EPIDEMIOLOGIC NOTES AND REPORTS HUMAN LEAD ABSORPTION -- Texas

As part of its continuing commemoration of CDC's 50th anniversary in June 1996, MMWR is reprinting selected MMWR articles of historical interest to public health, accompanied by a current editorial note. Reprinted below is the first published report (published December 8, 1973) of a large-scale systematic study of community exposure to emissions from a lead smelter.

In December 1971, the City-County Health Department in El Paso, Texas, discovered that an ore smelter in El Paso was discharging large quantities of lead and other metallic wastes into the air. Between 1969 and 1971, this smelter had released 1,116 tons of lead, 560 tons of zinc, 12 tons of cadmium, and 1.2 tons of arsenic into the atmosphere through its stacks (Table_1).

Twenty-four hour air samples to determine the amounts of lead and other heavy metals suspended in the atmosphere were collected throughout 1971 and again between July 1972 and June 1973 by the local health department. Both series of tests showed that mean concentrations of metallic wastes in the air were highest immediately downwind of the smelter and that levels decreased logarithmically with distance from the smelter. The annual mean lead level immediately downwind of the smelter in 1971 was 92 uG/m3 and in 1972-73 was 43 uG/m3; the U.S. Environmental Protection Agency's proposed safe upper limit for airborne lead content is 2.0 uG/m3 of air (1). No metallic emissions were found near any of 15 other industrial establishments studied in El Paso.

Similarly, soil samples taken by the health department at selected sites within the urban area between June and December 1972 showed the highest concentrations of lead and other metals to be in surface soil from within 0.2 miles of the smelter (Figure_1). Samples of drinking water, milk, and food obtained from homes in El Paso between January and March 1972 by the health department were uniformly free of lead.

Preliminary testing programs to evaluate the effect of the environmental contamination on human blood lead levels were conducted in El Paso between January and March 1972 by the local health department, the smelting company, and CDC. These initial studies showed that 43% of persons in all age groups and 62% of children through age 10 years living within 1 mile of the smelter had blood lead levels greater than or equal to 40 uG%, a level considered to be evidence of undue lead absorption (2). There was a lower prevalence among persons living at greater distances from the smelter. No cases of overt lead poisoning were noted.

In August 1972, a random survey of the entire population living within 4.1 miles of the smelter in south and west El Paso was conducted by the health department and CDC. The area was divided along census tract lines into 3 strata, roughly concentric about the smelter and each with a radius of 1.0-1.5 miles. In the small, innermost stratum, all households were visited; in the 2 outer strata, approximately 2% of households were selected. Of 833 occupied households included in the survey, 672 (80.6%) were reached for the interview. A venous blood sample for lead analysis by atomic absorption spectrophotometry (AAS) was obtained from all persons up to age 20 years and from every other person above that age; samples of paint, soil, household dust, and pottery were also collected in each home for lead analysis by AAS. In all age groups, the percentage of blood levels greater than or equal to 40 uG% was found to be highest in those persons living nearest the smelter (Figure_2), and the prevalence was highest in the youngest individuals; migration rates among these persons were low. In area I, 5 (8.5%) of 59 persons 1-19 years of age with blood lead levels greater than or equal to 40 uG% had moved into the area in the 2 years preceding the survey. In areas II and III, the migration rate for persons 1-19 years of age with blood levels greater than or equal to 40 uG% was 8.2% (4 of 49); 1 person in this group had moved from area I.

A total of 1,971 paint samples were collected for lead analysis. In area I, 9 (39.1%) of 23 children 1-4 years had exposure to at least 1 paint sample with a lead content of 1.0% or more; the comparable figures for areas II and III were 11 (33.3%) of 33 and 17 (34.0%) of 50 children, respectively. These three rates were virtually identical (pgreater than 0.9 by Chi-square).

Analysis of over 4,000 soil and household dust samples indicated that the mean content of lead in these specimens was significantly higher in area I than in areas II and III. Furthermore, persons 1-19 years with blood lead levels greater than or equal to 40 uG% were found to have been exposed to soil and dust samples with significantly higher (pless than 0.001) mean lead contents (3,264 ppm for soil, 3,522 ppm for dust) than persons with blood lead levels below 40 uG% (means: 1,032 ppm and 1,279 ppm).

Pottery vessels were used for food storage or preparation in 37 homes visited. After 1% hydrochloric acid incubation for 6 hours, 2 of 6 vessels from sector I, 6 of 19 from sector II, and 4 of 12 from sector III had a lead content greater than or equal to 100 G per ml in the eluate. (Reported by Bernard F. Rosenblum, M.D., M.P.H., Director, El Paso City-County Health Department; James M. Shoults, Acting Environmental Engineer, El Paso City-County Health Department; J. Julian Chisolm, Jr,. M.D., Chief of Pediatrics, Baltimore City Hospitals; Community and Environmental Management Activities, Bureau of State Services, CDC; the Field Services Branch, Bureau of Epidemiology, the Toxicology Section, Clinical Chemistry, Hematology, and Pathology Branch, Bureau of Laboratories, CDC; and a team of EIS Officers.)

editorial Note: It may be estimated from this prevalence survey, using 1970 U.S. Census data, that at least 2,700 persons 1-19 years of age in El Paso had blood lead levels greater than or equal to 40 uG% at the time of the survey (Table_2). These results indicate that the problem of undue lead absorption affects persons across all of south and west El Paso to a distance of at least 4 miles from the smelter. Lead emitted by the smelter and deposited in soil and dust would appear to be the major source of the lead absorbed by humans; the accumulation in the soil and dust of emitted lead is facilitated by several features of the local environment, particularly the aridity, the sheltering effect of the high mountains, and the frequent thermal inversions. Ingestion of lead-based paint may account for a small fraction of cases of undue absorption (at most 1/3) in the youngest children. Careful neurologic and psychologic studies of persons in El Paso with blood lead levels greater than or equal to 40 uG% have been conducted and are being compared with results of similar studies in a matched group with lower lead levels. This story will make it possible to ascertain objectively whether any persons are suffering subtle but possibly permanent neurologic or psychologic sequelae from prolonged lead absorption.

Control measures undertaken to date include partial reduction of smelter emission and relocation to more distant public housing of approximately 500 persons who had lived closely adjacent to the smelter property. references

1. Written Communication. U.S. Environmental Protection Agency, 1972

2. Medical Aspects of Childhood Lead Poisoning. Pediat 48:464-468, 1971

   Editorial Note

Editorial Note 1997: When a team of Epidemic Intelligence Service officers from CDC, led by Dr. Philip Landrigan, joined the local health department in El Paso, Texas, in March 1971 to investigate lead exposure associated with an ore smelter, the scientific understanding of pediatric lead toxicity was about to enter a period of rapid progress. Many studies have since documented the public health threat posed by poorly controlled lead emissions from lead smelters around the world (1). The range of lead exposure produced in populations living near lead smelters has, in turn, facilitated studies of the mechanisms and health consequences of pediatric lead exposure.

A major objective of the El Paso investigation was to determine whether high blood lead levels (BLLs) in children were associated with smelter emissions or were explained by other lead sources also found in the community. A high level of lead emissions in a residential area was not then assumed to be a public health threat, as it is today. A 1972 National Academy of Sciences report on lead, while motivated by growing concern about widespread dispersal of lead in the environment, stated in its preface: "lead attributable to emission and dispersion into the general ambient environment has no known harmful effects" (2). In El Paso, the inverse gradient in air (3), dust, and soil contamination as one moved away from the smelter, and the parallel blood lead gradient (also found in a complementary investigation of lead exposure in Juarez, Mexico {4}) supported the argument that soil and dust are important vehicles of exposure. This finding foreshadowed subsequent research demonstrating the pathway from lead in soil and dust to lead contamination of hands to lead in blood, presumably from normal hand-to-mouth behavior and ingestion of contaminated soil and dust (5-7).

In 1975 and 1976, CDC investigators, led by Dr. Edward Baker, documented the potential for exposure to leaded dust among children of workers at a secondary lead smelter in Tennessee (8). Their findings and those of other investigations of "take-home" lead exposure that followed brought about provisions in the 1978 Occupational Safety and Health Administration (OSHA) standard for occupational lead exposure requiring hygienic measures in general industry to prevent lead workers from carrying lead dust home on their skin, shoes, and clothing (9).

In the 1960s and 1970s, children living near smelters or in the households of smelter workers were only a small part of a widespread national problem of "undue lead absorption" (10). In urban areas, deteriorated lead paint in older housing made the problem especially acute. In the same year as the El Paso survey, a door-to-door survey of inner-city children in Rochester, New York, found a mean BLL of 44 ug/dL (5 ), which was close to that measured near the El Paso smelter.

Since the early 1970s, it also has become more clear that lead is a multimedia contaminant and that demonstrating the importance of a given source does not rule out the contribution of other sources. For example, data from the Second National Health and Nutrition Examination Survey (NHANES II) conducted from 1976 through 1980 indicated that the mean BLL among children aged less than 6 years residing in rural areas was 14 ug/dL (average levels were 3-6 ug/dL higher among children living in more urbanized areas) (11). During the same period, widespread population exposure to lead emissions was reflected in average BLLs that declined in close parallel to the decreasing consumption of leaded gasoline (12). Thus, children living near the El Paso smelter, children in the homes of lead workers, and children in downtown Rochester probably shared with children across the country a contribution to their BLLs from lead in gasoline. Local sources, added to the higher background exposure prevalent at the time, resulted in BLL distributions that are extremely high by today's standards.

Perhaps the most telling indication of how the scientific view of lead exposure has changed since 1971 is that, in 1971 "undue lead absorption" referred only to BLLs greater than or equal to 40 ug/dL. Numerous subsequent studies documented that BLLs much lower than 40 ug/dL, then considered acceptable, adversely impact the health of children without causing overt symptoms. For example, investigators from CDC's Bureau of Epidemiology, again led by Dr. Landrigan, found an inverse relation between BLLs and nerve conduction velocities among children exposed to emissions from a smelter near Kellogg, Idaho (13). As the decade closed, Dr. Herbert Needleman's landmark study was published, demonstrating lower cognitive test scores and higher teachers' ratings of behavioral problems among children with higher tooth lead levels but no history of clinically overt lead poisoning (14).

Epidemiologic studies identified subclinical effects of lead by comparing the health of children with different levels of lead exposure. For most U.S. populations studied in the 1970s, the least exposed children had BLLs well above the average in the U.S. population today. Thus, health effects at lower levels could not be detected. As population BLLs decreased through the 1980s, careful prospective studies found subtle effects of lead on learning and behavior at BLLs well below those of the least exposed children in El Paso (15).

In addition to contributing to scientific knowledge about lead exposure and its effects on health, findings from the El Paso survey and others precipitated measures to reduce emissions at lead smelters. In 1977, a follow-up investigation by CDC and the El Paso Health Department found that BLLs among children living nearest the smelter had decreased by approximately 50% (16). More importantly, the El Paso survey was a prelude to a large body of continuously refined epidemiologic investigations that provided the impetus for actions to dramatically reduce population lead exposure from lead in gasoline, soldered food cans, drinking water conduits, and other sources in the United States. As a result, mean BLLs among children have declined nationally by greater than 80% overall and by similar amounts in population subgroups defined by age, race, ethnicity, income levels, and urbanization (17,18). More recently, international agreements to reduce the use of leaded gasoline may bring about significant reductions in worldwide lead exposure. Ironically, the unfortunate epidemics of lead toxicity near smelters in El Paso and elsewhere ultimately enabled more rapid progress in understanding and controlling lead exposure than might otherwise have been possible. 1997 Editorial Note by Thomas Matte, MD, MPH, Medical Epidemiologist, Henry Falk, MD, Director, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

References

1. Roberts RM, Hutchinson TC, Paciga J, et al. Lead contamination around secondary smelters: estimation of dispersal and accumulation by humans. Science 1974;186:1120-3.

2. Committee on Biologic Effects of Atmospheric Pollutants. Lead: airborne lead in perspective. Washington, DC: National Academy of Sciences, 1972.

3. Landrigan PJ, Gehlbach SH, Rosenblum BF, et al. Epidemic lead absorption near an ore smelter: the role of particulate lead. N Engl J Med 1975;292:123-9.

4. Ordonez BR, Romero LR, Mora R. Epidemiologic investigation regarding levels of lead in the pediatric population and in the household environment in the city of Juarez, Chihuahua, in relation to a smelter in El Paso, Texas {Spanish}. Boletin de la Oficina Sanitaria Panamericana 1976;80:303-17.

5. Charney E. Lead poisoning in children: the case against household lead dust. In: Chisholm JJ, O'Hara DM, eds. Lead absorption in children -- management, clinical, and environmental aspects. Baltimore, Maryland: Urban and Schwarzenberg, 1982.

6. Roels HA, Buchet JP, Lauwerys RR, et al. Exposure to lead by the oral and the pulmonary routes of children living in the vicinity of a primary lead smelter. Environ Res 1980;22:81-94.

7. Clark CS, Bornschein RL, Succop P, Que Hee SS, Hammond PB, Peace B. Condition and type of housing as an indicator of potential environmental lead exposure and pediatric blood lead levels. Environ Res 1985;38:46-53.

8. Baker EL, Folland DS, Taylor TA, et al. Lead poisoning in children of lead workers: home contamination with industrial dust. N Engl J Med 1977;296:260-1.

9. US Department of Labor. Occupational Safety and Health Administration. 29 Code of Federal Regulations 1910.1025 Lead.

10. Lin-Fu JS. Historical perspective on health effects of lead. In: Mahaffey KR, ed. Dietary and environmental lead: human health effects. New York: Elsevier Science Publishers, 1985.

11. Mahaffey KR, Annest JL, Roberts J, Murphy RS. National estimates of blood lead levels: United States, 1976-1980: association with selected demographic and socioeconomic factors. N Engl J Med 1982;307:573-9.

12. Annest JL, Pirkle JL, Makuc D, Neese JW, Bayse DD, Kovar MG. Chronological trend in blood lead levels between 1976 and 1980. N Engl J Med 1983;308:1373-7.

13. Landrigan PJ, Baker EL Jr, Feldman RG, et al. Increased lead absorption with anemia and slowed nerve conduction in children near a lead smelter. J Pediatr 1976;89:904-10.

14. Needleman H, Gunnoe C, Leviton A, et al. Deficits in psychologic and classroom performance in children with elevated dentine lead levels. N Engl J Med 1979;300:689-95.

15. Schwartz J. Low-level lead exposure and children's IQ: a meta-analysis and search for a threshold. Environ Res 1994;65:42-55.

16. Morse DL, Landrigan PJ, Rosenblum BF, Hubert JS, Housworth J. El Paso revisited: epidemiologic follow-up of an environmental lead problem. JAMA 1979;242:739-41.

17. CDC. Update: blood lead levels -- United States, 1991-1994. MMWR 1997;46:141-6.

18. Pirkle JL, Brody DJ, Gunter EW, et al. The decline in blood lead levels in the United States: The National Health and Nutrition Examination Surveys (NHANES). JAMA 1994;272:284-91.

Table 1 Particulate Waste Stack Emissions (in Tons {t}), by Year
El Paso Smelter, 1969-1971
===================================================================
Year    Total Particulates     Lead    Cadmium    Zinc   Arsenic
-------------------------------------------------------------------
1969          1,443t            292t     3.3t     139t   0.3t
1970          2,274             511      4.9      264    0.6
1971          1,282             313      3.8      157    0.3

Total         4,999t          1,116t    12.0t     560t   1.2t
===================================================================

Table 2 Estimated Numbers of Persons 1-19 Years With Blood Lead Levels >=40 uG%, by Distance from Shelter El Paso, Texas -- August 1972
============================================================================================================================================
                                         Sample Group                                       Population 1-19 Years *
                               ------------------------------------------     --------------------------------------------------------------
Distance from Smelter (Miles)   No. Tested    % With Blood Lead >=40 uG%       No. of Children      Projected No. with Blood Lead >=40 uG%
--------------------------------------------------------------------------------------------------------------------------------------------
  0-1.0                             259                  43.2                         723                             312
1.1-2.4                             246                  11.0                      12,316                           1,355
2.5-4.1                             253                   9.5                      11,486                           1,091

Total                               758                  19.9                      24,525                           2,758
--------------------------------------------------------------------------------------------------------------------------------------------
* 1970 Census.
============================================================================================================================================

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