report writting

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

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

1Department of Inorganic Chemistry, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
2Faculty of Agronomy and Agricultural Sciences, School of Wood, Water and Natural Resources, University of Dschang,
Ebolowa Campus, P.O. Box 786, Ebolowa, Cameroon
3Department of Chemistry, Higher Teacher Training College, University of Yaoundé I, P.O. Box 47, Yaoundé, Cameroon

Correspondence should be addressed to Gilbert Feuyit; [email protected]

Received 20 December 2018; Accepted 30 April 2019; Published 4 July 2019

Academic Editor: Andrea Gambaro

Copyright © 2019 Gilbert Feuyit et al. ‘is 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.

Landfill operations generate particulate matters (PM) and toxic gases that can jeopardize human health. ‘is study was conducted
in February 2016 to assess the air quality in the residential areas around the Nkolfoulou landfill in Yaoundé. ‘e concentrations of
PM2.5 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 PM2.5 and PM10 crossed the daily safe
limits. ‘e 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. ‘e concentrations of CH4 were less than its lower explosive limit while those of CO2 were far below the safe
limit for occupational health. ‘e 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. 'us, 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 gen- erate air pollutants such as particulate matters (PM) and gases [4]. 'e landfill gases (LFG) emitted into the envi- ronment 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 carcin- ogen 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 sub- stantiated by several epidemiological studies [11–14]. Chronic exposure to PM2.5 and PM10 damages the re- spiratory 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 Hindawi Journal of Chemistry Volume 2019, Article ID 3021894, 9 pages https://doi.org/10.1155/2019/3021894 mailto:[email protected] https://orcid.org/0000-0001-6626-4250 https://creativecommons.org/licenses/by/4.0/ https://doi.org/10.1155/2019/3021894 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. 'erefore, this study focuses on the in- fluence of the Nkolfoulou landfill activities on the ambient air quality. 2. Materials and Methods 2.1. Study Site Description. 'e study area has tropical cli- mate and is located at the apex of a hill called Nkolfoulou. 'e 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 mea- surements 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. 'e concentration of gases was measured using a handheld Aeroqual Gas Sensor model S-500L, battery-op- erated, 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. 'us, 192 readings were recoded for each gaseous pollutant per site during a day (24 hours). 'e airborne particulates (PM10 and PM2.5) 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. 'e 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 manu- facturer’s instructions. 'e 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]: HQ � EC MRL , (1) where EC = exposure concentration (μg/m3) and MRL = minimal risk level (μg/m3). CR � IUR × EC, (2) 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 HQ � CA MRL , (3) CR � IUR × CA. (4) For exposure to multiple non-carcinogenic substances, the resulting hazard index (HI) was calculated from the following equation [29, 30]. HI � 􏽘 n i HQi. (5) 'e 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. 'e concentrations of each air pol- lutant were averaged for each hour and then for 24 hours. 'e levels of outdoor PM2.5 and PM10 measured at the monitoring sites are encapsulated in Table 2. 'e lowest hourly mean level of PM2.5 was recorded at RA10 (9.53 μg/m 3), while the highest was registered at RA3 (44.02 μg/m 3). 'e hourly mean levels of PM10 varied from 18.86 (RA10) to 114.45 μg/m 3 (RA3). 'e hourly high level of PM2.5 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]. 'e daily mean concentrations of PM2.5 and PM10 varied from 18.59μg/m3 (RA9) to 37.57μg/m 3 (RA3) and 28.84 μg/m 3 (RA10) to 97.69μg/m 3 (RA3), respectively. 'e daily mean levels of PM2.5 of 32.75 (RA2), 37.57 (RA3), and 31.39μg/m 3 (RA6) were higher than the daily safe limit of 25μg/m 3 set by the WHO [6]. Likewise, the daily mean levels of PM10 of 91.34 (RA2), 97.69 (RA3), and 82.91μg/m 3 (RA6) surpassed the daily Table 1: Specifications of the monitoring sites. Site code GPS coordinates DLB (m) E N SL (m) RA0 11°34′17.043″ 3°56′25.866″ 694 1000.00 RA1 11°34′15.801″ 3°55′27.96″ 701 161.37 RA2 11°34′36.123″ 3°55′29.889″ 720 34.40 RA3 11°34′43.421″ 3°55′29.084″ 734 118.58 RA4 11°34′26.945″ 3°55′49.69″ 730 239.06 RA5 11°34′24.22″ 3°56′0.289″ 708 305.02 RA6 11°34′12.123″ 3°55′58.821″ 661 58.25 RA7 11°34′4.757″ 3°55′54.325″ 667 165.74 RA8 11°34′0.786″ 3°55′52.929″ 693 255.33 RA9 11°33′59.289″ 3°55′46.615″ 669 189.27 RA10 11°33′51.403″ 3°55′37.557″ 673 279.40 SL � sea level; DLB � distance from the landfill boundary. 2 Journal of Chemistry safe limit of 50μg/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]. 'e hourly and daily average levels of PM2.5 and PM10 recorded at the proximity of the landfill were lower than those registered at Table 2: Concentration of particulate matter at the monitoring sites (n � 24). Site code PM2.5 (μg/m 3) PM10 (μg/m 3) Range of hourly mean Daily mean Range of hourly mean Daily mean Min Max Min Max RA0 10.50 17.50 12.85 18.90 31.50 23.12 RA1 12.09 22.34 19.19 25.39 46.91 40.29 RA2 12.50 39.50 32.75 35.00 110.60 91.34 RA3 18.20 44.02 37.57 47.32 114.45 97.69 RA4 12.57 21.75 19.23 18.86 42.63 35.71 RA5 13.40 22.58 20.49 28.14 47.42 43.04 RA6 14.20 36.80 31.89 36.92 95.68 82.91 RA7 13.91 21.56 19.56 29.21 45.28 41.07 RA8 12.20 23.19 20.36 24.16 45.92 40.32 RA9 9.53 21.35 18.59 20.34 40.65 37.84 RA10 11.64 24.82 21.63 26.70 42.95 28.84 RA � residential area; ND � not detected; n � number of measurements per day (24 hours). 3° 56 ′ 15 ″ N 3° 55 ′ 50 ″ N 3° 55 ′ 25 ″ N 3° 56 ′ 15 ″ N 3° 55 ′ 50 ″ N 3° 55 ′ 25 ″ N 11°34′10″E 11°34′35″E 11°34′10″E 11°34′35″E Legend Landfill Monitoring site Major road Healthcare area Educational area Main stream Tributary Figure 1: Map of the study area. Journal of Chemistry 3 the background site RA0, implying that the landfill operations might be contributing to PM2.5 and PM10 to the ambient air. 'e movement of vehicles and motorbikes on the unpaved and poorly maintained roads in the study area as well as the on- going 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 fre- quently 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. 'e 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/m 3 (RA3) and 5.73 (RA9) to 26.18 μg/m 3 (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 concen- trations 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. 'e 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 ('ailand) [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 ('ailand) [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]. 'eir 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/m 3 (RA6), and ND to 28.56 μg/m3 (RA3), respectively, while their daily average varied from 14.49 (RA5) to 32.25 μg/m 3 (RA1), 8.74 (RA5) to 28.06 μg/m3 (RA6), and 1.05 (RA9) to 4.18 μg/m 3 (RA3) in the same order. 'e 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/m 3. 'ese 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]. 'ese gases may worsen the poor health conditions of pa- tients 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, re- spectively, 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 at- mosphere [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. 'e 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]. 'ey are generated during the putrefaction of waste. 'e CH4 and CO2 con- centrations in the study area are depicted in Table 6. 'e 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. 'e 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 at- tributable 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 4 Journal of Chemistry concentration level for occupational health [41]. 'erefore, 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. ‘e correlation matrices for 9
measured air pollutants at the vicinity of the landfill are
illustrated in Table 7. ‘e significant positive correlation
observed between PM2.5 and CO (r � 0.65, p≤0.05), PM10
and CO2 (r � 0.69, p≤0.05), and PM10 and CO (r � 0.89,
p≤0.01) signifies that CO and CO2 are the major con-
tributors 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)

Table 3: Concentration of odourless gases at the monitoring sites (n1 � 12; n2 �192).

Site code

CO (mg/m3) O3 (μg/m
3) NO2 (μg/m

3)
Range of hourly

mean Daily mean
Range of hourly

mean Daily mean
Range of hourly

mean Daily mean
Min Max Min Max Min Max

RA0 ND 0.30 0.05 ND 10.51 1.32 ND ND NC
RA1 ND 1.00 0.27 ND 40.01 5.73 ND ND NC
RA2 ND 4.58 0.92 ND 58.90 10.63 ND 75.26 35.92
RA3 ND 8.02 1.48 ND 39.41 6.54 ND 94.07 49.60
RA4 ND 1.55 0.42 ND 58.90 6.54 ND ND NC
RA5 ND 4.01 0.46 ND 137.42 26.18 ND ND NC
RA6 ND 7.44 1.07 ND 38.94 5.73 ND ND NC
RA7 ND 1.86 0.36 ND 39.26 8.18 ND ND NC
RA8 ND 0.64 0.13 ND 78.53 6.54 ND ND NC
RA9 ND 1.37 0.05 ND 19.63 5.89 ND ND NC
RA10 ND 2.40 0.04 ND 58.90 19.63 ND ND NC
RA � residential area; ND � not detected; NC � not calculated because not detected; n1 � number of measurements per hour; n2 � number of measurements
per day (24 hours).

Table 4: Concentration of odorous gases at the monitoring sites (n1 � 12; n2 � 192).

Site code

CH2O (μg/m
3) H2S (μg/m

3) SO2 (μg/m
3)

Range of hourly
mean Daily mean

Range of hourly
mean Daily mean

Range of hourly
mean Daily mean

Min Max Min Max Min Max
RA0 ND ND NC ND ND NC ND 1.74 0.82
RA1 ND 185.56 32.25 ND 152.97 20.45 ND 14.28 2.14
RA2 ND 133.95 24.88 ND 139.06 19.60 ND 26.18 3.56
RA3 ND 130.32 22.02 ND 122.49 11.02 ND 28.56 4.18
RA4 ND 172.20 25.71 ND 166.87 22.45 ND 11.90 2.28
RA5 ND 138.62 14.49 ND 62.97 8.74 ND 6.80 1.30
RA6 ND 206.76 30.83 ND 236.40 28.06 ND 16.66 1.70
RA7 ND 147.15 28.13 ND 194.68 25.13 ND 12.14 1.90
RA8 ND 181.10 27.79 ND 180.78 24.02 ND 11.05 1.45
RA9 ND 149.08 21.65 ND 139.06 20.25 ND 4.92 1.05
RA10 ND 142.03 17.59 ND 125.15 17.53 ND 5.35 1.18
RA � residential area; ND � not detected; NC � not calculated because not detected; n1 � number of measurements per hour; n2 � number of measurements
per day (24 hours).

Table 5: WHO ambient air quality standards.

Pollutant
Averaging
duration

Maximum allowable
limit

Reference

PM2.5
24 hours 25 μg/m3 [6]
Annual 10 μg/m3 [6]

PM10
24 hours 50 μg/m3 [6]
Annual 20 μg/m3 [6]

CO

15 minutes 100 mg/m3 [5]
30 minutes 60 mg/m3 [5]
1 hour 30 mg/m3 [5]
8 hours 10 mg/m3 [5]

SO2
10 minutes 500 µg/m3 [6]
24 hours 20 μg/m3 [6]

CH2O 30 minutes 0.1 mg/m
3 [5]

H2S 24 hours 150 μg/m
3 [5]

O3 8 hours 100 μg/m
3 [6]

NO2
1 hour 200 μg/m3 [5]
Annual 40 μg/m3 [5]

Journal of Chemistry 5

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 sig-
nificant high positive correlation was observed between CH4
and H2S (r � 0.93, p≤0.01), CH4 and CH2O (r � 0.71,
p≤0.05) and between CH2O and H2S (r � 0.89, p≤0.01)
indicating that these pair variables have the same source
which could be the landfill through the degradation of re-
fuse. ‘e negative significant correlation observed between
O3 and CH2O (r �−0.69, p≤0.05) signifies that when one of
the variable rises, the other decreases. ‘is is because O3 is
formed from CH2O by photochemical reactions.

3.6. Non-cancer and Cancer Risk Assessment. ‘e non-
carcinogenic 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 in-
halation 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]. ‘e CR values>10−6
indicate that potential carcinogenic effects may occur,
whereas CR values≤10−6 represent an admissible level [43].
‘e 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 HQCH2O, HQH2S, and
HQSO2 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].

‘e risk levels in this study might have been over-
estimated as the chemical concentrations were measured
solely for 24 hours instead of one year. Contrastingly, risks
might have been underestimated because only the con-
centrations of CH2O, H2S, and SO2 among a multitude of
volatile toxic compounds that might be present were con-
sidered for the assessment of health risk. Furthermore, only
exposure via inhalation was considered although exposure

Table 7: Correlation matrix.

PM2.5 PM10 CH4 H2S CH2O CO2 SO2 CO O3
PM2.5 1
PM10 0.564 1
CH4 −0.320 0.042 1
H2S −0.309 −0.139 0.927∗∗ 1
CH2O −0.212 −0.091 0.709∗ 0.818∗∗ 1
CO2 0.420 0.685∗ 0.018 −0.127 0.188 1
SO2 0.410 0.600 −0.030 0.018 0.382 0.576 1
CO 0.648∗ 0.891∗∗ 0.042 −0.067 0.127 0.697∗ 0.697∗ 1
O3 0.350 −0.043 −0.615 −0.572 −0.689∗ −0.332 −0.117 −0.049 1
∗Correlation is significant at the 0.05 level; ∗∗Correlation is significant at the 0.01 level; bold values are statistically significant.

Table 6: Level of potential greenhouse gases at the monitoring sites (n1 � 12; n2 � 192).

Site code
CH4 (ppm) CO2 (ppm)

Range of hourly mean
Daily mean

Range of hourly mean
Daily mean

Min Max Min Max
RA0 ND ND NC 421.00 498.04 461.82
RA1 ND 0.06 0.03 450.25 503.12 481.64
RA2 ND 0.05 0.02 478.61 602.41 550.16
RA3 ND 0.03 0.01 490.25 649.27 573.02
RA4 ND 0.07 0.04 420.31 510.00 464.39
RA5 ND 0.04 0.01 425.50 503.74 466.41
RA6 ND 2.30 1.76 451.63 612.10 541.37
RA7 ND 0.18 0.08 428.50 505.31 467.32
RA8 ND 0.09 0.05 421.75 510.80 459.85
RA9 ND 0.07 0.04 401.60 507.28 469.63
RA10 ND 0.06 0.01 425.00 501.37 460.11
RA � residential area, ND � not detected, NC � not calculated because ND, n1 � number of measurements per hour, n2 � number of measurements per day
(24 hours).

6 Journal of Chemistry

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 land�ll, 30% of the daily mean concentrations of
PM2.5 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 signi�cantly reduce air quality and
imperil public health and welfare. �e values of cancer risk
(CR) and hazard index (HI), respectively, were higher than

10−6 and less than the unity. �us, the nearby residents to
the Nkolfoulou land�ll may experience an increase in risks
of developing cancer while there was no signi�cant in-
crease of non-cancer risks. 96.76% of the daily average
levels of air pollutants recorded in the neighborhood of the
Nkolfoulou land�ll exceeded those found at the remote
control site, implying that the land�ll 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 land�ll site.

(b) �e road linking the highway to the land�ll should be
paved or thoroughly watered daily to keep the
concentrations of PM at bay.

0.0E + 00

5.0E – 05

1.0E – 04

1.5E – 04

2.0E – 04

2.5E – 04

3.0E – 04

3.5E – 04

4.0E – 04

4.5E – 04

C
an

ce
r r

is
k

Sites
RA0 RA1 RA2 RA3 RA4 RA5 RA6 RA7 RA8 RA9 RA10

Figure 3: Cancer risks (CR) at the monitoring sites (CR at RA0 was not calculated because CH2O was not detected at that site).

0.0E + 00

2.0E – 01

4.0E – 01

6.0E – 01

8.0E – 01

1.0E + 00

1.2E + 00

N
on

-c
an

ce
r r

is
k

RA0 RA1 RA2 RA3 RA4 RA5 RA6 RA7 RA8 RA9 RA10
Sites

HQ (H2S)HQ (CH2O)
HQ (SO2) HI

Figure 2: Non-cancer risks at the monitoring sites (the non-cancer risks of CH2O and H2S at RA0 were not calculated because they were not
detected at that site; the horizontal line represents the admissible level of non-cancer risk [42, 43]).

Journal of Chemistry 7

(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

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

Acknowledgments

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

References

[1] F. J. Flores-Tena, A. L. Guerrero-Barrera, F. J. Avelar-
González, E. M. Ramı́rez-López, and M. C. Mart́ınez-Saldaña,
“Pathogenic and opportunistic gram-negative bacteria in soil,
leachate and air in San Nicolás landfill at …

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