Superfund sites and lead levels Dear Sir: In the April 1992 ESBTarticle entitled “Cleanup Delays at the Largest Superfund Sites” (p. 658) it is stated that “the maximum contaminant level for lead in drinking water was set by EPA at 50,000 ppb, but no federal standards exist for lead levels in soil.” The maximum concentration level for lead is 50 ppb, not 50,000 ppb. Also, EPA may not have a “standard” for lead level in soil, but this has not prevented them from removing soil containing 500 ppm Pb at small sites in New Mexico regardless of the form of lead or the bioavailability of the lead or any showing of harmful effects of the lead (Billing site, CalWest site, and Cimarron-Sierra Blanca site). Perhaps because of the pressure on EPA for successful cleanup of Superfund sites they are cleaning up these small sites because it is easy to have a successful cleanup where there is no problem. But it is also very wasteful of time and money. A citizens’ group in Aspen, Colorado, is currently trying to prevent EPA from cleaning up lead at a Superfund site at Smuggler Mountain, which has soil lead in some areas that exceed 100,000 ppm. Despite these high levels, residents show lower-than-average levels of lead in their blood. The national average is 4-6 pg/dL. A 1990 study of 125 residents showed an average of 3.4 pg/dL for adults. The reason is that the lead is not bioavailable, something EPA does not consider when making remedial investigations or cleanup decisions. Lynn Brandvold New Mexico Bureau of Mines & Mineral Resources Socorro, NM 87801
Carbon dioxide levels Dear Sir: A news item in the Currents column (ESBT, August 1992, p. 1474) reports that carbon dioxide [CO,) levels in the atmosphere were about five times higher during the Cretaceous Period than they are now, and the atmospheric temperature was also very high. Both the CO, and the temperature have been quite high in the more recent past,
also. For example, about 130,000 years ago, both were above the present-day levels. The CO, and temperature have tracked each other upwards and downwards to a remarkably precise degree (see for example CBEN, April 2 7 , 1992, p. 16). It is very likely that there is a positive feedback effect, where the higher the temperature goes, the higher the CO, level goes, and vice versa, due to exsolution of gas from the oceans and increased IR absorption in the air. The positive feedback would be expected to operate in a downward direction, also. At the e n d of a n upward (or downward) spiral, there has to be another powerful driving force to stop the trend and reverse it. This overwhelming natural force has been cyclic, according to the geological record, leading to the periodic ice ages. There is no reason to think that it has stopped operating. The Earth’s axis tilt and the orbit eccentricity have been highly correlated with the temperature cycles over the past several hundreds of thousands of years. The tilt and eccentricity affect the Earth’s heat input from the sun. This is usually called the “Milankovitch Effect.” Although some atmosphere scientists calculate that this effect alone should be too small to cause the “ice age” cycles, the positive feedback with various dissolved gases and possibly with biological activity could magnify the effect by a large factor. Actually, the overlay of temperature with the orbital eccentricity is so nearly perfect over many cycles that it seems extremely unlikely that this is from chance alone (see Physics Today, May 1977, p. 17). The most rational explanation is an astronomical root cause of the temperature changes, with feedback from gases. Whatever the true driving force was in previous cycles, it is very important for us to realize that, even when the CO, level was greater than it is now, this was not sufficient to prevent the next downturn. There is no evidence that present-day, manmade gases will prevent the next ice age, because higher levels in the past did not. Astronomical measurements and calculations tell us that there has
0013-936X/92/0926-1857$03.00/0 0 1992 American Chemical Society
been a time lag of about 6000 years between the Milankovitch cyclic peak and each ensuing plunge into an ice age. We are just about 6000 years past the latest Milankovitch peak. In fact, the long-term temperature trend (on a thousand-year scale of time) is already headed downward, regardless of whatever minor short-term ups and downs might be caused by man-made CO,, and the like (see the above-mentioned CbENarticle, p. 11.) What we should all worry about is the huge natural force that has already triggered the next ice age, not a possible greenhouse effect, We cannot say exactly when the deep plunge i n temperature will be reached, but it is almost inevitable, based on the astronomical/geological records of past millennia. Daniel J. Shanefield Ceramics Engineering Department Rutgers University Piscataway, NJ 08855
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Environ. Sci. Technol., Vol. 26,No. 10,1992 1857
