Environ. Sci. Technol. 2000, 34, 4254
Response to Comments on “Effects of Reducing Lead in Gasoline: An Analysis of the International Experience” SIR: We are puzzled by Harrison and Whelan’s (1) critique of our paper. It is well established that gasoline lead is not the only contributor to population lead exposure, and we say so in our paper. Rather than making “passing reference” to the Christchurch data, we give it considerable attention, just to make the point that Harrison and Whelan say we “almost wholly ignore”. To quote from our paper, “Changes in other sources of lead can also affect population blood lead levels. This is made particularly clear by the Christchurch, New Zealand, study that reports a nearly 50% drop in blood lead concentrations while gasoline lead concentrations remained unchanged” (2). However, we must challenge some of Harrison and Whelan’s arguments. Harrison and Whelan dwell on the sharp drop in U.K. gasoline lead levels between 1985 and 1986, which was not reflected in a correspondingly sharp drop in U.K. blood lead levels in the same year. They conclude that this “clearly implies that other sources of exposure were highly influential”. We think this is reading too much into one data point. Strong correlations between blood lead and gasoline lead, for the U.K. as well as other locations, emerge when the data are examined over a number of years. Naturally there are year-to-year fluctuations, which may reflect variations in the populations sampled, measurement error, or actual fluctuations in exposures. At intervals of less than 1 year, fluctuations in blood lead levels on a seasonal basis have been widely reported (3). Harrison and Whelan claim to find a discrepancy between the slope factor (for blood lead versus air lead) obtained from our data on the U.S. population in comparison with published slope factors. These slope factors are reported by Brunekreef (3), who has derived them by comparing the blood lead levels of populations living near lead emissions sources with those of populations living farther away. Both Brunekreef and we report a wide range of slopes, and the two data sets actually have similar averages and
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standard deviations. A case for inconsistency can be constructed only by a selective use of the data. Specifically, Brunekreef reports slopes ranging from 0.7 to 31 (µg/dL)/ (µg/m3), with an average of 5.3 and a standard deviation of 5.1, while the slopes of our data range from 1.2 to 14.6, with an average of 6.8 and a standard deviation of 4.8. Harrison and Whelan base their argument on the highest slope in our data set, the U.S. slope of 14.6. In short, by revisiting specific data from single locations, Harrison and Whelan miss what we believe to be the key contribution of our paper: by analyzing data sets from 17 locations on lead in gasoline and population blood lead levels, we arrive at a more robust view of the association of these two environmental variables than any single-location analysis can provide. Harrison and Whelan emphasize that lead-based paint, lead-soldered food cans, and lead in plumbing systems can be significant sources of lead exposure. We agree. This does not take away from the fact that gasoline lead reductions appear to be a major factor in the decreases in population lead exposures that have now been observed in many countries worldwide.
Literature Cited (1) Harrison, R. M.; Whelan, M. Environ. Sci. Technol. 2000, 34, 4252-4253. (2) Thomas, V. M.; Socolow, R. H.; Fanelli, J. J.; Spiro, T. G. Environ. Sci. Technol. 1999, 33 (22), 3942-3948. (3) Brunekreef, B. Sci. Total Environ. 1984, 38, 79-123.
Valerie M. Thomas* and Robert H. Socolow Center for Energy and Environmental Studies Princeton University Princeton, New Jersey 08544
James J. Fanelli and Thomas G. Spiro Department of Chemistry Princeton University Princeton, New Jersey 08544 ES002014A
10.1021/es002014a CCC: $19.00
2000 American Chemical Society Published on Web 09/01/2000
