RESEARCH

Studies & Findings

LEAD EXPOSURE IN DEVELOPING COUNTRIES

Drs. Mauricio Hernandez-Avila, Marlene Cortez-Lugo, Ilda Munoz,

Martha Maria Tellez, Rojo-Soliz

In humans, lead poisoning of occupational or environmental origin may alter virtually all biochemical process and organ systems; lead can interfere with the reproductive and cardiovascular systems, with the blood formation process, vitamin D function, neurological processes, among others (1). Of special concern has been lead’s impact on the cognitive development of children (2-5). Various studies have reported that relative small concentrations of lead in blood are associated with persistent problems in learning and school performance. Children with higher blood lead levels have been shown to have lower intelligence scores than their counterparts from a similar socioeconomic background, but with lower blood lead levels (5). Early recognition of these toxic effects has prompted interventions worldwide that have resulted in major reductions in lead exposure in many countries.

In contrast with developed countries where lead exposure is on the decline due to the implementation of environmental and occupational regulations (1), in developing countries lead poisoning continues to be one of the most important problems of environmental and occupational origin (6). There are many reasons that suggest that without proper actions lead exposure will remain a threat to many generations of children in the developing world (6).

Lead-intoxication coexists with other important health problems like low immunization coverage, malnutrition or sanitation deficiencies, which are considered at a higher priority. In addition to the other competing health priorities, adequate control of lead exposure is also hampered by the difficulties experienced in implementing and enforcing new environmental and occupational regulations. The approval and execution of new norms often face resistance from politicians and policy makers who are more concerned about employment figures or containment of inflation than about a clean environment. The private sector favors low production costs at higher environmental impacts, in order to maintain profits in a global economy. In developed countries, organized and informed workers and groups counterbalance resistance to new regulations. However, in developing countries these counterbalancing forces are largely nonexistent, underdeveloped or largely under funded. This situation has delayed the allocation of resources needed to adequately assess, evaluate, control and prevent lead exposure in most urban conglomerates located in these countries. In developing countries, with the exception of leaded gasoline, most sources remain largely understudied and uncontrolled.

Although lead exposure is recognized as an important public health problem there are few studies published from developing countries. Further more, most published studies have not evaluated the effect of lead exposure among children aged six to 24 months who are at higher risk of exposure and of suffering the neurotoxic health effects of lead exposure. Therefore the real magnitude of the problem remains unknown. In Table 1, we have summarized recent published studies. Reported concentrations vary significantly between countries, probably reflecting the different sources and the populations selected. However, most studies show that lead continues to be a problem in these countries. Targeting effective control measures to reduce lead exposure will require special attention to the local patterns of exposure.

Potential sources of lead exposure may vary within and between countries. For example in the United States lead in paint is an important source of exposure, while for Mexico and many other countries in Latin America this source is largely irrelevant (1). In Mexico, food prepared in lead-glazed ceramics is a recurrent source of exposure to lead (7), while in the United States this source is only responsible for small limited outbreaks of lead poisoning in children of Mexican origin (8). Therefore, in order to develop integrated programs to control important sources of lead, it is essential to conduct epidemiological studies to better define sources and to assess their relative importance in order to adequately target and evaluate interventions to reduce lead exposure.

The growing recognition of lead’s dangerous effects has led to a worldwide initiative to reduce lead content of gasoline (9). This initiative has already conditioned important reductions in ambient air lead levels and population blood lead levels. For example, in the United States the removal of leaded gasoline from 1976 to 1991, conditioned a reduction of 78% blood lead levels (10). In Mexico City introduction of unleaded gasoline in 1990 was associated with a decline in lead ambient concentrations from an annual average of 1.2 ug/m3 to an annual average of 0.2 m g/m3 in 1998 (figure 1). As expected, corresponding changes were also observed in blood lead levels. Blood lead levels among 1st graders children attending to the same school in the south Mexico City have declined from 17 ug/dl in 1990 to 6.2 ug/dl in 1997 (figure 2). Other studies have reported an estimated decline of 7.6 m g/dl in the mean blood lead of children living in Mexico City (11).

Although blood lead levels have declined, children born in Mexico City will still face the risk and consequences of intra-uterine lead exposure (12). The skeleton is the primary storage site for approximately 95 percent of lead in the adult human body. Accumulating evidence suggests that during pregnancy exposure to lead may increase due to the mobilization of endogenous bone-lead stores. During pregnancy, fetal calcium requirements are met in part through an increase in maternal bone turnover, allowing the possibility of a greater increment in bone lead released into circulation. Bone-lead release during pregnancy has been associated with lower birth weights, suggesting that even at low blood lead levels, exposure may occur due to the mobilization of endogenous lead sources. In Figure 3 we present a comparative analysis regarding bone lead levels observed among women living in Boston, US and in Mexico City, Mexico. Recent environmental exposure to leaded gasoline explains the higher bone lead levels observed among Mexican women.

It is likely that transition from leaded to unleaded gasoline will reduce lead exposure in the population at large. However, there is concern that all internationally supported activities will concentrate in this transition, while living other sources of lead exposure are largely unattended. Therefore it is important to sum up activities to control other lead sources against those implemented and funded by initiatives related to phasing lead out of gasoline. This is important given that as opposed to the almost universal exposure that results from the use of leaded gasoline, that resulting from other sources tends to be concentrated in less privileged population living under poverty. The continued exposure to lead in these populations perpetuates the circle of poverty and underdevelopment. Therefore it is important to change the perception that no additional research is needed in relation to lead epidemiology. Applied epidemiological research within countries will be needed to characterize and control exposure resulting from mining related activities and from informal cottage industries that recycle batteries, fabricate ceramics or repair radiators, among others.

Several studies give indication of the importance of different sources. Bonilla et al (13) in a study conducted in Nicaragua, compared blood lead levels of children (aged 6 months to 13 years) living in the neighborhood of a battery factory with those living in a comparable community with no documented lead exposure. Results of this study documented that children living close to the factory had a mean blood lead level of 17.2 ug/dl, while children in the control community had a mean blood lead level of 7.4 ug/dl. Similar results have been reported from Berat, Albania (14), that children living close to a battery factory had a mean blood lead level of 43.4 ug/dl, while comparable children of similar age living at a distance greater than 2 km from the plant had a mean blood lead level of 15.0 ug/dl.

Actions driven by the findings in these studies differed, while in Nicaragua the plant was closed, in Albania the population received advice regarding how to avoid lead exposure. Families depending on employment in polluting industries may have a double side impact when severe control measures are implemented. On one side, their children may be suffering health effects due to exposure to the toxic, while on the other, children may suffer consequences of unemployment if the factory is closed. Current technology allows clean production and therefore substantial reductions in emission rates. These cases illustrate some of the complicated issues regarding environmental control.

Other studies have documented the impact of mining activities. In Torreon, Mexico (15) roadside surface-dust samples from residential neighborhoods in the vicinity of a metal smelter documented unusually high lead levels (2,448 ug/g recommended value 550 ug/g). Although these samples were collected in 1995, the impact of this environmental exposure remained unattended until 1999, when local newspapers reported in the issue. Recently, community driven interest has forced the company and governmental agencies to evaluate the problem and to initiate remedial actions for the affected area.

Other sources of lead exposure have been linked to cottage industry in many parts of the world. For example backyard repair and recycling of batteries have been documented in Jamaica (16) and Brazil (17). A recent study conducted by Vahter et al documented this problem in the Ecuadorian Andes. The authors studied two communities that had close to 2600 inhabitants and whose main activity was the production of lead-glazed tiles. Tiles were produced in about 200 family owned tile-glazing shops. Lead for glazin was obtained from discarded car batteries. The mean blood lead levels for children aged 4-15 years was 51 ug/dl. Children whose families were directly involved in fabrication of tiles had a blood level of 60. ug/dl, while those children whose families were not directly involved had a blood lead level of 21 ug/dl. Similar, although lower levels of exposure have been documented by Fernandez et al in Mexico. In this study children, less than 5 years of age, whose families were involved in the fabrication of glazed ceramics had mean blood levels of 25 ug/dl. In Mexico, lead needed for the glaze is not obtained from car batteries, this difference in the source of lead may explain the large observed differences in blood lead levels in these populations.

In addition to the different cultural patterns of manufacture of lead related products that take place in developing countries, diet is likely to play an important role (19,20). Lead absorption may be modulated by nutritional status. Nutrient deficiency such as calcium, iron and zinc have been associated with high blood lead levels (20), and several studies conducted in Mexico City among children and women of reproductive age have shown that calcium intake was inversely related to blood lead levels (21,22). However, the potential therapeutic effect of dietary calcium or iron has not yet been adequately evaluated in relation to lead absorption in human populations(23). Further more, there is some evidence suggesting that toxic adverse effects of lead may be more important among subjects with iron deficiency. Iron deficiency is a prevalent condition all over the world, but it is particularly prevalent among poor children, who are more likely to be exposed to lead.

Control of lead exposure in developing countries will require additional efforts to properly target interventions to account for the particular condition in which exposure takes place. Further research will be needed to identify sources of lead and the populations at risk of exposure. Interventions will need the allocation of financial resources to support targeted screening activities, educational programs and regulatory and enforcement actions. Interventions will also require identification and engaging of different stakeholders. The identification and engagement of stakeholders is a key activity for any intervention development. Decisions that are made in collaboration and with the active participation of stakeholders will be more effective.

Finally, it is important to note that universal screening programs will not reduce lead exposure unless this activity is coupled with environmental actions to reduce lead emissions and to conduct the proper rehabilitation of affected sites. Educational and medical interventions to reduce lead levels are needed once the primary source has been identified and removed.

References

1. Howson PC, Hernandez-Avila M, Rall DP. Lead in the Americas. A Call for Action. Institute of Medicine, USA, 1995

2. Dietrich KN, Krafft KM, Bornschein RL, Hammond PB, Berger O, Succop PA, Bier M. Low-level fetal lead exposure effect on neurobehavioral development in early infancy. Pediatrics 1987;80:721-730.

3. Bellinger D, Leviton A, Waternauz C, Needleman H, Rabinowitz M. Longitudinal analyses of prenatal and postnatal lead exposure and early cognitive development. N Engl J Med 1987;316:1037-1043.

4. Bellinger D, Leviton A, Rabinowitz M, Allred E, Needleman H, Schoenbaum S. Weight gain and maturity in fetuses exposed to low levels of lead Environ Res 1991;54:151-158.

5. Banks EC, Ferreti LE, Shucard DW. Effects of low level lead exposure on cognitive function in children: A review of behavioral, neuropsychological and biological evidence. Neurotoxicology 1997;18:237-282.

6.- Romieu I. Lacasana M. McConnell R. Lead exposure in Latin America and the Caribbean. Environ Health Persp 1997;105:398-405.

7. Romieu I. Palazuelos E. Hernandez Avila M. Rios C. Munoz I. Jimenez C. Cahero G. Sources of lead exposure in Mexico City. Environmental Health Perspectives. 1994;102:384-9.

8. MMWR. Lead poisoning associated with imported candy and powdered food coloring-California and Michigan. Morbidity and Mortality Weekly Reports 1998;47:1041-1043.

9. Lovei M., Phasing out lead from gasoline. World Bank Technical paper no 397, 1998.

10. Pirkle JL, Brody DJ, Gunter EW, Kramer A, Paschal DC, Flegal KM, Matte TD. The Decline in Blood Lead Levels in the United States: The National Health and Nutrition Examination Surveys (NHANES). JAMA. 1994;272:284-291.

11. Rothenberg SJ. Schnaas L. Perroni E. Hernandez RM. Karchmer S. Secular trends in blood lead levels in a cohort of Mexico City children. Archives of Environmental Health. 1998;53(3):231-5.

12. Gonzalez-Cossio T. Peterson KE. Sanin LH. Fishbein E. Palazuelos E. Aro A. Hernandez-Avila M. Hu H. Decrease in birth weight in relation to maternal bone-lead burden. Pediatrics. 1997;100:856-62.

13. Bonilla CM and Mauss EA. A community-initiated study of blood lead levels of Nicaraguan Children living near a battery factory. Am J Public Health 1998;88:1843-1845.

14. Tabaku A. Bizgha V. Rahlenbeck SI. Biological monitoring of lead exposure in high risk groups in Berat, Albania. Journal of Epidemiology & Community Health. 1998;52(4):234-6.

15. Benin AL, Sargent JD, Dalton M, Roda S. High concentrations of heavy metals in neighborhoods near ore smelters in Northern Mexico. Environ Health Persp 1999;107:279-284.

16 Matte TD. Figueroa JP. Ostrowski S. Burr G. Jackson-Hunt L. Baker EL. Lead exposure from conventional and cottage lead smelting in Jamaica. Archives of Environmental Contamination & Toxicology. 1991;21(1):65-71.

17. Silvany-Neto AM, Carvalho FM, Tavares TM, et al. Lead poisoning among children of Santo Amaro, Bahia, Brazil in 1980, 1985, and 1992. Bull Pan Am Health Organ. 1996;30:51-62.

18 Vahter M. Counter SA. Laurell G. Buchanan LH. Ortega F. Schutz A. Skerfving S., Extensive lead exposure in children living in an area with production of lead-glazed tiles in the Ecuadorian Andes. International Archives of Occupational & Environmental Health. 70(4):282-6, 1997

19. Peraza MA. Ayala-Fierro F. Barber DS. Casarez E. Rael LT. Effects of micronutrients on metal toxicity. Environ Health Perspect. 106 Suppl 1:203-16, 1998

20. Mahaffey KR. Nutrition and lead: strategies for public health. Environmental Health Perspectives. 1995;103(Suppl 6)191-196.

21. Lacasana-Navarro M. Romieu I. Sanin-Aguirre LH. Palazuelos-Rendon E. Hernandez-Avila M. Calcium intake and blood lead in women in reproductive age Revista de Investigacion Clinica. 1996;48:425-430.

22. Hernandez-Avila M. Sanin LH. Romieu I. Palazuelos E. Tapia-Conyer R. Olaiz G. Rojas R. Navarrete J. Higher milk intake during pregnancy is associated with lower maternal and umbilical cord lead levels in postpartum women. Environ Res. 1997;74:116-121.

23. Sargent JD. The role of nutrition in the prevention of lead poisoning in children. Pediatric Annals. 1994;23:636-642.

24. Stoltzfus RJ. Rethinking anemia surveillance. Lancet. 349:1764-6,1997.

25. Fernandez GO. Martinez RR. Fortoul TI. Palazuelos E. High blood lead levels in ceramic folk art workers in Michoacan, Mexico. Archives of Environmental Health. 52(1):51-5, 1997.

26. Shen XM. Yan CH. Guo D. Wu SM. Li RQ. Huang H. Ao LM. Zhou JD. Hong ZY. Xu JD. Jin XM. Tang JM. Umbilical cord blood lead levels in Shanghai, China. Biomedical & Environmental Sciences. 1997;10:38-46

27. Heinze I. Gross R. Stehle P. Dillon D. Assessment of lead exposure in schoolchildren from Jakarta. Environmental Health

 

Table I. Recent published studies describing blood lead levels among selected population in developing countries.

Author and year of publication

City and country

Age group

(years)

Population studied

Sample size

Sources of exposure

identified

blood levels in mg/dl

Song HQ (1993)

Beijing, China

5-6

children

128

Air & food

7.7

Shen XM (1998)

Shanghai, China

At birth

Newborns

348

Proximity to major traffic road

Paternal occupation

9.2

Heinze I (1998)

Jakarta, Indonesia

7

Schools children

131

Leaded gasoline

7.7

Hwang YH (1990)

Taipei, China

At birth

Newborns

205

Air Lead

7.4

Saxena DK (1994)

Lucknow,India

At birth

Newborns

Not identified

16.9

Potula V (1996)

Madras,India

26-55

Office workers

10

Gasoline & ambient air

4.1

Autoshop workers

9

17.5

Bus drivers

22

12.1

Traffic police

88

11.2

Bonilla C, 1998

Villa Venezuela, Nicaragua

1-14 years

children

30

Air lead

7.4

Managua, Nicaragua

6months to 13 years

Children

97

Living close to a Battery factory

17.2

Counter SA (1997)

Rural communities

Ecuador

4-15

children

82

Recycling of batteries

52.6

Schutz A

(1997)

Montevideo

Uruguay

2-14

Children

96

Exposure to traffic

9.5

Lopez-Carrillo

1996

 

 

 

Mexico City

Mexico

1-5

Children

603

Ambient air

Lead Glazed Ceramics

15.0

Romieu I

1995

1-5

Children

200

Ambient air

Lead glazed ceramics

9.9

Hernandez-Avila

1998

At birth

Children

238

Ambient air

Lead glazed ceramics

7.1

Farias P

1996

13-43

Pregnant women

513

Ambient air

Lead glazed ceramics

11.08

Ramirez AV

1997

Lima, Peru

18-50

Adult

320

 

Degree of industrialization

26.9

Huancayo, Peru

22.4

La Oroya, Peru

34.8

Yaupi, Peru

14.0

Nriagu J (1997)

Durban Metropolitan region

3-10

Children

1200

Ambient air

10.0

 

Vulamehlo

South Africa

3.8

 

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