Constructing Scientific Authorities: Issue Framing of Chlorinated Disinfection Byproducts in Public Health

The practice of chlorine disinfection of drinking water to reduce microbial risks provides substantial benefits to public health. However, increasing concern around potential risks of cancer associated with exposure to chlorinated disinfection byproducts confuses this issue. This article examines the science agenda regarding chlorinated disinfection byproducts (CDBP) and cancer in Canada and the United States, focusing on the social construction of scientific knowledge claims and evidence. Data for this analysis were obtained from published documents as well as from in-depth interviews with epidemiologists and toxicologists centrally involved with the issue in both countries. Results of the analysis suggest that toxicological scientists want to close the door on the "chloroform issue" due to increasing evidence that chloroform is safe at low doses, because epidemiological scientists can no longer move forward the cancer science until significant improvements can be made in assessing human exposures, and because the scientific foci of research on DBP have shifted accordingly. Further, a distinction emerges in terms of how scientific uncertainties are interpreted when they cross-cut disciplines in the context of human health risk assessment. We suggest this tension reflects a balance of how uncertainty and authorities are managed in a mandated science-policy domain. Sufficient evidence was provided to keep the DBP issue on the regulatory agenda and to generate additional research, yet authorities and concomitant interpretations of uncertainty were contested. Such science generation and contestation inevitably influences complex risk assessment processes with respect to what water-related health risks are addressed and how.     

Exposure to Persistent Organochlorines in Canadian Breast Milk: A Probabilistic Assessment

Exposure to persistent organochlorines in breast milk was estimated probabilistically for Canadian infants. Noncancer health effects were evaluated by comparing the predicted exposure distributions to published guidance values. For chemicals identified as potential human carcinogens, cancer risks were evaluated using standard methodology typically applied in Canada, as well as an alternative method developed under the Canadian Environmental Protection Act. Potential health risks associated with exposure to persistent organochlorines were quantitatively and qualitatively weighed against the benefits of breast-feeding. Current levels of the majority of contaminants identified in Canadian breast milk do not pose unacceptable risks to infants. Benefits of breast-feeding are well documented and qualitatively appear to outweigh potential health concerns associated with organochlorine exposure. Furthermore, the risks of mortality from not breast-feeding estimated by Rogan and colleagues exceed the theoretical cancer risks estimated for infant exposure to potential carcinogens in Canadian breast milk. Although levels of persistent compounds have been declining in Canadian breast milk, potentially significant risks were estimated for exposure to polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans. Follow-up work is suggested that would involve the use of a physiologically based toxicokinetic model with probabilistic inputs to predict dioxin exposure to the infant. A more detailed risk analysis could be carried out by coupling the exposure estimates with a dose–response analysis that accounts for uncertainty.     

Chloroform Exposure and the Health Risk Associated with Multiple Uses of Chlorinated Tap Water

Recently, showers have been suspected to be an important source of indoor exposure to volatile organic compounds (VOC). The chloroform dose to an individual from showering was determined based on exhaled breath analysis. The postexposure chloroform breath concentration ranged from 6.0-21 micrograms/m3, while all corresponding background breath concentrations were less than 0.86 micrograms/m3. The internal dose from showering (inhalation plus dermal) was comparable to estimates of the dose from daily water ingestion. The risk associated with a single, 10-min shower was estimated to be 1.22 x 10(-4), while the estimated risk from daily ingestion of tap water ranged from 0.130 x 10(-4) to 1.80 x 10(-4) for 0.15 and 2.0 L, respectively. Since the estimates of chloroform risk from domestic water use for the three exposure routes--ingestion, inhalation, and dermal--are similar, all routes must be used to calculate the total risk when making policy decisions regarding the quality of the municipal water supply.     

The Possibility for "Natural" Generation of Chlorinated Organic Compounds

There is continuing concern for the exposure of persons to various chlorinated organics via the environment, for example, chlorinated disinfection byproducts in drinking water.⁽¹⁾ Some of these may be carcinogenic,⁽²⁾ although the evidence is far from strong.⁽³⁾ There is an accumulating body of evidence that one of the normal human immunological responses to foreign agents is the generation of hypochlorous acid. This evidence will be summarized. The possibility that this HOCl generated in vivo could result in the formation of organo-chlorine compounds does not appear to have been seriously considered. Based on best available information, the amount of such byproduct formation will be estimated.