Round and round it goes: the epidemiology of childhood lead poisoning, 1950-1990.

In the 40 years from 1950 to 1990, lead epidemiology and public policy based on it made enormous strides. Exposure levels that caused concern in the medical and public health community fell from 80 to 10 micrograms/dL of blood. In the space of 20 years, beginning in 1970, first the surgeon general and then the CDC lowered the official "level of concern" from 50 or 60 to 10 micrograms/dL. The public health community has turned its attention from the prevention of poisoning that results in encephalopathy, mental retardation, and death to the reduction of exposure to avoid subtle neurobehavioral deficits that are detectable only in fairly large epidemiological studies. Numerous advances in technology and analysis have facilitated progress in lead epidemiology. In order to show that intellectual deficits were related to lead exposure rather than to such confounding variables as parental education, parental IQ, income, or parents' age at time of birth, researchers performed extensive regression analyses of fairly large sample populations, controlling for as many as 39 confounding variables. These analyses would have been virtually impossible but for the development of computer software programs that became available beginning in the late 1960s and early 1970s. Handling of large data bases, such as NHANES II, also required access to computer hardware and software not generally available earlier. The existence of the data depended on other technological innovations that made screening of large populations inexpensive and relatively simple. In 1973, erythrocyte protoporphyrin screening transformed testing for lead poisoning. With the advent of atomic absorption spectroscopy and rapid improvement in equipment for blood lead analysis, obtaining blood lead levels became less expensive and easier and produced more accurate results. Increasing attention both to preventing environmental contamination of samples and to controlling laboratory quality also improved the accuracy of data collected. Advances in screening and analytical technology made the mass screening of the 1970s possible--both the programs coordinated by the CDC and NHANES II. NHANES II showed the extent of the problem of lead exposure to be even greater than previously thought. It was estimated that in 1980 almost 2 percent of all children aged six months to five years had blood lead levels over the CDC level of concern of 30 micrograms/dL. More than 13 percent of black children had levels above 30 micrograms/dL. Lead was certainly the most widespread threat to child health in America. In 1985, when the CDC lowered the level of concern to 25 micrograms/dL, the population defined to be at risk tripled.(ABSTRACT TRUNCATED AT 400 WORDS)