"Truth is so obscure in these times, and falsehood so established, that, unless we love the truth, we cannot know it." -- Blaise Pascal, 1623-1662, French Mathematician
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Monthly Archives: July 2011
This paper presents an improved risk assessment for the current standard for tritium in drinking water that results in higher estimates than the USEPA’s point estimate. The resulting risk estimates, however, are essentially the same order of magnitude as the upper 10-4 “acceptable” risk level USEPA uses for regulating other cancer-causing contaminants in drinking water.
Kocher, D.C. and F.O. Hoffman. Drinking water standard for tritium-what’s the risk? Health Physics, Sep;101(3):274-85.
SENES Oak Ridge, Inc., 102 Donner Drive, Oak Ridge, TN 37830.
The abstract for this study is below. Click here to obtain the full paper.
Abstract (National Library of Medicine)
This paper presents an assessment of lifetime risks of cancer incidence associated with the drinking water standard for tritium established by the U.S. Environmental Protection Agency (USEPA); this standard is an annual-average maximum contaminant level (MCL) of 740 Bq/L.
This risk assessment has several defining characteristics: (1) an accounting of uncertainty in all parameters that relate a given concentration of tritium in drinking water to lifetime risk (except the number of days of consumption of drinking water in a year and the number of years of consumption) and an accounting of correlations of uncertain parameters to obtain probability distributions that represent uncertainty in estimated lifetime risks of cancer incidence; (2) inclusion of a radiation effectiveness factor (REF) to represent an increased biological effectiveness of low-energy electrons emitted in decay of tritium compared with high-energy photons; (3) use of recent estimates of risks of cancer incidence from exposure to high-energy photons, including the dependence of risks on an individual’s gender and age, in the BEIR VII report; and (4) inclusion of risks of incidence of skin cancer, principally basal cell carcinoma.
By assuming ingestion of tritium in drinking water at the MCL over an average life expectancy of 80 y in females and 75 y in males, 95% credibility intervals of lifetime risks of cancer incidence obtained in this assessment are (0.35, 12) × 10-4 in females and (0.30, 15) × 10-4 in males. Mean risks, which are considered to provide the best single measure of expected risks, are about 3 × 10-4 in both genders. In comparison, USEPA’s point estimate of the lifetime risk of cancer incidence, assuming a daily consumption of drinking water of 2 L over an average life expectancy of 75.2 y and excluding an REF for tritium and incidence of skin cancer, is 5.6 × 10-5. Probability distributions of annual equivalent doses to the whole body associated with the drinking water standard for tritium also were obtained.
Means and 97.5 percentiles of maximum annual doses to females and males, which occur at age <1 y, all are less than the annual equivalent dose of 40 μSv used by USEPA to establish the MCL.
Nahle 2011: Repeatability of Professor Robert W. Wood’s 1909 Experiment on the Theory of the Greenhouse
In 1909 an experiment was conducted at Johns Hopkins University by Professor Robert W. Wood demonstrating that the greenhouse effect cannot cause global warming. The following researcher has repeated the experiment. Through a series of controlled experiments, the warming effect in a real greenhouse is demonstrated to not be caused by longwave infrared radiation trapped inside the greenhouse, but to the blockage of convective heat transfer with the surroundings, as proven by Professor Wood in his 1909 experiment.
Nahle, N.S. 2011. Repeatability of Professor Robert W. Wood’s 1909 Experiment on the Theory of the Greenhouse. July 5, 2011. Biology Cabinet Online-Academic Resources and Principia Scientific International. Monterrey, N.L.
Now, there appears to be three general views on the greenhouse effect. They are: (1) the greenhouse effect exists and will cause runaway warming. (2) the greenhouse effect exists but CO2 is not a significant factor in warming. (3) there is no greenhouse effect at all.
Clearly, view #1 above is not true based on the best available science. However, the scientists who support views #2 and #3 are still having spirited and vigorous exchanges.
To confuse matters further, some scientists acknowledge that what happens in the atmosphere is not exactly the same as what happens in a glassed greenhouse, but they still use the term “greenhouse effect” as a matter of convenience and tradition to refer to atmospheric warming.
Atmospheric modelers must assume the greenhouse effect occurs, that they understand how it works, that their models are accuarte representations of the actual phenomena, and that the output of their models are accurate and reliable, despite the lack of physical atmospheric measurements of the effect itself. Prior posts here and at other websites have addressed these assumptions.
On July 27, 2011 the California Office of Environmental Health Hazard Assessment (OEHHA) moved to finalize the proposed public health goal for chromium 6 (Cr-VI) in drinking water at 0.02 ppb. (Click here for press release.)
This action follows on the heals of the congressional hearing held by Senator Boxer (D-CA) on drinking water (click here), where expert testimony (click here) contradicted the claim that low levels of Cr-VI posed a significant health risk.
There is frequent confusion regarding the significance of the PHG. The OEHHA fact sheet (click here) notes:
“Q. Is drinking water dangerous if it contains a contaminant that exceeds the PHG?
A. A PHG is NOT a boundary line between a “safe” and “dangerous” level of a contaminant. Drinking water can still be acceptable for public consumption if it contains contaminants at levels higher than the PHG. A PHG is a health-protective level of a contaminant in drinking water that California’s public water systems should strive to achieve iftechnically and economically feasible.”
As is typical with these types of regulatory documents, the OEHHA response to public comments on the draft PHG (click here) is largely pro forma. In other words, OEHHA simply disagrees with the public comment (our “experts” versus others) without ever having to resolve the disagreement or determine which scientific position is correct. Regulatory agencies can usually satisfy public comment requirements using this approach and force a regulatory action forward.
Click here for the final Cr-VI PHG technical support document. The summary is provided below:
This appears to be a review paper. No affiliation is provided for the author of this paper so the bias of the author is not clear from the abstract. The abstract (click here) is below, and the full text is also avialable (click here; open source with registration). This review provides one perspective on the toxicological data for Cr-VI.
Zhitkovich, A. 2011. Chromium in Drinking Water: Sources, Metabolism and Cancer Risks. Chem. Res. Toxicol., Just Accepted Manuscript. DOI: 10.1021/tx200251t; Publication Date (Web): July 18, 2011.
Abstract (National Library of Medicine)
Drinking water supplies in many geographic areas contain chromium in the +3 and +6 oxidation states. Public health concerns are centered on the presence of hexavalent Cr that is classified as a known human carcinogen via inhalation. Cr(VI) has high environmental mobility and can originate from anthropogenic and natural sources. Acidic environments with high organic content promote reduction of Cr(VI) to nontoxic Cr(III). The opposite process of Cr(VI) formation from Cr(III) also occurs, particularly in the presence of common minerals containing Mn(IV) oxides. Limited epidemiological evidence for Cr(VI) ingestion is suggestive of elevated risks for stomach cancers. Exposure of animals to Cr(VI) in drinking water induced tumors in the alimentary tract, with linear and supralinear responses in the mouse small intestine. Chromate, the predominant form of Cr(VI) at neutral pH, is taken up by all cells through sulfate channels and is activated nonenzymatically by ubiquitously present ascorbate and small thiols. The most abundant form of DNA damage induced by Cr(VI) is Cr-DNA adducts, which cause mutations and chromosomal breaks. Emerging evidence points to two-way interactions between DNA damage and epigenetic changes that collectively determine the spectrum of genomic rearrangements and profiles of gene expression in tumors. Extensive formation of DNA adducts, clear positivity in genotoxicity assays with high predictive values for carcinogenicity, the shape of tumor-dose responses in mice and a biological signature of mutagenic carcinogens (multi-species, multi-site and trans-sex tumorigenic potency) strongly support the importance of the DNA-reactive mutagenic mechanisms in carcinogenic effects of Cr(VI). Bioavailability results and kinetic considerations suggest that 10-20% of ingested low-dose Cr(VI) escapes human gastric inactivation. The directly mutagenic mode of action and the incompleteness of gastric detoxification argue against a threshold in low-dose extrapolation of cancer risk for ingested Cr(VI).
Short news story on proactive efforts in Tucson, Arizona to address 1,4-Dioxane found in ground water (click here).
Yang et al 2011: Epidemiological Survey and Analysis on an Outbreak of Gastroenteritis due to Water Conatmination
Yang, Z., X. Wu, T. Li, M. Li, Y. Zhong, Y. Liu, Z. Deng, B. DI, C. Huang, H. Liang, and M. Wang 2011. Epidemiological Survey and Analysis on an Outbreak of Gastroenteritis due to Water Contamination. Biomed Environ Sci. 2011 Jun;24(3):275-83.
Guangzhou Center for Disease Control and Prevention, Guangzhou 510080, Guangdong, China.
Abstract (National Library of Medicine) (Click here)
Objective: To document the investigation and control of an outbreak of gastroenteritis in City G, South China, and provide a reference for preventing future outbreaks.
Methods: An ambispective cohort study was designed. Attack rate (AR) and relative risks (RR) were calculated to identify the causes of gastroenteritis. Investigations using questionnaires included personal interviews with patients and doctors, reviews of medical records, laboratory examinations of fecal specimens and continuous hygiene monitoring of water samples from the waterworks.
Results: Overall, 427/71534 (AR=5.97%) cases were identified between October 31 and November 12 2010. Geographic distribution was highly localized, with 80% of cases occurring in the areas supplied by waterworks-A. Consumption of water provided solely by waterworks-A was found to be associated with illness (RR=8.20, 95 CI%:6.12-10.99) compared with that from waterworks-B. Microbiological analyses confirmed the presence of Norovirus in six of eight fecal samples from symptomatic patients, two water samples from waterworks-A and two sewage samples. After taking effective measures, the hygienic indices of waterworks-A met health criteria again on November 9 and no cases were reported 3 days later.
Conclusion: The outbreak reported here was caused by drinking tap water contaminated with sewage at the source. Early identification of possible contamination sources and awareness of changes that might negatively impact water quality are important preventive measures to protect public health.