Previous Next

Health of People, Places and Planet

7

Environmental Lead Exposure and Childhood Development

The Port Pirie Cohort Study

Shilu Tong

Abstract

‘Environmental health’ is as broad as it is diverse in scope. As seen from this book, Tony McMichael contributed and advanced many aspects of the discipline, and indeed the field more broadly. In particular, his influence on the direction of the discipline and the policy responses to so many of the key issues that he addressed are recognised throughout this book as being seminal. Lead is one of the topics to which Tony’s research contributed. I was fortunate at the time to have been an eager student and the lead project was one in which I participated.

Background

In the late 1970s and early 1980s, another important but unanswered question was whether environmental lead exposure might affect young children’s health and development. Lead, from old house paint flakes, car exhaust and some industrial activity was a widespread pollutant. Many cross-sectional studies examined whether exposure to environmental lead at levels previously believed to be innocuous affected neuropsychological development and most of them found an inverse association between exposure measures and neuropsychological performance (Needleman et al., 1979; Smith et al., 1983; Winneke et al., 1983; Harvey et al., 1984; Schroeder et al., 1985; Lansdown et al., 1986; Fulton et al., 1987; Pocock et al., 1987; Hatzakis et al., 1989).

Cross-sectional studies cannot address the temporal relationship between exposure to environmental lead and neuropsychological development because they measure the exposure and outcome(s) at the same time. To test this hypothesis and address the limitations of cross-sectional studies, cohort studies have subsequently been conducted in several countries.

The Port Pirie Lead Smelter Study

Port Pirie, South Australia, has the largest lead smelter in the southern hemisphere. The Port Pirie cohort study (PPCS) commenced in 1979 (McMichael et al., 1988). This was the world’s first and largest long-term follow-up study of the influence of early childhood exposure to environmental lead on the neurological and cognitive development of children. The research team had recruited a cohort of 723 children by 1981. These represented an estimated 90 per cent of all pregnancies in and around Port Pirie over a three-year period.

Blood samples were taken from each child at specified ages, and blood lead concentration was measured. Children’s ‘first teeth’ – after they were shed – were collected to provide a further measure of accumulated lead exposure. Lead exposures varied greatly within the community, depending both on the proximity of residence to the smelter and on the levels of lead contamination in house dust and soil. At children’s ages 2, 4, 7 and 12, a structured interview was conducted with one of the parents (usually the mother) and neuropsychological tests were administered by a well-trained research psychologist.

I came from China to join Tony and his team in early 1990, to work on the ongoing PPCS. Tony was then Professor of Environmental and Occupational Medicine in the Department of Community Medicine at the University of Adelaide. Shortly after I arrived in Adelaide, Tony wanted me to learn a little about Australian culture and environment and took me to Victor Harbour, which was about 70 km away from the town. Tony and I enjoyed the natural beauty there. By the time I joined the PPCS, the children were around 10 years old. For my PhD research (my supervisors: Tony, Drs Peter Baghurst and Michael Sawyer), I coordinated the follow-up and neuropsychological assessments in the later stage of childhood, at ages 11–13.

Results and Discussion

Of the 723 singleton live births recruited into the study, 601 were assessed at age 2, 548 at age 4, 494 at age 7 and 375 at 11–13 years of age. The geometric mean blood lead concentration of the children in this cohort increased from 8.3 μg/dl (0.40 μmol/l) at birth to 21.2 μg/dl (1.02 μmol/l) at age 2, and decreased to 7.9 μg/dl (0.38 μmol/l) by the age of 11–13. The PPCS collected information on critical features of lead exposure, such as the timing and extent, together with many other socio-environmental factors that might confound the relationship between lead exposure and neuropsychological development. In this study, we found that exposure to lead in this cohort of children was associated inversely with cognitive performance at ages 2, 4, 7 and 11–13, and that this association was still apparent after adjustment for a wide range of confounding factors.

Similar to the PPCS, most other cohort studies (Needleman et al., 1990; Dietrich et al., 1991; Baghurst et al., 1992; Bellinger et al., 1992; Wasserman et al., 1992; Fergusson and Horwood, 1993; McMichael et al., 1994; Lanphear et al., 2005), but not all (Cooney et al., 1989; Ernhart et al., 1989), also found a significant inverse relationship between early exposure to environmental lead and cognitive functioning in childhood after adjustment for confounding factors. However, an important question was raised about whether the apparent deleterious effect of early-life exposure to lead could be reversed when, later in childhood, exposure was reduced. Such exposure reduction could occur either by environmental management or as a consequence of the decreased absorption that appears to accompany growth.

The children’s lifetime average blood lead level covered a wide range, from a low level of around 3–5 μg/dl up to around 30 μg/dl (Tong et al., 1996). Figure 7.1 shows that the children are grouped into three exposure categories: low, medium and high, by thirds of lifetime average blood lead concentration up to age 2 (the age when the children’s developmental status was assessed for the first time in this cohort study). Their development score, on the vertical axis, changed in a fairly linear way across those three categories, and that was similar at each of the four assessment ages – shown by the four coloured bars. There  was an approximately 5 per cent decline in IQ across a whole range of blood lead levels, after potential confounders had been taken into account.

Figure 7.1 Developmental status at different ages by thirds of lifetime average blood lead concentration at age 2.

Source: Author’s work.

Additionally, we assessed the reversibility of the apparent effects of lead on cognitive abilities in early childhood by testing whether reductions in blood lead concentrations beyond the age of 2 were associated with improvements in cognition (Tong et al., 1998). The key finding was that the cognitive deficits associated with exposure to environmental lead in early childhood appeared, at most, to be only partially reversed by a subsequent decline in blood lead (Table 7.1). The results from the PPCS indicate that the putative effects of lead on the neuropsychological development of children are genuinely irreversible, and therefore efforts to reduce the exposure of children to environmental lead from a very early age become increasingly important.

Table 7.1 Changes in blood lead concentration and changes in cognitive functioning between 2, 4 and 7 and 11–13 years.

Decline in blood

ΔZ scorea

lead (μg/dl)

N

Mean (SD)

95% CI

P-valueb

From 2 to 11–13 years

<10.2

109

0.03 (0.94)

–0.15 to 0.21

10.2~16.2

108

0.04 (1.01)

–0.15 to 0.23

0.74

>16.2

109

–0.01 (1.02)

–0.20 to 0.18

From 4 to 11–13 years

<6.0

109

0.05 (0.90)

–0.12 to 0.23

6.0–10.3

108

0.01 (0.91)

–0.17 to 0.18

0.42

>10.3

109

0.01 (0.96)

–0.17 to 0.19

From 7 to 11–13 years

<2.3

109

–5.4 (8.3)

–3.8 to –7.0

2.3–4.9

108

–5.0 (9.3)

–3.2 to –6.8

0.45

>4.9

109

–3.8 (7.9)

–2.3 to –5.3

Notes:

a ΔZ score = (Z11–13 – Z2) or ΔZ score = (Z11–13 – Z4) or ΔZ score = (Z11–13 – Z7)

b analysis of variance test.

Source: Tong et al., 1998.

Conclusion

This study provided strong evidence of the detrimental and dose-related impact of lead exposure on early child development, and showed the irreversible nature of lead effects. It demonstrated the importance of prevention and the early treatment of children with lead poisoning. However, lead contamination in a community can last for a long time and is difficult to eliminate. For example, there has not been much reduction in lead smelter emissions, and lead contamination is still widespread in Port Pirie (Taylor et al., 2013).

These results contributed to Australia’s move to mandatory lead-free petrol in the 1990s, and were important in the World Health Organization (WHO) and Organisation for Economic Co-operation and Development (OECD) revisions of lead exposure standards soon after. Tony, in conjunction with Drs Peter Baghurst, Graham Vimpani and Neil Wigg, led this seminal study, which made a significant contribution to protecting children from lead effects, both nationally and internationally (Burns et al., 1999; Tong et al., 2000).

Acknowledgements

The author thanks Drs Tony McMichael, Peter Baghurst, Graham Vimpani and Neil Wigg for their constant support and mentoring; Mrs Maureen Wauchope for blood sampling and interviews; Mr Charles Greeneklee for assessing the packed cell volume of blood samples; Ms Elaine Witham for blood lead and iron analyses; Mr Jim Lyster for supervising developmental assessments; and the families who participated in this study.

The PPCS was supported by a series of grants from the National Health and Medical Research Council, the Channel 7 Children’s Research Foundation and the University of Adelaide, Australia.

References

Baghurst, P.A., McMichael, A.J., Wigg, N.R., Vimpany, G.V., Robertson, E.F., Roberts, R.J., et al. 1992. Environmental exposure to lead and children’s intelligence at the age of seven years: The Port Pirie cohort study. The New England Journal of Medicine 327, 1279–84.

Bellinger, D., Stiles, K. & Needleman, H.L. 1992. Low-level lead exposure intelligence and academic achievement: a long-term follow-up study. Pediatrics 90, 855–61.

Burns, J.M., Baghurst, P.A., Sawyer, M.G., McMichael, A.J. & Tong, S.L. 1999. Lifetime low-level exposure to environmental lead and children’s emotional and behavioral development at ages 11–13 years. The Port Pirie cohort study. The American Journal of Epidemiology 149, 740–9.

Cooney, G.H., Bell, A., McBride, W. & Carter, C. 1989. Low-level exposure to lead: the Sydney Lead Study. Developmental Medicine & Child Neurology 31, 640–9.

Dietrich, K.N., Succop, P.A., Berger, O.G., Hammond, P.B. & Bornschein, R.L. 1991. Lead exposure and the cognitive development of urban preschool children: the Cincinnati lead study cohort at age 4 years. Neurotoxicology and Teratology 13, 203–11.

Ernhart, C.B., Morrow-Tlucak, M., Wolf, A.W., Super, D. & Drotar, D. 1989. Low level lead exposure in the prenatal and early preschool periods: intelligence prior to school entry. Neurotoxicology and Teratology 11, 161–70.

Fergusson, D.M. & Horwood, L.J. 1993. The effects of lead levels on the growth of word recognition in middle childhood. International Journal of Epidemiology 22, 891–7.

Fulton, M., Raab, G.M., Thomson, G.O.B., Laxen, D.P.H., Hunter, R. & Hepburn, W. 1987. Influence of blood lead on the ability and attainment of children in Edinburgh. The Lancet 1, 1221–6.

Harvey, P.G., Hamlin, M.W., Kumar, R. & Delves, H.T. 1984. Blood lead, behaviour and intelligence test performance in preschool children. Science of the Total Environment 40, 45–60.

Hatzakis, A., Kokkevi, A., Maravelias, C., Katsouyanni, K., Salaminios, F., Kalandidi, A., et al. 1989. Psychometric intelligence deficits in lead-exposured children. In: Smith, M., Grant, L. & Sors, A. (eds) Lead Exposure and Child Development: An International Assessment. Kluwer Academic Publishers, Lancaster, UK, 211–23.

Lanphear, B.P., Hornung, R., Khoury, J., Yolton, K., Baghurst, P., Bellinger, D.C., et al. 2005. Low-level environmental lead exposure and children’s intellectual function: an international pooled analysis. Environmental Health Perspectives 113, 894–989.

Lansdown, R., Yule, W., Urbanowicz, M.-A. & Hunter, J. 1986. The relationship between blood lead concentrations, intelligence, attainment and behaviour in a school population: the second London study. International Archives of Occupational Environmental Health 57, 225–35.

McMichael, A., Baghurst, P., Wigg, N., Vimpani, G., Robertson, E. & Roberts, R. 1988. Port Pirie Cohort Study: childhood blood lead history and neuropsychological development at age four years. The New England Journal of Medicine 319, 468–75.

McMichael, A.J., Baghurst, P.A., Vimpany, G.V., Robertson, E.F., Wigg, N.R. & Tong, S.L. 1994. Tooth lead levels and IQ in school age children – The Port Pirie cohort study. The American Journal of Epidemiology 140, 489–99.

Needleman, H.L., Gunnoe, C., Leviton, A., Reed, R., Peresie, H., Maher, C., et al. 1979. Deficits in psychologic and classroom performance of children with elevated dentine lead levels. The New England Journal of Medicine 200, 689–95.

Needleman, H.L., Schell, A., Bellinger, D., Leviton, A. & Allred, E.N. 1990. The long-term effects of exposure to low doses of lead in childhood: an 11-year follow-up report. The New England Journal of Medicine 322, 83–8.

Pocock, S., Ashby, D. & Smith, M. 1987. Lead exposure and children’s intellectual performance. International Journal of Epidemiology 16, 57–67.

Schroeder, S.R., Hawk, B., Otto, D.A., Mushak, P. & Hicks, R.E. 1985. Separating the effect of lead and social factors on IQ. Environmental Research 38, 144–54.

Smith, M., Delves, T., Lansdown, R., Clayton, B. & Graham, P. 1983. The effects of lead exposure on urban children: the Institute of Child Health/Southampton study. Developmental Medicine & Child Neurology 47, 1–54.

Taylor, M.P., Camenzuli, D., Kristensen, L.J., Forbes, M. & Zahran, S. 2013. Environmental lead exposure risks associated with children’s outdoor playgrounds. Environmental Pollution 178, 447–54.

Tong, S.L., Baghurst, P.A., McMichael, A.J., Sawyer, M. & Mudge, J. 1996. Lifetime exposure to environmental lead and children’s intelligence at 11–13 years: the Port Pirie cohort study. BMJ 312, 1569–75.

Tong, S.L., Baghurst, P.A., Sawyer, M., Burns, J.M. & McMichael, A.J. 1998. Declining blood lead levels and changes in cognitive function during childhood: the Port Pirie Cohort Study. Journal of the American Medical Association 280, 1915–9.

Tong, S.L., von Schirnding, Y. & Prapamontol, T. 2000. Environmental lead exposure: a public health problem of global dimensions. Bulletin of the World Health Organization 78, 1068–77.

Wasserman, G., Graziano, J.H., Factor-Litvak, P., Popovac, D., Morina, N., Musabegovic, A., et al. 1992. Independent effects of lead exposure and iron deficiency anemia on developmental outcome at age 2 years. Journal of Pediatrics 122, 695–703.

Winneke, G., Krämer, U., Brockhaus, U., Ewer, U., Kujanek, G., Lechner, H., et al. 1983. Neuropsychological studies in children with elevated tooth-lead concentrations. II. Extended study. International Archives of Occupational Environmental Health 51, 231–52.


Previous Next