Drowning in disinfection byproducts? Assessing swimming pool water

Disinfection is mandatory for swimming pools: public pools are usually disinfected by gaseous chlorine or sodium hypochlorite and cartridge filters; home pools typically use stabilized chlorine. These methods produce a variety of disinfection byproducts (DBPs), such as trihalomethanes (THMs), which are regulated carcinogenic DBPs in drinking water that have been detected in the blood and breath of swimmers and of nonswimmers at indoor pools. Also produced are halogenated acetic acids (HAAs) and haloketones, which irritate the eyes, skin, and mucous membranes; trichloramine, which is linked with swimming-pool-associated asthma; and halogenated derivatives of UV sun screens, some of which show endocrine effects. Precursors of DBPs include human body substances, chemicals used in cosmetics and sun screens, and natural organic matter. Analytical research has focused also on the identification of an additional portion of unknown DBPs using gas chromatography (GC)/mass spectrometry (MS) and liquid chromatography (LC)/MS/MS with derivatization. Children swimmers have an increased risk of developing asthma and infections of the respiratory tract and ear. A 1.6-2.0-fold increased risk for bladder cancer has been associated with swimming or showering/bathing with chlorinated water. Bladder cancer risk from THM exposure (all routes combined) was greatest among those with the GSTT1-1 gene. This suggests a mechanism involving distribution of THMs to the bladder by dermal/inhalation exposure and activation there by GSTT1-1 to mutagens. DBPs may be reduced by engineering and behavioral means, such as applying new oxidation and filtration methods, reducing bromide and iodide in the source water, increasing air circulation in indoor pools, and assuring the cleanliness of swimmers. The positive health effects gained by swimming can be increased by reducing the potential adverse health risks.     

Formation of bromochlorodibenzo-p-dioxins and dibenzofurans from the high-temperature oxidation of a mixture of 2-chlorophenol and 2-bromophenol

The homogeneous, gas-phase oxidative thermal degradation of a 50:50 mixture of 2-bromophenol and 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, with a reaction time of 2.0 s, over a temperature range of 300 to 1000 degrees C. Observed products in order of decreasing yield included the following: dibenzo-p-dioxin (DD), 4-bromo-6-chlorodibenzofuran (4-B,6-CDF), phenol, 4,6-dibromodibenzofuran (4,6-DBDF), 2,6-dibromophenol, 4,6-dichlorodibenzofuran (4,6-DCDF), 2-bromo-4-chlorophenol, 2,4-dibromophenol, 2-chloro-4-bromophenol, 4-monobromodibenzofuran (4-MBDF), 4-monochlorodibenzofuran (4-MCDF), dibenzofuran (DF), 1-monobromodibenzo-p-dioxin (1-MBDD), 1-monochlorodibenzo-p-dioxin (1-MCDD), 2,4,6-tribromophenol, naphthalene, chloronaphthalene, bromonaphthalene, chlorobenzene, bromobenzene, and benzene. The results are compared and contrasted with previous results reported for the oxidations of pure 2-chlorophenol and 2-bromophenol as well as results for the pyrolysis of the mixture of 2-chlorophenol and 2-bromophenol. 4,6-DBDF and 4,6-DCDF were observed in higher yields than under pyrolytic conditions but considerably less than the yields observed for the individual oxidation of 2-chlorophenol and 2-bromophenol. The effect on chlorine and bromine on the concentration of hydroxyl radical is shown to control the dioxin-to-furan ratio.     

Surface-mediated formation of polybrominated dibenzo-p-dioxins and dibenzofurans from the high-temperature pyrolysis of 2-bromophenol on a CuO/silica surface

We studied the surface-mediated pyrolytic thermal degradation of 2-bromophenol, a model brominated hydrocarbon that may form brominated dioxins in combustion and thermal processes, on silica-supported copper oxide in a 1 mm i.d., fused silica flow reactor at a constant concentration of 88 ppm over a temperature range of 250-550 degrees C. Observed products included dibenzo-p-dioxin (DD), 1-monobromodibenzo-p-dioxin (1-MBDD), dibromo-dibenzo-p-dioxin (DBDD),tribromodibenzo-p-dioxin (TrBDD), 4-monobromodibenzofuran (4-MBDF), dibenzofuran (DF), 2,4,6-tribromophenol, 2,4- and 2,6-dibromophenol, and polybrominated benzenes. These results are compared and contrasted with previous work on surface-catalyzed pyrolysis of 2-chlorophenol. Polybrominated dibenzofurans (PBDFs) are formed by the Langmuir-Hinshelwood mechanism, and the formation of polybrominated dibenzo-p-dioxins (PBDDs) is through an Eley-Rideal mechanism. Yields of PBDDs are at least 16x greater for 2-bromophenol than for analogous PCDDs from 2-chlorophenol. Higher yields of polybrominated phenols and polybrominated benzenes are also observed. This can be attributed to the relative ease of bromination over chlorination and the higher concentration of bromine atoms in the 2-bromophenol system versus chlorine atoms for the 2-chlorophenol system.     

溴苯酚对对虾海鲜风味的影响

在水产品的整体可接受性中,风味是十分重要的感官特性。溴苯酚物质是海洋水产品所含有的不同于陆地生物的特有的风味物质,而且在养殖产品中这类风味物质会大量缺失。本文介绍了溴苯酚对对虾海鲜风味的影响、讨论了导致野生品种和养殖品种风味差异的可能原因以及水产品中溴苯酚物质的最新分析方法。     

Mechanisms of dioxin formation from the high-temperature oxidation of 2-bromophenol

The homogeneous, gas-phase oxidative thermal degradation of 2-bromophenol was studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, reaction time of 2.0 s, over a temperature range from 300 to 1000 degrees C. Observed products in order of yield were dibenzo-p-dioxin (DD) > 4,6-dibromodibenzofuran (4,6-DBDF) > 4-monobromodibenzofuran (4-MCDF), dibenzofuran (DF), 1-monobromodibenzo-p-dioxin (1-MBDD), naphthalene, bromonaphthalene, 2,4-dibromophenol, 2,6-dibromophenol, phenol, bromobenzene, and benzene. This result is in contrast to the oxidation of 2-chlorophenol, where the major product is 4,6-dichlorodibenzofuran (4,6-DCDF). 4,6-DBDF was observed in high yields in contrastto our previous results for the pyrolysis of 2-bromophenol, where 4,6-DBDF was not detected. The increase in 4,6-DBDF yields is attributed to hydroxyl radical being the major chain carrier under oxidative conditions, which favors hydrogen-abstraction reactions that lead to formation of 4,6-DBDF. However, DD is still the highest yield product under oxidative conditions because of the relative ease of displacement of Br in the ring-closure reaction.     

Formation of bromochlorodibenzo-p-dioxins and furans from the high-temperature pyrolysis of a 2-chlorophenol/2-bromophenol mixture

The homogeneous, gas-phase pyrolytic thermal degradation of a 50:50 mixture of 2-bromophenol and 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a total concentration of 88 ppm, reaction time of 2.0 s, and temperatures from 300 to 1000 degrees C. Observed products included (in decreasing yield) naphthalene, dibenzo-p-dioxin (DD), phenol, dibenzofuran (DF), bromobenzene, chloronaphthalene, 4-bromo-6-chlorodibenzofuran (4-B,6-CDF), bromonaphthalene, benzene, 4,6-dichlorodibenzofuran (4,6-DCDF), chlorobenzene, 4-monobromodibenzofuran (4-MBDF), 4-monochlorodibenzofuran (4-MCDF), 1-mono-bromodibenzo-p-dioxin (1-MBDD), 2-chloro,4-bromophenol, 2,4-dibromophenol, and 2-bromo-4-chlorophenol. Unlike the case for the pyrolysis of pure 2-chlorophenol, 4,6-DCDF was observed, but the analogous 4,6-DBDF remained undetected similar to the individual results with 2-MBP. This indicates that the presence of bromine increases the concentration of chlorine atoms available for the formation of 4,6-DCDF. Due to bromine atoms acting as better leaving groups than chlorine atoms, the yield of DD was increased over that observed for the pyrolysis of 2-chlorophenol. The addition of bromine to a chlorinated hydrocarbon system results in an increase in the total yield of PCDD/Fs as well as PBDD/Fs and mixed PBCDD/Fs due to the ease of bromine elimination reactions as well as an increase of the chlorine atom concentration.     

Volatile disinfection byproduct formation resulting from chlorination of organic-nitrogen precursors in swimming pools

Clinical studies have documented the promotion of respiratory ailments (e.g., asthma) among swimmers, especially in indoor swimming pools. Most studies of this behavior have identified trichloramine (NCl3) as the causative agent for these respiratory ailments; however, the analytical methods employed in these studies were not suited for identification or quantification of other volatile disinfection byproducts (DPBs) that could also contribute to this process. To address this issue, volatile DBP formation resulting from the chlorination of four model compounds (creatinine, urea, L-histidine, and L-arginine) was investigated over a range of chlorine/precursor (Cl/P) molar ratios. Trichloramine was observed to result from chlorination of all four model organic-nitrogen compounds. In addition to trichloramine, dichloromethylamine (CH3NCl2) was detected in the chlorination of creatinine, while cyanogen chloride (CNCl) and dichoroacetonitrile (CNCHCl2) were identified in the chlorination of L-histidine. Roughly 0.1 mg/L (as Cl2) NCl3, 0.01 mg/L CNCHCl2, and 0.01 mg/L CH3NCl2 were also observed in actual swimming pool water samples. DPD/FAS titration and MIMS (membrane introduction mass spectrometry) were both employed to measure residual chlorine and DBPs. The combined application of these methods allowed for identification of sources of interference in the conventional method (DPD/FAS), as well as structural information about the volatile DBPs that formed. The analysis by MIMS clearly indicates that volatile DBP formation in swimming pools is not limited to inorganic chloramines and haloforms. Additional experimentation allowed for the identification of possible reaction pathways to describe the formation of these DBPs from the precursor compounds used in this study.     

Pyrolysis study of halogen-containing aromatics reflecting reactions with polypropylene in a posttreatment decontamination process

Halogen-containing aromatics, mainly bromine-containing phenols, are harmful compounds contaminating pyrolysis oil from electronic boards containing halogenated flame retardants. In addition,theirformation increases the potential for evolution of polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs) at relatively low temperature (up to 500 degrees C). As a model compound, 2,4-dibromophenol (DBP) was pyrolyzed at 290-450 degrees C. While its pyrolysis in a nitrogen flow reactor or in encapsulated ampules yields bromine-containing phenols, phenoxyphenols, PBDDs, and PBDFs, pyrolysis of DBP in a hydrogen-donating medium of polypropylene (PP) at 290-350 degrees C mainly results in the formation of phenol and HBr, indicating the occurrence of a facile hydrodebromination of DBP. The hydrodebromination efficiency depends on temperature, pressure, and the ratio of the initial components. This thermal behavior of DBP is compared to that of 2,4-dichlorophenol and decabromodiphenyl ether. A treatment of halogen-containing aromatics with PP offers a new perspective on the development of low-environmental-impact disposal processes for electronic scrap.     

Occurrence of a new generation of disinfection byproducts

A survey of disinfection byproduct (DBP) occurrence in the United States was conducted at 12 drinking water treatment plants. In addition to currently regulated DBPs, more than 50 DBPs that rated a high priority for potential toxicity were studied. These priority DBPs included iodinated trihalomethanes (THMs), other halomethanes, a nonregulated haloacid, haloacetonitriles, haloketones, halonitromethanes, haloaldehydes, halogenated furanones, haloamides, and nonhalogenated carbonyls. The purpose of this study was to obtain quantitative occurrence information for new DBPs (beyond those currently regulated and/or studied) for prioritizing future health effects studies. An effort was made to select plants treating water that was high in total organic carbon and/or bromide to enable the detection of priority DBPs that contained bromine and/or iodine. THMs and haloacetic acids (HAAs) represented the two major classes of halogenated DBPs formed on a weight basis. Haloacetaldehydes represented the third major class formed in many of the waters. In addition to obtaining quantitative occurrence data, important new information was discovered or confirmed at full-scale plants on the formation and control of DBPs with alternative disinfectants to chlorine. Although the use of alternative disinfectants (ozone, chlorine dioxide, and chloramines) minimized the formation of the four regulated THMs, trihalogenated HAAs, and total organic halogen (TOX), several priority DBPs were formed at higher levels with the alternative disinfectants as compared with chlorine. For example, the highest levels of iodinated THMs-which are not part of the four regulated THMs-were found at a plant that used chloramination with no prechlorination. The highest concentration of dichloroacetaldehyde was at a plant that used chloramines and ozone; however, this disinfection scheme reduced the formation of trichloroacetaldehyde. Preozonation was found to increase the formation of trihalonitromethanes. In addition to the chlorinated furanones that have been measured previously, brominated furanones-which have seldom been analyzed-were detected, especially in high-bromide waters. The presence of bromide resulted in a shift to the formation of other bromine-containing DBPs not normally measured (e.g., brominated ketones, acetaldehydes, nitromethanes, acetamides). Collectively, -30 and 39% of the TOX and total organic bromine, respectively, were accounted for (on a median basis) bythe sum of the measured halogenated DBPs. In addition, 28 new, previously unidentified DBPs were detected.These included brominated and iodinated haloacids, a brominated ketone, and chlorinated and iodinated aldehydes.     

Tribromopyrrole,brominated acids,and other disinfection byproducts produced by disinfection of drinking water rich in bromide

Using gas chromatography/mass spectrometry (GC/MS), we investigated the formation of disinfection byproducts (DBPs) from high bromide waters (2 mg/L) treated with chlorine or chlorine dioxide used in combination with chlorine and chloramines. This study represents the first comprehensive investigation of DBPs formed by chlorine dioxide under high bromide conditions. Drinking water from full-scale treatment plants in Israel was studied, along with source water (Sea of Galilee) treated under carefully controlled laboratory conditions. Select DBPs (trihalomethanes, haloacetic acids, aldehydes, chlorite, chlorate, and bromate) were quantified. Many of the DBPs identified have not been previously reported, and several of the identifications were confirmed through the analysis of authentic standards. Elevated bromide levels in the source water caused a significant shift in speciation to bromine-containing DBPs; bromoform and dibromoacetic acid were the dominant DBPs observed, with very few chlorine-containing compounds found. Iodo-trihalomethanes were also identified, as well as a number of new brominated carboxylic acids and 2,3,5-tribromopyrrole, which represents the first time a halogenated pyrrole has been reported as a DBP. Most of the bromine-containing DBPs were formed during pre-chlorination at the initial reservoir, and were not formed by chlorine dioxide itself. An exception wasthe iodo-THMs, which appeared to be formed by a combination of chlorine dioxide with chloramines or chlorine (either added deliberately or as an impurity in the chlorine dioxide). A separate laboratory study was also conducted to quantitatively determine the contribution of fulvic acids and humic acids (from isolated natural organic matter in the Sea of Galilee) as precursor material to several of the DBPs identified. Results showed that fulvic acid plays a greater role in the formation of THMs, haloacetic acids, and aldehydes, but 2,3,5-tribromopyrrole was produced primarily from humic acid. Because this was the first time a halopyrrole has been identified as a DBP, 2,3,5-tribromopyrrole was tested for mammalian cell cytotoxicity and genotoxicity. In comparison to other DBPs, 2,3,5-tribromopyrrole was 8x, 4.5x, and 16x more cytotoxic than dibromoacetic acid, 3-chloro-4-(dichloromethyl)-5-hydroxy-2-[5H]-furanone [MX], and potassium bromate, respectively. 2,3,5-Tribromopyrrole also induced acute genomic damage, with a genotoxic potency (299 microM) similar to that of MX.     

Microbial O-methylation of the flame retardant tetrabromobisphenol-A

We demonstrated the O-methylation of tetrabromobisphenol-A (TBBPA) [4,4'-isopropylidenebis (2,6-dibromophenol)] to its mono- and dimethyl ether derivatives by microorganisms present in different sediments. A most probable number assay of a marsh sediment suggested that up to 10% of the total aerobic heterotrophs may be capable of O-methylation. Although TBBPA dimethyl ether is not produced in industry, it has been detected in terrestrial and aquatic sediments. Our study supports the hypothesis that TBBPA dimethyl ether is a product of microbial O-methylation. The O-methylation of TBBPA, as well as its analog, tetrachlorobisphenol-A (TCBPA), was also demonstrated in cultures of two chlorophenol-metabolizing bacteria, Mycobacterium fortuitum CG-2 and Mycobacterium chlorophenolicum PCP-1. These strains also mediated the O-methylation of 2,6-dibromophenol and 2,6-dichlorophenol, analogs of TBBPA and TCBPA, to their corresponding anisoles, but 2,6-fluorophenol was not transformed. Due to the addition of hydrophobic methyl groups, O-methylated derivatives are more lipophilic, increasing the probability of bioaccumulation in the food chain. Future research regarding the toxicological effects of the O-methylated derivatives of TBBPA is recommended and will further elucidate potential risks to environmental and human health.     

Alveolar air and urine analyses as biomarkers of exposure to trihalomethanes in an indoor swimming pool

The exposure of workers and swimmers at an indoor swimming pool to trihalomethanes (THMs) as a consequence of water chlorination was evaluated by analyzing alveolar air and urine samples. Environmental monitoring of THMs in water and ambient air was also performed in order to assess the possible correlation between environmental and biological samples. The sampling was done concurrently, taking the urine and alveolar air samples before and after the work shift for 15 workers and the swimming activity for 12 swimmers. A high THM uptake was observed in alveolar air and urine of subjects exposed, with chloroform being the most abundant THM. Mean chloroform levels in alveolar air and urine before exposure were 4 microg/ m3 and 475 ng/L, respectively. After 2 h of exposure, concentration increases of ca. 8 times in alveolar air and 2 times in urine were observed in workers. After 1 h swimming, the increases found in swimmers were ca. 20 and 3 times in alveolar air and urine, respectively. High increases have also been observed in bromodichloromethane levels. We have obtained excellent correlations between the chloroform concentrations found in the swimming pool ambient air/alveolar air, and between the urine/ alveolar air of the participants after exposure (r > 0.9). In conclusion, alveolar air provides better response sensitivity and shorter reaction time to external exposure than urine, being therefore the most sensitive biomarker.     

Assessment of exposure of workers and swimmers to trihalomethanes in an indoor swimming pool

A simultaneous study on workers' and swimmers' exposure to trihalomethanes (THMs) in an indoor swimming pool has been carried out by analyzing urine samples using the headspace and gas chromatography-mass spectrometry technique. The subjects of this study were male and female workers of an indoor swimming pool as well as swimmers regularly attending the pool. The results reported show that only chloroform and bromodichloromethane were detected in the urine of those people exposed, which can be used as a specific index of exposure to these compounds. THM uptake of swimmers after 1 h of swimming was higher than that of workers after a 4 h work shift since THM levels in the workers' urine were associated only with inhalation, while levels in swimmers' urine were mainly associated with dermal absorption, apart from inhalation and occasional ingestion, as well as increased uptake due to the physical stress (swimming). The kinetics of THM excretion in the urine of the participants exposed has been calculated after termination of the exposure to select the sampling time and determine the elimination process. An interval of 15 min after exposure was selected as the sampling time, and the absorbed dosage was eliminated by 2 h after exposure. A good correlation between THM concentrations found in the swimming pool water and the urinary THM concentrations of the people affected after exposure has also been obtained.     

Mechanisms of dioxin formation from the high-temperature pyrolysis of 2-bromophenol

Brominated hydrocarbons are the most commonly used flame retardants. Materials containing brominated hydrocarbons are frequently disposed in municipal and hazardous waste incinerators as well as being subjected to thermal reaction in accidental fires. This results in the potential for formation of brominated dioxins and other hazardous combustion byproducts. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. As a model brominated hydrocarbon that may form brominated dioxins, we studied the homogeneous, gas-phase pyrolytic thermal degradation of 2-bromophenol in a 1-cm i.d., fused-silica flow reactor at a concentration of 90 ppm, with a reaction time of 2.0 s, and over a temperature range of 300 to 1000 degrees C. Observed products included dibenzo-p-dioxin (DD), 1-monobromodibenzo-p-dioxin (1-MBDD), 4-monobromodibenzofuran (4-MBDF), dibenzofuran (DF), naphthalene, bromonaphthalene, 2,4- and 2,6-dibromophenol, phenol, bromobenzene, and benzene. These results are compared and contrasted with previous results reported for 2-chlorophenol. At temperatures lower than 700 degrees C, formation of 2-bromophenoxyl radical, which decomposes through CO elimination to form a bromocyclopentadienyl radical, forms naphthalene and 2-bromonaphthalene through radical recombination/rearrangement reactions. However, unlike the results for 2-chlorophenol, where naphthalene is the major product, DD becomes the major product for the pyrolysis of 2-bromophenol. The formation of DD and 1-MBDD are attributed to radical-radical reactions involving 2-bromophenoxyl radical with the carbon- (bromine) centered radical and the carbon- (hydrogen) centered radical mesomers of 2-bromophenoxyl radical, respectively. The potential product, 4,6-dibromodibenzofuran (4,6-DBDF) for which the analogous product, 4,6-dichlorodibenzofuran (4,6 DCDF), was observed in the oxidation of 2-chlorophenol, was not detected. This is attributed to the pyrolytic conditions of our experiments (e.g., shorter reaction times and higher temperatures) that favor reaction intermediates that form DD and 1-MBDD.     

Cobalt-mediated activation of peroxymonosulfate and sulfate radical attack on phenolic compounds. implications of chloride ions

The sulfate radical pathway of the room-temperature degradation of two phenolic compounds in water is reported in this study. The sulfate radicals were produced by the cobalt-mediated decomposition of peroxymonosulfate (Oxone) in an aqueous homogeneous system. The major intermediates formed from the transformation of 2,4-dichlorophenol were 2,4,6-trichlorophenol, 2,3,5,6-tetrachloro-1,4-benzenediol, 1,1,3,3-tetrachloroacetone, pentachloroacetone, and carbon tetrachloride. Those resulting from the transformation of phenol in the presence of chloride ion were 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 1,1,3,3-tetrachloroacetone, and pentachloroacetone. In the absence of chloride ion, phenol transformed into 2,5-cyclohexadiene-1,4-dione (quinone), 1,2-benzenediol (catechol), and 1,4-benzenediol (hydroquinone). Several parameters were varied, and their impact on the transformation of the organic compounds is also discussed. The parameters varied were the initial concentration of the organic substrate, the dose of Oxone used, the cobalt counteranion, and in particular the impact of chloride ions and the quenching agent utilized for terminating the reaction. This is one of the very few studies dealing with intermediates formed via sulfate radical attack on phenolic compounds. It is also the first studythat explores the sulfate radical mechanism of oxidation, when sulfate radicals are generated via the Co/Oxone reagent. Furthermore, it provides strong evidence on the interaction of chloride ions with sulfate radicals leading to halogenation of organics in water.     

游泳池池水高温天气管理的研究

在高温天气下，游泳人数剧增，游泳池池水容易变质，为了保障游泳者的身体健康，节约水资源，本文提出了效果好、经济、简单易行的池水管理方法。     

Electrochemical hydrodehalogenation of 2,4-dibromophenolin paraffin oil using a solid polymer electrolyte reactor

A new technology for remediation of halogenated organics-oil systems, which can cause serious environmental problems, has been demonstrated using the electrochemical hydrodehalogenation of 2,4-dibromophenol (DBP) in paraffin oil in a solid polymer electrolyte reactor. The reactor has been evaluated in terms of cathode materials and structure and the ratio of the cathode surface area to the solution volume. A cathode of titanium minimesh with a palladium electrocatalyst produced by electrodeposition was particularly effective. Current efficiencies of up to 85% and percentage of DBP removal of up to 62%, space-time yields of up to 7.6 kg DBP m(-3) h(-1), and energy consumption as low as 1.6 kW h (kg of DBP)(-1) were achieved. The reactor showed stable operation for periods of up to 170 h. The results demonstrated that electroreduction could be an alternative technology to electrooxidation forthe treatment of wastes and toxic halogenated compounds, making the process simpler in comparison to electrooxidation.     

Formation of chloroform and chlorinated organics by free-chlorine-mediated oxidation of triclosan

The widely used antimicrobial agent triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) readily reacts with free chlorine under drinking water treatment conditions. Overall second-order kinetics were observed, first-order in free chlorine and first-order in triclosan. Over the pH range of 4-11.5, the kinetics were pH sensitive as a result of the pH dependent speciation of both triclosan and free chlorine. Using a Marquardt-Levenberg routine, it was determined that this pH effect indicates that the dominant reaction in this system is between the ionized phenolate form of triclosan and hypochlorous acid (HOCl). The overall second-order rate coefficient was determined to be kArO- = 5.40 (+/- 1.82) x 10(3) M(-1) s(-1). Three chlorophenoxyphenols and two chlorophenols were identified by gas chromatographic-mass spectroscopic analysis. The chlorophenoxyphenol compounds include two monochlorinated triclosan derivatives (5,6-dichloro-2-(2,4-dichlorophenoy)phenol and 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol) and one dichlorinated derivative (4,5,6-trichloro-(2,4-dichlorophenoxy)phenol); these species form via bimolecular electrophilic substitution of triclosan. 2,4-Dichlorophenol was detected under all reaction conditions and forms via ether cleavage of triclosan. In experiments with excess free chlorine, 2,4,6-trichlorophenol was formed via electrophilic substitution of 2,4-dichlorophenol. Chloroform formation was observed when an excess of free chlorine was present. A Hammett-type linear free-energy relationship (LFER) using Brown-Okamoto parameters (sigma+) was established to correlate the reactivity of HOCI and the phenolate forms of triclosan and other chlorophenols (log kArO- = -(10.7 +/- 2.2)Sigmasigma(+)o,m,p + 4.43). This LFER was used to obtain estimates of rate coefficients describing the reactivity of the intermediates 5,6-dichloro-2-(2,4-dichlorophenoy)phenol (kArO- approximately equal to 6 x 10(2)), 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol (kArO- approximately equal to 3 x 10(2)), and 4,5,6-trichloro-(2,4-dichlorophenoxy)phenol (kArO- approximately equal to 4 x 10(1)).     

Anaerobic biotransformation of tetrabromobisphenol A, tetrachlorobisphenol A, and bisphenol A in estuarine sediments

Biotransformation of the flame retardants tetrabromobisphenol A and tetrachlorobisphenol A, and their ultimate biodehalogenation product, bisphenol A, was examined in anoxic estuarine sediments. Dehalogenation of tetrabromobisphenol A and tetrachlorobisphenol A was examined under conditions promoting either methanogenesis or sulfate reduction as the primary terminal electron-accepting process. Complete dehalogenation of tetrabromobisphenol A to bisphenol A with no further degradation of bisphenol A, was observed under both methanogenic and sulfate-reducing conditions. Dehalogenation of tetrachlorobisphenol A under both methanogenic and sulfate-reducing conditions resulted in the accumulation of a persistent dichlorinated bisphenol A isomer, while no bisphenol A was formed. Co-amendment of sediment enrichments with either 2,6-dibromo- or 2,6-dichlorophenol did not affect the extent of dehalogenation as compared to sediments that were amended only with the flame retardants. Sediment cultures pre-acclimated on 2-bromophenol dehalogenated the flame retardants in a manner similar to that of fresh sediments. No loss of bisphenol A was observed in separate incubations within 162 days under conditions promoting either methanogenesis, sulfate-reduction, iron(III)-reduction, or nitrate-reduction. Furthermore, identical enrichments that readily degraded 4-hydroxybenzoate, a structural analogue of bisphenol A, did not exhibit bisphenol A degradation. The dehalogenation of tetrabromo- and tetrachlorobisphenol A and the potential for accumulation of bisphenol A in anoxic sediments is significant given the widespread use of these chemicals.     

Chemotherapy of fascioliasis. 3. Amides derived from 4-cyano-2-iodo-6-nitrophenol (nitroxynil) and 2,6-di-iodo-4-nitrophenol (disophenol)

Amides have been prepared utilising 4-hydroxy-3-iodo-5-nitrobenzoic acid or 5-cyano-2-hydroxy-3-iodoaniline, the acid and amine respectively corresponding to 4-cyano-2-iodo-6-nitrophenol (nitroxynil). Analogous anilides were made from 3,5-di-iodo-4-hydroxybenzoic acid or 4-amino-2,6-di-iodophenol which bear a similar relationship to 2,6-di-iodo-4-nitrophenol (disophenol). None of the products was useful against Fasciola hepatica infections.