Cancer Risk to Naval Divers Questioned
Amitai, Yona, Almog, Shlomo, Herut, Barak, Environmental Health Perspectives
In the report by Richter et al. (2003) on increased risk for cancer in naval commando divers in the Kishon River in Israel, there are three systematic errors in estimating the degree of exposure to environmental water contaminants (their Table 3).
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). …