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Environmental Research 100 (2006) 319–322 www.elsevier.com/locate/envres
Reductions in blood lead levels among school children following the introduction of unleaded petrol in South Africa Angela Matheea,b,, Halina Ro¨llina, Yasmin von Schirndingc, Jonathan Levina, Ina Naikd a
South African Medical Research Council, P.O. Box 87373, Houghton 2041, South Africa b University of the Witwatersrand c World Health Organization d National Institute for Occupational Health
Received 11 February 2005; received in revised form 1 August 2005; accepted 4 August 2005 Available online 6 October 2005
Abstract Epidemiological studies have indicated that in the 1980s and early 1990s (a period in which petrol lead concentrations in South Africa ranged from 0.836 to 0.4 g/L), large proportions of urban South African children were at risk of excessive exposure to environmental lead. In 1991, when the maximum permissible petrol lead concentration in the country equaled 0.4 g/L, a study determined that the mean blood lead level among children attending inner city schools in the Cape Peninsula equaled 16 mg/dL, with well over 90% of children having blood lead levels equaling or exceeding the internationally accepted guideline level of 10 mg/dL. Socio economic status, housing conditions, and proximity of children’s schools and homes to heavily trafficked roads were among the factors significantly associated with blood lead concentrations. In 1996, unleaded petrol was introduced in South Africa. A study undertaken in 2002 (at the same schools as in 1991), when unleaded petrol constituted around 30% of the market share of petrol in the country, has shown significant reductions in the mean blood lead concentration among Cape Peninsula inner city children and in the proportion of children with elevated blood lead levels. The mean blood lead level for the total sample (n ¼ 429) of children whose mean age equaled 7 years (range: 5–11 years) was 6.4 mg/dL (range: 1.0–24.5 mg/dL) and 10% of children had blood lead levels equalling or exceeding 10 mg/dL. The mean blood lead levels among children attending schools in an inner city and in a less heavily trafficked periurban suburb were 6.9 and 4.8 mg/dL, respectively. r 2005 Elsevier Inc. All rights reserved. Keywords: Blood lead; Children; South Africa
1. Introduction Over the past several decades, an overwhelming body of evidence which has associated even relatively low levels of lead in blood with a range of health effects in children has mounted. For example, studies have indicated associations between blood lead levels around 10 mg/dL and below and adverse neurological outcomes and behavioral effects (Lanphear et al., 2000; Davis, 1990; Pocock et al., 1994; Schwartz, 1994; Tong, 1998). It is increasingly thought that
Corresponding author. South African Medical Research Council, P.O. Box 87373, Houghton 2041, South Africa. Fax: +27 11 642 6832. E-mail address:
[email protected] (A. Mathee).
0013-9351/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.envres.2005.08.001
there may be no threshold of safety for certain lead-related health effects (Canfield et al., 2003). Reflecting research findings, steps have been taken by international organizations and countries around the world to reduce the risk of childhood lead exposure. For example, standards and guidelines for children’s blood lead levels have been lowered over time, and the internationally accepted action level for lead in children’s blood now equals 10 mg/dL (CDC, 1991). In recent years, concern has been expressed about the levels and nature of exposure to lead among children in various African settings in particular (Nriagu et al., 1996; Tong et al., 2000). Epidemiological studies undertaken in and around the South African city of Cape Town in the 1980s and 1990s showed that large proportions of children had blood lead
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concentrations equaling or exceeding 10 mg/dL (von Schirnding et al., 1991a, b, 2001). In 1984, the maximum permissible petrol lead concentration in South Africa equaled 0.836 g/L. Around that time the mean blood lead level among Cape Town inner city children equaled 16 mg/dL (von Schirnding et al., 1991a, b), and well over 90% of children had blood lead concentrations X10 mg/dL. By 1991, despite a reduction in the maximum permissible petrol lead level to 0.6 g/L in 1986, and yet again to 0.4 g/L in 1989, studies undertaken in the same suburbs as those in 1984 indicated that little change in children’s blood lead levels had occurred (von Schirnding et al., 2001). The mean blood lead level among children attending inner city schools still equaled 16 mg/dL, and more than 90% of children continued to have unacceptably high blood lead concentrations. The failure to observe a reduction in children’s blood lead levels following petrol lead reductions was attributed to the passing of insufficient time for reductions in lead concentrations in vehicular emissions to have translated to lowered lead levels in surface soil and dust and consequently children’s risk of exposure. Potential reductions in children’s blood lead concentrations following lowering of petrol lead concentrations may also have been masked by other sources of lead exposure associated with poor home environments, which were also found to be important in the study area. In addition, changes in socio economic status and traffic densities may have occurred over this period (von Schirnding et al., 2001). The study reported here was undertaken in 2002 and aimed to assess the impact on South African children’s blood lead concentrations of the introduction of unleaded petrol in 1996, which currently constitutes around 30% of the petrol market share in the country. 2. Methods A cross-sectional analytical study was conducted in three suburbs of the Cape Peninsula (Hout Bay, Woodstock, and Mitchell’s Plain) that were expected to have varying degrees of lead exposure as a consequence of variations in traffic levels. For example, Woodstock is an inner city suburb characterized by relatively heavy traffic, whereas Hout Bay is a coastal suburb located around 30 km south of central Cape Town. Mitchell’s Plain is an expansive suburban housing development around 20 km east of central Cape Town. All primary schools in Woodstock (seven) and Hout Bay (three) were included in the study, while in Mitchell’s Plain one primary school was chosen at random. The study population comprised first grade pupils with a median age of 7 years (range: 5–11 years) attending the selected schools. Similar cross-sectional studies of blood lead concentrations had been conducted at the same study schools in 1991, prior to the introduction of unleaded petrol. The parents of 69% of potential participants consented to their children’s participation in the study. The major portion of refusals to participate were concerned with the HIV/AIDs epidemic currently underway in South Africa reflecting fear either of infection or of covert testing. Of those for whom written informed parental consent was obtained, 15% were not included in the study due to absenteeism on the day of fieldwork and anxiety about or difficulty in blood sampling. A sample of approximately 7 mL of blood was successfully drawn from each of 429 children by medically trained personnel, using sterile disposable equipment. Blood samples were collected into tubes containing EDTA and stored at 4 1C until analysis, which was undertaken by the South African
National Institute for Occupational Health. Blood lead concentrations were measured using a flameless atomic absorption method of addition (Model Perkin–Elmer Analyst 300 with HGA 850) adapted from Baily et al. (1997). The accuracy of analyses was assessed by including certified quality control samples (Seronorm Trace Elements in Whole Blood, lot MR 9067, level 2). The laboratory participates in an international external quality assessment scheme (NEQUAS) and in the South African national quality control scheme for analyzing lead in blood (Ro¨llin et al., 1988). The limit of detection of lead in blood equaled 0.1 mg/dL. Structured questionnaires were self-administered by the parents or guardians of participating children to obtain information on socio economic status and potential risk factors for lead exposure.
3. Results Blood lead levels for the total sample of 429 children ranged from 1 to 24.5 mg/dL, with the mean and median levels, respectively, equaling 6.4 and 6.1 mg/dL. Table 1 gives the mean blood lead levels by area. As indicated, there were significant area differences in blood lead levels, with the mean blood lead level among children attending Hout Bay schools being significantly lower than that among their counterparts attending schools in either Mitchell’s Plain or Woodstock (Po0:0001). The proportion of children with blood lead levels equaling or exceeding 10 mg/dL was 10% for the total sample, while the proportions for Woodstock, Mitchell’s Plain, and Hout Bay, respectively, equaled 12%, 12%, and 3% (see Table 2). Mean blood lead levels at individual schools varied considerably and ranged from 3.3 mg/dL at one Hout Bay school to 8.1 mg/dL at a school in Woodstock. The proportion of children with high blood lead levels at individual schools ranged from zero at two schools (one in Hout Bay and the other in Woodstock) to 27% at a Woodstock school. With regard to blood lead levels in relation to South Africa’s apartheid-based population groups, the mean blood lead level among White children was significantly lower (3.5 mg/dL) than that among their Colored (mixed heritage) (7.0 mg/dL) or African black (6.0 mg/dL) counterparts (see Table 2). As can also be seen from Table 2, among White, Colored and African black children, respectively, 4%, 17%, and 9% had blood lead levels equaling or exceeding 10 mg/dL. The distribution of population groups differed considerably by area, with Hout Bay having significantly more White children.
Table 1 Mean blood lead levels by area N
Mean
SD
Minimum
Maximum
Woodstock Mitchell’s plain Hout Bay
239 95 95
6.9 6.9 4.8
2.8 3.1 2.3
1.0 2.0 1.4
18.7 24.5 11.6
Total
429
6.4
2.9
1.0
24.5
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Area
Woodstock 243 Mitchell’s 104 plain Hout bay 115
Population African group black Colored White
in 1991, this proportion was reduced to 22% in 2002 (see Table 2). The mean blood lead concentration in this group was similarly reduced from 16 to 7 mg/dL.
2002 Mean
%X N 10 mg/dL
Mean
%X 10 mg/dL
4. Discussion Between 1991 and 2002 significant reductions in the blood lead levels of children attending schools in the Cape Town suburbs of Woodstock, Mitchell’s Plain, and Hout Bay were observed, with a consequent reduction in the proportion of children at risk of the neurobehavioral and other health and social ill effects associated with elevated lead exposure. It is highly likely that this reduction, at least in part, is associated with phased reductions in the maximum permissible petrol lead concentration in South Africa since 1986 and the introduction in 1996 of unleaded petrol. There is little evidence to indicate that factors such as changes in socio economic status or the profile of economic/industrial activity might have made a major contribution to the reductions in blood lead levels observed. For example, while no data for the specific suburbs that were the focus of this study are available, it is known that unemployment within the City of Cape Town increased from 10% in 1991 to 18% in 2000 (www.capetown.gov.za). Under the umbrella of the apartheid system of government, schools in Woodstock, Hout Bay, and Mitchell’s Plain were largely reserved for White and Colored students. The desegregation of schools associated with the dismantling of Apartheid was followed by an influx of Black African children, on average of low socio economic status, into the study schools between 1991 and 2002 (see Table 2). These developments might have been expected to contribute to an increase rather than to a decrease in the blood lead concentrations of the study population. Significant area differences in blood lead concentrations remain in the Cape Peninsula, with children attending schools in the relatively heavily trafficked suburbs of Woodstock and Mitchell’s Plain having significantly higher blood lead concentrations than their counterparts in Hout Bay, where traffic density levels are lower. The mean blood lead level at one Hout Bay school now equals 3.3 mg/dL, which is approaching the concentrations being measured among children in countries such as the USA and the UK (Thomas et al., 1999). At some inner city schools, however, mean blood lead concentrations as high as 8.8 mg/dL were measured, and considerable proportions of children (as many as 29%) were found to have high blood lead levels. Nevertheless, the blood lead concentrations determined in this study are lower than those in some other African settings, for example in Nigeria and Egypt (Omar et al., 2001; Nriagu et al., 1997). The reductions in blood lead levels observed among children in this study are broadly comparable with what transpired in the USA between 1976 and 1991, when children’s mean blood lead levels declined by more than 70% and the proportion of children with blood lead levels equaling 10 mg/dL or higher decreased by around 70–80% (Pirkle et al., 1994). Further reductions in urban South
16 15
99 93
239 95
6.9 6.9
12 12
14
95
95
4.8
3
29
16
100
154
6.0
9
426 51
16 14
98 96
247 23
7.0 3.5
17 4
70
% OF SAMPLE
60 50 40 30 20 10 0
0 to 4
5 to 9 10 to14 15 to19 20 to 24 BLOOD LEAD LEVEL (ug/ dl) 1991
321
> 24
2002
Fig. 1. Comparison of blood lead distribution in Woodstock (1991 and 2002).
As can be seen from Fig. 1, the blood lead distribution determined in the 2002 study is significantly reduced relative to that measured in 1991. Using a two-sample t test, this reduction is statistically highly significant (t ¼ 40:9, Po0:0001). A further breakdown of the mean blood lead concentrations and the proportion of children with elevated blood lead levels by area and by population group in 1991 and 2002 is included in Table 2. As can be seen, in Woodstock, Mitchell’s Plain, and Hout Bay, mean blood lead concentrations in 2002 were reduced by 57%, 54%, and 66%, respectively, compared to those in 1991. The proportion of children with elevated blood lead levels had also decreased substantially between 1991 and 2002. In both 1991 and 2002 the mean blood lead concentration was lower in the relatively sparsely populated and less trafficked suburb of Hout Bay than in either Woodstock or Mitchell’s Plain, though the margin of difference in 2002 was distinctly greater than that in 1991. Similarly, substantial reductions in mean blood lead concentrations, and in the proportion of children with elevated blood lead levels were observed in 2002, relative to the 1991 study, with regard to population group. For example, whereas 98% of Colored children had elevated blood lead levels
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African children’s blood lead concentrations are expected to occur as the market share of unleaded petrol in the country increases in anticipation of the planned phase-out of leaded petrol by 2006. Nevertheless the blood lead levels measured in this study continue to constitute a major public health concern for South Africa, especially in light of emerging evidence of health effects below 10 mg/dL and the likelihood that the slope of the dose–effect relationship may be considerably steeper at levels below rather than above 10 mg/dL (Canfield et al., 2003). There is a particular need in South Africa to examine the contributions of non-petrol sources to children’s blood lead levels, including those from lead-based paint, transfer of particles from lead-related workplace settings into the home environment, and ‘‘cottage industries’’ that make use of lead, for example the dismantling of car batteries for lead recycling, repairs to electrical appliances using lead solder, and backyard motor vehicle repairs. A recent case study highlighted in particular the potential for South African children, especially those with pica tendencies, to be exposed to lead-based paint used to decorate their homes and school buildings (Mathee et al., 2003). The required research needs to be implemented in the context of an integrated cross-sectional plan of action to prevent childhood lead poisoning in South Africa. Such a lead poisoning prevention program needs to include aspects related to education programs to address current low levels of awareness of lead hazards among children, parents, teachers, and health workers, surveillance and screening in high risk areas and groups, development of blood lead standards for children, regulation of the permissible lead content of paint intended for residential use and on children’s toys and furniture, remediation of highly contaminated homes, schools, and other settings, and secondary prevention as necessary. Acknowledgments Financial and in-kind support from the South African Medical Research Council, the National Institute for Occupational Health, the United States Environmental Protection Agency, and Engen is gratefully acknowledged. Ms. Pam Cerff is thanked for her role in fieldwork coordination, and the children and parents who made the study possible are gratefully acknowledged. References Baily, P., Norval, E., Kilroe-Smith, T.A., Skikne, M.I., Ro¨llin, H., 1997. The application of metal-coated graphite tubes to the determination of
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