Air quality and health risks in chemical supply shops in southeastern Nigeria

Abstract

This study assessed the concentrations of sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and hydrogen sulfide (H₂S) in chemical stores at Ogbete Market, Enugu, and Ogbo-ogwu Market, Onitsha, southeastern Nigeria, during the wet season (June to August 2024). Air quality measurements, taken from six randomly selected stores in each market and a control site (clothing store) located at about 900 m away, revealed that while concentrations of SO₂ and NO₂ far exceeded public health guidelines (WHO), they remained below Occupational Safety and Health Administration (OSHA) limits. However, chronic low-level exposure, even within OSHA limits, can still lead to respiratory symptoms and reduced work productivity over time, especially in poorly ventilated indoor shops. Sampling was conducted at a height of 2 m above ground to reflect the breathing zone of an average adult, with data collected during morning and afternoon sessions to capture fluctuations in market activity. Using the Aeroqual Series 300 gas monitor, real-time results indicated hazardous conditions in many stores, and exposure factor–adjusted air concentrations (EF-AACs) were calculated to assess actual exposure scenarios. Hazard quotients (HQs) for each pollutant showed a concerning risk of respiratory diseases, particularly from SO₂ and NO₂ exposure, with multiple stores exhibiting HQ values greater than 1. The findings highlight the urgent need for improved ventilation and stricter regulations in these markets, while also contributing to the limited research on air quality in commercial environments in Nigeria. This study lays the foundation for future interventions aimed at protecting the health of workers in informal markets, advancing public health initiatives in regions with underdeveloped regulatory frameworks.

Keywords

Air quality gaseous pollutants occupational health chemical supply shops southeastern Nigeria

Introduction

Occupational exposure to air pollution has emerged as a critical concern in industrial and commercial settings owing to its direct implications for workers’ health and safety. In particular, chemical supply shops (shops that stock and sale fine and heavy chemicals) in low- and middle-income countries, such as those in Nigeria, often lack proper ventilation systems, personal protective equipment (PPE) protocols, and regulatory enforcement, thereby increasing the risk of exposure to hazardous gaseous pollutants (Madu et al., 2022, 2024). Storekeepers in these shops and other workers in chemical allied workplaces are often exposed to elevated concentrations of sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and hydrogen sulfide (H₂S)—gases known for their harmful respiratory and systemic health effects (Madu et al., 2022, 2025). From an occupational health and safety (OHS) perspective, prolonged or repeated exposure to such pollutants can significantly increase the risk of acute and chronic respiratory illnesses, underscoring the need for robust exposure assessment and risk mitigation strategies (Ko et al., 2007; Nishida and Yatera, 2022).

While global organizations such as the World Health Organization (WHO) have established ambient air quality guidelines, it is more appropriate in occupational health to refer to occupational exposure limits (OELs) set by institutions such as the Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH), and the American Conference of Governmental Industrial Hygienists (ACGIH). For instance, OSHA sets the permissible exposure limit (PEL) for SO₂ at 5 ppm (13 mg/m³) as a time-weighted average (TWA) over 8 hours (OSHA, 2021), while NIOSH recommends a lower exposure limit of 2 ppm (5 mg/m³) as a short-term exposure limit (STEL) (OSHA, 2021). Similarly, the NIOSH recommended exposure limit for NO₂ is 1 ppm (1.88 mg/m³) as a ceiling concentration, and for H₂S, it is 10 ppm (14 mg/m³) as a TWA, with an STEL of 15 ppm (OSHA, 2021).

SO₂ is commonly emitted from the combustion of sulfur-containing materials and industrial activities. Exposure to SO₂ has been linked to respiratory tract irritation, bronchoconstriction, and aggravation of pre-existing respiratory conditions such as asthma (Nicholas and Ukoha, 2023; Venners et al., 2001). NO₂, primarily released from combustion engines and chemical processes, is a potent oxidant gas capable of deep lung penetration, leading to inflammation, reduced lung function, and increased susceptibility to respiratory infections (Samoli et al., 2006; Ciencewicki and Jaspers, 2007; Malley et al., 2018; Bălă et al., 2021). H₂S, often released during the storage and degradation of sulfur-containing chemicals, is neurotoxic and can impair respiratory and central nervous system function at elevated concentrations (Reiffenstein et al., 1992).

Chemical supply shops in sub-Saharan Africa and other developing regions are characterized by poor infrastructure and inadequate regulatory oversight, which contribute to the accumulation of hazardous air pollutants in indoor environments. Studies conducted in Nigerian chemical markets have reported pollutant levels exceeding occupational exposure thresholds, indicating substantial health risks (Madu et al., 2024; Okunromade et al., 2022). Comparative studies from other regions, such as Southeast Asia and Latin America, have also demonstrated similarly high levels of occupational exposure in unregulated chemical and industrial vicinities (Idrees et al., 2023; Rosenstock et al., 2006), reinforcing the global relevance of this issue.

To assess the potential health risks from gaseous pollutants in occupational environments, metrics such as the exposure factor–adjusted air concentration (EF-AAC) and the hazard quotient (HQ) are increasingly employed in occupational risk assessments (ATSDR, 2020). The EF-AAC accounts for real-world exposure scenarios by adjusting pollutant concentrations based on the frequency and duration of exposure, thus providing a more realistic estimate of internal dose or concentration (ATSDR, 2020; Madu et al., 2025). The HQ is a dimensionless ratio of the estimated exposure to a reference dose, with HQ values exceeding 1 indicating a potential health risk (Kortei et al., 2020; Miletić et al., 2023; Radfard et al., 2023; Yi et al., 2017). These metrics have been applied in multiple occupational exposure studies globally, including those assessing chemical industries, wastewater treatment facilities, and informal e-waste recycling sites (Decharat and Kiddee 2022; Pachoulis et al., 2022; Rezapour et al., 2024). In the context of chemical supply shops in Nigeria, recent studies have reported elevated EF-AAC and HQ values for particulates, suggesting significant risk to respiratory health (Madu et al., 2025).

Despite growing evidence, there remains a notable research gap in sub-Saharan Africa regarding the systematic evaluation of gaseous pollutant exposure and its health effects in occupational settings such as chemical supply shops. Workers in these environments are disproportionately exposed to health hazards due to the absence of control measures and occupational health programs. This underscores the urgent need for comprehensive monitoring, health risk assessments, and policy interventions to safeguard the respiratory health and general well-being of these vulnerable worker populations. The aim of this study was to monitor the concentrations of three key gaseous pollutants—sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and hydrogen sulfide (H₂S)—in chemical stores and assess the associated health risks to storekeepers.

Materials and methods

This study was conducted over a three-month period, from June to August 2024, during the wet season, in two major chemical markets: Ogbete Market in Enugu and Ogbo-ogwu Market in Onitsha, Nigeria. Chemical markets are markets or sections of a larger market that deal with the buying, selling, and distribution of fine and heavy chemicals for industrial, laboratory, hospital, agricultural, educational, and pharmaceutical purposes. The Aeroqual Series 300 Gas Monitor was employed for monitoring of these pollutants.

Study sites

The two selected markets are significant commercial hubs in southeastern Nigeria, characterized by a high density of chemical stores that stock various industrial chemicals, solvents, and pharmaceuticals. Ogbete Market in Enugu is a large urban market, while Ogbo-ogwu Market in Onitsha (Figure 1) is one of the largest chemical markets in West Africa. Both markets experience heavy traffic and poor ventilation, contributing to elevated levels of gaseous pollutants.

Instrumentation

The concentrations of SO₂, NO₂, and H₂S were measured using the Aeroqual Series 300 Gas Monitor (Aeroqual Limited, Auckland, New Zealand), a portable and highly sensitive device designed for air quality monitoring. The Aeroqual Series 300 is equipped with interchangeable electrochemical gas sensors designed for workplace and environmental exposure assessments, making it suitable for air pollution monitoring in occupational settings (Whitehill et al., 2022). Each sensor is factory-calibrated and periodically validated using standard gas calibrations to ensure accuracy and reliability.

The monitor was equipped with specific gas sensors for each pollutant: SO₂ (range: 0–10 mg/m³, accuracy: ±0.01 mg/m³), NO₂ (range: 0–10 mg/m³, accuracy: ±0.01 mg/m³), and H₂S (range: 0–10 ppm, accuracy: ±0.01 ppm) (Whitehill et al., 2022). The Aeroqual Series 300 is calibrated by the manufacturer to ensure accurate and reliable readings. Sensor performance was cross-checked against standard gas calibrations at the start and end of each sampling day.

Sampling strategy

The sampling strategy was designed to assess potential exposure risks in chemical supply shops, considering principles of industrial hygiene and occupational medicine (ACGIH, 2025). Fixed-location area sampling was chosen over personal sampling to capture variations in pollutant concentrations within each shop environment, allowing for comparisons between locations and time periods (Tanaka and Akiyama, 1985). This approach aligns with environmental monitoring practices used in workplace assessments where multiple workers and customers are present. Measurements were taken from six randomly selected chemical supply shops in each market. A control location (clothing store), located at least 900 m away from the chemical supply shops was also monitored for background air pollutant levels. The sampling height for all measurements was approximately 2 m above ground level to simulate the breathing zone of an average adult.

Sampling was conducted during the morning (9:00–11:00 a.m.) and afternoon (2:00–4:00 p.m.) each day, to capture variations in pollutant concentrations due to market activity levels according to the methods described by Madu et al. (2022). One gas was measured at a time by fixing the appropriate sensor to the monitor. The gas monitor was then turned on and raised to a height of about 2 m. Each measurement session lasted 15 minutes per store, during which the Aeroqual Series 300 recorded continuous readings every minute. The recorded values were averaged over the 15-minute period to obtain a mean concentration for each store and each sampling period. Sampling was carried out three times per week to ensure a comprehensive dataset over the study period of 3 months.

Data quality control

To ensure data accuracy, the Aeroqual Series 300 Gas Monitor was recalibrated weekly using standard gas calibration techniques. Field blanks were also used to correct for any background contamination or sensor drift. Duplicate measurements were taken for 20% of the total samples to assess precision, and the relative percentage difference (RPD) was calculated for quality control. The RPD between duplicate samples remained below 5%, indicating good precision (Masiol et al., 2018).

Exposure factor–adjusted air concentration (EF-AAC) calculation

The concentrations of SO₂, NO₂, and H₂S were further adjusted using the exposure factor (EF) to account for the actual exposure scenario of the storekeepers. EF refers to the proportion of time an individual is exposed to a contaminant or hazardous substance relative to a given time frame, often a year. It helps estimate the chronic daily intake (CDI) of a chemical and is a key component in quantifying exposure dose (ATSDR, 2020). The EF helps adjust the dose (concentration) calculation to reflect real-world exposure—not everyone is exposed 24/7, year-round. For example, someone living near a contaminated site may only be exposed during the summer months (dry season), or a worker may only be exposed during work hours on weekdays. The EF in the present study was calculated based on the average time a storekeeper spends inside the store per day (8 hours) and the average number of days per week (6 days) that the store is open. EF-AAC is a term used in environmental health risk assessments to describe the air pollutant concentration adjusted for how often and how long a person is actually exposed. It refines the raw pollutant data (like average annual concentration) by factoring in real-world exposure patterns—so it’s a more accurate input for calculating inhalation doses or health risks. EF-AAC gives a more realistic estimate of the air concentration someone is actually exposed to over time. It’s often used in calculating the reference concentration (RfC) (ATSDR, 2020).

The EF-AAC for each pollutant in the present study was calculated using the following formula:

EF - AAC = C \times EF (ATSDR, 2020)

where C is the mean concentration of the pollutant measured and EF is the exposure factor, calculated as

E F = (\frac{t_{e x p o s u r e}}{24 h o u r s}) \times (\frac{d_{w o r k d a y s}}{7 d a y s}) (ATSDR, 2020)

In this case, t_exposure = 8 hours/day and d_workdays = 6 days/week.

Health risk assessment: Hazard quotient (HQ) Calculation

The health risks associated with exposure to SO₂, NO₂, and H₂S were quantified using the HQ. The HQ for each pollutant was calculated by dividing the EF-AAC by the minimal risk level (MRL) provided by the Agency for Toxic Substances and Disease Registry (ATSDR) (2025).

H Q = \frac{E F - A A C}{M R L} (ATSDR, 2020)

where HQ is the hazard quotient, EF-AAC is the exposure factor–adjusted air concentration, and MRL is the minimal risk level.

An MRL is an estimate of the daily human exposure to a hazardous substance (usually via ingestion or inhalation) that is likely to be without appreciable risk of adverse non-cancer health effects over a specified duration of exposure (ATSDR, 2020). The MRLs for SO₂, NO₂, and H₂S are 0.01 ppm, 0.1 mg/kg/day, and 0.07 ppm, respectively (ATSDR, 2024). An HQ greater than 1 indicates a potential health risk, while an HQ less than 1 suggests no significant health concerns.

Statistical analysis

Descriptive statistics, including means and standard deviations, were calculated for the measured concentrations of SO₂, NO₂, and H₂S across the chemical stores. One-way analysis of variance (ANOVA) was used to determine significant differences in pollutant concentrations between stores and control locations. Post-hoc comparisons were performed using Tukey’s HSD test to identify specific pairs of stores with significant concentration differences. Statistical significance was set at p < .05. All statistical analyses were conducted using SPSS software (version 25.0, IBM Corp., Armonk, NY).

Ethical considerations

The study was conducted in accordance with ethical guidelines for occupational health research. Consent was obtained from storekeepers before measurements were taken in their stores. All participants were informed of the purpose of the study, and air quality data were shared with the market authorities to promote awareness and possible interventions. Efforts were made to minimize any disruption to business activities during the sampling process.

Results

In Ogbete Market, concentrations of sulfur dioxide (SO₂) in stores ranged from 0.11 to 0.26 mg/m³, significantly exceeding the WHO standard of 0.01 mg/m³ (WHO, 2021). Similarly, Ogbo-ogwu Market reported high SO₂ concentrations, with a peak of 0.32 mg/m³, also surpassing the WHO standard. For nitrogen dioxide (NO₂), concentrations in Ogbete Market varied between 0.98 mg/m³ and 1.85 mg/m³, while in Ogbo-ogwu, they ranged from 0.07 to 0.21 mg/m³, both exceeding the WHO NO₂ standard of 0.04–0.06 mg/m³ (WHO, 2021). Hydrogen sulfide (H₂S) concentrations in Ogbete Market ranged from 0.19 ppm to 5.13 ppm, remaining well below the WHO limit of 10 ppm, although some stores recorded higher values. In contrast, H₂S values in Ogbo-ogwu Market were much lower, ranging from 0.10 to 0.30 ppm, which was well below the WHO standard (Tables 1 and 2). However the concentrations of all the gaseous pollutants in all the shops in both markets were less than the occupational exposure limits (OELs) given by OSHA (OSHA, 2021). In all shops (except NO₂ in shop 3 from Ogbo-ogwu market) the concentrations of all gaseous pollutants in both markets were statistically different (p ≤ .05) from the controls.

Table 1.

Concentrations of gaseous pollutants in chemical shops at Ogbete Market, Enugu.

Shops	SO₂ (mg/m³)	NO₂ (mg/m³)	H₂S (ppm)
1	0.19	1.84 ± 0.5^e	0.19 ± 0.01^f
2	0.21	1.85 ± 0.3^b	0.46 ± 0.04^e
3	0.26	1.85 ± 0.2^b	2.62 ± 0.10^b
4	0.11	0.98 ± 0.1^d	5.12 ± 1.2^d
5	0.24	1.52 ± 0.0^c	4.90 ± 1.00^c
6	ND	1.86 ± 0.2^b	2.62 ± 0.90^b
Control	ND	0.03 ± 0.00^a	0.10 ± 0.00^a
WHO Std	0.01	1.4 – 0.06	10.00
OSHA PEL	13.00	1.88	10.00

Values are means of triplicate measurements ± standard deviation (SD). Means within each column that share the same superscript letter (a, b, c, etc.) are not significantly different from each other (p > .05). ND = not detected. WHO Std refers to World Health Organization air quality standards (WHO, 2021); OSHA PEL refers to Occupational Safety and Health Administration Permissible Exposure Limits (OSHA, 2021).

Table 2.

Concentrations of gaseous pollutants in chemical shops at Ogbo-ogwu, Onitsha main market, Anambra.

Shops	SO₂ (mg/m³)	NO₂ (mg/m³)	H₂S (ppm)
1	0.26	0.17 ± 0.04^f	0.28 ± 0.09^e
2	0.32	0.19 ± 0.01^e	0.30 ± 0.1^d
3	ND	0.12 ± 0.03^a	0.10 ± 0.01^c
4	ND	0.21 ± 0.05^d	0.10 ± 0.02^c
5	ND	0.07 ± 0.00^c	0.20 ± 0.09^b
6	0.14	0.14 ± 0.01^b	0.19 ± 0.00^b
Control	ND	0.11 ± 0.01^a	0.10 ± 0.02^a
WHO Std	0.01	0.04 – 0.06	10.00
OSHA PEL	13.00	1.88	10.00

The EF-AACs for sulfur dioxide (SO₂) in Ogbete Market indicated significant occupational exposure, with values in most shops reaching up to 0.06 mg/m³, while Ogbo-ogwu Market exhibited a similar trend, with EF-AAC values peaking at 0.07 mg/m³; both were notably higher than the control value of 0.00 mg/m³ (Tables 3 and 4). For nitrogen dioxide (NO₂), EF-AAC values in Ogbete Market ranged from 0.21 to 0.40 mg/m³, whereas in Ogbo-ogwu Market, they ranged from 0.01 to 0.04 mg/m³, with both markets showing significantly (p ≤ .05) higher values than the control. Hydrogen sulfide (H₂S) EF-AAC values in Ogbete Market also reflected higher exposure, ranging from 0.04 to 1.10 ppm, with Store 4 recording the highest value. In comparison, Ogbo-ogwu Market displayed lower H₂S EF-AAC values, ranging from 0.02 to 0.06 ppm, which were considerably less than those observed in Ogbete Market but still higher than the control.

Table 3.

Exposure factor–adjusted air concentrations (EF-AACs) for SO₂, NO₂, and H₂S across the shop in Ogbete Market.

Shops	EF-AAC SO₂ (mg/m³)	EF-AAC NO₂ (mg/m³)	EF-AAC H₂S (ppm)
1	0.04	0.39	0.04
2	0.04	0.39	0.10
3	0.06	0.40	0.56
4	0.02	0.21	1.10
5	0.05	0.32	1.05
6	0.00	0.40	0.56
Control	0.00	0.01	0.02

Table 4.

Exposure factor–adjusted air concentrations (EF-AACs) for SO₂, NO₂, and H₂S at Ogbo-ogwu Market, Onitsha.

Shops	EF-AAC SO₂ (mg/m³)	EF-AAC NO₂ (mg/m³)	EF-AAC H₂S (ppm)
1	0.06	0.04	0.06
2	0.07	0.04	0.06
3	0.00	0.03	0.02
4	0.00	0.04	0.02
5	0.00	0.01	0.04
6	0.03	0.03	0.04
Control	0.00	0.02	0.02

The HQ analysis revealed significant potential health risks associated with exposure to gaseous pollutants in both markets (Figures 2 and 3). For sulfur dioxide (SO₂), several stores exceeded an HQ value of 1, indicating potential health risks, with Ogbete Market reporting a maximum HQ of 2.78 in Shop 3, while Ogbo-ogwu Market had the highest HQ of 3.42 in Store 2, highlighting a greater risk of adverse health effects from SO₂ exposure in both locations. In terms of nitrogen dioxide (NO₂), Ogbete Market consistently showed high HQ values across all shops, with Shop 6 exhibiting the highest HQ of 7.93; although Ogbo-ogwu Market’s values were generally lower, Store 4 still presented an HQ of 0.89, indicating some potential risks. For hydrogen sulfide (H₂S), HQ values were notably lower overall, with Ogbete Market showing Shops 4 and 5 with values exceeding 1, thus indicating some health risks, while Ogbo-ogwu Market maintained H₂S HQs below 1, suggesting lower risk levels from H₂S exposure.

Discussion

This study provided a novel investigation into the concentrations of sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and hydrogen sulfide (H₂S) in chemical stores located in two major markets in southeastern Nigeria—Ogbete Market, Enugu, and Ogbo-ogwu Market, Onitsha—during the wet season (June–August 2024). The study’s findings contribute to the limited body of knowledge on air quality in commercial chemical environments in Nigeria and other developing countries, where regulatory enforcement of occupational health standards is often weak. By integrating real-time monitoring techniques with a detailed risk assessment framework, this project breaks new ground in assessing the health risks associated with gaseous pollutants in such environments, especially as most previous studies have focused on general outdoor air pollution rather than the specific occupational exposures of chemical storekeepers.

Air pollutant concentrations and comparisons with WHO standards OSHA OELs

The results indicated that SO₂, NO₂, and H₂S concentrations in many of the chemical stores exceeded the WHO’s air quality guidelines for ambient environments. For SO₂, the WHO standard is 0.01 mg/m³, while the NO₂ guideline ranges from 0.04 to 0.06 mg/m³ (WHO, 2021). In this study, SO₂ concentrations in the stores ranged from 0.11 to 0.320 mg/m³, with both markets recording values significantly above WHO standards. NO₂ concentrations also ranged from 0.98 to 1.85 mg/m³ in Ogbete Market and 0.07 to 0.21 mg/m³ in Ogbo-ogwu Market, again exceeding the recommended limits. These elevated concentrations may be attributed to the high density of chemicals stored in confined spaces, poor ventilation, and the combustion of fuels or solvents often used by the storekeepers (Madu et al., 2024). Furthermore, while the measured H₂S concentrations were generally within acceptable limits of 10 ppm as set by the WHO, certain stores in Ogbete Market recorded concerning values as high as 5.13 ppm, indicating the potential for localized pollution spikes (Aneja et al., 2021).

The results revealed significant air quality concerns in both Ogbete and Ogbo-ogwu markets, particularly for sulfur dioxide (SO₂) and nitrogen dioxide (NO₂), when compared with WHO ambient air quality standards. However, from an occupational safety perspective, based on the OSHA exposure limits, the concentrations remained within acceptable thresholds. The concentrations of SO₂ significantly exceeded WHO ambient standards, indicating poor air quality in terms of public health. However, the values remained far below OSHA’s permissible exposure limits (OSHA, 2021) for occupational settings, suggesting that acute toxicity risk in a typical workday is low, though chronic exposure could still be a concern due to cumulative effects, particularly for vulnerable workers (e.g., those with respiratory conditions). NO₂ concentrations in both markets exceeded WHO guidelines, again indicating public health concerns. Nonetheless, these levels were well below OSHA’s OEL, suggesting that immediate occupational exposure risks were minimal. However, the statistically significant difference from control values (p ≤ .05) indicated measurable occupational exposure that could have long-term respiratory implications for shop workers, particularly in Ogbete Market where levels were notably higher. H₂S levels were well within both WHO and OSHA limits in both markets, though some shops in Ogbete Market approached mid-range levels. This indicated that H₂S is not an immediate occupational hazard in this context, but higher values recorded in certain stores should be monitored regularly, especially in poorly ventilated environments. The statistical analysis (p ≤ .05) confirmed that in almost all cases, pollutant concentrations in market shops differed significantly from the control values—demonstrating that the market environment contributed substantially to indoor air pollution exposure. The exception of NO₂ in Shop 3 of Ogbo-ogwu suggests either better ventilation, reduced emission sources, or variability in sampling.

Seasonal and market-specific variations

The study’s findings also demonstrated distinct variations in pollutant concentrations between the two markets. Ogbete Market consistently recorded higher concentrations of SO₂, NO₂, and H₂S compared to Ogbo-ogwu Market. One possible explanation for this is the difference in ventilation and market layouts. Ogbete Market has denser store arrangements and narrower pathways, potentially trapping pollutants more efficiently than the relatively open and well-ventilated Ogbo-ogwu Market. This aligns with previous research that suggests that poor ventilation can contribute significantly to the accumulation of indoor air pollutants in industrial or commercial spaces (Holden et al., 2023).

Furthermore, this study was conducted during the wet season, when atmospheric dispersion of pollutants is expected to be more efficient because of rainfall. Rainwater scavenges particulate and gaseous pollutants from the atmosphere, generally leading to lower pollutant concentrations (Sokhi et al., 2022). However, despite the wet season, the results show high pollutant concentrations in the chemical stores, which may imply that the pollutant sources (chemicals, solvents, and combustion byproducts) were continuously replenished within the enclosed spaces of the stores, minimizing the effect of rainfall on indoor pollutant concentrations.

Exposure factor–adjusted concentrations (EF-AACs) and health risk assessments

A key novelty of this project lies in the use of EF-AAC values to more accurately assess the potential health risks faced by storekeepers. By accounting for the actual exposure times and workdays, the EF-AAC values provided a more realistic estimate of storekeepers’ exposure compared to ambient air quality guidelines, which are typically based on continuous (24-hour) exposures. For example, while the ambient concentration of SO₂ in one store was recorded as 0.21 mg/m³, the EF-AAC value was adjusted to 0.04 mg/m³ based on the typical work schedule of storekeepers. This adjustment is critical for a more accurate health risk evaluation and highlights the importance of tailoring risk assessments to specific occupational environments (ATSDR, 2020).

Hazard quotients (HQs) and implications for public and occupational health

The HQs calculated for SO₂, NO₂, and H₂S revealed that storekeepers in several shops at both markets were potentially at risk for adverse health effects, with HQ values greater than 1 for both SO₂ and NO₂ in multiple stores. For instance, Shop 3 in Ogbete Market had an HQ for SO₂ of 2.78 and for NO₂ of 7.90, indicating a significant risk for respiratory irritation and other long-term health issues (ATSDR, 2020). Although H₂S concentrations generally did not pose as high of a risk, certain stores with elevated levels (e.g., Shop 4 in Ogbete Market with an HQ of 1.10) could still be problematic, particularly for individuals with pre-existing respiratory conditions (Elwood, 2021).

This study highlights a significant occupational health concern for storekeepers in these chemical markets. Given the relatively high HQ values for SO₂ and NO₂, these workers may be at increased risk for respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma, conditions that have been linked to long-term exposure to elevated concentrations of these gases (Zhang et al., 2018). These findings are consistent with the broader literature on indoor air pollution in commercial environments, which has demonstrated that poor air quality in occupational settings can contribute to a range of chronic health conditions (Sundell, 2004).

Limitations and future research directions

While this study provided important insights into air quality and health risks in chemical markets, several limitations should be noted. First, the study was conducted exclusively during the wet season, and pollutant concentrations may differ during the dry season when atmospheric dispersion is less effective, and emissions from surrounding traffic may be higher. Future research should include year-round monitoring to capture seasonal variations in air quality.

Second, this study focused on gaseous pollutants, but chemical markets may also expose workers to other hazardous substances. Expanding the scope of future studies to include these pollutants would provide a more comprehensive assessment of air quality in chemical markets. Moreover, long-term epidemiological studies are needed to investigate the direct health impacts on workers over extended periods of exposure.

Novel contributions

This project represents a novel approach to air quality monitoring in chemical markets, combining real-time pollutant measurements with adjusted exposure assessments to provide a more realistic evaluation of health risks. The results indicated that chemical storekeepers in Ogbete and Ogbo-ogwu markets were exposed to concentrations of SO₂, NO₂, and H₂S that exceeded safe levels, highlighting the need for improved ventilation, regulatory oversight, and protective measures in such commercial environments. This study contributed to the growing body of research on occupational air quality in developing countries, where informal and unregulated work environments are common, and underscores the importance of targeted interventions to protect the health of vulnerable workers.

Conclusion

This study provided critical insights into the air quality within chemical stores at Ogbete Market, Enugu, and Ogbo-ogwu Market, Onitsha. While concentrations of SO₂ and NO₂ far exceed public health guidelines (WHO), they remain below occupational limits (OSHA). However, chronic low-level exposure, even within OSHA limits, can still lead to respiratory symptoms and reduced work productivity over time, especially in poorly ventilated indoor shops. Moreover, the application of the EF-AAC and HQs allowed for a more precise assessment of the workers’ exposure and risks, emphasizing the importance of context-specific evaluations in occupational health studies.

The novelty of this research lies in its focus on the under-explored environments of chemical stores in markets, where regulatory oversight is minimal, and in its approach of tailoring exposure assessments to actual working conditions. This study underscores the need for urgent interventions, including better ventilation, improved occupational health policies, and regular monitoring, to mitigate the adverse health impacts of air pollutants in these environments.

Footnotes

Acknowledgements

The authors thank the owners and storekeepers of the chemical stores at Ogbete market, Enugu, and Ogbo-ogwu (main market) Onitsha, for their support and assistance.

Declaration of conflicting interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This Research was funded by the TETFund National Research Fund 2023.

Ethical statement

ORCID iDs

Francis Ugochukwu Madu

Eni-yimini Solomon Agoro

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