Shortly put: There are PLENTY of studies.
There are three uptake routes for chemicals while showering/bathing: Dermal, Inhalation and Ingestion.
When water is cleaned (chlorinated) you've got byproducts from the process. Some of the major byproducts are trihalomethanes (THMs), chloroform (CHCl3), bromodichlormethane (BDCM), dibromochloromethane (DBCM) and bromoform. Any/all of these can be present in the water after purification.
However, since I could go on about this all day, I'll limit my study sampling to just THMs and Chloroform studies.
THMs and showering/bathing:
There's been considerable research performed here:
Backer, LC, et al. (2000) Household exposures to drinking water disinfection byproducts whole blood trihalomethane levels. J. Expo Anal Environ Epidemol Jul-Aug;10(4):321-6.
The highest levels of THMs were found in the blood samples from people
who took 10 min showers, whereas the lowest levels were found in the
blood samples from people who drank 1 l of water in 10 min. The
results from this study indicate that household activities such as
bathing and showering are important routes for human exposure to THMs.
Miles, AM, et al. 2002. Comparison of trihalomethanes in tap water and blood. Environ Sci Technol Apr 15;36(8):1692-8.
Results indicated that THMs in the blood rose significantly as a
result of showering, that showering shifted the THM distribution in
the blood toward that found in the corresponding tap water, and that
THMs measured in the blood of women living in the two locations
reflected species and concentration differences in their respective
tap waters. In general, blood concentrations were not significantly
correlated with tap water concentrations. This finding suggests that
other factors, in addition to tap water concentrations, may be
important in determining THM concentrations in the blood
Nuckols, John R., et al. 2005. Influence of tap water quality and household water use activities on indoor air and internal dose levels of trihalomethanes. Environ Health perspect. July;113(7):863-870.
All hot water use activities yielded a 2-fold increase in blood or
breath THM concentrations for at least one individual. The greatest
observed increase in blood and exhaled breath THM concentration in any
participant was due to showering (direct and indirect), bathing, and
hand dishwashing. Average increase in blood THM concentration ranged
from 57 to 358 pg/mL due to these activities. More research is needed
to determine whether acute and frequent exposures to THM at these
concentrations have public health implications. Further research is
also needed in designing epidemiologic studies that minimize data
collection burden yet maximize accuracy in classification of dermal
and inhalation THM exposure during hot water use activities.
Lynberg, M., et al. 2001. Assessing exposure to disinfection by-products in women of reproductive age living in Corpus Christi Texas and Cobb county Georgia: descriptive results and methods. Environ Health Perspect. Jun;109(6):597-604.
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
THMs and Assessed Risk
Chowdhury, Shakhawat and Pascale Champagne. 2009. Risk from exposure to trihalomethanes during shower: Probabilistic assessment and control. Science of the Total Environment Feb 407(5):1570-1578.
Using THMs in warm water, cancer and non-cancer risks to human health
were predicted for three major cities in Ontario (Canada). The
parameters for risk assessments were characterized by statistical
distributions. The total cancer risks from exposure to THMs during
showering were predicted to be 7.6 × 10− 6, 6.3 × 10− 6 and 4.3 × 10−
6 for Ottawa, Hamilton and Toronto respectively. The cancer risks
exceedance probabilities were estimated to be highest in Ottawa at
different risk levels. The risks through inhalation exposure were
found to be comparable (2.1 × 10− 6–3.7 × 10− 6) to those of the
dermal contact (2.2 × 10− 6–3.9 × 10− 6) for the cities. This study
predicted 36 cancer incidents from exposure to THMs during showering
for these three cities, while Toronto contributed the highest number
of possible cancer incidents (22), followed by Ottawa (10) and
Hamilton (4). The sensitivity analyses showed that health risks could
be controlled by varying shower stall volume and/or shower duration
following the power law relationship.
Villaneuva, Christina M., et al. 2007. Disinfection by-products through ingestion, bathing, showering and swimming in pools. Am. J. Epidemiol. 165(2):148-156.
Lifetime personal information on water consumption and water-related
habits was collected for 1,219 cases and 1,271 controls in a 1998–2001
case-control study in Spain and was linked with THM levels in
geographic study areas. Long-term THM exposure was associated with a
twofold bladder cancer risk, with an odds ratio of 2.10 (95%
confidence interval: 1.09, 4.02) for average household THM levels of >49
versus ≤8 μg/liter. Compared with subjects not drinking
chlorinated water, subjects with THM exposure of >35 μg/day through
ingestion had an odds ratio of 1.35 (95% confidence interval: 0.92,
1.99). The odds ratio for duration of shower or bath weighted by
residential THM level was 1.83 (95% confidence interval: 1.17, 2.87)
for the highest compared with the lowest quartile. Swimming in pools
was associated with an odds ratio of 1.57 (95% confidence interval:
1.18, 2.09). Bladder cancer risk was associated with long-term
exposure to THMs in chlorinated water at levels regularly occurring in
Weisel, C.P. and W.K. Jo 1996. Ingestion, inhalation and dermal exposures to chloroform and trichloroethane from tap water. Envron Health Perspect Jan;104(1):48-51.
Analysis of chloroform and trichloethene in expired breath, compounds
regulated in water, was also used to determine uptake from tap water
by each route (inhalation, ingestion, or absorption). Each route of
exposure contributed to the total exposure of these compounds from
daily water use. Further, the ingestion dose was completely
metabolized before entering the bloodstream, whereas the dose from the
other routes was dispersed throughout the body. Thus, differences in
potential biologically effective doses depend on route, target organ,
and whether the contaminant or metabolite is the biologically active
Jo. Wan K., Weisel, Clifford P. and Paul J. Lioy. 1990. Routes of chloroform exposure and body burden from showering with chlorinated tap water. Risk Analysis Dec. 10(4):575-580.
The postexposure chloroform breath concentrations ranged from 6.0–21
μg/m3 for normal showers and 2.4 to 10 μg/m3 for inhalation-only
exposure, while the pre-exposure concentrations were all less than the
minimum detection limit of 0.86 μg/m3. According to an F-test, the
difference between the normal shower and the inhalation-only exposures
was considered significant at a probability of p= 0.0001. Based on the
difference, the mean internal dose due to dermal exposure was found to
be approximately equal to that due to the inhalation exposure. The
effect of the showering activities on the concentration of chloroform
shower air was examined by comparing air concentrations during a
normal shower with the air concentrations obtained when the shower was
unoccupied. The F-test showed that there is no significant difference
between the two sets of data
Chloroform and Cancer Risk
(Good news here!)
Lévesque, B. et, al. 2002. Cancer risk associated with household exposure to chloroform. J. Toxicol Environ Health A Apr 12;65(7):489-502.
Exposure to CHCl3 was assessed for 18 men (age: mean 38 years; range
23-51) following a 10-min shower in their respective residences
located in the Quebec City region (Canada). CHCl3 concentration was
measured in alveolar air samples collected before, immediately after,
and 15 min and 30 min following the shower. Indoor air and water
concentrations were determined concomitantly. Mean CHCl3
concentrations in the air of the shower stall and in water were
respectively 147 microg/m3 (SD = 56.2 microg/m3) and 20.1 microg/L (SD
= 9.0 microg/L). Water concentrations were comparable to those
documented in a large proportion of distribution networks in Canada.
The mean increase in alveolar air CHCl3 concentration (deltaCHCIALV)
at the end of the shower was 33 microg/m3 (SD = 14.7 microg/m3). A
multiple-regression analysis revealed that deltaCHCl3ALV values were
only associated with chloroform concentration in air of the shower
stall. DeltaCHCl3ALV were described using a physiologically based
pharmacokinetic (PBPK) model. This model was then used to estimate
concentrations of CHCl3 metabolites bound to liver and kidney
macromolecules following a shower, and also according to exposure
scenarios that integrate drinking-water ingestion and air inhalation.
The concentration predicted in the liver following a worst-case
exposure scenario was 0.41 microg CHCl3 equivalents/kg of tissue, some
6,000 times lower than the lowest concentration that did not increase
the incidence of hepatic tumors in laboratory animals. Data indicate
that for this range of exposure the safety margin appears therefore
considerable with respect to the potential carcinogenic effect of
household exposure to CHCl3.