Cancer risk to naval divers questioned.
First, Richter et al.'s report on the concentrations of heavy metals in water (Table 3; Richter et al. 2003) is misleading and is not supported by references within the Kishon Commission's report (Investigation Committee for the Effects of Military Activities in the Kishon River 2001). The concentrations reported by Richter et al. (2003) are in fact a meaningless mixture of values, most of which were measured in the river sediment [several of their maximal values were reported by Herut et al. (1993)]. Thus, the values of water contaminant concentration used by Richter et al. in Fick's equation, describing the molar diffusion flux related to a concentration gradient, were derived from averaged data obtained from two completely different phases, water and sediment, assuming a simple and homogenous system. In fact, the system is very complicated, consisting of four interlinked reservoirs of chemicals: water, sediment, suspended particles, and interstitial water. The partitioning of each of the individual chemicals between the water and the sediment compartments is governed by many factors, including aqueous solubility, sediment binding, pH, and temperature. For most environmental contaminants, at steady state the sediment/water ratio is about 2-4 and up to 6 orders of magnitude for hydrophobic compounds. This explains the very wide range of reported values presented in Table 3 (Richter et al. 2003). For instance, the range of lead concentrations is 0.0002-252 ppm (mg/L) and of that of chromium is 0.305-462 ppm (mg/L). To reduce the uncertainty in estimating the bioavailable chemical concentration, it is recommended to use unfiltered water samples with minimum turbidity [U.S. Environmental Protection Agency (EPA) 1995]. In fact, the observed concentrations of suspended particulate matter and particulate heavy metals in the Kishon River (Herut and Kress 1997) were 2-4 orders of magnitude lower than those reported by Richter et al. (2003). Furthermore, the mean values calculated by Richter et al. are much higher (e.g., 5-fold for cadmium and 10-fold for Cr) than the metal concentrations measured in the effluents discharged by the fertilizer plants from which nearly all metals were introduced (Herut et al. 1993). The level of exposure reported by Richter et al. was also higher than the actual exposure, because the vast majority of diving activities of the naval divers were in the Kishon Harbor sea water, rather then in the river itself.
Second, the particulate-bound chemicals in aqueous medium are much less bioavailable for dermal absorption because of inefficient adsorption of suspended particles to the skin surface and a slower rate of absorption into the skin. Richter et al. (2003) used a "conservative" value of 1 cm/hr to describe the permeability constant of all chemical contaminants presented in their Table 3. In fact, for a given skin, the permeability constant describes "dermaphilicity" and strongly depends on the physicochemical properties of the individual compounds such as the oil/water partition coefficient ([K.sub.OW]) and molecular weight. A detailed list of permeability coefficients has been published elsewhere (U.S. EPA 2001). For the heavy metals presented by Richter et al. in their Table 3, the values are 3-4 orders of magnitude lower.
Third, Richter et al. (2003) used a bioavailability factor of 1.0 to estimate the oral absorption of water swallowed while diving. Absorption values for the heavy metals presented in their Table 3 were recently reported (U.S. EPA 2001) and are markedly lower than unity (0.025, 0.013, 0.07, 0.04, and 0.05 for Cd, Cr, mercury, nickel, and Pb, respectively).
In keeping with the recommendations and guidelines for assessment of dermal and oral absorption (U.S. EPA 1995), it is our understanding that Richter et al. (2003) overestimated the dose intake by a factor of [greater than or equal to] [10.sup.5]. To support this conclusion, the estimates for Cd and Pb calculated by Richter et al. were 34.87 and 269.79 mg/kg/24 hr, respectively. According to their calculations, the intake of these metals during 20 hr of diving in 1 week for a person weighing 70 kg would be 2,034 mg Cd and 15,738 mg Pb. The cumulative intake in 2,475 hr of diving would be 252 g Cd and 1.95 kg Pb. These amounts would have caused severe and potentially fatal acute and chronic toxicity. In fact, none of the naval divers developed overt symptoms of heavy metal toxicity. Furthermore, in June 2001, blood Pb and Cd levels were measured in 70 naval divers, of whom 6 were diving regularly in the Kishon Harbor during the 1980s through 1993. Their blood Pb levels were 2-5 [micro]g/dL, and Cd in blood was below detection limits in all 6. Because Pb and Cd have elimination half-lives of several years following chronic exposure, these findings rule out exposure to the levels suggested by Richter et al. (2003).
The authors declare they have no conflict of interest.
Ministry of Health
Institute of Toxicology and Clinical Pharmacology Sheba Medical Center
Tel Hashomer, Israel
Israel Oceanographic and Limnological Research Ltd.
Herut B, Kress N. 1997. Particulate metals contamination in the Kishon River Estuary, Israel. Mar Poll Bull 34:706-711.
Herut B, Shirav M, Kress N, Hornung H, Illani S, Olga Y. 1993. Sediments Composition and Pollution Levels along the Kishon River and Its Drainage Basin. Report H25/93 GSI/23/93. Haifa, Israel:Israel Oceanographic and Limnological Research and Geological Survey of Israel.
Investigation Committee for the Effects of Military Activities in the Kishon River. 2001. Report of the Investigation Committee for the Effects of Military Activities in the Kishon River and the Region's Water on the Health of IOF Soldiers Activated There [in Hebrew]. Part 1. Available: http://www.tau.ac.il/~bhkishon/[accessed 28 July 2003].
Richter ED, Friedman LS, Tamir Y, Barman T, Levy O, Westin JB, et al. 2003. Cancer risks in naval divers with multiple exposures to carcinogens. Environ Health Perspect 111:609-517.
U.S. EPA. 1995. Groundwater Sampling Workshop--A Workshop Summary. EPA/600/r-94/205. Dallas, TX:U.S. Environmental Protection Agency.
--. 2001. Risk Assessment Guidance for Superfund. Vol 1. Human Health Evaluation Manual. EPA/540/R/99/005. Washington, DC:U.S. Environmental Protection Agency.
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|Publication:||Environmental Health Perspectives|
|Date:||Sep 1, 2003|
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