Carbon monoxide (CO) remains a leading cause of work-related chemical poisoning. Vehicular emissions are the primary daily ambient source of CO in urban Nigerian motor parks, where there have been few human exposure studies. Using a cross-sectional comparative design, we assessed carboxyhaemoglobin levels (% COHb), a biomarker of CO exposure, among traders at three motor parks (AMP, IMP, and NMP) and other traders (nonmotor park workers) in Ibadan, Nigeria, using a noninvasive pulse CO-dosimeter (Rad 57). Ninety-three traders were proportionally allocated between motor parks; 93 other traders were selected based on specific study inclusion criteria. Mean ages of motor park traders and other traders were comparable,
Air pollution is an important public health problem in most cities in less developed countries (LDCs) [
CO is a colorless, odourless, and nonirritating gas produced as a byproduct of incomplete combustion of carbonaceous materials [
Haemoglobin has greater affinity for CO than oxygen; hence, CO binds with haemoglobin to form a relatively stable complex called carboxyhaemoglobin (COHb). The presence of COHb in the blood reduces the oxygen carrying capacity of the blood and restricts the access of body tissues to oxygen, resulting in tissue hypoxia [
People are exposed to CO via several polluted environments such as travelling in motor vehicles, at their workplaces, visits to urban locations associated with combustion sources, and cooking and heating with domestic gas, charcoal, or wood fires and wherever there is tobacco smoke. However, the most prominent outdoor sources of CO exposure for many individuals are vehicular emissions [
CO is toxic [
Dose and time duration of exposure are factors that determine the effects and severity of health risks in CO exposure [
Acute CO poisoning occurs as a result of the inability of body tissues to access oxygen. Signs and symptoms of CO toxicity, in order of increasing severity include headache, nausea, dilation of cutaneous vasculature, vomiting, dizziness, and blurred vision, confusion, syncope, chest pain, dyspnea, weakness, tachycardia, tachypnea rhabdomyolysis, palpitations, cardiac dysrhythmias, hypotension, myocardial ischemia, cardiac arrest, respiratory arrest, pulmonary edema, seizures, and coma [
Exposures to CO assessed in controlled outdoor and occupational environments represent only a fraction of total human exposure to CO. Elevated levels of CO have been recorded, for example, in motor parks and tunnels because of the accumulation of exhaust fumes [
There are limited data on traffic-related exposure assessment by near or on-road measurements despite a recent increase in research; challenges in exposure assessment for recent studies include differences in measuring methods and a lack of strict quality control, hence, making it difficult to compare findings between studies [
Motor parks are common public spaces found in every urban area in Nigeria and these motor parks vary in their design, nature, environment, and services. The importance of motor parks is apparent because of the utilization of public transport systems [
This study was aimed at generating baseline information on exposure levels of traders to CO using COHb as the biomarker given limited data on exposure to CO in public transit waiting areas such as motor parks and bus stops. In Nigeria, studies on human exposure to vehicular emissions like CO have been limited. Furthermore, there are limited studies on COHb in Nigeria, and in the few available, study participants were not traders in motor parks. Previous studies on COHb were performed on smokers, commercial bus drivers, and artisans and had employed an invasive method of obtaining blood samples through venipuncture [
This study was a cross-sectional comparative study which involved the assessment of carboxyhaemoglobin (% COHb) levels among traders in three motor parks and nonmotor park traders in Ibadan, Nigeria.
The study area was Ibadan, the capital of Oyo state, one of the 36 states in Nigeria. Ibadan is positioned on longitude 3°53′ east of Greenwich Meridian and latitude 7°23′ north of the equator. This ancient city is located close to forest and grassland boundary of south western Nigeria and about 145 km North East. Due to its location, Ibadan serves as a meeting point for people and products from forest and grassland areas [
This research was carried out in three major motor parks in Ibadan: Akinyele Motor Park (AMP) in Akinyele Local Government Area (LGA); Iwo Road Motor Park (IMP) in Ibadan North East LGA; and “New Garage” Motor Park (NMP) located in Ibadan South West LGA, within Ibadan municipal area. AMP caters for transport linking cities in northern region which includes Kaduna, Abuja, Kano, and other major cities. IMP caters for transport needs of passengers going towards eastern region comprising Benin, Warri, Port Harcourt, Uyo, Calabar, and others. NMP links other major cities in the south west which includes Lagos, Abeokuta, Epe, Ijebu-Ode, and other coastal towns. These study sites were chosen purposively as they are the major exit points to reach northern, eastern, and other western parts of the country. Many transportation devices such as taxis, mini-buses, and buses originate and terminate at these points [
The participants for this study were traders in the three motor parks and nonmotor park traders in Ibadan. Sociodemographic characteristics such as age, gender, educational status, marital status, religion, and state of origin were collected from the traders.
The formula this study used [
Hence,
Therefore
Sample size reduction was applied because the sample size (219) was more than the population of traders in the three motor parks that satisfied the inclusion criteria for the study. As at the period of data collection, the number of traders that satisfied the inclusion criteria at AMP, Ojoo, IMP, Iwo road and NMP, Apata were 30, 77, and 54, respectively, adding up to 161. The sample size
Purposive sampling technique was used to select the three motor parks as these motor parks serve as the major exit points to reach northern, eastern, and other western parts of the country. Taxis, mini-buses, and buses originate and terminate at these points. Permission was sought and obtained from the Chairmen, National Union of Road Transport Workers (NURTW) of these parks to conduct COHb assessment of traders within the motor parks. 93 motor park traders were proportionally allocated between the three motor parks as shown in Table
Population of traders and proportional allocation.
Motor park | Number of traders | Proportional allocation in study sample |
---|---|---|
AMP, Ojoo | 30 | 17 |
IMP, Iwo road | 77 | 45 |
NMP, Apata | 54 | 31 |
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| | |
Noninvasive pulse CO-dosimeter (Rad-57) by Masimo Corporations, USA (Figure
Example of noninvasive pulse CO-dosimeter (Rad 57).
Carboxyhaemoglobin assessment of a motor park trader (photo by Olasunkanmi Williams, September, 2014).
Data was entered and analysed using statistical package for the social sciences (SPSS) version 20. Descriptive and inferential statistics were used in this study. Descriptive statistics was used to summarize data. Mean ± Standard Deviation (SD) and range were calculated for % COHb of the two groups of traders (motor park traders and nonmotor park traders) and compared with WHO guideline of 2.5% [
Table
Sociodemographic characteristics of study respondents.
Sociodemographic characteristics | Subgroups | AMP, Ojoo traders | IMP, Iwo road traders | NMP, Apata traders | Nonmotor park traders |
---|---|---|---|---|---|
Age | 18–20 | 2 (11.8%) | 1 (2.2%) | 3 (9.7%) | 3 (3.2%) |
21–30 | 1 (5.9%) | 10 (22.2%) | 7 (22.6%) | 16 (17.2%) | |
31–40 | 5 (29.4%) | 14 (31.1%) | 11 (35.5%) | 33 (35.5%) | |
41–50 | 9 (52.9%) | 12 (26.7%) | 6 (19.4%) | 30 (32.3%) | |
51–60 | - | 8 (17.8%) | 2 (6.5%) | 11 (11.8%) | |
61–70 | - | - | 2 (6.5%) | - | |
| |||||
Gender | Male | 17 (100%) | 35 (77.8%) | 21 (67.7%) | 23 (24.7%) |
Female | - | 10 (22.2%) | 10 (32.3%) | 70 (75.3%) | |
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Educational status | No education | 1 (5.9%) | 2 (4.4%) | 1 (3.2%) | 6 (6.5%) |
Primary education | 3 (17.6%) | 14 (31.1%) | 6 (19.4%) | 35 (37.6%) | |
Secondary education | 10 (58.8%) | 19 (42.2%) | 12 (38.7%) | 44 (47.3%) | |
Tertiary education | 3 (17.6%) | 10 (22.2%) | 12 (38.7%) | 8 (8.6%) | |
| |||||
Marital status | Single | 6 (35.3%) | 7 (15.6%) | 12 (38.7%) | 11 (11.8%) |
Married | 11 (64.7%) | 37 (82.2%) | 21 (67.7%) | 82 (88.2%) | |
Widow/widower | - | 1 (2.2%) | - | - | |
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Religion | Christianity | 3 (17.6%) | 21 (46.7%) | 15 (48.4%) | 55 (59.1%) |
Islam | 14 (82.4%) | 24 (53.3%) | 13 (41.9%) | 38 (40.9%) | |
Traditional | - | - | 2 (6.4%) | - | |
No religion | - | - | 1 (3.2%) | - | |
| |||||
State of origin | Abia | - | - | 1 (3.2%) | 1 (1.1%) |
Benue | - | 1 (2.2%) | - | - | |
Cross Rivers | - | 1 (2.2%) | - | - | |
Delta | - | 1 (2.2%) | - | 1 (1.1%) | |
Edo | 1 (5.9%) | - | - | 3 (3.2%) | |
Ekiti | - | - | 2 (6.5%) | 4 (4.3%) | |
Kogi | - | - | - | 1 (1.1%) | |
Kwara | 1 (5.9%) | 1 (2.2%) | 1 (3.2%) | - | |
Lagos | - | 1 (2.2%) | - | - | |
Ogun | - | 3 (6.7%) | 8 (25.8%) | 15 (16.1%) | |
Ondo | - | 2 (4.4%) | - | 7 (7.5%) | |
Osun | 4 (23.5%) | 9 (20.0%) | 3 (9.7%) | 10 (10.8%) | |
Oyo | 11 (64.7%) | 26 (57.8%) | 16 (51.6%) | 51 (54.8%) |
Table
Mean and range of % COHb among study participants.
AMP traders | IMP traders | NMP traders | Nonmotor park traders |
---|---|---|---|
| | | |
6–19 | 5–22 | 3–18 | 2–8 |
Carboxyhaemoglobin levels among study participants.
Table
Comparison of % COHb among study participants within and between groups.
AMP traders | IMP traders | NMP traders | Nonmotor park traders | | | |
| ||||||
% COHb | | | | 0.573 | 0.566 | |
% COHb (group mean) | | | 24.153 | < |
We also conducted a comparison between mean % COHb among motor park traders (three sites combined) with the WHO guideline and the comparison between mean % COHb among nonmotor park traders with the WHO guideline (2.5%). There were statistically significant differences between the WHO guideline and the mean % COHb of both motor park traders and nonmotor park traders.
The range of % COHb among traders at AMP, Ojoo, IMP, Iwo road, NMP, Apata, and nonmotor park traders was 6–19, 5–22, 3–18, and 2–8, respectively. Mean % COHb was highest among traders at NMP, Apata
There was a statistically significant difference between % COHb among motor park and nonmotor park traders (
There are several complications that may arise as a result of exposure to high CO concentration. Metabolic energy production may be impaired due to a reduction in oxygen delivery because of the elevated COHb level, exacerbated by impaired perfusion resulting from hypoxic cardiac dysfunction, which potentially impairs cellular oxidative metabolism. This occurs because hypoxia and reduction in blood flow may allow CO to bind to cytochrome c-oxidase, which inhibits aerobic adenosine triphosphate synthesis [
Nonmotor park traders are also not exempted from CO exposure as their mean COHb level
Other studies conducted in Nigeria were consistent with this research. In a pilot study which assessed COHb levels in some Lagos dwellers by Uko et al. [
It should be noted that the present study had some limitations. The present study focused on quantitative field measures of % COHb; we did not conduct outdoor area measures of CO, a well-known byproduct of combustion of fossil fuels, or a questionnaire about reported symptoms. An exposure biomarker like % COHb is a relatively more rigorous measure than area or even personal air concentration and self-reported survey data. In general, self-reported outcomes would be nonvalidated, subject to recall bias and possible misclassification error. Furthermore, some reported symptoms of CO exposure have other known causal agents, e.g., other chemical pollutants, infectious diseases (flu virus, illnesses like colds, etc.), and dust/particulate matter. Future studies could incorporate quantitative and qualitative data.
This study assessed carboxyhaemoglobin levels (% COHb) of traders in three motor parks and of nonmotor park traders in Ibadan, Nigeria. Mean % COHb among motor park traders was about three times higher than mean % COHb of nonmotor park traders and about four times higher than the current World Health Organization (WHO) guideline of 2.5%. Motor park traders had high blood carbon monoxide (CO) levels and are thus more likely to experience health risks from CO exposure and its known symptoms like headache, nausea, vomiting, dizziness, and so forth. Furthermore, given mean % COHb of both groups were above the current WHO guideline of 2.5%, nonmotor park traders are also likely to experience mild health effects of CO exposure. Therefore, this study suggests enhancing general worker awareness on adverse health effects of CO and encouraging the conduct of regular % COHb assessment, especially among motor park traders, to ascertain CO exposure levels. Reductions in vehicular emissions and improvements in monitoring and enforcement of related regulations are also warranted. Finally, controlling emissions from other known incomplete combustion-related sources contributing to outdoor air pollution at motor parks and worker homes and communities, e.g., smoking product-related activities (tobacco, e-cigarettes) and portable generators for electrical power, is recommended.
This study was approved by the Institutional Review Board, University of Ibadan.
There are no conflicts of interest to report for any of the authors listed above.
This work was supported for some equipment used and travel for participation in this study by The Atlantic Philanthropies (grant to D. G. Shendell, 2007-2008, while at Georgia State University). The authors are grateful to Mr. Opeoluwa Oluwatosin Oluseye, whose support facilitated the successful completion of this study. Sincere appreciation also goes to the staff and students of the Department of Environmental Health Sciences, Faculty of Public Health, College of Medicine, University of Ibadan, Ibadan, Nigeria, for timely contributions.