* Neurotoxicology Division, NHEERL/ORD, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, 27711; University of North Carolina, Chapel Hill, North Carolina, 27599;
NTP, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, 27709;
Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, 24061; and ¶ Pathology Associates Division of Charles River Laboratories, Frederick, Maryland, 21701
Received October 10, 2003; accepted January 14, 2004
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key Words: dibromoacetic acid; disinfection by-products; neurotoxicity; behavior; neuropathology; rats.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Dichloroacetic acid (DCA), the most prominent HAA, and dibromoacetic acid (DBA) are structural analogs, yet considerably less is known about DBA. DCA is carcinogenic and a reproductive toxicant in rats (DeAngelo et al., 1996; Linder et al., 1997a
). Direct comparisons between DCA and DBA reveal that DBA produces spermatotoxicity at levels as low as 0.05 and 0.14 mM/kg/day (10 and 30 mg/kg/day), and is in fact similar to, but more potent than, DCA (lowest observable spermatotoxic effect of DCA found at 0.49 mM/kg/day, or 62.5 mg/kg/day; Linder et al., 1994a
).
DCA is neurotoxic in both laboratory animals and humans (Bhat et al., 1991; Cicmanec et al., 1991
; Katz et al., 1981
; reviewed in Stacpoole, 1998
). Administration of high doses of DCA produces peripheral neuropathy in humans, and laboratory studies of DCA in rats and dogs report hindlimb weakness, paralysis, neuropathology, and myelin vacuolation. The neurobehavioral toxicity produced by DCA has been characterized in Fischer 344 rats at dosages similar to those producing reproductive toxicity (Moser et al., 1999
). In that study, DCA produced neuromuscular toxicity including limb weakness (decreased hindlimb grip strength) and deficits in gait and righting reflex, as well as mild tremors, ocular abnormalities, and a unique chest-clasping response. The neurotoxicity was progressive with continued exposure and was observed at DCA intake levels as low as 16 mg/kg/day in subchronic studies. This dosage is in the range of doses (around 30 mg/kg/day) producing reproductive toxicity (Mather et al., 1990
; Toth et al., 1992
).
A few studies of DBA mention neurological clinical signs at high dose levels. In oral gavage studies with daily dosing of Sprague-Dawley rats, mild lethargy was observed during the first week of dosing at 270 mg/kg/day (Linder et al., 1994b). In another study (Linder et al., 1995
), subchronic exposure to 250 mg/kg/day DBA produced transient diarrhea and weight loss early on, followed by signs of excitability, awkward gait, atypical movement of limb, and abnormal posturing, and progressing to tremors and immovable hindlimbs. No such effects were observed at the next lower dose, 50 mg/kg/day. In yet another study, a single dose of 10002000 mg/kg of DBA produced "excessive drinking," hypomobility (defined as difficulty moving hindlimbs), labored breathing, and mild diarrhea and ataxia (Linder et al., 1994a
).
Since DBA and DCA are similar in that both produce reproductive toxicity and neurotoxicity at high doses, this study was initiated to examine the potential neurotoxicity of DBA at lower doses and to compare it to DCA, by using a focused neurological screening battery. A thorough neurotoxicological evaluation of DBA could not be found in the literature. We used drinking water as the route of exposure in light of our findings that DCA is more potent when administered in the drinking water compared to gavage (Moser et al., 1999). We also reported that Fisher 344 rats are more sensitive to the effects of DCA, and that neurotoxicity is most evident when exposure begins in weanling rats (Moser et al., 1999
). We therefore designed this DBA study with those experimental parameters. The study was intended to characterize the potential neurotoxicity of DBA during 6-month exposure in the drinking water, using a neurobehavioral screening battery to detect neurological and functional changes, and followed by perfusion fixation at the end of dosing for neuropathological evaluation.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals.
Fischer-344 derived rats were obtained from Charles River Breeding Laboratories (Raleigh, NC) at 24 days of age, and housed at the U.S. EPA AAALAC-accredited animal facility. The animal room was maintained at 70 ± 2°F, 50 ± 10% humidity, with a 12-hour light:dark cycle. Since DBA exposure began at 28 days of age, acclimation was limited to several days. Male and female rats (n = 12/concentration/sex) were assigned to treatment groups based on stratification of body weight at 25 days of age. Rats were individually housed in polycarbonate cages with heat-treated pine shavings for bedding and feed (Purina Rat Chow #5001) available ad libitum. All testing was conducted during the light cycle.
Drinking water was provided in 8-oz. (240-ml) amber glass bottles fitted with a Teflon liner inside the cap, and double ball-bearing sipper tubes. Pilot studies showed that these bottles drip less than 0.5 ml/day under simulated conditions. Bottles were weighed and replaced with clean ones twice a week.
Experimental testing.
Initial neurobehavioral testing (functional observational battery, or FOB, and motor activity) took place on days 26, 27, and 28 (32 rats each day, counterbalanced across concentration group, sex, and time of day). In the afternoon of day 28, bottles containing DBA were placed on the cages. Additional neurobehavioral testing occurred during the middle 3 days of weeks 4, 9, 17, and 26 of exposure (corresponding to 1, 2, 4, and 6 months). All rats were weighed weekly during cage-side observations and when tested with the FOB. DBA exposure continued until the rats were perfused.
The FOB protocol used in this study consisted of twenty-eight endpoints that evaluated different aspects of nervous system function; a detailed protocol is most recently described in McDaniel et al. (1993). Following brief assessment of the rat in its home cage, the rat was removed from the cage and held in the observer's hand to allow scoring of reactivity and observations of general appearance. The rat was then placed in the open field (top of a laboratory cart with a rim and covered with clean absorbent paper). During three minutes of exploration, the observer counted the number of rears and ranked and/or described any gait abnormalities, arousal, activity level, abnormal motor movements, and excretion level (urination, defecation). Next, sensorimotor responses were ranked following stimulation by a metal clicker, a tail pinch, approach of a pen, and light touch. Aerial righting and the pupillary reflex were tested next. Forelimb and hindlimb grip strength were measured with wire mesh screens attached to a strain gauge. Landing foot splay and core temperature were recorded. Since DCA produces a pronounced and unusual chest-clasping response (see Moser et al., 1999
), all rats were suspended briefly by the tail to test for this response. This test was only conducted at the end of exposure. Clinical observations and FOB testing were conducted by the same personnel throughout, and they were unaware of the treatment level of the rats.
Shortly after FOB testing, motor activity was measured in an automated device shaped like a figure eight and composed of a series of interconnected alleys with two blind alleys projecting from the central arena (Reiter, 1983). Eight phototransmitter-diodes were spaced at specific locations throughout the figure eight, and horizontal activity was defined as the number of photocell interruptions throughout the session. In addition, the central arena had four phototransmitter-diodes located 14 cm above the floor of the chamber to detect vertical activity.
Specific cage-side observations took place each week for the duration of exposure, except for the weeks when the FOB was conducted. Each rat was removed from its cage and evaluated on three specific criteria (based on observations during a range-finding study); any other notable observations were recorded by exception. Each rat was examined for hair loss (if present, the location was noted), and evidence of diarrhea (on the rat or in the cage). Body tone was judged by muscle resistance, and hypotonia or hypertonia was recorded.
Neuropathological evaluation.
The day after the last FOB testing, rats were deeply anesthetized with pentobarbital and perfused via the left ventricle with an initial flushing solution of 0.9% sodium chloride containing 1000 units/l heparin sodium and 1 ml/l of 1% sodium nitrite (approximately 1 min) followed by 4% formaldehyde:1% gluteraldehyde at a rate of approximately 30 ml/min (1015 min). Tissues from the central and peripheral nervous systems, skeletal muscle, and eyes with optic nerves were harvested and placed into perfusate. The following tissues were prepared from the control and high-concentration rats for histopathologic evaluation: brain (cross sections including the forebrain, center of cerebrum, midbrain, cerebellum, pons, and medulla oblongata), mid-cervical and mid-lumbar spinal cord (cross and oblique sections), skeletal muscle (thigh), eyes with optic nerves, trigeminal ganglion, cervical ganglion with attached dorsal root, cervical ventral root, lumbar ganglion with attached dorsal root, lumbar ventral root, and sciatic, tibial, and sural nerves (cross and longitudinal sections). In addition, brain and spinal cord sections (cervical and lumbar) were prepared and evaluated from the mid-concentration animals, and spinal cord sections (cervical and lumbar) were prepared and evaluated from the low-concentration rats.
The brain and spinal cord sections, skeletal muscle, and eyes with optic nerves were embedded in paraffin, sectioned at approximately 5 µm, and stained with hematoxylin and eosin (H&E). Additional brain sections were stained with luxol-fast blue/periodic acid Schiff's stain (LFB/PAS) and anti-glial fibrillary acidic protein (GFAP). Sections of sciatic, tibial and sural nerves, trigeminal ganglion, cervical and lumbar ganglion with attached dorsal roots, and cervical and lumbar ventral roots were embedded in glycomethacrylate (GMA), sectioned at approximately 23 µm, and stained with H&E.
At microscopic evaluation, all tissue changes were graded by using a semi-quantitative scale as follows: normal (0); minimal (1) indicated a microscopic change that was very focal in the tissue section or affected multifocal isolated portions of the tissue; mild (2) indicated a change affecting <10% of the tissue section; moderate (3) indicated a change affecting 1040% of the tissue; severe (4) indicated a change affecting >40% of the tissue. More specifically, with regards to nerve fiber degeneration in the spinal cord, minimal (1) indicated that single, scattered axons were affected; mild (2) indicated multiple small clusters of axons or up to 10% of the total axons were affected; moderate (3) indicated that 1040% of the axons were affected, and severe (4) indicated that greater than 40% of the axons were affected. Concerning the diagnosis of cellular vacuolation, minimal (1) indicated one or a few scattered vacuolated cells in the section, and mild (2) indicated more than a few or at least one cluster of vacuolated cells.
Additional processing was conducted in select DBA-treated rats in order to further investigate the finding of cellular vacuolation in the spinal cord. Paraffin-embedded blocks of spinal cord tissue (the same blocks from which sections had been examined via light microscopy) from a representative high-concentration male, high-concentration female, and a control female were cut with a razor to section the tissue into approximately 3x3x3 mm blocks. These blocks were deparaffinized, and the tissues were buffer-rinsed, post-fixed in osmium tetroxide, dehydrated, infiltrated with epoxy resin, and embedded in epoxy resin. Thick sections (1 micron plastic sections) were prepared, stained with toluidine blue, and reviewed. Grids for evaluation via transmission electron microscopy (TEM) were prepared from the areas of interest and examined.
Data analysis.
All initial analyses included a grouping factor of concentration and gender, with time of testing as a repeated (within-subject) factor. When significant overall effects were obtained, step-down analyses were conducted. If there were no interactions with gender in the model, then the data for males and females were combined for subsequent analyses. Where the overall concentration-by-time interaction was significant, analyses at each time point were conducted to determine which time points were significant, followed by post hoc analyses to determine which exposure groups differed from control. Analyses of data averaged across all test times were conducted if the overall analyses showed a significant concentration effect but no interaction with time.
Continuous data (e.g., body weight, fluid intake, grip strengths, etc.) were analyzed by a general linear model (GLM; SAS, 1990). Rank-order data (e.g., gait score, sensorimotor response scores, pathology scores, etc.) were analyzed by using a categorical modeling procedure (CATMOD; SAS, 1990) that fits linear models to functions of response frequencies, which was then analyzed by weighted regression. Incidence of pathological findings were analyzed by using Fisher's exact test (FREQ; SAS, 1990). In all cases, resulting probability values <0.05 were considered significant.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Fluid intake was calculated for each rat twice weekly and averaged, and the overall average water intake for each concentration group is presented in Table 1. Control intake increased from 16.6 and 14.4 ml/day (males and females, respectively) within the first 6 weeks of study and stabilized thereafter at about 21 and 17 ml/day (males and females). Analysis of the weekly data showed a significant three-way interaction of concentration, gender, and time (F(75,2200) = 2.60, p < 0.0001). Subsequent analyses indicated that, in male rats, the high concentration level suppressed intake initially (first week intake = 13.6 ml/day) and for just a few days in the second month of dosing. On the other hand, female rats drinking the high concentration showed lower intake (about 14 ml/day) only in the last 2 months of study. Male rats drinking the middle concentration drank significantly more (about 25 ml/day) throughout the exposure period, but in females, a similar increase at that concentration was only observed in the first 3 weeks of exposure (averaging 21 m/day). One female rat in the middle-concentration group consistently drank considerably more throughout the study (34.1 ml/day compared to the average of 17.8 ml/day in the rest of that group, and 17.1 ml/day in controls). This one rat was closely monitored and no evidence of spillage (e.g., wet bedding) was ever observed. For intake calculations only, the data from that rat were excluded.
|
|
Weekly observations of the rats revealed a concentration-related increased incidence of diarrhea (unformed, liquid stools) and hair loss that was confined to the top of the head between the ears. These changes were most prominent in the first month of exposure, peaking at two to three weeks after exposure began, and then decreasing for the remaining months. Diarrhea occurred in all exposure groups in males (25%, 58%, and 92% of rats drinking 0.2, 0.6, and 1.5 g/l, respectively), and in the two higher concentration groups in females (25% and 83% at 0.6 and 1.5 g/l). In contrast, the incidence of diarrhea in control male rats was 017%, mostly occurring in the fifth and sixth months, and 0% in control female rats. Hypotonia was observed after about two weeks of exposure and continued throughout in the high-concentration groups (peak occurrence 75100%). Forehead hair loss was evident in both genders in almost all rats (8392%) in the two higher concentration groups but was observed only in the first month of exposure. We could identify no possible reasons for this hair loss, and the only metal edges in the cages (against which the rats could rub) were the tips of the sipper tubes. Hypotonia and forehead hair loss were observed in only one female control rat at one time throughout the study.
Overall results of the FOB data are presented in Table 2. For almost all endpoints, there were no significant interactions with gender; therefore, male and female data were combined for subsequent analyses. There were, however, mostly concentration-by-time interactions, such that step-down analyses were conducted at each time point to determine effective concentrations.
|
|
|
|
Nerve fiber degeneration was diagnosed when axonal segments were noted to have variable combinations of the following: segmental dilation of myelin sheaths, accumulations of axonal debris, foamy macrophages within dilated myelin sheaths, and nuclear debris. The fiber degeneration was primarily noted in white matter, and was seen at both cervical and lumbar levels (the only cord regions studied). The incidence and average severity of nerve fiber degeneration are listed in Table 4. The increased incidence of this finding was statistically significant (Fisher's exact test, p < 0.05) in the cervical and lumbar spinal cord of high-concentration males and females, and also in lumbar spinal cord of the mid-concentration females.
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The filtered tap water provided in this study was the same as that prepared for National Toxicology Program (NTP) studies of DBA. Analyses indicated that, at all sampling times, the control water contained less than 0.31 µg/ml, the limit of detection for DBA. The water was not, however, analyzed for the presence of other DBPs, and thus there is the possibility that other DBPs or a mixture thereof could have influenced these findings. While the concentration dependencies of the behavioral and pathological findings suggest that they were indeed a result of DBA exposure, the possibility of other interactions cannot be ruled out.
The pattern of changing fluid intake and rapid growth produced a high intake of DBA, particularly over the first month, which then decreased rapidly and stabilized over the last three months (Figure 1). The behavioral data also showed that most effects emerged early, when the DBA intake was high, and remained stable thereafter. This pattern was in marked contrast to the progressive nature of DCA effects (Moser et al., 1999). The DBA pattern could be indicative of prolonged effects resulting from the high initial intake. Alternatively, the magnitude of behavioral effects may have reached an asymptote after the first month. Both DBA and DCA inhibit their own metabolism, leading to nonlinear kinetics and higher levels following repeated doses (Gonzalez-Leon et al., 1997
; Schultz et al., 1999
). On the other hand, DBA was not shown to accumulate with drinking water exposure (Christian et al., 2001
). Since exposure began in adolescence, it is possible that the younger rats were more sensitive than adults, and the results may have differed if we had begun exposure in adulthood.
There were both similarities and differences in the behavioral effects of DBA and DCA (Moser et al., 1999), although we had originally hypothesized that they would appear similar. Both compounds altered neuromuscular function (e.g., decreased grip strength and gait changes). Chest clasping was observed with DBA, but only in females, and this was not as prominent as with DCA. DBA produced no tremors or changes in the righting reflex, which was seen with DCA. In further contrast to DCA, DBA altered sensorimotor function and decreased motor activity. Earlier studies (Linder et al., 1994b
, 1995
), using high oral gavage doses, also reported alterations in hindlimb function. Even the highest concentration used in the present study (1.5 g/l, leading to intake averaging 161 mg/kg/day) was not as high as these earlier studies (
250 mg/kg/day), which could explain the less severe effects reported here. Overall, the neurobehavioral alterations observed with DBA were of mild to moderate severity. For example, rats showed significantly less response to the sensory stimuli, yet all rats still responded. Furthermore, grip strength was decreased approximately 2535% throughout the study, which was less than the 4050% decrease observed with DCA. While differences of this magnitude may not be obvious to the casual observer, they would nonetheless impact the normal neurobehavioral function of the rat
DBA effects on behavioral function could not be fully attributed to body weight changes or other general toxicity. For example, forelimb grip strength was decreased by both the mid and high concentrations, but only the high concentration suppressed weight gain. Furthermore, numerous studies conducted in our laboratory have shown dissociation between body weight and grip strength (see for example, Moser et al., 1998). Treated rats generally looked in good health, other than the evidence of diarrhea (mostly in the cage) and the transient hair loss. Finally, the specific neuromuscular and sensorimotor deficits observed in these rats cannot be explained by nonspecific toxicity, especially considering that the lower-concentration groups did not even show altered body weight gain.
Nerve fiber degeneration is a relatively common change in the spinal nerve roots and the dorsal spinal cord tracts of aging rats of multiples strains, including the Fischer 344s (Mitsumori and Boorman, 1990). However, those changes are generally most pronounced in animals greater than one year of age, whereas the rats at the end of this study were only 7 months old. Further complicating the interpretation of nerve fiber degeneration in the spinal cord are the artifacts that are inherent in paraffin-processed tissue. In this study, spinal cord nerve fiber degeneration, although observed in control animals, was present at incidences that indicated a treatment effect. The actual pathogenesis of the axonal degeneration was not apparent. We cannot rule out that nerve fiber degeneration may have occurred earlier in the study, but was no longer evident at the terminal sacrifices. Given the minimal to mild severity of nerve fiber degeneration in the DBA-treated rats, it was not possible to directly attribute any of the neurobehavioral abnormalities to the spinal cord changes. However, the absence of an obvious association does not invalidate the significance of either set of findings.
Earlier studies of DCA reported neuropathology at high dose levels. Bhat et al. (1991) reported vacuolization in the brain, mostly associated with myelinated axons, as well as a positive GFAP response. Others also reported vacuolization in myelinated tracts in the brains of both dogs and rats (Cicmanec et al., 1991
; Katz et al., 1981
). In several different reports, Spencer and coworkers have reported degenerative changes in scattered neurons, and vacuolar demyelination in spinal cord, as well as gray matter vacuolation (Spencer et al., 1981
; Spencer and Bischoff, 1982
; Spencer and Schaumburg, 1985
). In the present study, DBA produced neural degeneration, as well as neuronal vacuolization, but these findings were restricted to the spinal cord. Unlike previous reports of DCA, no brain lesions or gliosis were observed. Thus, there may be similarity between the neuropathology produced by DCA and DBA, but further analysis of DCA-treated spinal cord tissue is necessary to confirm this.
The most unusual morphologic abnormality noted in this study was the presence of intracellular vacuoles in the spinal cord sections from mid- and high-concentration animals. At the light microscopic examination, these vacuoles were believed to be a component of the overall nerve fiber degeneration associated with DBA treatment. TEM examination was used as an adjunct to the light microscopic evaluation of this morphologic change, even though only a few samples were evaluated. Furthermore, it was understood that the use of previously paraffin-embedded spinal cord sections for examination via TEM could result in extensive artifact. However, the increased probability of identifying vacuolated cells from specimens with already-identified lesions was deemed an acceptable compromise, and the specimens were of diagnostic value.
The exact constituency and cellular nature of the vacuoles could not be definitively determined. Neuronal cell bodies were largely ruled out due to the lack of Nissl substance in the vacuole-containing structures. Similarly, glial cells were ruled out because of the lack of any cellular characteristics that indicated glia. Dendrites and axons were not ruled out as a possible location, and indeed, the cytoplasm surrounding the vacuoles was consistent with axon cytoplasm. The lack of any discernable myelin surrounding the cells containing the vacuoles indicated the structures were not myelinated axons, or that the surrounding myelin was removed during the six months of the study. There were no detectable glial cell responses (astrocytosis or microgliosis) at light and electron microscopic evaluations. Thus, these cellular vacuoles are a unique finding that merits further evaluation.
DCA produces a myriad of metabolic changes, many of which have been proposed to produce its toxicity. Some of these metabolic effects have led to its therapeutic use for diabetes, hyperlipidemia, and other metabolic disorders (reviewed in Stacpoole, 1998). The hypothesis that stimulation of thiamine-dependent enzymes would lead to thiamine deficiency, and its concomitant neurological complications, was supported in studies using thiamine supplementation to reverse the effects of DCA (Stacpoole et al, 1990
). A more recent line of research has revealed that DCA, as well as DBA, inactivates glutathione transferase zeta (GSTZ) and thereby inhibits tyrosine catabolism and, in addition causes hepatic glycogen accumulation and altered serum insulin and insulin-signaling proteins (Anderson et al., 1999
; Kato-Weinstein et al., 1998
, 2001
; Lantum et al., 2003
; Lingohr et al., 2001
). Several of these studies (although in mice) were conducted using drinking water concentrations similar to those used in the present study. These actions are gaining acceptance as potential mechanisms of DCA-induced hepatic carcinogenicity; however, the extent to which these metabolic alterations influence neuropathology and behavioral changes, such as those reported here, is unclear. Clearly, further research on DBA neurotoxicity should address such mechanisms.
In the present study, the lowest concentration tested (0.2 g/l), which produced an average intake of about 20 mg/kg/day, produced sensorimotor changes. Thus, a no-effect level (NOEL) could not be established for the neurobehavioral effects. This concentration was, however, a NOEL for the neuropathological changes. This effective level is in the same dose range as that which produces spermatotoxicity, the most sensitive reproductive endpoint reported to date (Christian et al., 2002; Linder et al., 1997b
). These levels are considerably higher than human exposure to haloacetic acids via drinking water as currently regulated, yet regulatory assessments for exposure to haloacetic acids are based currently on potential reproductive toxicity and carcinogenicity. The findings from this study serve to raise awareness that neurotoxicity is another endpoint of interest in the toxicological evaluation of DBA, and that both neurotoxicity and reproductive toxicity should be considered collectively when assessing noncancer risk attributable to the haloacetic acids.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
NOTES |
---|
1 To whom correspondence should be addressed at Neurotoxicology Division (MD B105-04), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711. Fax: (919) 541-4849. E-mail: moser.ginger{at}epa.gov
Portions of this research were presented at the annual Society of Toxicology meeting, March 16-21, 2002
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Baughman, L. R. (1998). Formulation stability study of dibromoacetic acid and dibromoacetic acid mixed with 5-bromo-2-deoxyuridine (BRDU) in drinking (tap) water. Report to the National Institute of Environmental Health Sciences, Research Triangle Park, NC, CHEM03600.
Baughman, L. R. (1997). Dose formulation developmental study report dibromoacetic acid. Report to the National Institute of Environmental Health Sciences, Research Triangle Park, NC, CHEM02413.
Bhat, H. K., Kanz, M. F., Campbell, G. A., and Ansari, G. A. S. (1991). Ninety day toxicity study of chloroacetic acids in rats. Fundam. Appl. Toxicol. 17, 240253.[ISI][Medline]
Boorman, G. A. (1999). Drinking water disinfection byproducts: Review and approach to toxicity evaluation. Environ. Health Perspect. 107 (Suppl. 1), 207217.[ISI][Medline]
Christian, M. S., York, R. G., Hoberman, A. M., Diener, R. M., Fisher, L. C., and Gates, G. A. (2001). Biodisposition of dibromoacetic acid (DBA) and bromodichloromethane (BDCM) administered to rats and rabbits in drinking water during range-finding reproduction and developmental toxicity studies. Int. J. Toxicol. 20, 239253.[CrossRef][ISI][Medline]
Christian, M. S., York, R. G., Hoberman, A. M., Frazee, J., Fisher, L. C., Brown, W. R., and Creasy, D. M. (2002). Oral (drinking water) two-generation reproductive toxicity study of dibromoacetic acid (DBA) in rats. Int. J. Toxicol. 21, 237276.[CrossRef][ISI][Medline]
Cicmanec, J. L., Condie, L. W., Olson, G. R., and Wang, S. R. (1991). 90-Day toxicity study of dichloroacetate in dogs. Fundam. Appl. Toxicol. 17, 376389.[ISI][Medline]
DeAngelo, A. B., Daniel, F. B., Most, B. M., and Olson, G. R. (1996). The carcinogenicity of dichloroacetic acid in the male Fischer 344 rat. Toxicology 114, 207221.[CrossRef][ISI][Medline]
Egorov, A. I., Tereschenko, A. A., Altshul, L. M., Vartiainen, T., Samsonov, D., LaBrecque, B., Maki-Paakkanen, J., Drizhd, N. L., and Ford, T. E. (2003). Exposures to drinking water chlorination by-products in a Russian city. Int. J. Hyg. Environ. Health 206, 539551.[ISI][Medline]
George, S. E., Nelson, G. M., Swank, A. E., Brooks, L. R., Bailey, K., George, M., and DeAngelo, A. (2000). The disinfection by-products dichloro-, dibromo-, and bromochloroacetic acid impact intestinal microflora and metabolism in Fischer 344 rats upon exposure in drinking water. Toxicol. Sci. 56, 282289.
Gonzalez-Leon, A., Schultz, I. R., Xu, G., and Bull, R. J. (1997). Pharmacokinetics and metabolism of dichloroacetate in the F344 rat after prior administration in drinking water. Toxicol. Appl. Pharmacol. 146, 189195.[CrossRef][ISI][Medline]
Kato-Weinstein, J., Lingohr, M. K., Orner, G. A., Thrall, B. D., and Bull, R. J. (1998). Effects of dichloroacetate on glycogen metabolism in B6C3F1 mice. Toxicology 130, 141154.[CrossRef][ISI][Medline]
Kato-Weinstein, J., Stauber, A. J., Orner, G. A., Thrall, B. D., and Bull, R. J. (2001). Differential effects of dihalogenated and trihalogenated acetates in the liver of B6C3F1 mice. J. Appl. Toxicol. 21, 8189.[CrossRef][ISI][Medline]
Katz, R., Tai, C. N., Diener, R. M., McConnell, R. F., and Semonick, D. E. (1981). Dichloroacetate, sodium: 3-Month oral toxicity studies in rats and dogs. Toxicol. Appl. Pharmacol. 57, 273287.[ISI][Medline]
Krasner, S. W., McGuire, M. J., Jacangelo, J. G., Patania, N. L., Reagan, K. M., and Aieta, E. M. The occurrence of disinfection by-products in US drinking water. (1989). J. Am. Water Works Assoc. 81, 4153.
Lantum, H. B. M, Cornejo, J., Pierce, R. H., and Anders, M. W. (2003). Perturbation of maleylacetoacetic acid metabolism in rats with dichloroacetic acid-induced glutathione transferase zeta deficiency. Toxicol. Sci. 74, 192202.
Linder, R. E., Klinefelter, G. R., Strader, L. F., Narotsky, M. G., Suarez, J. D., Roberts, N. L., and Perreault, S. D. (1995). Dibromoacetic acid affects reproductive competence and sperm quality in the male rat. Fundam. Appl. Toxicol. 28, 917.[CrossRef][ISI][Medline]
Linder, R. E., Klinefelter, G. R., Strader, L. F., Suarez, J. D., and Dyer, C. J. (1994a). Acute spermatogenic effects of bromoacetic acids. Fundam. Appl. Toxicol. 22, 422430.[CrossRef][ISI][Medline]
Linder, R. E., Klinefelter, G. R., Strader, L. F., Suarez, J. D., and Roberts, N. L. (1997a). Spermatotoxicity of dichloroacetic acid. Reprod. Toxicol. 11, 681688.[CrossRef][ISI][Medline]
Linder, R. E., Klinefelter, G. R., Strader, L. F., Suarez, J. D., Roberts, N. L., and Dyer, C. J. (1994b). Spermatotoxicity of dibromoacetic acid in rats after 14 daily exposures. Reprod. Toxicol. 8, 251259.[CrossRef][ISI][Medline]
Linder, R. E., Klinefelter, G. R., Strader, L. F., Veeramachaneni, D. N., Roberts, N. L., and Suarez, J. D. (1997b). Histopathologic changes in the testes of rats exposed to dibromoacetic acid. Reprod. Toxicol. 11, 4756.[CrossRef][ISI][Medline]
Lingohr, M. K., Thrall, B. D., and Bull, R. J. (2001). Effects of dichloroacetate (DCA) on serum insulin levels and insulin-controlled signaling proteins in livers of male B6C3F1 mice. Toxicol. Sci. 59, 178184.
Mather, G. G., Exon, J. H., and Koller, L. D. (1990). Subchronic 90 day toxicity of dichloroacetic and trichloroacetic acid in rats. Toxicology 64, 7180.[CrossRef][ISI][Medline]
McDaniel, K. L., and Moser, V. C. (1993). Utility of a neurobehavioral screening battery for differentiating the effects of two pyrethroids, permethrin and cypermethrin. Neurotoxicol. Teratol. 15, 7183.[CrossRef][ISI][Medline]
Mitsumori, K., and Boorman, G. (1990). Spinal cord and peripheral nerves. In Pathology of the Fischer Rat (G. Boorman, S. L. Eustis, M. R. Elwell, C. A. Montgomery, and W. F. MacKenzie, Eds.), Academic Press, San Diego, CA. pp. 179207.
Moser, V. C., Phillips, P. M., McDaniel, K. L., and MacPhail, R. C. (1999). Behavioral evaluation of the neurotoxicity produced by dichloroacetic acid in rats. Neurotoxicol. Teratol. 21, 719731.[CrossRef][ISI][Medline]
Moser, V. C., Phillips, P. M., Morgan, D. L., and Sills, R. C. (1998) Carbon disulfide neurotoxicity in rats: VII. Behavioral evaluations using a functional observational battery. Neurotoxicology 19, 147158.[ISI][Medline]
Pourmoghaddas, H., Stevens, A. A., Kinman, R. N., Dressman, R. C., Moore, L. A., and Ireland, J. C. (1993). Effects of bromide ion on formation of HAAs during chlorination. J. Am. Water Works Assoc. 85, 8287.
Reiter, L. W. (1983). Chemical exposures and animal activity: Utility of the figure-eight maze. Dev. Toxicol. Environ. Sci. 11, 7384.[Medline]
Schultz, I. R., Merdink, J. L., Gonzalez-Leon, A., and Bull, R. J. (1999). Comparative toxicokinetics of chlorinated and brominated haloacetates in F344 rats. Toxicol. Appl. Pharmacol. 15, 102114.
Sérodes, J.-B., Rodriguez, M. J., Li, H., and Bouchard, C. (2003). Occurrence of THMs and HAAs in experimental chlorinated waters of the Quebec City area (Canada). Chemosphere 51, 253263.[CrossRef][ISI][Medline]
Singer, P. C., and Chang, S. D. (1989). Correlations between trihalomethanes and total organic halides formed during water treatment. J. Am. Water Works Assoc. 81, 6165.
Spencer, P. S., and Bischoff, M. C. (1982). Spontaneous schwann cell remyelination of spinal cord plaques in rats orally treated with sodium dichloroacetate. J. Neuropathol. Exp. Neurol. 41, 373.
Spencer, P. S., Bischoff, M. C., and Stacpoole, P. W. (1981). Differential neurotoxicity of dichloroacetate and 2,5-hexanedione: Implications for the pathogenesis of gamma-diketone neuropathy. Toxicologist 1, 51.
Spencer, P. S., and Schaumburg, H. H. (1985). Organic solvent neurotoxicity. Facts and research needs. Scand. J. Work Environ. Health 11 (Suppl. 1), 5360.[ISI][Medline]
Stacpoole, P. W., Harwood, H. J., Jr., Cameron, D. F., Curry, S. H., Samuelson, D. A., Cornwell, P. E., and Sauberlich, H. E. (1990). Chronic toxicity to dichloroacetate: Possible relation to thiamine deficiency in rats. Fundam. Appl. Toxicol. 14, 327337.[ISI][Medline]
Stacpoole, P. W., Henderson, G. N., Yan, Z., Cornett, R., and James, M. O. (1998). Pharmacokinetics, metabolism, and toxicology of dichloroacetate. Drug Metab. Rev. 30, 499539.[ISI][Medline]
Toth, G. P., Kelty, K. C., George, E. L., Read, E. J., and Smith, M. K. (1992). Adverse male reproductive effects following subchronic exposure of rats to sodium dichloroacetate. Fundam. Appl. Toxicol. 19, 5763.[ISI][Medline]
U.S. Environmental Protection Agency. (2003). National Primary Drinking Water Regulations: Stage 2 Disinfectants and Disinfection By-Products (Stage 2 DBPR). Fed. Reg. 68, 4954849681.
|