Predicting children’s blood lead levels from exposure to school drinking water in Addis Ababa, Ethiopia

Human beings could be exposed to impacts associated with heavy metals such as lead (Pb) through drinking water. The objective of this study was to evaluate quality of water consumed by kindergarten school children in Addis Ababa city, who are highly susceptible to issues related to heavy metals in water. Through conducting chemical analysis, using microwave plasma atomic emission spectrophotometry (MP-AES), the level of lead (Pb) was measured at 38 selected schools in the city. Drinking water samples were taken from three water supply sub-systems: Akaki, Legedadi, and Gefersa. Results revealed the average Pb concentration in the city was 62.37 μg/L which is significantly higher than the World Health Organization (WHO) recommended threshold value of 10 μg/L. The children’s blood lead levels and exposure to Pb were also calculated using the integrated exposure uptake bio-kinetic (IEUBK) model as per USEPA guidelines. Estimated geometric mean blood lead levels (BLLs) for each school ranged from 4.4 to 13.2 μg/dL. On average, the model predicted that 20% of children in the city will have blood lead levels above the WHO recommended 10 μg/dL. The study can be considered as an unprecedented piece of work as it addresses critical issues and methods to mitigate problems caused by high concentration of Pb in water supply distribution infrastructure. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/wh.2020.248 ://iwaponline.com/jwh/article-pdf/18/4/595/731107/jwh0180595.pdf Dawit Debebe (corresponding author) Fiseha Behulu Zerihun Getaneh School of Civil and Environmental Engineering, Addis Ababa Institute of Technology (AAiT), Addis Ababa University, Addis Ababa, Ethiopia E-mail: dawit6619@gmail.com


INTRODUCTION
Lead (Pb) is a toxic metal whose widespread use has caused extensive environmental contamination and health problems in many parts of the world (Cañas et al. ).
Exposure to lead is associated with a wide range of effects, including various neurodevelopmental effects, mortality (mainly due to cardiovascular diseases), impaired renal function, hypertension, impaired fertility, and adverse pregnancy outcomes. The presence of Pb in human organs is unwanted as it disturbs metabolic processes (WHO ). When exposed to high doses of lead, damage occurs in the brain, the red blood cells, and the kidney (USEPA ).
Lead in drinking water may come from contamination at the source, but it can also be present in tap water as a result of its dissolution from natural sources; rather, its presence is primarily from household plumbing systems containing lead in pipes, joints, fittings, or the service connections to homes (WHO ).
Children may be more exposed to lead than adults due to their behavior, diet, and metabolic and physiologic characteristics (Albalak et al. ). They take in more air, water, and food per unit of body weight per day than adults (Wigle et al. ). In addition, school-aged children spend many hours in and around school facilities that may expose them to potentially contaminated sources of water by lead. Further, schools are high-risk environments due to both the complex nature of their drinking water systems and the vulnerability of the users (WHO ). For these reasons assessing lead contamination in schools' water is very important.
Non-occupational exposure of the general population to lead is most likely to occur in developing countries like Ethiopia through the ingestion of contaminated drinking water because of the old water distribution systems (Haider et al. ). In the present study, the oldest water supply system in the country (almost back-dated to 100 years) was evaluated in view of Pb concentration. However, one of the key observations is that the authority mandated for the water delivery and administration in the metropolitan city, Addis Ababa Water and Sewerage Authority (AAWSA), does not monitor the level of any heavy metals in its drinking water system. On the other hand, unlike the industrialized countries, there are very limited studies conducted on the status of Pb, and therefore, it has been a major challenge to find data (Getaneh et al. ).
The intensity of lead exposure is mainly measured by blood lead levels. The USEPA has recommended the integrated exposure uptake bio-kinetic (IEUBK) model as a predictor of potential long-term blood lead levels for children (USEPA ). Child health risk assessment and blood lead levels in children were conducted using this model. The model has been widely used by several countries to estimate pediatric blood lead levels and its predictions have demonstrated close agreement with the measured blood lead level (USEPA ). The main objective of this study is to assess the levels of lead in drinking water at kindergarten schools and to assess the children's health risk through predicting blood lead levels.

MATERIALS AND METHODS
The study was conducted in Addis Ababa, the capital city of Ethiopia, which has a population of more than four million in an area of 540 km 2 (CSA ). The city gets its treated water from three sub-systems: A. Akaki subsystem has a ground water source and its treatment system is only disinfection (chlorination).
B. Legedadi subsystem has both ground and surface water sources.
• Its surface water source has a conventional water treatment system. This system includes pre-chlorination, coagulation, sedimentation, filtration, and post-chlorination (AAWSA ).
• The ground water source has a treatment system of disinfection (chlorination). These two systems then join at a reservoir.
C. Gefersa subsystem has a surface water source and it has a conventional water treatment system. This system is the same as Legedadi and includes pre-chlorination, coagulation, sedimentation, filtration, and post-chlorination (AAWSA ).
According to Addis Ababa Education Bureau, there are 164,072 kindergarten children in the city. Fifteen kindergarten schools from the Akaki sub-system, fifteen from Legedadi, and eight schools from Gefersa sub-systems were selected according to the sub-systems' coverage areas.
Samples were randomly chosen to make the schools dispersed and representative of the catchments, as shown in Figure 1. The sampling was carried out based on the standardized sampling techniques as outlined in USEPA guidelines for water testing (USEPA ).
One water sample was taken from each school giving a total of 38 samples. However, from the sources, two water samples were taken from each treatment plant, before and after the water is treated, which means six samples have been taken from the three treatment plants. The total number of samples taken is 44. Flushed water samples were taken and each sample had a volume of 500-1,000 mL, collected using pre-labeled 500-1,000 mL sterile plastic bottles. The bottles were initially cleaned using standard detergents and distilled water. The water samples were transported to the Addis Ababa University Faculty of Science, Department of Chemistry laboratory, and acidified and digested to a pH < 2 with 69% HNO 3 immediately and stored at 4 C in a refrigerator before analysis. Digestion and examining lead levels of the water samples were made based on the standard analytical method of the water quality (APHA ).

RESULTS AND DISCUSSION
Lead concentration in raw and schools' drinking water The findings revealed that all raw water samples taken from  (Table 1). These results showed that the lead concentrations between the three sources significantly differed from each   Table 2 shows that the lead concentration in Addis Ababa's tap water is higher than the other cities. Therefore, countermeasures should be taken to handle this high amount of lead in the water distribution system.

Blood lead levels (BLLs)
The blood lead level was predicted for each school and for the three catchments using their average lead concen-  USEPA recommends these percentages to be less than 5%, therefore, taking countermeasures for these problems is critical. There was also significant difference of average BLLs between the sub-systems (p < 0.001). From Tukey's multiple comparison test, the average BLLs of Legedadi sub-system were greater than the others (p < 0.001).
The average water lead concentration in Addis Ababa city being 62.7 μg/L, the average BLL and percentage of a child's probability of having BLL above 10 μg/L was 6.75 μg/dL and 20.17%, respectively ( Figure 2). For the present study, if soil and air lead concentrations were measured, more children in the city would have BLLs above 10 μg/dL. The study conducted in Jimma by Getaneh et al. () showed the mean lead concentration of the soil from the four quadrants of the town was 220.08 ± 135.95 μ/g and the average air lead concentration was 1.01 ± 0.41 μg/m 3 . As was justified by the same study, the high air lead content may be related to pollutants emitted from cars, buses, and trucks (Getaneh et al.

).
Since Addis Ababa is densely populated and has heavy traffic movement, air lead concentrations would be greater than or equal to that of Jimma town. This, in turn, causes more children in the city to have BLLs above 10 μg/dL. showed that soil lead level would also be higher than the default selected values in the model and more children would be exposed to lead contamination in Addis Ababa.

CONCLUSION
In general, the content of mean lead in water from the selected sub-systems is above the acceptable level set by the WHO, 10 μg/L. Children could also be affected by exposure to lead (Pb); many different organs and physiological functions (neurological, hematological, cardiovascular, renal, immune, and other functions) are affected even at very low exposure levels of lead. According to different studies carried out on dose-response association between blood lead levels and IQ, revealed failure is stronger at blood lead levels lower than 10 μg/dL. The American Control for Disease Center (CDC) also sets a lead poisoning reference of 5 μg/ dL. If we take this value as a benchmark, the exposure would be even higher than the results in this study.
Conducting research to identify the exact sources of Pb in the piped drinking water and at the source is crucial. Standard environmental safeguard implementation practices should be followed by the government. Some of these practices include reduced or limited use of agricultural inputs that may lead to excess production of heavy metals including lead, catchment protection through afforestation practices and reduction of sediment yield by building check dams in the upstream part, monitoring, evaluation and periodic review of lead levels in drinking water, soils, and air (environment) at regular intervals and maintaining a database either by Regional or Federal EPA Downloaded from http://iwaponline.com/jwh/article-pdf/18/4/595/731107/jwh0180595.pdf by guest of Ethiopia is mandatory. Also, monitoring of lead-composed insecticides, rodenticides, and herbicides in agricultural sectors is necessary since it could be the source of lead in the raw water samples.