Exposure and Health Risk Assessment of Lead in Communities of Jimma Town, Southwestern Ethiopia Zerihun Getaneh, Seblework Mekonen & Argaw Ambelu
Bulletin of Environmental Contamination and Toxicology ISSN 0007-4861 Volume 93 Number 2 Bull Environ Contam Toxicol (2014) 93:245-250 DOI 10.1007/s00128-014-1293-7
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Author's personal copy Bull Environ Contam Toxicol (2014) 93:245–250 DOI 10.1007/s00128-014-1293-7
Exposure and Health Risk Assessment of Lead in Communities of Jimma Town, Southwestern Ethiopia Zerihun Getaneh • Seblework Mekonen Argaw Ambelu
•
Received: 5 December 2013 / Accepted: 10 May 2014 / Published online: 24 May 2014 Ó Springer Science+Business Media New York 2014
Abstract Human beings could be exposed to lead arising from different environmental sources, such as air, water and soil. Tap water, air and soil samples were collected from four quadrants of Jimma town in southwestern Ethiopia. Eighty samples from each environmental source: water, air and soil samples were collected and analyzed for lead concentration. Prediction of the blood lead level and risk characterization was made using integrated exposure uptake biokinetic model and lead risk was calculated using USEPA guideline. Average concentration of lead in water, air and soils were 24.55 ± 10.01, 1.01 ± 0.41 lg/m3, and 220.08 ± 135.95 lg/g respectively. Uptake of lead by children is significantly higher than the adults. The total risk value was 1.41 for children and 0.37 for adults. The finding revealed that children are more at risk than adults. Keywords Environmental samples Ethiopia Exposure assessment Lead poisoning Risk quotient Lead is a toxic metal whose widespread use has caused extensive environmental contamination and health problems in many parts of the world (Can˜as et al. 2013). Children are particularly vulnerable to the neurotoxin effects of lead and even relatively low levels of exposure can cause serious and, in some cases, irreversible
Z. Getaneh (&) School of Civil and Environmental Engineering, Addis Ababa University, Addis Ababa, Ethiopia e-mail:
[email protected] S. Mekonen A. Ambelu Department of Environmental Health Sciences and Technology, College of Public Health and Medical Science, Jimma University, Jimma, Ethiopia e-mail:
[email protected]
neurological damage (Lidsky and Schneider 2003). Lead is rarely 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, solder, fittings or the service connections to homes (WHO 2006). Soil is one of the sources of lead to human and most important pathway of its human exposure as well as sink for lead (Davies 1980; Miller 2007). Motor vehicle emissions are one source of lead in the environment (Alloway 1995) specifically to the ambient air. Heaviest contamination of ambient air occurs near the highway (ATSDR 2006). Another source of lead contamination of air is incineration of lead containing waste and lead in electric wires as well as recovery processes (Amitai et al. 1991; WHO 2006). Unlike that of the industrialized regions, data from developing countries is very scarce (Ukhun et al. 1990; Nriagu et al. 1996). In Ethiopia, despite existence of huge number of potential sources of lead into the environment, human lead exposure and health risk in older cities, like Jimma town, has never been studied. Non-occupational exposure of the general population to lead is most likely to occur in Ethiopia through the ingestion of contaminated food or drinking water and by the inhalation of lead particulates from ambient air (Ahmed et al. 2008). The USEPA has recommended integrated exposure uptake biokinetic (IEUBK) model as a predictor of potential long-term blood lead levels for children and adults in residential settings (USEPA 2005). Comparisons between measured blood lead data and IEUBK model predictions have demonstrated close agreement (USEPA 2002). Therefore, the main objective of this study was to determine lead concentration in tap water, soil and air samples and predict the human health risk from the contamination using IEUBK.
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Materials and Methods The study was conducted in Jimma town, southwestern Ethiopia, which has a population of 159,009 in an area of 46.23 km2 (CSA 2007). For the purpose of this study, the town was divided into four quadrants. Figure 1 illustrates the location of Jimma town in Ethiopia and the sampling
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sites. Potential environmental anthropogenic lead sources at each quadrant are listed in Table 1. From each quadrant; 20 water, 20 soil and 20 air samples were collected. In total, 80 samples from each environmental medium (water, soil and air) were collected. Water samples were obtained from a private tap of the municipal water distribution system. Consequently, the soil and air samples were
Fig. 1 Location of Jimma town in Ethiopia and the sampling sites (white dots) at the different quadrants (divided in white dash line). Map was taken from Google earth
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Table 1 Distribution of known anthropogenic lead sources (Haider et al. 2002; Ahmed et al. 2008; Winther et al. 2010; Adela et al. 2012) in the four study quadrants of Jimma town Quadrant
Availability anthropogenic lead sources
Information source
Quadrant 1
Moderate automobile traffic, one gasoline station, no garage, old pipe lines relatively closer to the municipal water treatment plant
Personal observation
Quadrant 2
Mainly new settlement area, moderate automobile traffic, one gasoline station, closer to treatment plant, there are about five metal workshops
Personal observational
Quadrant 3
Heavy automobile traffic (taxi station), many metal workshops, very far from the treatment plant and very old (more than 60 years) dwelling houses (perhaps very old water distribution pipelines)
Personal observation
heavy automobile traffic, bus stations, more than five garages, there are four gasoline stations, old water pipe lines, relatively closer to the treatment plant
Personal observation
Quadrant 4
Jimma town municipality
Jimma town municipality
Jimma town municipality
collected from the ambient environment at the vicinity where water samples are collected. As a reference site, a village near Doyo located 20 km far from Jimma town and free from known anthropogenic lead source was selected. From this village the available two drinking water sources, five soil and five air samples were analyzed for lead concentration. Water samples were transported to the Environmental Health Sciences and Technology Department Laboratory and acidified to a pH \2 with 70 % HNO3 (Carlo ErbaÒ, Analytical Grade Reagent) immediately and stored at 4°C in a refrigerator before analysis. While taking soil samples, gloves were worn and approximately the top 1.5 cm of soil in the area was scooped up with plastic spoon from five places and made one composite sample. The samples were stored in polyethylene bags then treated and analyzed separately. In all aspects permission was sought and received from property owners or occupants prior to sampling. Air samples were collected with personal air sampler (AirCheckÒ 52 Personal Sample Pump) that able to provide constant flow within a range of 1,000–3,000 mL/min was used. Air was filtered using cassette containing a 37 mm mixed cellulose ester filter with a pore size of 0.8 lm. Blank samples were used following similar procedure without air filtration through the filter. Digestion of samples were made based on the standard analytical method of the water quality (American Public Health Association et al. 2005), the USEPA analytical method (USEPA 1991) and NIOSH manual of analytical method number 7082 (NIOSH 1994) respective for water,
soil and air samples. After digestion the samples were analyzed by flame atomic absorption spectrophotometer (NOVAAÒ 300 FAAS, Analytic Jena, Germany) with lead hollow cathode lamp. Prior to the analysis of lead, the spectrometer settings and the flame (air/acetylene) were optimized to obtain maximum signal. Background correction was carried out by using deuterium arc lamp to minimize background signal. In order to increase the accuracy of the measurements, the AAS machine was programmed to read averages of triplicate readings. Blank and spiked sample analyses were also made using the optimized instrument parameters. During analyses of lead with FAAS, slit width of 1.2 nm, wave length of 283.3 nm, current of 3 mA, acetylene–air ration of 0.138 and burner length of 6 mm were used. Based on the environmental samples, exposure and risk assessment was made considering all people living in this area as receptors. Because of their behavior, especially their hand–mouth habits, children are particularly vulnerable to lead contamination. In addition, the breathing system in children is significantly different from that of in adults. Thus, for exposure assessment the subjects were divided into children and adults. In this study, two exposure routes were investigated: ingestion for water and soil, and inhalation for air. The amount of a chemical which is ingested, inhaled, or dermal taken is referred to as ‘‘Intake’’ or ‘‘dose’’, and is calculated using the USEPA daily chemical intake equation. Generally recognized steps described by the USEPA (2005) was used to undertake exposure assessment. During the exposure assessment, age and body weight were respectively assumed to be less than 7 years and 15 kg for children and greater than 15 years and 70 kg for adults. Hazard quotient (HQ) was calculated as: HQ = DI/RfD, where DI is daily intake (mg/kg/day), and RfD the reference dose (mg/kg/day). When HI values greater than unity (i.e. HI [ 1), it indicates that there is the likelihood of adverse non-carcinogenic health impact (USEPA 1991). For exposure assessment, the amount of air inhaled per day was assumed to 20 and 6 m3 respectively for adults and children. Water consumption was estimated to be 2 L/ day for adults and 1 L/day for children. Soil ingestion was estimated to 100 mg/day for adults and 200 mg/day for children (USEPA 1989). Absorption of inhaled lead is assumed to be 40 % for adults and children. Absorption of lead from drinking water is assumed to be 50 % for children and 10 % for adults. Absorption of lead from soil is assumed to be 30 % for children and 10 % for adults (Bois et al. 1989). Data analyses was made using SPSS version 16.0. Turkey’s multiple comparison tests were computed to compare lead concentrations between groups. The a value was set at 0.05 with p \ 0.05 considered significant in the analysis.
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Table 2 Summary statistics of lead concentration in water, air and soil samples collected from the different quadrants of Jimma town Sample source
Sampling sites
Water
Quadrant 1
Air
Soil
Reference site
Minimum
Maximum
Mean
SD
Medium 8.79
23.59
15.48
Child Qdt 1
4.43
Adult Qdt 2
Qdt 3
Qdt 4
Qdt 1
Qdt 2
Qdt 3
Qdt 4
Quadrant 2
6.19
31.33
17.39
7.13
Quadrant 3 Quadrant 4
20.33 20.63
38.13 41.13
30.34 35.00
4.71 5.79
Water
1.16
1.16
2.02
2.33
0.44
0.5
0.87
1
Air
0.31
0.27
0.31
0.62
0.22
0.25
0.22
0.47
Quadrant 1
0.52
1.13
0.77
0.258
Soil
1.39
3.68
2.76
3.9
0.15
0.39
0.3
0.42
Quadrant 2
0.70
1.10
0.86
0.179
Total
2.86
5.11
5.09
6.85
0.81
1.14
1.39
1.89
Quadrant 3
0.57
1.20
0.77
0.288
Risk index
0.82
1.46
1.45
1.96
0.23
0.33
0.4
0.54
Quadrant 4
1.52
1.80
Quadrant 1
42.69
140.90
1.63
0.121
104.6
32.14 115.87
Quadrant 2 131.6
489.60
276.1
Quadrant 3
96.03
359.70
207.0
91.44
Quadrant 4
49.45
635.30
292.6
184.33
Water
1.03
3.10
2.11
0.82
Air
0.13
0.70
0.50
0.21
Soil
15.32
31.63
28.69
8.33
Results and Discussion The method detection limit of lead in water, soil and air was found to be 1.08, 1.35 and 1.08 lg/L respectively. The mean lead concentration of lead from soil, water and air samples of the reference site were significantly lower than the respective sample of Jimma town (p \ 0.01). Lead concentrations from water, soil and air samples are presented in Table 2. The mean lead concentration from tap water samples was 10.63 ± 0.14 mg/L. All the water samples from each quadrant have lead concentration greater than the WHO (2006) recommended value of 10 lg/L. Water samples collected relatively far from the treatment plant has higher lead concentration than the closest sites. There was strong positive significant correlation (r = 0.72, p value \0.01) between the lead concentrations of tap water and distance of the sampling points from the treatment plant. This could suggest that the longer the distance from the water treatment plant the higher lead concentration in tap water of Jimma town. This may be due to the fact that the water flowing through the pipe to a longer distance has higher contact time with the piping materials than the closer sites. The longer water remains standing in the plumbing systems, the more lead it can absorb from any lead sources accessible to it (Owen 1990; Reboˆcho et al. 2006). The lead concentration of water samples between quadrants significantly differed to each other (p value \0.001). From Tukey’s multiple comparison tests, the quadrant 4 was significantly greater than the rest of the three quadrants.
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Table 3 The exposure level (lg/kg/day) and probable risks of children and adults calculated from water, air and soil for all quadrants (Qdt) for children and adults
The volume of air sample collected for lead analysis ranged from 810 to 1,230 L. The average lead concentration of quadrant 1, 2, 3 and 4 was 0.77 ± 0.26, 0.86 ± 0.18, 0.77 ± 0.29 and 1.63 ± 0.12 lg/m3 respectively (Table 3). There was significant difference of air lead concentration between the different quadrants (p value \0.001). From Turkey’s multiple comparison test the mean lead concentration of air in quadrant 4 was greater than the others (p value \0.001). High value of lead observed in quadrant 4 is highly related with being the area where high traffic density exists. The high lead content may be related to pollutants emitted from cars, buses, trucks, etc. (Bilos et al. 2001). The mean air lead concentration of the town was 1.01 ± 0.41 mg/m3 which is above the permissible level of 0.15 lg/m3 (USEPA 2008). The lead concentration in the soil ranged from 42.69 to 635.3 mg/kg (Table 3). The soil lead concentrations significantly differed between quadrants (p value \0.001). From Turkey’s multiple comparison test, the mean lead concentration of soil at quadrant 4 is significantly greater than the others quadrants (p value \0.01). The mean lead concentration of the soil from the four quadrants of the town was 220.08 ± 135.95 lg/g which is less than the safe limit value of 400 mg/kg set by U.S. Department of Housing and Urban Development (2001). The contribution of water to the average intake of lead is estimated to be 39.73 % and 62.7 % for children and adult respectively. The relative contribution of air to average intake is estimated to be 7.94 % and 15.9 % where as the contribution of soil is estimated to be 54.22 % and 21.01 % for children and adults, respectively. The total lead uptake for children in Jimma is estimated to be 29.44 lg/day. The relative contribution of water, air and soil for the total lead uptake is was about 51.53 %, 6.09 % and 42.19 % respectively. The lead uptake by adults in Jimma is 14.3 lg/day, the relative contribution from water, air and soil being 42.45 %, 43.08 % and 14.48 % respectively.
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Table 4 Total lead intake (lg/day), uptake (lg/day) and predicted exposure (lg/kg/day) of lead in the Jimma town for children and adults Medium
Conc.
Child
Adult
Intake (%)
Uptake (%)
Exposure (%)
Intake (%)
Uptake (%)
Exposure (%)
Water
24.55 lg/L
24.55 (39.73)
12.28 (51.53)
1.62 (32.86)
49.1 (62.7)
4.91 (42.45)
0.7 (53.85)
Air
1.01 lg/m3
6.06 (7.94)
2.42 (6.09)
0.4 (8.11)
20.2 (15.9)
8.08 (43.08)
0.29 (22.3)
Soil
220.08 mg/kg
44.02 (54.22)
13.16 (42.19)
2.93 (59.43)
22.01 (21.39)
2.2 (14.48)
0.31 (23.85)
76.36
29.44
4.93
96.78
14.3
1.3
Total RI
In all quadrants the main contributor of lead intake in children was soil followed by water and air. On the other hand the main contributor of lead intake in adult is water followed by soil and air, except for quadrant 4 in which water is the main contributor followed by air and soil. From the three compartments of environment (pathways) the main pathways for lead risk in children is through soil. This may be because of the influence of the age, biological and behavioral characteristics of children, mainly hand to mouth behavior that increases the uptake of lead (Lanphear et al. 1996). The average daily intake of lead by children was 3.5 lg/ kg/day. Based on lead concentration from water, air and soil at each quadrant, the probable risk was calculated and presented in Table 3. The probable risk of children was 0.82, 1.46, 1.45 and 1.96; and for adult it is estimated to be 0.23, 0.33, 0.40 and 0.54 respectively for quadrants 1–4. Except for quadrant 1, children in all quadrants were at risk while the probable risk for adults were less than the risk value of unity. As the consumption rate of different food items and lead concentration to each item was not known, uptake from and exposure could be even more than what we have predicted. The calculated probable risk (Table 4) for children is about 1.41 times greater than the recommended value (one) and 0.37 times greater for adults. Studies done with IEUBK prediction by Griffin et al. (1999) and Laidlaw et al. (2005) have also found higher risk to lead among children living in lead contaminated areas. Our study indicated the relative contribution of water, air and soil to average probable risk is estimated to be 32.86 %, 8.11 % and 59.43 % for children and 53.85 %, 22.3 % and 23.85 % for adults respectively. The probable risk computed for adult is below the USEPA safe limit value of unity. Whereas, the probable risk computed for children is found to be above the safe level. This makes infants and young children (age less than 7 years) more susceptible to the adverse effects of environmental lead contamination. This is due to the fact that children have higher intake of lead per unit of body weight than adults (WHO 2010). Therefore in Jimma town, young children could be more vulnerable to the effects from lead exposure. Specifically, the
1.41
0.37
calculated risk showed that 7.51 % of the children are expected to have blood lead levels greater than 10 lg/dL. The Model also predicted the average lead blood level of adults to be 5.09 lg/dL. While this lead values do not exceed the acceptable level of WHO/CDC which is 10 lg/dL. However, adults also could be affected by lead exposure as many different organs and physiological functions (neurological, hematological, cardiovascular, renal, immune, and other functions) are affected by even at very low exposure levels of lead (USEPA 2007). According to different studies carried on dose–response association between blood lead levels and intelligence quotient revealed that IQ failure is stronger at blood lead levels lower than 10 lg/dL (Lanphear et al. 1996). As lead has no any physiological relevance, exposure to lead has to be as minimum as possible. In general, the content of mean lead in water is above acceptable level set by WHO, whereas the mean lead concentrations in air and soil were found below the USEPA guideline values. The main contaminated area in town from all sources is located in quadrant 4, most probably due to the heavy traffic, the existence of garages and gasoline stations. Ingestion of soil is the main route of exposure to lead for children and ingestion of water is the main route of exposure to lead for adult. In general, children living in Jimma town are at risk of elevated lead exposure. Proper urban planning and zoning that help to isolate the human residence from potential sources could minimize the lead exposure and associated health risks. Acknowledgments The Authors are most grateful to Jimma University for the financial support.
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