Maternal and Umbilical Cord Blood Lead Levels in Selected Informal Settlements in Nairobi, Kenya: A Cross-Sectional Study

Introduction

Lead (Pb) is a well-characterized neurodevelopmental toxicant that can cross the placenta.¹ In prior Nairobi-based studies, the prevalence of blood lead levels (BLLs) $>10\mathrm{\mu }\mathrm{g}/\text{dL}$ was 70% in pregnant women² and 30% in children 2–20 years of age.³ To our knowledge, no prior studies have reported umbilical cord BLLs in Nairobi and data more recent than one to two decades ago on maternal BLLs in sub-Saharan Africa (SSA) are lacking.

In 2020–2021, we measured Pb in maternal and cord blood in a convenience sample of mothers delivering at a hospital that caters to women from the Nairobi informal settlements, Dandora and Kariobangi. Dandora is home to Nairobi’s main dumpsite; studies of environmental samples show heavy contamination with Pb.⁴ Kariobangi is clustered with cottage industries, including informal lead acid battery recycling.⁵ We aimed to characterize current maternal Pb exposures in these communities and explore associations between potential Pb sources and BLLs.

Methods

Mothers delivering at Pumwani Hospital, $\ge 18$ years of age, residing in Dandora or Kariobangi for $>1$ y, with singleton pregnancy and no known pregnancy complications, were recruited/eligible. Of 150 enrolled mothers with informed consent, 100 were included in the analysis; those excluded were due to refusal (22), new pregnancy complications or fetal/infant death (20), and sample mislabeling (8). Kenyatta National Hospital–University of Nairobi–Ethics and Research Committee (P835/10/2019) approved this study.

At delivery, a nurse drew $2\mathrm{mL}$ of maternal venous and $1\mathrm{mL}$ of umbilical cord blood into trace element-free dipotassium ethylenediaminetetraacetic acid Vacutainer tubes (BD).⁶ For every 20 samples, a field blank was collected. Samples and blanks were stored at $4 Degrees Celsius$,² then digested using $4\mathrm{mL}$ of 69% nitric acid (${\text{HNO}}_3$) on a hot plate inside a fume hood for $\sim 3$ h at $100°\mathrm{C}$ as described.⁶ One distilled–deionized water blank was digested each day along with the samples.

Working Pb standards of 10, 20, 30, 40, and 50 ppb were prepared from a stock standard traceable to ISO 17025 (Reagecon). Assays for total Pb were done in triplicate using an inductively coupled plasma mass spectrometer (ICP-MS) (Thermo Scientific, ICAP RC model) at the Government Chemist Laboratory (Nairobi), with the mean used for analysis. Trace metals grade ${\text{HNO}}_3$ (Thermo Fisher Scientific) and the clean procedures described by Benoit et al.⁷ were used.

The method detection limit (MDL) was set at the lowest calibrant concentration. Pb was not detected in any blanks. Machine values were used for six cord blood samples with Pb concentrations < MDL (range $0.718–0.913\mathrm{\mu }\mathrm{g}/\text{dL}$). Accuracy was evaluated using matrix spikes and certified reference material (CRM) ClinChek Whole Blood Control, lyophilized, for Trace Elements, Level I, II, III (RECIPE Chemicals + instruments GmbH).

After delivery, a trained nurse administered a brief standardized questionnaire regarding demographics and potential sources of Pb adapted from Were et al.⁸ and World Health Organization recommendations on environmental risk factors surveys for pregnant women.

We calculated descriptive statistics and evaluated bivariate associations between BLLs and demographic and Pb exposure characteristics using R/RStudio (version 2022.07; Posit). We used multivariable linear regression to evaluate associations between natural log-transformed maternal BLLs and age, education, and potential exposure sources (yes/no). A reduced model including only age and a full model containing all variables were fit to the data and evaluated by examining residual plots and the adjusted $R^2$. The same approach was used with natural log-transformed cord BLLs. We exponentiated regression coefficients ($\mathrm{\beta }$), used the formula $[{\text{exp}}^{\left(\mathrm{\beta }\right)}-1]\times 100$ to express results as a percentage change in BLL per predictor increment, and considered predictors without 0 in their 95% confidence interval (CI) statistically significant.

Results and Discussion

Maternal BLLs ranged from $4.0\text{\hspace{0.17em}to\hspace{0.17em}}91.2\mathrm{\mu }\mathrm{g}/\text{dL}$ (mean $27.3\pm 15.5\mathrm{\mu }\mathrm{g}/\text{dL}$), and cord BLLs ranged from $0.7\text{\hspace{0.17em}to\hspace{0.17em}}9.9\mathrm{\mu }\mathrm{g}/\text{dL}$ (mean $2.7\pm 1.9\mathrm{\mu }\mathrm{g}/\text{dL}$) (Table 1). Maternal and cord BLLs were positively correlated (${\mathrm{\rho }}_{\text{Spearman}}=0.65$, $p<0.0001$); 23% and 100%, respectively, of the cord and maternal BLLs exceeded the US Centers for Disease Control and Prevention’s blood Pb reference value of $3.5\mathrm{\mu }\mathrm{g}/\text{dL}$.⁹

Table 1.

Demographic and potential characteristics related to lead (Pb) exposure and blood lead levels in participants ($N=100$) delivering at Pumwani Maternity Hospital (Nairobi, Kenya) in 2020–2021.

Characteristic	$n$
Maternal age [y (median)]	30.5
Residence location
Dandora	52
Kariobangi	48
Maternal highest level of education
Primary school	30
Secondary school or higher	65
No formal education	5
Maternal occupation
Housewife	18
Business	11
Cleaner	10
Other service jobsa	58
Battery recycling/smelting	3
Other jobs with potential Pb exposureb	0
Years in this occupation
0–5	78
$>5\text{\hspace{0.17em}to\hspace{0.17em}}10$	22
Live in a painted house
No	13
Yes	87
House paint peeling or chipping
No	29
Yes	58
Median years living in this house	2
Live in a building undergoing renovation or construction
No	80
Yes	20
Live or work near (within $1\text{-km}$ radius) an active lead smelter/battery recycling plant
No	52
Yes	48
Drinking water passes through old pipes and fixtures
No	47
Yes	53
Use old painted pottery or glazed pottery at home
No	43
Yes	57
Live near a dumpsite (within $1\text{-km}$ radius)
No	44
Yes	56
Ingested non-food items such as soil or stones in pregnancy (pica)
No	60
Yes	40
Aware of Pb as a toxicant or Pb poisoning
No	100
Yes	0
Maternal blood Pb ($\mathrm{\mu }\mathrm{g}/\text{dL}$)
$\text{Mean}\pm \text{SD}$	$27.3\pm 15.5$
Max (min)	91.2 (4.0)
Percentile
25th	14.6
50th	26.7
75th	33.9
Cord blood Pb ($\mathrm{\mu }\mathrm{g}/\text{dL}$)
$\text{Mean}\pm \text{SD}$	$2.7\pm 1.9$
Max (min)	9.9 (0.7)
Percentile
25th	1.6
50th	2.1
75th	3.2
Excluding 3 highly Pb-exposed battery recycling workers ($n=97$)
Maternal blood Pb ($\mathrm{\mu }\mathrm{g}/\text{dL}$)
$\text{Mean}\pm \text{SD}$	$26.2\pm 12.9$
Max (min)	64.3 (4.0)
Percentile
25th	14.7
50th	26.6
75th	33.2
Cord blood Pb ($\mathrm{\mu }\mathrm{g}/\text{dL}$)
$\text{Mean}\pm \text{SD}$	$2.6\pm 1.7$
Max (min)	9.9 (0.7)
Percentile
25th	1.6
50th	2.1
75th	3.1

Note: All characteristics besides blood lead levels were self-reported. Max, maximum; min, minimum; SD, standard deviation.

^a Bus conductor, carpenter, cook, grocery attendant, street vendor, money transfer attendant, nanny, salon worker, security, and shop attendant.

^b Construction, electronics recycling/repair, garbage collection/burning, house painting, and welding.

Three mothers reported working as battery recyclers and had maternal (cord) BLLs of $91.2\mathrm{\mu }\mathrm{g}/\text{dL}$ ($9.8\mathrm{\mu }\mathrm{g}/\text{dL}$), $86.0\mathrm{\mu }\mathrm{g}/\text{dL}$ ($9.2\mathrm{\mu }\mathrm{g}/\text{dL}$), and $13.8\mathrm{\mu }\mathrm{g}/\text{dL}$ ($1.5\mathrm{\mu }\mathrm{g}/\text{dL}$). We considered them highly Pb-exposed workers and excluded them from the regressions. In the reduced models, each maternal age year was associated with 11% (95% CI: 9%, 12%) and 5% (3%, 8%) increases in maternal and cord BLL, respectively. Living in a painted house was also significantly associated with maternal and cord BLLs in bivariate analyses. In the full models (Figure 1), each maternal age year was associated with 9% (95% CI: 7%, 11%), or 0.07 $\left(0.06,0.09\right)\mathrm{\mu }\mathrm{g}/\text{dL}$, and 4% (1%, 6%), or 0.015 $\left(0.004,0.02\right)\mathrm{\mu }\mathrm{g}/\text{dL}$, increases in maternal and cord BLLs, respectively. Living in a painted house with no peeling/chipping paint was associated with 58% (95% CI: 19%, 109%), or 0.5 $\left(0.2,0.9\right)\mathrm{\mu }\mathrm{g}/\text{dL}$ increases in maternal BLL and 75% (18%, 161%), or 0.3 $\left(0.07,0.6\right)\mathrm{\mu }\mathrm{g}/\text{dL}$, increase in cord BLLs, compared with not living in a painted house, whereas living in a painted house with peeling/chipping paint was associated with 76% (95% CI: 36%, 128%), or 0.6 $\left(0.3,1.0\right)\mathrm{\mu }\mathrm{g}/\text{dL}$ increase in maternal and 87% (30%, 169%), or 0.3 $\left(0.1,0.6\right)\mathrm{\mu }\mathrm{g}/\text{dL}$, increase in cord BLLs. Living near battery recycling (vs. not) was associated with a 16% (95% CI: 1%, 34%), or 0.1 $\left(0.01,0.3\right)\mathrm{\mu }\mathrm{g}/\text{dL}$, increase in maternal BLL but was not significantly associated with cord BLLs. Education level, home renovation, proximity to dumpsite, pica, drinking from old pipes, and using glazed pottery were not significantly associated with BLLs in the maternal or cord blood models.

Figure 1.

Associations between demographic or environmental factors and natural log-transformed (A) maternal and (B) cord blood lead levels in multivariable linear regression models using data from 97 participants delivering at Pumwani Maternity Hospital (Nairobi, Kenya) in 2020–2021 (adjusted $R^2$: maternal blood model 0.72, cord blood model 0.30; points indicate coefficient estimates, error bars indicate 95% CIs). Three participants employed at a battery recycling facility were excluded. Numeric data are available at https://github.com/anneried/Lumumba-et-al/tree/main. Note: CI, confidence interval; Ref, reference category.

These high Pb levels are concerning, considering the neurodevelopmental effects associated with even very low levels of BLL ($<5\mathrm{\mu }\mathrm{g}/\text{dL}$).⁹ Furthermore, they reveal a global disparity, where BLLs are declining in high-income countries (HICs), such as the United States, but remain high in low and middle-income countries (LMICs).¹⁰ A 2018 systematic review reported a weighted mean BLL of $26.24\mathrm{\mu }\mathrm{g}/\text{dL}$ in pregnant women in SSA comprising data from 14 surveys from 1997–2013.¹⁰ One included study, from a comparable community in Nairobi in 1998, reported a mean BLL of $28.4\mathrm{\mu }\mathrm{g}/\text{dL}$,² similar to our data. It should be noted that a legal limit was established in 2018 to phase out lead in paint in Kenya, although the implementation process is quite slow, particularly in the informal settlements with poor housing conditions.⁵ Persistent lead exposure may occur during sweeping and dusting in houses painted with lead-based paints.

Multilevel strategies have been adopted in HICs, including policy changes to remove lead from gasoline, restrict lead in residential paint, regulate airborne lead emissions, address lead in water infrastructure, and limit lead in some foods and children’s products. Although leaded gasoline was banned in Kenya in 2006⁸ and actions on leaded paints are in progress, screening and surveillance are nonexistent and medical system and public education on lead hazards are absent. Kenya and other LMICs should consider implementing established strategies to reverse the increasing global disparity in lead exposure.