Individual Trihalomethanes Research Articles

A comparison of the role of two blue–green algae in THM and HAA formation

The contribution of two blue–green algae species, Anabaena flos-aquae and Microcystis aeruginosa, to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) was investigated. The experiments examined the formation potential of these disinfection by-products (DBPs) from both algae cells and extracellular organic matter (EOM) during four algal growth phases. Algal cells and EOM of Anabaena and Microcystis exhibited a high potential for DBP formation. Yields of total THMs (TTHM) and total HAAs (THAA) were closely related to the growth phase. Reactivity of EOM from Anabaena was slightly higher than corresponding cells, while the opposite result was found for Microcystis. Specific DBP yields (yield/unit C) of Anabaena were in the range of 2–11 μmol/mmol C for TTHM and 2–17 μmol/mmol C for THAA, while those of Microcystis were slightly higher. With regard to the distributions of individual THM and HAA compounds, differences were observed between the algae species and also between cells and EOM. The presence of bromide shifted the dominant compounds from HAAs to THMs.

Risk of Birth Defects in Australian Communities with High Levels of Brominated Disinfection By-products

BackgroundBy international standards, water supplies in Perth, Western Australia, contain high trihalomethane (THM) levels, particularly the brominated forms. Geographic variability in these levels provided an opportunity to examine cross-city spatial relationships between THM exposure and rates of birth defects (BDs).ObjectivesOur goal was to examine BD rates by exposure to THMs with a highly brominated fraction in metropolitan locations in Perth, Western Australia.MethodsWe collected water samples from 47 separate locations and analyzed them for total and individual THM concentrations (micrograms per liter), including separation into brominated forms. We classified collection areas by total THM (TTHM) concentration: low (< 60 μg/L), medium (> 60 to < 130 μg/L), and high (≥ 130 μg/L). We also obtained deidentified registry-based data on total births and BDs (2000–2004 inclusive) from post codes corresponding to water sample collection sites and used binomial logistic regression to compare the frequency of BDs aggregately and separately for the TTHM exposure groups, adjusting for maternal age and socioeconomic status.ResultsTotal THMs ranged from 36 to 190 μg/L. A high proportion of the THMs were brominated (on average, 92%). Women living in high-TTHM areas showed an increased risk of any BD [odds ratio (OR) = 1.22; 95% confidence interval (CI), 1.01–1.48] and for the major category of any cardiovascular BD (OR = 1.62; 95% CI, 1.04–2.51), compared with women living in low-TTHM areas.ConclusionsBrominated forms constituted the significant fraction of THMs in all areas. Small but statistically significant increases in risks of BDs were associated with residence in areas with high THMs.

Effect of bromide ion on isolated fractions of dissolved organic matter in secondary effluent during chlorination

The role of bromide ion in the trihalomethane (THM) formation and structure of dissolved organic matter (DOM) during chlorination of the secondary effluent taken from the Wenchang Wastewater Treatment Plant (Harbin, China) was investigated. DOM was fractionated using XAD resins into five fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). The patterns of individual THM species with increased bromide concentrations were similar for all DOM fractions. The THM speciation as well as halogen fraction for these five fractions followed similar trends with the Br −/Cl 2 ratio. Chlorination resulted in decreased ultraviolet (UV) absorbance across wavelengths from 250 to 280 nm for DOM fractions whether bromide ions existed or not, and bromide addition led to lower differential UV absorbance values. Fourier-transform infrared (FT-IR) results indicated that chlorination, whether bromide ions existed or not, resulted in the near elimination of aromatic C H and amide peaks, increased C O absorption intensity and occurrence of C O and C Cl peaks for HPO-A, HPO-N, TPI-A and TPI-N. Furthermore, bromide addition in chlorination led to the occurrence of C Br peak for all four fractions.

Chemometric modeling and prediction of trihalomethane formation in Barcelona's water works plant

Formation and occurrence of trihalomethanes ( CHCl 3 , CHBr 3 , CHCl 2 Br , and CHBr 2 Cl ) are investigated in water chlorination disinfection processes in the Barcelona's water works plant (WWP). Twenty-three WWP variables were measured and investigated for correlation with trihalomethane formation. Multivariate statistical methods including principal component analysis (PCA), multilinear regression (MLR), stepwise MLR (SWR), principal component regression (PCR) and partial least squares regression (PLSR) have been used and compared to model and predict the complex behavior observed for the measured trihalomethane concentrations. The results, obtained by PCA as well as the evaluation of the statistical significance of the coefficients in the linear regression vectors, revealed that the most important WWP variables for trihalomethane formation were: water temperature, total organic carbon, added chlorine concentrations, UV absorbance and turbidity at different sites of the WWP, as well as other variables like wells supply flow levels and carbon filters age. Overall, MLR and PLSR methods performed the best and gave similar good predictive properties. Best results were obtained for the total sum of trihalomethane concentrations, TTHM, with average modeling and prediction relative errors of 12% and 16%, respectively. Among the individual trihalomethanes, the concentrations of CHBr 3 were the worst predicted ones with average modeling and prediction relative errors between 21–25% and 29–31%, respectively, followed by CHCl 2 Br with 23–26% and 25–27%. Better predictions were obtained for the concentrations of CHBr 2 Cl with relative modeling and prediction errors varying between 14–17% and 21%, and for the concentrations of CHCl 3 with 21–24% and 23–25% errors, respectively.

Cometabolism of trihalomethanes by mixed culture nitrifiers

Three mixed-culture nitrifier sources degraded low concentrations (25–450 μg/L) of four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Individual THM rate constants ( k 1 THM ) increased with increasing THM bromine-substitution with TBM>DBCM>BDCM>TCM and were comparable to previous studies with the pure culture nitrifier, Nitrosomonas europaea. A decrease in temperature resulted in a decrease in both ammonia and THM degradation rates with ammonia rates affected to a greater extent than THM degradation rates. The significant effect of temperature indicates that seasonal variations in water temperature should be a consideration for technology implementation. Product toxicity, measured by transformation capacity ( T c), was similar to that observed with N. europaea. Because both rate constants and product toxicities increase with increasing THM bromine-substitution, a water's THM speciation is an important consideration for process implementation during drinking water treatment. Even though a given water is kinetically favored, the resulting THM product toxicity may not allow stable treatment process performance.

Cometabolism of Trihalomethanes by Nitrosomonas europaea

The ammonia-oxidizing bacterium Nitrosomonas europaea (ATCC 19718) was shown to degrade low concentrations (50 to 800 mug/liter) of the four trihalomethanes (trichloromethane [TCM], or chloroform; bromodichloromethane [BDCM]; dibromochloromethane [DBCM]; and tribromomethane [TBM], or bromoform) commonly found in treated drinking water. Individual trihalomethane (THM) rate constants (k1THM) increased with increasing THM bromine substitution, with TBM > DBCM > BDCM > TCM (0.23, 0.20, 0.15, and 0.10 liters/mg/day, respectively). Degradation kinetics were best described by a reductant model that accounted for two limiting reactants, THMs and ammonia-nitrogen (NH3-N). A decrease in the temperature resulted in a decrease in both ammonia and THM degradation rates with ammonia rates affected to a greater extent than THM degradation rates. Similarly to the THM degradation rates, product toxicity, measured by transformation capacity (Tc), increased with increasing THM bromine substitution. Because both the rate constants and product toxicities increase with increasing THM bromine substitution, a water's THM speciation will be an important consideration for process implementation during drinking water treatment. Even though a given water sample may be kinetically favored based on THM speciation, the resulting THM product toxicity may not allow stable treatment process performance.

Application of oxidative removal of NOM to drinking water and formation of disinfection by-products

Water samples of different origins (Buyukcekmece and Omerli, Istanbul, Turkey, and Alento, Salerno, Italy) were treated by coagulation, ozonation, and coagulation followed by ozonation and photocatalysis. Disinfection by-products (DBPs) formation potential of raw and treated water samples was compared in relation to removal efficiencies by the respective treatment methods. The major DBPs, namely trihalomethanes (THMs) and haloacetic acids (HAAs), and other DBPs were identified and quantified. Besides major THMs and HAAs, the presence of bromoform in high amounts was also detected due to the high levels of bromide ions in raw Buyukcekmece and Omerli water samples. Depending on the natural organic matter (NOM) removal efficiencies of each treatment process, the distribution of individual THMs and HAAs was found to be NOM-site specific. Other DBPs were also detected and chloral hydrate (C 2H 3Cl 3O 2) was found in significant amounts. The responsible precursor sites could only be reduced by photocatalytic treatment of NOM.

RELATION OF INDIVIDUAL TRIHALOMETHANE CONCENTRATIONS IN PUBLIC WATER SUPPLIES TO STILLBIRTH AND BIRTH WEIGHT PREVALENCE IN THREE WATER REGIONS

ISEE-242 Introduction: This study, in three water regions, is the largest yet conducted of the association between disinfection by-products in the public water supply, as measured by individual trihalomethanes (THMs), and stillbirth and birth weight prevalence. Methods: Modelled estimates of quarterly individual THM concentrations in water zones by year, categorised as low (for chloroform, >20 μg/l; for bromodichloromethane (BDCM) and total brominated THMs (TBTHM), >6 μg/l), medium (for chloroform, 20–40 μg/l; for BDCM and TBTHM, 6–12 μg/l) or high (for chloroform, <40 μg/l; for BDCM and TBTHM, <12 μg/l), were linked to 1,015,298 routine birth and still birth records using maternal residence at time of birth through the use of Geographical Information Systems. Results: In one region, a trend of increasing prevalence of stillbirth and low and very low birth weight from low to medium to high chloroform exposure areas was observed — for example, with adjustment for potential confounders including maternal age and social deprivation, risks of stillbirth and low birth weight in high chloroform compared with low chloroform exposure areas were 1.15 (95% CI 1.01 to 1.32) and 1.17 (95% CI 1.13 to 1.22) respectively. There was no significant relation between chloroform and excess adverse birth outcomes in the other regions. In a meta-analysis across the three regions, small, but significant, excess risks were found in areas with high chloroform concentrations for both stillbirths (OR 1.12; 95% CI 1.02 to 1.23) and low birth weight (OR 1.10; 95% CI 1.07 to 1.13); no associations were found with very low birth weight. Concentrations of BDCM and TBTHMs did not show any significant association with risk of stillbirths, low and very low birth weight in all three regions separately and combined. Analysis of stillbirth risk associated with specific THMs was also conducted by cause-of-death sub-category. Discussion: These findings suggest a need to focus on specific individual (as opposed to total) THMs and/or other disinfection by-products in relation to stillbirth and low birth weight risk. This type of focused research, which is very under-developed at present, informs cross-study comparisons and helps to refine risk estimates in order to differentiate between possible causal and alternative (non-causal) explanations.

Analysis of in vivo and in vitro DNA strand breaks from trihalomethane exposure

BackgroundEpidemiological studies have linked the consumption of chlorinated surface waters to an increased risk of two major causes of human mortality, colorectal and bladder cancer. Trihalomethanes (THMs) are by-products formed when chlorine is used to disinfect drinking water. The purpose of this study was to examine the ability of the THMs, trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and tribromomethane (TBM), to induce DNA strand breaks (SB) in (1) CCRF-CEM human lymphoblastic leukemia cells, (2) primary rat hepatocytes (PRH) exposed in vitro, and (3) rats exposed by gavage or drinking water.MethodsDNA SB were measured by the DNA alkaline unwinding assay (DAUA). CCRF-CEM cells were exposed to individual THMs for 2 hr. Half of the cells were immediately analyzed for DNA SB and half were transferred into fresh culture medium and incubated for an additional 22 hr before testing for DNA SB. PRH were exposed to individual THMs for 4 hr then assayed for DNA SB. F344/N rats were exposed to individual THMs for 4 hr, 2 weeks, and to BDCM for 5 wk then tested for DNA SB.ResultsCCRF-CEM cells exposed to 5- or 10-mM brominated THMs for 2 hr produced DNA SB. The order of activity was TBM>DBCM>BDCM; TCM was inactive. Following a 22-hr recovery period, all groups had fewer SB except 10-mM DBCM and 1-mM TBM. CCRF-CEM cells were found to be positive for the GSTT1-1 gene, however no activity was detected. No DNA SB, unassociated with cytotoxicity, were observed in PRH or F344/N rats exposed to individual THMs.ConclusionCCRF-CEM cells exposed to the brominated THMs at 5 or 10 mM for 2 hr showed a significant increase in DNA SB when compared to control cells. Additionally, CCRF-CEM cells exposed to DBCM and TBM appeared to have compromised DNA repair capacity as demonstrated by an increased amount of DNA SB at 22 hr following exposure. CCRF-CEM cells were found to be positive for the GSTT1-1 gene, however no activity was detected. No DNA SB were observed in PRH or F344/N rats exposed to individual THMs.

Trihalomethane levels in home tap water and semen quality.

Trihalomethanes (THMs) are byproducts of drinking water chlorination whose effects on semen quality have not been previously studied in humans. We examined the relationship of THMs to semen quality in 157 healthy men from couples without known risk factors for infertility. Total THM (TTHM) levels were assigned based on water utility measurements taken during the 90 days preceding semen collection. We analyzed continuous semen parameters in relation to total and individual THMs, adjusting for potential confounders by using repeated measures analyses. TTHM level was not associated with decrements in semen quality. Percent normal morphology decreased and percent head defects increased at higher levels of an ingestion metric (TTHM multiplied by cold home tap water consumption). At the highest level of the ingestion metric (>160 mug/L x glasses/day, which is equivalent to >2 glasses/day of water containing 80 mug/L) we observed a difference of -7.1 (95% confidence interval = -12.7 to -1.6) for percent morphologically normal sperm compared with the lowest level (</= 40 mug/L x glasses/day). Of the individual THMs, bromodichloromethane exposure was inversely related to linearity (a motility parameter); we observed a small decrease (beta = -0.09, SE 0.04) for every unit increase in bromodichloromethane. Although our study had a limited exposure assessment and a selective sample, our results suggest the need for further study of the effects of THMs on semen quality.

CHLORINATION DISINFECTION BY-PRODUCTS AND ADVERSE BIRTH OUTCOMES

Recent epidemiological studies of the relationship between disinfection by-products (DBPs), from chlorination, in public drinking water supply and adverse birth outcomes, have reported inconsistent and inconclusive findings. We report here on the largest study to date to examine the relationship of total trihalomethanes (TTHMs) and the individual trihalomethanes (THMs) to birth weight and still birth prevalence, between 1993 and 1998, for regions covered by three water companies in England. Initial results from this ongoing study using modelled annual TTHM estimates were found to differ between each of the three water supply areas. There was some evidence of confounding by social deprivation and ethnicity, which was further explored by analysis of information on the lifestyle characteristics of all women of reproductive age in the study regions from National survey data. Here, we report on the next stage of the study using modelled quarterly (3 monthly) estimates of the individual THMs in water zones. We modelled THM measurements using a Bayesian hierarchical mixture model, taking into account heterogeneity in THM levels between water originating from different source types (e.g. ground, lowland surface or upland surface), quarterly variation in THM levels and uncertainty in the true value of undetected and rounded measurements. These modelled estimates were linked using Geographical Information Systems to routine birth and stillbirth records based on location of maternal residence at the time of birth to obtain a weighted third trimester exposure estimate for each birth. Exposure categories were constructed as follows: for chloroform (low ( 40 mg/l), bromodichloromethane (low ( 12 mg/l), dibromoehloromethane (low ( 5 mg/l) and total brominated compounds low ( 12 mg/l) respectively. After exclusion of multiple births and births from water zones without valid THM data, we studied a total of 934,843 live and stillbirths. Exposure-response relationships were explored using multiple logistic regression analysis with weighted third trimester individual THM estimates and adjustment for e.g. gender, maternal age and deprivation. Analysis of the individual THMs, as opposed to TTHMs. is essential to characterise more precisely the effects of complex mixtures of DBPs on the developing foctus, and refine our understanding of this important area of research.

Chlorination by-products in drinking water and menstrual cycle function.

We analyzed data from a prospective study of menstrual cycle function and early pregnancy loss to explore further the effects of trihalomethanes (THM) on reproductive end points. Premenopausal women ((italic)n(/italic) = 403) collected urine samples daily during an average of 5.6 cycles for measurement of steroid metabolites that were used to define menstrual parameters such as cycle and phase length. Women were asked about consumption of various types of water as well as other habits and demographics. A THM level was estimated for each cycle based on residence and quarterly measurements made by water utilities during a 90-day period beginning 60 days before the cycle start date. We found a monotonic decrease in mean cycle length with increasing total THM (TTHM) level; at > 60 microg/L, the adjusted decrement was 1.1 days [95% confidence interval (CI), -1.8 to -0.40], compared with less than or equal to 40 microg/L. This finding was also reflected as a reduced follicular phase length (difference -0.94 day; 95% CI, -1.6 to -0.24). A decrement in cycle and follicular phase length of 0.18 days (95% CI, -0.29 to -0.07) per 10 microg/L unit increase in TTHM concentration was found. There was little association with luteal phase length, menses length, or cycle variability. Examining the individual THMs by quartile, we found the greatest association with chlorodibromomethane or the sum of the brominated compounds. Incorporating tap water consumption showed a similar pattern of reduced cycle length with increasing TTHM exposure. These findings suggest that THM exposure may affect ovarian function and should be confirmed in other studies.

Trihalomethane exposures from municipal water supplies and selected congenital malformations.

Concerns about potential health effects of trihalomethanes (THMs) have prompted investigations on whether infants whose mothers were periconceptionally exposed to drinking water containing THMs are at greater risk of congenital malformations. We used two large case-control maternal interview studies that were conducted among California deliveries from 1987 through 1991. One study comprised 538 infants/fetuses with neural tube defects (NTDs) and 539 nonmalformed control infants. The second study included an additional 265 infants with NTDs, 207 infants with conotruncal heart defects, 409 infants with orofacial clefts, and 481 control infants. Expert personnel from municipal water companies estimated THM levels for a particular residence and specific periconceptional time period using quarterly monitoring measurements. Estimates were also made for four individual THM levels and for the total THM level. NTD risk in the first study was inversely associated with total THM exposure. Although the second study did not show the same inverse relationship for NTDs, there were no positive associations of NTDs or the other malformations with total THM as estimated from continuous models. Elevated risks were observed for the lowest category of exposure (1-24 ppb), but risks were either not substantially elevated or were imprecise for higher exposure levels. Thus no evidence was observed for an exposure-response relation. Our results do not provide a clear pattern of association between THM exposure and risks of specific congenital malformations. Imprecise exposure measures coupled with a lack of information about other possible sources of THM exposure may have caused associations to be underestimated.

Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters.

The formation and speciation of disinfection byproducts (DBPs) resulting from chlorination of nanofilter permeates obtained from various source water locations and membrane types are examined. Specific ultraviolet absorbance and bromide utilization are shown to decrease following nanofiltration. Both dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm were found to correlate strongly with trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) concentrations in chlorinated nanofilter permeates, suggesting that they can be employed as surrogates for DBPs in nanofiltered waters. Because smooth curves were obtained for individual THM and HAA species as well as bromine and chlorine incorporation into THMs and HAAs as a function of Br-/DOC molar ratio, it is likely that mole fractions of these DBPs are more strongly influenced by chlorination conditions, Br-, and DOC concentrations than NOM source and membrane type. Mole fractions of mono-, di-, and trihalogenated HAAs were found to be independent of Br-/DOC. Even at a very low Br-/DOC of 2.9microM/mM, the mixed bromochloro- and tribromoacetic acids constituted 20% of total HAAs on a molar basis. This increased to approximately 50% as Br-/DOC increased to approximately 25microM/mM or more, proving that a large fraction of HAAs may not be covered under existing federal regulations. Total THM and HAA9 concentrations decreased in permeate waters with increasing Br-/DOC suggesting that nanofilter permeates are limited with respect to DBP precursors.

Use of routinely collected data on trihalomethane in drinking water for epidemiological purposes

OBJECTIVESTo explore the use of routinely collected trihalomethane (THM) measurements for epidemiological studies. Recently there has been interest in the relation between byproducts of disinfection of public drinking water and...

Assessing exposure to disinfection by-products in women of reproductive age living in Corpus Christi, Texas, and Cobb county, Georgia: descriptive results and methods.

We conducted a field study in Corpus Christi, Texas, and Cobb County, Georgia, to evaluate exposure measures for disinfection by-products, with special emphasis on trihalomethanes (THMs). Participants were mothers living in either geographic area who had given birth to healthy infants from June 1998 through May 1999. We assessed exposure by sampling blood and water and obtaining information about water use habits and tap water characteristics. Two 10-mL whole blood samples were collected from each participant before and immediately after her shower. Levels of individual THM species (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) were measured in whole blood [parts per trillion (pptr)] and in water samples (parts per billion). In the Corpus Christi water samples, brominated compounds accounted for 71% of the total THM concentration by weight; in Cobb County, chloroform accounted for 88%. Significant differences in blood THM levels were observed between study locations. For example, the median baseline blood level of bromoform was 0.3 pptr and 3.5 pptr for participants in Cobb County and Corpus Christi, respectively (p = 0.0001). Differences were most striking in blood obtained after showering. For bromoform, the median blood levels were 0.5 pptr and 17 pptr for participants in Cobb County and Corpus Christi, respectively (p = 0.0001). These results suggest that blood levels of THM species vary substantially across populations, depending on both water quality characteristics and water use activities. Such variation has important implications for epidemiologic studies of the potential health effects of disinfection by-products.

Potential impact of chlorination of Sandy bottom swimming areas on drinking water sources

The concentrations of trihalomethanes and haloacetic acids, disinfection by‐products (DBPs) of chlorine, were measured in sandy bottom swimming areas to determine their potential impact on surface and ground water that are sources of drinking water. Total trihalomethanes and individual haloacetic acid concentrations in several swimming area samples were higher than the drinking water standards (current and proposed). Individual trihalomethanes (except bromoform) also exceeded ground and surface water release standards. No release standard exists for haloacetic acids. The DBPs, while exceeding standards, would be diluted by the ground water and microbially degraded prior to reaching the drinking water plant. So while DBPs from swimming areas contributed to groundwater concentrations, the current drinking water standards could still be met using source waters impacted by chlorinated swimming areas. It is suggested, though, that any release of chlorinated DBPs to surface and ground water be minimized to obtain the highest quality water sources for drinking water.

Carbon isotopic constraints on the contribution of plant material to the natural precursors of trihalomethanes

The δ 13C values of individual trihalomethanes (THM) formed on reaction of chlorine with dissolved organic carbon (DOC) leached from maize (corn; Zea maize L.) and Scirpus acutus (an aquatic bulrush), and with DOC extracted from agricultural drainage waters were determined using purge and trap introduction into a gas chromatograph-combustion-isotope ratio monitoring mass spectrometer. We observed a 16.8‰ difference between the δ 13C values of THM produced from the maize and Scirpus leachates, similar to the isotopic difference between the whole plant materials. Both maize and Scirpus formed THM 12‰ lower in 13C than whole plant material. We suggest that the low value of the THM relative to the whole plant material is evidence of distinct pools of THM-forming DOC, representing different biochemical types or chemical structures, and possessing different environmental reactivity. Humic extracts of waters draining an agricultural field containing Scirpus peat soils and planted with maize formed THM with isotopic values intermediate between those of maize and Scirpus leachates, indicating maize may contribute significantly to the THM-forming DOC. The difference between the δ 13C values of the whole isolate and that of the THM it yielded was 3.9‰, however, suggesting diagenesis plays a role in determining the δ 13C value of THM-forming DOC in the drainage waters, and precluding the direct use of isotopic mixing models to quantitatively attribute sources.

Trihalomethanes in Drinking Water and Spontaneous Abortion

Trihalomethanes (chloroform, bromoform, bromodichloromethane, and chlorodibromomethane) are common contaminants of chlorinated drinking water. Although animal data indicate that these compounds may be reproductive toxicants, little information exists on their relation to spontaneous abortion in humans. We examined exposure to trihalomethanes and spontaneous abortion in a prospective study of 5,144 pregnant women in a prepaid health plan. Seventy-eight drinking water utilities provided concurrent trihalomethane sampling data. We calculated total trihalomethane levels by averaging all measurements taken by the subject's utility during her first trimester. We calculated exposures to individual trihalomethanes in an analogous manner. Women who drank > or = 5 glasses per day of cold tapwater containing > or = 75 micrograms per liter total trihalomethanes had an adjusted odds ratio (OR) of 1.8 for spontaneous abortion [95% confidence interval (CI) = 1.1-3.0]. Of the four individual trihalomethanes, only high bromodichloromethane exposure (consumption of > or = 5 glasses per day of cold tapwater containing > or = 18 micrograms per liter bromodichloromethane) was associated with spontaneous abortion both alone (adjusted OR = 2.0; 95% CI = 1.2-3.5) and after adjustment for the other trihalomethanes (adjusted OR = 3.0; 95% CI = 1.4-6.6).

GlutathioneS-Transferase-Mediated Mutagenicity of Trihalomethanes inSalmonella typhimurium:Contrasting Results with Bromodichloromethane and Chloroform

Trihalomethanes (THMs) are the most prevalent disinfection by-products identified in chlorinated drinking water. Among the THMs, chloroform (CHCl3) generally occurs at the highest concentration in finished water, but the concentrations of each of the brominated THMs (CHBrCl2, CHBr2Cl, and CHBr3) can exceed that of CHCl3. Each of these four THMs was carcinogenic in rodents in chronic oral dosing studies. This study assessed THM mutagenicity in a strain ofSalmonella typhimuriumTA1535 that was transfected with rat theta-class glutathioneS-transferase T1-1 (+GST). The +GST strain and its nontransfected parent strain (−GST) were employed in a plate-incorporation assay and exposed for 24 hr to the vapor of individual THMs at concentrations up to 25,600 ppm in sealed Tedlar bags. Base-substitution revertants were produced in the +GST strain in a dose-dependent fashion by CHBrCl2but not by CHCl3. At 4800 ppm CHBrCl2, which produced a calculated agar concentration of 0.67 mm, there were 419 ± 75 revertants per plate compared to a spontaneous level of 23 ± 5. CHCl3produced a doubling of revertants only at the two highest concentrations tested (19,200 and 25,600 ppm). These results indicate that bromination of THMs confers the capability for theta-class GST-mediated transformation to mutagenic intermediates at low substrate concentrations, suggesting the possibility of a similar activation route in humans. Further, the very low affinity of the GSH-dependent pathway for CHCl3demonstrates that different THMs can induce adverse effects via different mechanisms, indicating that risk evaluations of THMs should not treat members of this class as if they shared a common mode of action.