Air Quality and Human Health Risk Assessment in the Residential Areas at the Proximity of the Nkolfoulou Landfill in Yaoundé Metropolis, Cameroon

Feuyit, Gilbert; Nzali, Serge; Lambi, John Ngolui; Laminsi, Samuel

doi:https://doi.org/10.1155/2019/3021894

Journal of Chemistry

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Abstract Introduction Materials and Methods Results and Discussion Conclusion Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2019 | Article ID 3021894 | https://doi.org/10.1155/2019/3021894

Air Quality and Human Health Risk Assessment in the Residential Areas at the Proximity of the Nkolfoulou Landfill in Yaoundé Metropolis, Cameroon

Gilbert Feuyit,¹Serge Nzali,²John Ngolui Lambi,³and Samuel Laminsi¹

Academic Editor: Andrea Gambaro

Received20 Dec 2018

Accepted30 Apr 2019

Published04 Jul 2019

Abstract

Landfill operations generate particulate matters (PM) and toxic gases that can jeopardize human health. This study was conducted in February 2016 to assess the air quality in the residential areas around the Nkolfoulou landfill in Yaoundé. The concentrations of PM_2.5 and PM₁₀ were determined with Dust Sentry while those of CO, O₃, NO₂, CH₄, CO₂, CH₂O, H₂S, and SO₂ were measured using gas sensors. At the landfill neighborhood, 30% of the daily mean concentrations of PM_2.5 and PM₁₀ crossed the daily safe limits. The concentrations of CO, O₃, NO₂, SO₂, and H₂S recorded at the propinquity of the landfill complied with the emission standards. Near the landfill, hourly mean concentrations of CH₂O and H₂S higher than their odour thresholds were recorded at each sampling site. The concentrations of CH₄ were less than its lower explosive limit while those of CO₂ were far below the safe limit for occupational health. The values of cancer risk (CR) due to the inhalation of CH₂O were >10⁻⁶ while those of hazard index (HI) due to the inhalation of CH₂O, H₂S, and SO₂ were <1. Thus, there might be increased cancer risks at the Nkolfoulou landfill neighborhood, whereas the increased non-cancer risks were low. 96.76% of the daily average levels of air pollutants registered near the landfill surpassed those recorded at the remote control site. Hence, the landfill operations might be supplying air pollutants to the neighbouring residential areas.

1. Introduction

Landfilling is the most widely used method of solid waste disposal across the world [1–3]. Landfill operations generate air pollutants such as particulate matters (PM) and gases [4]. The landfill gases (LFG) emitted into the environment may originate from the waste or may be generated during its decomposition [2]. Pristine air is a prerequisite for good health [5, 6]. Outdoor air pollutants are carcinogen Group 1 to humans; they induce lung cancer [7]. Air pollutants may conduce to the pathogenesis of upper airway diseases, viz., sinusitis, rhinitis, mild otitis, sinonasal cancer, and olfactory impairment [8]. Breathing polluted air during pregnancy may cause foetus growth retardation and abortion [6, 9, 10].

A link between short- or long-term exposure to airborne PM and human mortality and morbidity has been substantiated by several epidemiological studies [11–14]. Chronic exposure to PM_2.5 and PM₁₀ damages the respiratory and cardiovascular systems, while exposure to high concentrations of ozone (O₃) is a major factor in asthma morbidity and mortality [6]. High levels of sulfur dioxide (SO₂) reduce lung function and may provoke the irritation of the nose and the throat [15]. Hydrogen sulfide (H₂S) is the predominant landfill odour gas [16, 17]. Subjection to low and high concentrations of H₂S may induce the irritation of the throat and respiratory distress, respectively [18]. Formaldehyde (CH₂O) is not only a human carcinogen Group 1, causing cancer of the nasopharynx [19], but is also an irritant gas [20]. Many studies have been carried out elsewhere on the impact of landfill on the ambient air quality [4, 11, 21–25]. But, in Cameroon, data related to this issue are scanty. Therefore, this study focuses on the influence of the Nkolfoulou landfill activities on the ambient air quality.

2. Materials and Methods

2.1. Study Site Description

The study area has tropical climate and is located at the apex of a hill called Nkolfoulou. The Nkolfoulou landfill is situated at about 16 km away from the Yaoundé center. It was established in 1989 and was still in operation during this study. It covers a total land area of about 45 ha [26] and receives about 1300 tons of waste generated daily in the town of Yaoundé [27]. Employing a geographical positioning system (GPS) Magellan Triton-300, the geographical coordinates of the selected study stations were recorded. ArcGIS 10 software was used to draw the map of the study area and to gauge the distances between the sampling sites and the landfill boundary. Table 1 represents the locations of the monitoring sites, while Figure 1 displays the map of the study area.

2.2. Data Collection and Health Risk Evaluation

In February 2016, towards the end of the long dry season, the measurements of air pollutants were performed first at ten sites coded RA₁, RA₂, RA₃, RA₄, RA₅, RA₆, RA₇, RA₈, RA₉, and RA₁₀, selected in the residential areas around the landfill, and finally at a background site RA₀ carefully chosen for control. The concentration of gases was measured using a handheld Aeroqual Gas Sensor model S-500L, battery-operated, possessing an interchangeable sensor head. For each site, the concentrations of gases were recorded continuously for every 1 hour at intervals of 30 minutes, each making 16 hours of measurement daily (24 hours). For each hour, gas concentrations were measured after every 5 minutes giving 12 readings per hour for each gas. Thus, 192 readings were recoded for each gaseous pollutant per site during a day (24 hours). The airborne particulates (PM₁₀ and PM_2.5) measurements were carried out using a digital Aeroqual Dust Sentry (made by Aeroqual Limited, New Zealand) equipped with a laser. During measurements, the instrument was placed on a tripod of 1.5 m height. The measuring device was configured to record average concentrations of PM hourly at a flow rate of 2.0 L/min. Before measurements, all the instruments were calibrated according to the manufacturer’s instructions.

The non-cancer risks induced by the inhalation of CH₂O, H₂S, and SO₂ were evaluated by calculating the hazard quotient (HQ) using equation (3) deduced from equation (1), whereas the cancer risk (CR) due to the inhalation of CH₂O was computed from equation (4) deduced from equation (3) [28]:where EC = exposure concentration (μg/m³) and MRL = minimal risk level (μg/m³). where IUR = inhalation unit risk (μg/m³)⁻¹. HQ and CR are unitless.

For acute exposures (exposure lasting 24 hours or less), EC = CA [28], where CA = contaminant concentration in air (μg/m³). Hence, equations (1) and (2) become

For exposure to multiple non-carcinogenic substances, the resulting hazard index (HI) was calculated from the following equation [29, 30].

The MRLs of CH₂O, H₂S, and SO₂ are 0.04 ppm (49.2 μg/m³) [20], 0.07 ppm (98 μg/m³) [18], and 0.01 ppm (26.2 μg/m³) [15], respectively, for acute exposures while the IUR of CH₂O is 1.3 × 10⁻⁵ (μg/m³)⁻¹ [31].

3. Results and Discussion

3.1. Particulate Matter

The concentrations of each air pollutant were averaged for each hour and then for 24 hours. The levels of outdoor PM_2.5 and PM₁₀ measured at the monitoring sites are encapsulated in Table 2. The lowest hourly mean level of PM_2.5 was recorded at RA₁₀ (9.53 μg/m³), while the highest was registered at RA₃ (44.02 μg/m³). The hourly mean levels of PM₁₀ varied from 18.86 (RA₁₀) to 114.45 μg/m³ (RA₃). The hourly high level of PM_2.5 and PM₁₀ in the study area could be owing to landfill operations since they generate dust by a variety of mechanical and chemical processes [22].

The daily mean concentrations of PM_2.5 and PM₁₀ varied from 18.59 μg/m³ (RA₉) to 37.57 μg/m³ (RA₃) and 28.84 μg/m³ (RA₁₀) to 97.69 μg/m³ (RA₃), respectively. The daily mean levels of PM_2.5 of 32.75 (RA₂), 37.57 (RA₃), and 31.39 μg/m³ (RA₆) were higher than the daily safe limit of 25 μg/m³ set by the WHO [6]. Likewise, the daily mean levels of PM₁₀ of 91.34 (RA₂), 97.69 (RA₃), and 82.91 μg/m³ (RA₆) surpassed the daily safe limit of 50 μg/m³ laid down by the WHO [6]. Several studies have provided strong evidence that subjection to high concentration of PM may induce cardiopulmonary disease (CPD) and ischemic heart disease (IHD) mortality [32]. The hourly and daily average levels of PM_2.5 and PM₁₀ recorded at the proximity of the landfill were lower than those registered at the background site RA₀, implying that the landfill operations might be contributing to PM_2.5 and PM₁₀ to the ambient air. The movement of vehicles and motorbikes on the unpaved and poorly maintained roads in the study area as well as the ongoing construction works may have constituted additional sources of PM.

3.2. Odourless Gases

Although O₃ has a shocking smell, humans get rapidly acclimated to it. Moreover, the frequently associated presence of nitrogen oxides suppresses its perception [33]. For these reasons, it was classified among odourless gases in this study. Table 3 lists the concentrations of odourless gases in the study area.

The hourly mean concentrations of CO and O₃ ranged from ND (not detected) to 6.44 mg/m³ (RA₃) and ND to 137.42 μg/m³ (RA₅), respectively, while their daily average levels varied from 0.04 (RA₁₀) to 1.48 mg/m³ (RA₃) and 5.73 (RA₉) to 26.18 μg/m³ (RA₅) in the same order. NO₂ was detected only at RA₂ and RA₃. Its hourly and daily mean levels ranged from ND to 94.07 μg/m³ (RA₃) and 35.92 (RA₂) to 49.60 μg/m³ (RA₃). During this study, none of the CO value exceeded the safe limit of 100, 60, 30, and 10 mg/m³ for the averaging duration of 15 mn, 30 mn, 1 hr, and 8 hr, respectively, set by the WHO [5]. So also, all the concentrations of O₃ and NO₂ were far below their maximum emission limits laid down by the WHO in [5, 6], respectively. Relatively high levels of CO and NO₂ recorded at RA₂ and RA₃ compared with other sites may be attributable to their proximity to the highway.

The hourly mean value of 6.44 mg/m³ for CO registered in this work was lower than the 8-hour mean level of 7.79 mg/m³ recorded in a residential area around On-Nooch solid waste disposal site in Bangkok (Thailand) [21]. It was also less than 4 ppm (4.64 mg/m³) obtained in a residential area at the vicinity of Eneka landfill in Port Harcourt (Nigeria) [25]. But, the higher hourly mean value of 94.07 μg/m³ (0.947 mg/m³) for NO₂ recorded in this work was greater than the hourly mean figure of 0.034 mg/m³ found around On-Nooch dumpsite (Thailand) [21].

3.3. Odorous Gases

H₂S, CH₂O, and SO₂ are colorless and malodorous gases. H₂S has the characteristic odour of rotten eggs [18] while CH₂O has a pungent smell [20] as well as SO₂ [15]. Their concentrations are depicted in Table 4. In the residential areas adjacent to the landfill, the hourly mean levels of CH₂O, H₂S, and SO₂ ranged from ND to 206.76 μmg/m³ (RA₆), ND to 236.40 μg/m³ (RA₆), and ND to 28.56 μg/m³ (RA₃), respectively, while their daily average varied from 14.49 (RA₅) to 32.25 μg/m³ (RA₁), 8.74 (RA₅) to 28.06 μg/m³ (RA₆), and 1.05 (RA₉) to 4.18 μg/m³ (RA₃) in the same order. The maximum 30-minute mean limit of 100 μg/m³ for CH₂O [5] (Table 5) was crossed at all the sampling points near the landfill, whereas the maximum daily mean safe limit of 20 μg/m³ for SO₂ [6] (Table 5) was not violated at any site. Comparatively, all the daily mean values of SO₂ were much lower than the daily mean value of 8.91 mg/m³ recorded at the vicinity of On-Nooch dumpsite [21]. High concentrations of CH₂O irritate the nose, the throat, and the eyes [5, 20]. Subjection to a high level of SO₂ exacerbates asthma and can cause lung dysfunction [6, 15, 34].

At the proximity of the landfill, all the maximum hourly and daily mean values of H₂S were higher than its odour threshold contained in the approximate range of 0.5–8 ppb (0.7–11.2 μg/m³) [35, 36]. So also, all the maximum hourly and daily mean values of CH₂O at RA₁ and RA₆ exceeded its odour threshold which is in the range 30–600 μg/m³ [5]. Besides, all the daily mean concentrations of H₂S crossed the safe limit of 7 μg/m³, while all the maximum hourly mean concentrations of CH₂O violated the safe limit of 100 μg/m³. These safe limits are prescribed by the WHO [5] for an averaging time of 30 min to prevent annoyance and sensory effects. Subjection to low levels of H₂S may induce headaches and breathing difficulties in some asthmatic patients [18]. These gases may worsen the poor health conditions of patients in the healthcare center or bring about discomfort and annoyance to pupils in the primary school since both areas are situated close to RA₃.

At the background site RA₀, CH₂O and H₂S were not detected while the values of SO₂ were less than those recorded at the vicinity of the landfill, suggesting that the landfill may be the main contributor of CH₂O and H₂S to its surroundings. CH₂O and H₂S may have originated, respectively, from the decomposition of carbohydrate and protein [37] in the landfill. Meanwhile, CH₂O could have another source since aldehydes can be generated either from photochemical oxidation of hydrocarbons (HC) in the atmosphere [38] or through the incomplete combustion of fuel [39]. High hourly and daily mean concentrations of SO₂ registered at RA₃ cause one to think that the traffic was also contributing to SO₂ by the combustion of sulfur-containing fuels. The nearness of RA₆ to the landfill, the closeness of RA₂ to the entrance of the landfill and to the highway, and the proximity of RA₃ to the highway and the motorbike park may explain the high levels of CH₂O, H₂S, and SO₂ recorded at these sites.

3.4. Potential Greenhouse Gases

CH₄ and CO₂ are the main constituents of landfill gases (LFG) [40]. They are generated during the putrefaction of waste. The CH₄ and CO₂ concentrations in the study area are depicted in Table 6. The hourly mean levels of CH₄ and CO₂ were found, respectively, between ND and 2.30 ppm (RA₆) and 401.60 (RA₉) and 649.27 ppm (RA₃) while their daily average ranged from 0.01 (RA₁₀) to 1.76 ppm (RA₆) and 459. 85 (RA₈) to 573.02 ppm (RA₃) in the same order. The higher hourly and daily mean concentrations of CH₄ recorded at RA₆ could be due to its proximity to the landfill, whereas the higher hourly and daily mean concentrations of CO₂ recorded at RA₃ could be attributable to its location very close to both the gate of the landfill and the highway. So, it is reasonable to think that some CO₂ at these stations may have originated from the combustion of fuel in motor vehicles.

All the concentrations of CH₄ were less than its lower explosive limit (LEL) which is 5% [40] while all the levels of CO₂ were far below 5000 ppm as the maximum concentration level for occupational health [41]. Therefore, CH₄ and CO₂ are not a threat in the area under study for now.

Near the landfill, as far as the daily mean concentrations of gaseous pollutants were concerned, their abundance was in the following order: CO₂ > CO > CH₄ > CH₂O > H₂S > O₃ > NO₂ > SO₂.

3.5. Correlation Matrix

The correlation matrices for 9 measured air pollutants at the vicinity of the landfill are illustrated in Table 7. The significant positive correlation observed between PM_2.5 and CO (r = 0.65, ), PM₁₀ and CO₂ (r = 0.69, ), and PM₁₀ and CO (r = 0.89, ) signifies that CO and CO₂ are the major contributors of PM in the study area. At the 0.05 P level, a significant positive correlation was observed between CO and CO₂ (r = 0.70) and between CO and SO₂ (r = 0.70) implying that these pair variables have almost the same sources that could be either the combustion of fuel, fire wood, kerosene, or cooking gas in the study area. A significant high positive correlation was observed between CH₄ and H₂S (r = 0.93, ), CH₄ and CH₂O (r = 0.71, ) and between CH₂O and H₂S (r = 0.89, ) indicating that these pair variables have the same source which could be the landfill through the degradation of refuse. The negative significant correlation observed between O₃ and CH₂O (r = −0.69, ) signifies that when one of the variable rises, the other decreases. This is because O₃ is formed from CH₂O by photochemical reactions.

3.6. Non‐cancer and Cancer Risk Assessment

The noncarcinogenic risks associated with the exposure to CH₂O, H₂S, and SO₂ via inhalation were evaluated by calculating the hazard quotient (HQ) and the hazard index (HI), whereas the carcinogenic risks due to CH₂O through inhalation was estimated by computing the cancer risk (CR). HQ or HI values below 1.0 indicate that the pollutant under investigation is not likely to cause health impairment, whereas HQ or HI values above 1.0 indicate risk levels that are likely to damage health [42, 43]. The CR values > 10⁻⁶ indicate that potential carcinogenic effects may occur, whereas CR values ≤ 10⁻⁶ represent an admissible level [43]. The data for HQ and HI are depicted in Figure 2 while those for CR are displayed in Figure 3. In the residential areas bordering the landfill, the values of , and varied from 2.95E − 01 (RA₅) to 6.55E − 01 (RA₁) (mean 4.99E − 01), 8.92E − 02 (RA₅) to 2.86E − 01 (RA₃ and RA₆) (mean 2.24E − 01), and 4.01E − 02 (RA₉) to 1.36E − 01 (RA₂ and RA₃) (mean 7.66E − 02), respectively. In this same area, the HI values ranged from 4.33E − 01 (RA₅) to 9.76E − 01 (RA₆) (mean 8.00E − 01), while those of CR due to CH₂O was found between 1.88E − 04 (RA₅) and 4.19E − 04 (RA₁) (mean 3.19E − 04). None of the HQ and HI values exceeded the threshold value, set at the unity, implying that CH₂O, H₂S, and SO₂ are not likely to induce adverse health effects in the area under study for now. All the CR values were higher than 10⁻⁶ indicating that the nearby residents to the landfill are at risk of developing cancer in future owing to the inhalation of CH₂O. Comparatively, all the CR values due to CH₂O registered in this study were higher than 2.9 × 10⁻⁵ recorded near a plant treating organic waste in Catalonia (Spain) [44].

The risk levels in this study might have been overestimated as the chemical concentrations were measured solely for 24 hours instead of one year. Contrastingly, risks might have been underestimated because only the concentrations of CH₂O, H₂S, and SO₂ among a multitude of volatile toxic compounds that might be present were considered for the assessment of health risk. Furthermore, only exposure via inhalation was considered although exposure through ingestion and skin absorption may occur even if it is most often much lower [43].

4. Conclusion and Recommendations

According to the results of the present study, at the vicinity of the landfill, 30% of the daily mean concentrations of PM_2.5 and PM₁₀ and all the detected levels of CH₂O crossed the daily maximum safe limit, while the concentrations of CO, O₃, NO₂, SO₂, and H₂S were within the emission standards. However, noxious gases, viz., CH₂O and H₂S, were detected at the concentrations higher than their odour thresholds. Continuous dispatch of these gases into the ambient air may significantly reduce air quality and imperil public health and welfare. The values of cancer risk (CR) and hazard index (HI), respectively, were higher than 10⁻⁶ and less than the unity. Thus, the nearby residents to the Nkolfoulou landfill may experience an increase in risks of developing cancer while there was no significant increase of non-cancer risks. 96.76% of the daily average levels of air pollutants recorded in the neighborhood of the Nkolfoulou landfill exceeded those found at the remote control site, implying that the landfill operations might be contributing to air pollutants to the ambient air.

By this study, the following mitigation strategies can be recommended:(a)Daily cover of odorous wastes or odour treatment at the landfill site.(b)The road linking the highway to the landfill should be paved or thoroughly watered daily to keep the concentrations of PM at bay.(c)Planting trees around the landfill to absorb air pollutants.

Data Availability

All the data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that there are no conflicts of interest concerning the publication of this article.

Acknowledgments

The authors gratefully thank Mr. Tumenta Gerald Ndonwe and Mr. Sébastien Kengne for their assistance during the field work.

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Copyright © 2019 Gilbert Feuyit et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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