We would like to address the epidemiologic implications of Amitai et al.'s comments on the validity of our estimates of exposure, dermal contact and absorption, internal doses, and permeability coefficients that we reported in our article published in the April 2003 issue of EHP(Richter et al. 2003)
We now know that excessive skin contact occurred in the 1950s and 1960s when divers used defective and torn skin suits and applied skin greases [Governmental Commission of Inquiry (GICI) 2003]. Strikingly, all cases of melanoma occurred among those who began diving before 1970, and no melanoma was found in those who began diving after 1970 (Richter et al. 2003). The fact that seven of the eight divers with melanoma belonged to the 1960 cohort accounts for the sharp peak in observed/expected ratio (6.58) for all cancers combined in the 1960-1969 cohort.
Our calculations (Richter et al. 2003) were based on data from the GICI (2003). Both the Kishon Harbor and Haifa Bay were severely polluted, and dilution of effluents did not occur until well past the mouth of the Kishon River. Many samples were taken near apertures of effluent drains, where concentrations would be substantially higher before downstream dilution. Most diving took place at the mouth of the Kishon River, Haifa Bay, and Kishon Harbor, close to and downstream from these apertures.
Furthermore, divers frequently descended to sediment depths. Frequent dredging resulted in recirculation of sediment. Therefore, the data on toxics were probably reasonable indicators of the conditions of exposure.
For determining estimated potential exposure dose intake, we used reported water levels only, not substantially higher sediment levels (Richter et al. 2003). Measures such as biological oxygen demand, total suspended solids, and sediment levels for observed pollutants state the case for severe contamination, even if dose estimates based on concentrated water samples are too high.
Regulatory, agencies have used a permeability constant of 1.0 cm/hr and a bioavailability factor of 1.0 rather than measured or estimated values (Great Lakes Health Effects Division 1993). Correcting for the permeability coefficient and bioavailability factor suggests an overestimate of daily intakes by 1.5-3.0, not 5, as stated by Amitai et al. Even so, we are currently addressing the potential for high rates of intake from high concentrations of toxics in subsurface water and still higher concentrations in surface films of petroleum. Solvents, of course, have permeability constants and bioavailability factors higher than those for metals, and many exceed 1.0 (e.g., ethanol, toluene).
In our paper (Richter et al. 2003), we presented estimates normalized to 24 diving hours, not daily exposure, which was 3-4 hr/day for the first year and 2 hr/day for the remaining 3 years of full-time service (Table 3; Richter et al. 2003). Therefore, an estimate of absorption per workday should be approximately one order of magnitude less than the 24-hr value.
Our calculations based on the classical models of exposure and equations (Richter et al. 2003) probably provide substantial underestimates of exposure hazards under real-life conditions.
Several real-life conditions increased the hazard from exposure. First, wet suits acted as occlusive pressure dressings on the skin. Second, abrasions and open cuts facilitate higher penetration (ATSDR 1999b). Third, the divers used abrasive soaps (intended for cleaning horses) and turpentine-containing thinners to clean thick crusts off their skin. Fourth, the soaps, together with detergents in the Kishon waters, produced additional abrasions and surface injury to the skin. Fifth, the thinners removed the protective fat layer on the skin and …