipal wastewater treatment.

The presence of the synthetic chelating agent ethylenediaminetetraacetic acid (EDTA) in municipal wastewater has a significant impact on the efficacy of wastewater treatment plants because pollutant metal-EDTA complexes are difficult to remove. To understand the potential of FeCl3 addition during primary treatment to improve metal removal, laboratory experiments and a full-scale study were conducted. Results of laboratory experiments designed to simulate primary and secondary wastewater treatment indicate that a portion of pollutant metal-EDTA species can be converted into FeEDTA- by addition of FeCl3 during simulated primary treatment. Addition of FeCl3 also resulted in improved metal removal by adsorption. The combination of these two processes improved removal of Cu and Zn by 20% during simulated primary treatment. During full-scale treatment, a slight increase in the concentration of FeEDTA- in secondary effluent was observed when FeCl3 was added during primary treatment. However, FeCl3 addition had no observable effect on metal concentrations in the wastewater effluent. The most noticeable change in EDTA speciation at full scale occurred during primary treatment, where most of the pollutant metal-EDTA complexes were converted into FeEDTA-, irrespective of whether or not FeCl3 was added. The formation of FeEDTA- during primary treatment plays a potentially important role in metal removal and should be considered in future evaluations of wastewater treatment plant performance.

Adsorption↗

PubMed2003

Reduction of net mercury methylation by iron in Desulfobulbus propionicus (1pr3) cultures: implications for engineered wetlands.

Although one potential drawback of wetland construction and restoration is the formation of monomethylmercury, it may be possible to decrease net mercury methylation with the use of an appropriate sediment amendment. Using pure cultures of the sulfate-reducing bacterium Desulfobulbus propionicus (1pr3), we tested the hypothesis that adding ferrous iron to sulfidic wetland sediments decreases mercury solubility and bioavailability and, therefore, net methylation. In sediment-free cultures, net mercury methylation decreased with increasing [Fe(II)]. After 72 h of incubation, more than four times as much net methylmercury formed in the lowest ([Fe(II)] = 10(-6) M) treatment (180 +/- 33 pM) as compared with the highest ([Fe(II)] = 10(-2) M) treatment (42 +/- 14 pM). In cultures containing a model wetland sediment, more than three times as much methylmercury was observed in 10(-6) M Fe(II) treatments (1,010 +/- 95 pM) as compared with treatments amended with 10(-2) M Fe(II) (300 +/- 46 pM). Initial filterable mercury measurements and chemical equilibrium speciation predictions suggest that the lower net methylmercury production in the high-iron treatments was due to a decrease in sulfide activity and a concomitant decrease in the concentration of dissolved mercury. Although iron amendments could potentially minimize net mercury methylation in engineered wetland sediments, further research under field conditions is required to assess the efficacy of this approach.

Deltaproteobacteria↗

PubMed2003

Strong hg(II) complexation in municipal wastewater effluent and surface waters.

The speciation of mercury(II) in the aquatic environment is greatly affected by the presence of ligands capable of forming extremely strong complexes with Hg(II). In this study, a novel competitive ligand exchange (CLE) technique was used to characterize Hg(II)-complexing ligands in samples collected from three municipal wastewater treatment plants, a eutrophic lake, a creek located downstream of an abandoned mercury mine, and a model water containing dissolved Suwannee River humic acid. These samples contained 3.3-15.9 mg/L dissolved organic carbon and were amended with 1.0-1.7 nM Hg(II) for CLE analysis. Results indicated that all samples contained labile Hg(II)-complexing ligands with conditional stability constants similar to those of reduced sulfur-containing ligands. Two wastewater effluent samples also contained approximately 0.5 nM of ligands that formed extremely strong Hg(II) complexes that did not dissociate in the presence of competing ligands. The conditional stability constant of these extremely strong or nonlabile complexes (i.e., (c)K(HgL)) were estimated to be greater than 10(30), for the reaction Hg(2+) + L' = HgL. The third wastewater sample and the eutrophic lake sample contained lower concentrations, 0.07-0.09 nM, of nonlabile Hg(II)-complexing ligands. The results suggested that these extremely strong Hg(ll)-complexing ligands should account for most of the dissolved Hg(II) species in municipal wastewater effluent and may dominate Hg(II) speciation in effluent-receiving waters.

Ditiocarb↗

PubMed2003

A N-Nitrosodimethylamine (NDMA) precursor analysis for chlorination of water and wastewater.

N-nitrosodimethylamine (NDMA) is a potent carcinogen formed during chloramination of water and wastewater treatment plant effluents. A procedure is described for quantifying the concentration of the organic precursors of NDMA that could be formed during chlorination of wastewaters and natural waters. The method involves applying a high dose of monochloramine to a pH-buffered sample followed by a 10-day contact period, during which the monochloramine decays at a rate unrelated to the composition of the sample. Analyses of samples of municipal wastewater effluents and surface waters indicate that the method provides a robust and reproducible measurement of NDMA precursors over a wide range of conditions. A sensitive GC/CI/MS/MS analytical procedure for dimethylamine also is described and used to demonstrate that NDMA formation during chlorination of wastewater and natural waters cannot be explained by dimethylamine concentrations alone.

Carcinogens↗

PubMed2003

Quantification of steroid hormones with pheromonal properties in municipal wastewater effluent.

Many fish use steroid hormones as pheromones to initiate behavioral and physiological changes during spawning. To assess the occurrence of steroid hormones with pheromonal properties in the aquatic environment and to evaluate the possibility that municipal wastewater discharges contain compounds that could affect fish reproduction by interfering with pheromones, several estrogens, androgens, and progestins were quantified by gas chromatography/tandem mass spectroscopy in effluent samples from 12 municipal wastewater treatment plants. Samples also were analyzed from an engineered treatment wetland, three groundwater wells, and one reservoir. Estrogens (17beta-estradiol and estrone) were detected in wastewater effluent at maximum concentrations of 4 and 12 ng/L, respectively. Androgens (testosterone and androstenedione) were detected at concentrations as high as 6.1 and 4.5 ng/L, respectively, whereas the synthetic progestin medroxyprogesterone was detected at concentrations up to 15 ng/L. Data from an effluent-receiving engineered treatment wetland and shallow groundwater wells suggested that these compounds were not rapidly attenuated. The measured concentrations of steroids often exceeded olfactory detection thresholds at which fish detect these steroids, and in several cases, the steroid concentrations were comparable to levels at which pheromonal responses have been observed in fish.

Androgens↗

PubMed2002

Formation of N-nitrosodimethylamine (NDMA) from dimethylamine during chlorination.

Chlorine disinfection of secondary wastewater effluent and drinking water can result in the production of the potent carcinogen N-nitrosodimethylamine (NDMA) at concentrations of approximately 100 and 10 parts per trillion (ng/L), respectively. Laboratory experiments with potential NDMA precursors indicate that NDMA formation can form during the chlorination of dimethylamine and other secondary amines. The formation of NDMA during chlorination may involve the slow formation of 1,1-dimethylhydrazine by the reaction of monochloramine and dimethylamine followed by its rapid oxidation to NDMA and other products including dimethylcyanamide and dimethylformamide. Other pathways also lead to NDMA formation during chlorination such as the reaction of sodium hypochlorite with dimethylamine. However, the rate of NDMA formation is approximately an order of magnitude slower than that observed when monochloramine reacts with dimethylamine. The reaction exhibits a strong pH dependence due to competing reactions. It may be possible to reduce NDMA formation during chlorination by removing ammonia prior to chlorination, by breakpoint chlorination, or by avoidance of the use of monochloramine for drinking water disinfection.

Chloramines↗

PubMedDate not supplied

Bioavailability of wastewater-derived organic nitrogen to the alga Selenastrum Capricornutum.

Recent attempts to control cultural eutrophication in nitrogen-limited systems have focused on the simultaneous control of all forms of nitrogen with the underlying assumption that inorganic and organic nitrogen are equally bioavailable. To assess the validity of this assumption, algal growth bioassays were conducted on denitrified wastewater effluent samples, in the presence and absence of bacteria isolated from an effluent-receiving surface water. Bioassay results indicated that wastewater-derived dissolved organic nitrogen (DON) is not bioavailable to the algae Selenastrum Capricornutum in the absence of bacteria. However, approximately half of the wastewater-derived organic nitrogen was available to the algae in the presence of bacteria during a 2-week incubation. These results suggest that while it is inappropriate to assume that wastewater-derived DON cannot cause cultural eutrophication, it will not cause as much eutrophication as inorganic nitrogen. Additional research is needed to develop methods of minimizing the discharge of bioavailable forms of wastewater-derived organic nitrogen by wastewater treatment plants.

Biological Assay↗

PubMedDate not supplied

The fate of estrogenic hormones in an engineered treatment wetland with dense macrophytes.

Recently, the estrogenic hormones 17beta-estradiol (E2) and 17alpha-ethinyl estradiol (EE2) have been detected in municipal wastewater effluent and surface waters at concentrations sufficient to cause feminization of male fish. To evaluate the fate of steroid hormones in an engineered treatment wetland, lithium chloride, E2, and EE2 were added to a treatment wetland test cell. Comparison of hormone and tracer data indicated that 36% of the E2 and 41% of the EE2 were removed during the cell's 84-h hydraulic retention time (HRT). The observed attenuation was most likely the result of sorption to hydrophobic surfaces in the wetland coupled with biotransformation. Sorption was indicated by the retardation of the hormones relative to the conservative tracer. Biotransformation was indicated by elevated concentrations of the E2 metabolite, estrone. It may be possible to improve the removal efficiency by increasing the HRT or the density of plant materials.

Biodegradation, Environmental↗

PubMedDate not supplied

Sources and fate of nitrosodimethylamine and its precursors in municipal wastewater treatment plants.

To assess the occurrence and fate of nitrosodimethylamine (NDMA) and its precursors in wastewater treatment plants, samples from wastewater treatment plants and industrial sources were analyzed for NDMA, total NDMA precursors, and dimethylamine (DMA). The median concentration of NDMA in untreated wastewater was approximately 80 ng/L, with maximum concentrations up to 790 ng/L presumably occuring because of sources unrelated to domestic wastewater. Concentrations of DMA in untreated wastewater ranged from approximately 50 to 120 microg/L and accounted for a majority of the NDMA precursors. The removal of NDMA during secondary biological treatment exhibited considerable variability, with overall removal ranging from 0 to 75%. In contrast, removal of NDMA precursors and DMA generally exceeded 70%. The median concentration of NDMA in secondary effluent before disinfection was 46 ng/L. Although DMA was removed during secondary treatment, other NDMA precursors in wastewater effluent will result in formation of additional NDMA upon disinfection with chloramines.

Chlorine Compounds↗