Determination of blood lead levels and characterization of potential environmental exposures among children in Kibera, Nairobi

Abstract

BACKGROUND: Lead is a heavy metal which is introduced to the environment by human activities. Excessive lead exposure through air, water, soil and food is harmful to the health and intellectual development of millions of children (Markowitz et al, 2000). For instance, lead has ability to cause neurotoxic (nerve poison) effects, particularly in children whose growing bodies are highly susceptible (Markowitz et al, 2000). There is overwhelming evidence • of higher concentration than allowable environmental lead levels in Nairobi, yet relative dearth of information and action regarding lead poisoning in Kenya. Widespreao and potentially excessive lead exposure has been reported in Nairobi by Mungatana et al. (2004). Lead levels in kales, maize, tap water and soil were 5,053ug/kg, 1,948ug/kg, 5.5ug/l and 44,350ug/kg respectively. These were higher than the acceptable World Health Organization lead levels in kales, maize, tap water and soil, which are 300ug/kg, 200ug/kg, 10ug/I and 100 - 120ug/kg respectively. OBJECTIVE: A study was carried out in Kibera slums, Nairobi between April and August 2007, with the main objective to determine the blood lead levels among 6 - 59 months old children born in Kibera and their potential environmental exposures and risk factors for elevated blood lead concentrations (BLL >10 Hg/dl). METHODS AND MATERIALS: This was a descriptive, cross-sectional study of 387 children, who presented at Yes to Kids (Y2K) program, VIPS Health Services at Woodley, Nairobi between June and August 2007. Upon approval of the study by the Ethic and Research Committee, training of interviewers and Laboratory technicians was held in tandem with pre-testing of the questionnaires. Parental, guardians or care givers gave consent for children's participation in the study. Participating children were carefully screened for inclusion criteria by medical doctors. Trained laboratory technologists at the clinic using the capillary blood collection protocol collected blood for lead analysis using both LeadCare II blood lead analyzer on 387 samples at Y2K program and Graphite furnace, Atomic Absorption Spectrometer on 22 samples, following a standardized analytical methods (Flajnik et al, 1994) at the Massechussetts Public State Laboratory in Boston, USA. Coded and close ended questionnaires were introduced to parents, guardians or care givers, asking about socio-demographic profiles, and residence characteristics, as well as potential risk factors for lead exposure. Pooled samples from selected potential sources of exposure (water, soil, kales) were collected from the villages from which the tested children came. Environmental samples were collected following the sampling methodology according to the Community Environmental Health Resource Center (www. Cehrc.org, 2006) and analyzed using flame Atomic Absorption Spectrophotometry, following a Shimadzu AA6300 standardized analytical method (Shimadzu, 2002). DATA ANALYSIS: Data management and analysis was done using Statistical Package for Social Sciences (SPSS) software, version 10. The CDC permissible childhood blood lead level of 10pg/dl was used as a cutoff point in the analysis. The socio-demographic characteristics, residence characteristics, and potential risk factors for exposure to lead among children with a blood lead levels > 10 pg/dl were compared to those of children with a blood lead levels <10 pg/dl. Chisquare test for independence, Spearman's correlation, Eta correlation and Analysis of Variance (ANOVA) were used to determine measures of association and statistical significance. Statistical significance was set at p = 0.05. RESULTS: Three hundred and Eighty Seven (387) children were involved in the study, with 52.8% and 47.2% being boys and girls respectively. The .mean blood lead level (BLL) was 5.997ug/dl (median = 5.400ug/dl, SD =2.42, Range 3.30 - 24.70ug/dl). There were 27 (7%, N = 387) children with BLL > 10 hg/6\, which was above the WHO/CDC cut off for lead poisoning. Blood lead level > 10 ug/dl was associated with non-permanent housing (X2 = 0.0565, df = 1, p = 0.812), playing on potentially lead contaminated grounds (OR = 0.89; 95%CI: 0.25 - 2.34, p = 0.627) and pica behaviour (OR = 0.72; 95%CI: 0.31 - 1.68, p = 0.439). Low risk parental occupation (OR = 14.28; 95% CI: 3.05 - 66.75; p = 0.001) was significantly associated with BLL > 10ug/dl among the children. The questionnaire was probably not the best surrogate for occupational lead exposure hence those classified as low risk for lead exposure could, infact have been high risk for occupational lead exposure. Kales sourced from the market/kiosks (OR = 14.24; 95% CI: 3.05 - 66.45; p = 0.001) were significantly associated with BLL £ 10ug/dl yet concentration of lead in analyzed kales were below detectable levels. It is possible that the kales analyzed for lead concentration were from sources different from those ingested by the children in the study. Soil lead levels (SoilPb) ranged from 3,000 to 90,000ug/kg, which was very high compared to WHO acceptable range of 100 - 200ug/kg. There was weak linear association (r2 = 0.0160) between SoilPb and mean BLL for a given village. There were no detectable levels of lead in kales and tap water. CONCLUSIONS: About 7% (N = 387) of the children tested had childhood lead poisoning (BLL > 10ug/dl), which is higher than in economically advantaged countries. Soil was the significant source of exposure to lead (Range in Kibera slums: 3,365 - 89,570 ug/kg; WHO allowable range: 100 - 120ug/kg), among the children in Kibera slums. With such high soil lead levels, the prevalence of childhood lead poisoning in Kibera could be higher than found using convenient, clinic - based sample in this study. Knowledge of the prevalence will determine the choice of lead screening strategy and devices. The knowledge on lead poisoning (5.4%, N = 387) and potential sources of exposure (3.1%, N = 387) were very low. Intervention strategies at the community will require advocacy and education about childhood lead poisoning. In comparison with other parts of the world, socioeconomic factors seemed to play an important role in childhood lead poisoning. Given the socioeconomic status of most Kenyans, the 7% prevalence in the study and higher figures e.g. 10% in Kariobangi North (UNEP, 2006) have raised a health flag that must be addressed.