One difficulty in studying the effects<sup>of lead on health is that progress has in fact been</sup> made. Even though lead is still<sup>one of the six criteria pollutants in the U.S., it is no longer a real</sup> major problem; in most metropolitan<sup>areas gasoline is lead-free. The estimates here thus had to be</sup> almost entirely based on EPA (1985),<sup>considered the major publication on the issue, but with some</sup> estimates and parameters out of date. Additionally, dose-response relations between<sup>lead</sup> concentration in air and health<sup>effects are not straightforward with simple econometric</sup> representations. They often involve<sup>thresholds and have not been quantified in a rigorous manner.</sup> Children's treatment. We assumed<sup>that all children with BLL above 25 jtg/dl require</sup> a screening test. Those with BLL<sup>above 35 ug/dl have to undertake an EDTA testing, which requires</sup> a day in hospital plus follow-up<sup>tests and physicians' visits. According to EPA (1985), the most</sup> serious cases require an expensive<sup>treatment -chelation. The estimated population of children</sup> (under 18 years old) in MCMA is<sup>7.65 million. According to Secretaria de Salud (1991), 29 percent</sup> of children have BLL above 25 sg/dl,<sup>and 3 percent above 35 Ag/dl. Thus 2.25 million screening tests</sup> and 230,OOOEDTA tests are required. Chelation therapy<sup>is only required for approximately 1 percent</sup> of all children (also based on EPA 1985).

Data on hospital, medication, and<sup>treatment costs are unavailable in Mexico. We had</sup> to adjust the information of these<sup>costs in the U.S. to Mexican conditions. The only survey</sup> comparing treatment costs in the two<sup>countries was made for AIDS and indicated that they were 30</sup> times higher in the U.S. (Secretaria<sup>de Salud, personal communication). Because AIDS treatment</sup> is so technology intensive, and also<sup>because treatment conditions in the two countries are very</sup> different, we assumed that for other<sup>diseases the ratio between treatment costs would be half as high</sup> as for AIDS, thus 15 times higher<sup>in the U.S. We adjusted the cost estimates presented in EPA</sup> (1985) from 1985 US$ to 1990 US$<sup>using CPIs. The estimated costs are as follows: (a) each</sup> screening test costs US$131 in the<sup>U.S.,thus US$8.7 in Mexico; since 2.5 million tests are required,</sup> total costs are US$19.6 million;'<sup>6</sup> (b)<sup>each EDTA is estimated to cost US$655 in the U.S., thus</sup> US$44 in Mexico, including one day<sup>in hospital; since 230,000 tests are required, total costs are</sup> US$10 million; (c) three follow-up<sup>visits are required for those children subjected to EDTA test. For</sup> this item there are some data suggesting<sup>a lower bound for doctor's visit around US$20, so that the</sup> total costs would be US$13.8 million;<sup>(d) finally, the chelation therapy is supposed to cost US$3,250</sup> in the U.S.,or US$220 in Mexico. Since<sup>76,500cases require chelation, total costs are US$17 million.</sup> Total estimated costs for children's treatment<sup>is US$60 million."</sup> 7 _16. It is unlikely that so many children_<sup>_call in hospitals to make such tests. This certainly does_</sup> _not mean that there are no costs involved._<sup>_We thus assume other children to have the same or higher_</sup> _costs._ _17. As noted earlier, since there is indication_<sup>_that even minimal concentrations cause harmfid_</sup> _health effects, the estimates do not relate_<sup>_to legislation standards, but to zero concentration levels._</sup> 16