Environ. Sci. Technol. 1982, 16, 440
Kubly suggests that a radical difference between the physical settings in Switzerland and Seattle accounts for the difference in findings. In our original paper we also pointed out that the two locations may have dissimilar rates of automobile exhaust dilution. Kubly has amplified on the character of the Swiss town in his letter, and it is possible, as he suggests, that the Swiss results are due to an extreme type of setting. What is missing from both of the studies is an accurate measurement of exposure to automobile exhaust or fractions of it in the vicinity of the study subjects. Both studies used average daily traffic (ADT) as a surrogate for exposure. We would agree with Kubly that there is almost surely less exhaust dilution in the Swiss town than in Seattle. Another of Kubly’s points is that Seattle does not provide a sharp contrast between heavily travelled and less travelled roads. It is probably true that Seattle does not have many streets as quiet as some of those in the Swiss town. However, there was a wider range of exposures to traffic found among our study subjects than in the Swiss town. 74% of our 1330 subjects lived on streets with less than 2000 ADT, 16% lived on streets with 2000-15000 ADT, and 9% lived on streets with over 15000 ADT. The busy Swiss road carried 5000-6000 ADT, and the outer quarter of the town had, presumably, close to zero traffic. Kubly notes that Blumer was able to obtain very detailed information on the length of residence of the Swiss subjects. Indeed, our use of current residence to imply past exposure is a less powerful and less certain approach than use of length-of-residence data, which was available to Blumer. In our study only residence at diagnosis was available to us. We pointed out our lack of migration data and the potential importance of such data. If our subjects had been highly migratory, which is a possibility, then the imputed exposures could be in error. We have commented at length on the migration problem in environmental studies in another publication ( 4 ) . A point not discussed by Kubly is that excessive cancer deaths occurred for all sites combined in the Swiss study. The 75 cancer deaths along the busy road involved breast, uterus, ovaries, intestines, prostate, and other sites. It is unusual that an environmental insult has that general an effect. Would not the auto exhaust be expected to mimic the effects of smoking? Of the 75 cancer deaths along the busy road, only 11 were of the respiratory type. Is it possible that another mechanism-possibly stress-might play a role in the Swiss town? From Kubly’s description, the main road is an unpleasant place to live, and an unusual set of risk factors might be operating. By this time, the Swiss town has experienced an additional 11 years (1971-1981) of mortality that could be compared to the 12 years (1959-1970) reported on earlier. A replication study with very specific information on 9 variety of risk factors could possibly be carried out at this time. Other locations in the world may also have ideal settings for studying the effects of concentrated automobile exhaust. We thank A. A. Kubly and the editor for bringing some important points to our attention and providing us with the opportunity to comment on them. Literature Cited (1) Polissar, L.;Warner, H., Jr. Enuiron. Sci. Technol. 1981, 15, 713-714. ( 2 ) Blumer, W.; Jauman, T.; Reich, T. Schweiz. Rundsch. Med. (Praxis) 1972,61, 514-518. (3) Blumer, M.;Blumer, W.; Reich, T. Enuiron. Sci. Technol. 1977,11,1082-1084. 440
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(4) Polissar, L. Am. J . Epidemiol. 1980,111, 175-182.
Lincoln Polissar* Fred Hutchinson Cancer Research Center Program in Epidemiology and Biostatistics Seattle, Washington 98 104
Homer Warner, Jr. 1841 East 900 South Salt Lake City, Utah 84108
Comment on “Nature of Bonding between Metallic Ions and Algal Cell Walls” SIR The article by Crist and co-workers on the “Nature of Bonding between Metallic Ions and Algal Cell Walls” (Enuiron. Sci. Technol. 1981,15, 1212) raises some questions that we would like to address at this time. 1. The authors mention that the ZPC of algal cells is approximately at pH 3 (1). This is consistent with our observations of Chlorella. Electrophoretic mobility (EM) values decrease from pH 3 to pH 5. No further decrease is observed in EM with increases in pH to pH 9. Christ et al. observed significant proton dissociation at high pH values (Figure 1). This might suggest a higher ZPC than observed by other investigators. 2. The authors suggest that the response of intact cells and fragmented cells to cationic additions is similar. This is in contrast to our work. We have observed profound differences between active and inactive cells. Hydroxide titration curves (Figures 1 and 3) appear to exhibit a different response for intact and fragmented cells. Fragmented cells (Figure 3) have a low pH buffering capacity at pH 4 and a high buffering at pH 7, while intact cells (Figure 1) have a high buffering capacity at pH and a minimum buffering capacity at pH 7. These figures seem to contradict the authors contention that the ionic equilibria of intact and lysed cells is similar. 3. Our studies suggest that cell age and equilibration time are important when quantifying cationic adsorption/uptake by algal cells. Other studies have also reported similar results (2-4). The authors make no mention of equilibration times over which their cells were incubated. 4. Finally, we object to eq 2. Na+ + (ZnA) = (NaA) + Zn2+
(2)
An electroneutrality balance is a prerequisite to all aqueous transformations. We are at a loss to understand why it is not valid here. Literature C i t e d (1) Stumm, W.; Morgan, J. J. “Aquatic Chemistry”; WileyInterscience: New York, 1970;p 455. (2) Hassett, J. M.; Jennett, J. C.; Smith, J. E. Appl. Enuiron. Microbiol. 1981,41, 1097-1106. (3) Fujita, M; Hashizumie, K. Water Res. 1975,9, 889-894. (4) Button, K.S.Hostetter,H. P.J . Phycol. 1977,13,198-202.
Wllllam D. Schecher, James M. Haseett Charles T. Driscoll” Department of Civil Engineering Syracuse Unlversity Syracuse, New York 13210
0013-936X/82/0916-0440$01.25/0
@ 1982 American Chemical Society
