Adewemimo Oluwakunmi
Popoola
*a,
Lukuman Adekilekun
Jimoda
a,
Olusesan Abel
Olu-Arotiowa
a,
Oyetola
Ogunkunle
*b,
Opeyeolu Timothy
Laseinde
b,
Sunday Adekunle
Adebanjo
c and
Wuraola Abake
Raji
d
aDepartment of Chemical Engineering, Ladoke Akintola University of Technology, Oyo State, Nigeria. E-mail: aopopoola95@lautech.edu.ng
bDepartment of Mechanical and Industrial Engineering Technology, University of Johannesburg, South Africa. E-mail: oogunkunle@uj.ac.za
cDepartment of Chemical and Polymer Engineering, Lagos State University, Nigeria
dDepartment of Chemical and Petroleum Engineering, Igbinedion University, Okada, Nigeria
First published on 2nd June 2023
The emissions from open burning of municipal solid wastes (MSWs) are very harmful. Owing to the scarcity of information on the impact of open burning of MSW on the onsite workers and the population within the vicinity of the Sokoto-Aiyekale dump site in Ilorin, Kwara State, this study focused on examining the impact of open burning of solid waste at the dump site on its host communities. The criteria air pollutants (CAPs) such as particulate matter (PM) and volatile organic compounds (VOCs) were determined using the emission factor approach. Deposition gauges were deployed at selected sampling spots to collect particulates which were characterized for heavy metal concentrations for the wet and dry seasons using energy dispersive X-ray fluorescence (EDXRF). The seasonal deposition fluxes, the deposition velocities and the scavenging ratios of the elements were estimated. The ground level concentrations of each of the CAPs within a 15 km radius were predicted using the AERMOD software (Version 8.2.0). The results showed that the emission inventory for PM and VOCs is in the range of 2200.5–2481.1 and 5913.9–6668.0 tons per annum between 2016 and 2020, respectively. Fourteen elements (Fe, Au, Ag, Pd, Rh, Cd, Zn, In, Sn, Cu, Mn, Ti, Ru, and S) were identified from the deposition study, with Fe having the highest concentration of 67512.8 and 73845.5 μg m−3 in the wet and dry seasons, respectively. The wet and dry deposition fluxes ranged from 7.32 to 11.46 and 38.83 to 88.8 g per m2 per month, respectively. Deposition velocities of the trace metals were in the range of 0.0000528–0.00075444 and 0.0003377–0.0048183 m s−1 in the wet and dry seasons, respectively. The average 1, 8, 24 h, and annual concentrations were 16175, 6634, 3190 and 409 μg m−3 for PM and 20959, 7000, 3700 and 418 μg m−3 for VOCs, respectively. This research shows that open burning of solid wastes is characterized by harmful gaseous emissions and heavy metals with potential adverse effects on receptor communities. These findings will serve as baseline information for environmental protection agencies.
Environmental significanceThis research investigated the emissions from open burning of solid waste at the Sokoto-Aiyekale dump site. The ground level concentrations of criteria air pollutants were estimated using AERMOD. The criteria air pollutants (CAPs) such as particulate matter (PM) and volatile organic compounds (VOCs) were determined using the emission factor approach. This study established the fact that anthropogenic activities such as open burning of solid waste produce heavy metals in large concentrations, which has a negative impact on the environment. Baseline data were generated which can be adopted by the Federal Ministry of Environment and Environmental Protection Agency. This research provided a template for stakeholders in the environmental sector to take appropriate measures to attenuate the effects of open burning of solid waste on human health and the environment. |
Different types of materials are classified as municipal solid waste (MSW). These include refuse, sludge from a waste treatment plant, air pollution control facility and other discarded materials such as solid, liquid, semisolid, and/or gaseous materials resulting from industries. Waste from institutions such as schools and hospitals, community activities, as well as commercial sources, such as restaurants and small businesses, mining and agricultural operations, are also regarded as MSW.4 The rate and quantity of waste generation have recently increased. As the quantity of waste increases, so does the variety.5 As opposed to the prehistoric period, when wastes were merely a nuisance that had to be disposed, proper management was not a major concern because of the small number of people and a vast amount of land was available to the population at the time. During this period, the environment readily taken up by the amount of waste produced without any degradation.6
The World Bank predicts that waste generation will increase from 2.01 billion tonnes in 2016 to 3.40 billion tonnes in 2050. At least 33% of this waste is currently mismanaged globally through open dumping or burning.7 The rise in waste generation rate will result in an increase in environmental challenge if not effectively managed. Global MSW data revealed a generation rate of 0.68 billion tons per year in 2000 and 1.3 billion tons per year in 2010, with an estimated 2.2 billion tons per year in 2025 and 4.2 billion tons per year in 2055.8 Today, the rate at which waste is being generated is about 70% as compared to the total rate of its disposal which is 30%.9 Municipal solid waste management (MSWM), a vital feature in achieving sustainable metropolitan growth, entails the separation, storage, collection, relocation, processing, and disposal of solid waste in order to reduce its environmental impact. Unmanaged MSW contributes to the spread of numerous diseases.10 The earth is very good at resource recovery, but when the quantity of waste generated exceeds its capacity, it presents a serious threat to lives, a concept known as pollution, which occurs at varying concentrations and affects all forms of life.11
The global public health crisis is being exacerbated by dirty air. Over 90% of the global population lives in areas where air pollution exceeds World Health Organization standards.12 Some scientific studies have found a link between the formation of PM and VOC emissions.13 Shao et al.13 reported that VOCs play an important role in the formation of PM and oxidants, contributing to summertime air pollution under certain humid conditions. Their report suggested that some VOC groups may promote an increase in PM concentrations unless PM levels exceed 140 μg m−3 under humid conditions.
Particulate matter (PM) refers to all solid and liquid particles suspended in air, many of which are hazardous.14 Particulate matter is a broad term used to describe air pollutants that consist of suspended particles in the air that vary in composition and size as a result of various anthropogenic activities.15 The size, composition, and the concentration of the particulate matter depend on the type of gasifier and its operating conditions such as temperature, gas velocity, moisture content in fuels, and rate of gasification. The size of the particulate matter varies from less than 1 micron to larger than 100 microns. Besides posing health risk, particulate matter is also responsible for causing fouling, erosion, and corrosion of downstream equipment.16 Particulate matter is the main contributor for air pollution. It decreases the clarity in air and therefore affects the visibility and makes it difficult to breathe such air.17 Particulate matter includes all solid and liquid particles that are found in the suspended condition in air. Many of them are usually hazardous and act as major risk factors for imposing much co-morbidity in humans.18
Volatile organic compounds (VOCs) are gaseous chemicals emitted into the atmosphere by many of the solid or liquid products we use to build and maintain our homes.19 Volatile organic compounds have a high vapor pressure but a low water solubility. VOCs contain a wide range of chemicals, some of which may have short- and long-term negative health effects. Many VOC concentrations are consistently up to ten times higher indoors than outdoors.20 Once in the air, some can react with other gases to form other air pollutants. Some are toxic, including those that cause cancer and other health related issues.21 VOCs can be found in both indoor and outdoor air. Some of the more well-known VOCs are benzene, formaldehyde, and toluene. VOCs can irritate the eyes, nose, and throat, cause difficulty in breathing and nausea, and damage the central nervous system and other organs when inhaled. Some VOCs have been linked to cancer.19
Using mathematical formulations, air dispersion of a pollutant emitted by a source can be modelled.22 Vallero23 suggested that dispersion models can be used to estimate the distribution of pollutants in the atmosphere based on the emissions from a source and the atmospheric conditions. These models are commonly used to predict the concentration of pollutants at various downwind receptor locations. These models are commonly used in the management of the environmental impact of pollutant emissions. Air dispersion modelling is a widely used tool for managing the impacts of pollutant emissions on the environment. As Ryan and LeMasters24 noted, these models are commonly used for various purposes, such as environmental impact assessments, risk analysis, emergency planning, and source apportionment studies. The models estimate the dispersion of pollutants in the atmosphere and help to assess the potential impacts on human health and the environment. Air dispersion models play a significant role in the policy and decision-making process. By providing information on the potential impacts of emissions, they help policymakers and decision-makers to make informed choices about environmental policies and regulations, such as setting emission limits and establishing air quality standards. These models also assist in identifying areas where air quality management efforts are needed and can be used to evaluate the effectiveness of different mitigation strategies.
Open waste burning is common practice in low- and middle-income countries, but systematic and modelling studies and evidence of the practice are lacking.25 The scientific foundation for modelling the impact of emissions from open burning is also lacking. Exposure to open waste burning was found to pose the greatest risk to human and environmental health of all waste categories and disposal methods studied.3 This work was limited to the Kwara State Government approved dump site located at Sokoto Aiyekale, along the Jebba-Bode Sadu Road in Ilorin. It involves the estimation of the emission inventory from 2016 to 2020, determination of heavy metals in the ambient air through wet and dry deposition and forward trajectory modelling of the pollutants resulting from the combustion activities using AERMOD.
The indigenous area of town, known as the old residential area, is located in the central core area. The post-colonial area located around the city's core is the new residential area, whereas the government reserved area is the elevated neighbourhood area. Sobi Hill is an isolated hill in the city with an elevation of 394 m above sea level (ASL) in the north-western part and 200 m to 346 m in the east. Ilorin's drainage system has a dendritic pattern.28 The wet season runs from March to October, and the dry season runs from November to February. The city's average annual rainfall is 1200 mm.29 The government of Kwara State approved a bill in 2015 authorizing that all defunct landfilling locations within the city be demolished in order to make for growth and urbanization in the state, because it is an absolute mess for a state capital to have huge amounts of open refuse landfills on every accessible space on the road and street.
The emission factor used for the PM and VOC emissions from municipal solid waste combustion was adopted from the United States Environmental Protection Agency. The AP-42 compilation of air pollutant emissions developed by the United States Environmental Protection Agency (USEPA)31 states that the emission factor of PM and VOCs for municipal solid waste combustion is 8 kg Mg−1 and 21.5 kg Mg−1, respectively. It simply implies that for municipal solid waste combustion, the estimated amount of particulate matter emission is 8 kg Mg−1 of the quantity of solid waste combusted. Also, to estimate the quantity of VOCs emitted, an emission factor of 21.5 kg of VOCs per mg of the quantity of municipal solid waste combusted was considered. The word estimate here means an approximate value (plus or minus) given by USEPA.
(1) |
For year 2016,
(2) |
Weekly PM emission (g) = daily PM emission (g) × 7 | (3) |
Monthly PM emission (g) = daily PM emission (g) × 30 | (4) |
Annual PM emission (g) = daily PM emission (g) × 365 | (5) |
(6) |
Weekly VOC emission (g) = daily VOC emission (g) × 7 | (7) |
Monthly VOC emission (g) = daily VOC emission (g) × 30 | (8) |
Annual VOC emission (g) = daily VOC emission (g) × 365 | (9) |
The daily, weekly, monthly and annual CAPs for year 2017 to 2020 were estimated using eqn (2)–(9).
(10) |
(11) |
The scavenging ratio of heavy metals is of importance in the understanding of the influence of deposition on the lifetime of the heavy metals in the environment. Under the approximation that the concentration of pollutants in precipitation (Cp) depends on the concentration in the air (CA) within which precipitation is formed,36 the scavenging ratio (SR) is expressed as shown in eqn (12).
(12) |
Table 1 shows the PM and VOC pollutants emitted between 2016 and 2020. In 2016, the daily PM and VOCs emitted were calculated to be 6028800 g and 16202400 g respectively. The weekly values were 42201600 g and 113416800 g respectively. The monthly values were 180864000 g and 486072000 g respectively. The yearly values were calculated to be 2200512000 g and 5913876000 g respectively. In 2017, the daily PM and VOCs emitted were calculated to be 6212800 g and 16696900 g, respectively. The weekly values were 43489600 g and 116878300 g respectively. The monthly values were 186384000 g and 500907000 g respectively. The yearly values were calculated to be 2267672000 g and 6094368500 g respectively. In 2018, the daily PM and VOCs emitted were calculated to be 6401600 g and 17204300 g, respectively. The weekly values were 44811200 g and 120430100 g, respectively. The monthly values were 192048000 g and 516129000 g, respectively. The yearly values were calculated to be 2336584000 g and 6279569500 g, respectively. In 2019, the daily PM and VOCs emitted were calculated to be 6596800 g and 17728900 g, respectively. The weekly values were 46177600 g and 124102300 g, respectively. The monthly values were 197904000 g and 531867000 g, respectively. The yearly values were calculated to be 2407832000 g and 6471048500 g, respectively. In 2020, the daily PM and VOCs emitted were calculated to be 6797600 g and 18268550 g, respectively. The weekly values were 47583200 g and 127879850 g, respectively. The monthly values were 203928000 g and 548056500 g, respectively. The yearly values were calculated to be 2481124000 g and 6668020750 g, respectively.
2016 | 2017 | 2018 | 2019 | 2020 | ||||||
---|---|---|---|---|---|---|---|---|---|---|
PM (g) | VOCs (g) | PM (g) | VOC (g) | PM (g) | VOC (g) | PM (g) | VOC (g) | PM (g) | VOC (g) | |
Daily | 6028800 | 16202400 | 6212800 | 16696900 | 6401600 | 17204300 | 6596800 | 17728900 | 6797600 | 18268550 |
Weekly | 42201600 | 113416800 | 43489600 | 116878300 | 44811200 | 120430100 | 46177600 | 124102300 | 47583200 | 127879850 |
Monthly | 180864000 | 486072000 | 186384000 | 500907000 | 192048000 | 516129000 | 197904000 | 531867000 | 203928000 | 548056500 |
Yearly | 2200512000 | 5913876000 | 2267672000 | 6094368500 | 2336584000 | 6279569500 | 2407832000 | 6471048500 | 2481124000 | 6668020750 |
Table 1 also shows that the emission of VOCs, which is the second highest of all the criteria air pollutants resulting from the combustion of solid waste. There is an increase in the VOC emission from 2016 to 2020 due to the increase in the generation of solid waste. From 2016 to 2020, VOCs increase from 16.2 to 18.3 tons per day, from 113.4 to 127.9 tons per week, from 486.1 to 548.1 tons per month and 5913.9 to 6668.0 tons per year. These values must be controlled because of the effects of volatile organic compounds which include damaging of the audible and visual senses.38 The average, standard deviation, and uncertainty values of daily/weekly/monthly/annual emissions of PM and VOCs are presented in Table 2.
Average | Std. Dev. | Uncertainty | ||||
---|---|---|---|---|---|---|
PM | VOC | PM | VOC | PM | VOC | |
Daily | 6407520 | 17220210 | 303878.71 | 816674.04 | 135898.69 | 365227.73 |
Weekly | 44852640 | 120541470 | 2127150.99 | 5716718.28 | 951290.84 | 2556594.14 |
Monthly | 192225600 | 516606300 | 9116361.38 | 24500221.21 | 4076960.75 | 10956832.02 |
Yearly | 2338744800 | 6285376650 | 110915730.10 | 298086024.70 | 49603022.46 | 133308122.90 |
Likewise, the result revealed that the emission of PM, which is the third highest of all the criteria air pollutants results from the combustion of solid waste. There is an increase in the PM emission from 2016 to 2020 due to the increase in the generation of solid waste. From 2016 to 2020, PM increases from 6.0 to 6.8 tons per day, from 42.2 to 47.6 tons per week, from 180.9 to 203.9 tons per month and 2200.5 to 2481.1 tons per year. Wheezing, aggravation of asthma, shortness of breath, coughing and chest pain are some of the short-term effects of particulate matter inhalation. Long-term exposure to particulate matter can result in heart failure, respiratory disease and lung cancer.39 Children, the aged, and people with pre-existing respiratory conditions are mostly vulnerable to PM health impacts. Furthermore, pregnant mothers and their babies are at serious risk for mortality and health problems because of PM exposure.40 The emission of PM from the combustion of solid waste must be attenuated.
Sampling spot | Wet season (g per m2 per month) | Dry season (g per m2 per month) |
---|---|---|
1 | 9.55 | 41.37 |
2 | 10.82 | 48.70 |
3 | 8.59 | 38.83 |
4 | 11.46 | 64.61 |
5 | 7.32 | 60.47 |
6 | 10.18 | 71.93 |
7 | 7.96 | 52.51 |
8 | 9.87 | 42.97 |
9 | 9.23 | 88.80 |
10 | 7.64 | 79.89 |
Control | 0.95 | 33.74 |
The deposition fluxes of the control site were lower than those of the sampling sites because no history of open burning is recorded at the control site which is 6 km away from the study area. The result showed that the wet season fluxes were lower than the dry season fluxes due to the high precipitation that washes down the particulates in the wet season which is not so in the dry season when we have more particles resuspended in the atmosphere thereby resulting in high deposition fluxes.41
Iron (Fe) was predominantly high in all the sampling spots, which is similar to the result of Kumar et al.43 However, the highest concentration was recorded at sampling spot (SS) 2, as shown in Table 4 (111.65 × 103 ± 5.575 × 103 μg m−3) while the lowest concentration of 30.679 × 103 ± 4.222 × 103 μg m−3 was recorded at SS 9. The dry season analysis reveals that the highest concentration of 117.369 × 103 ± 4.603 × 103 μg m−3 was found at SS 2, while the lowest (58.841 × 103 ± 4.613 × 103 μg m−3) was found at SS 4 (Table 5). The concentrations during the two seasons (wet and dry) were higher than the standards recommended by USEPA and WHO. Also, the concentrations of Fe were greater than 25.3 μg m−3 (wet season) and 18.3 μg m−3 (dry season) reported by Kumar et al. (2018). In addition, these values are higher than 31 × 10−3 μg m−3 given by Antisari et al.44
Elements | μg m−3 (103) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SS 1 | SS 2 | SS 3 | SS 4 | SS 5 | SS 6 | SS 7 | SS 8 | SS 9 | SS10 | Control | |
a SS: sampling spot. | |||||||||||
Fe | 72.569 | 111.650 | 59.909 | 54.441 | 81.104 | 59.536 | 77.941 | 69.061 | 30.679 | 58.238 | 44.631 |
Au | — | — | — | — | — | 4.849 | — | — | 4.615 | — | — |
Ag | 15.191 | 11.554 | 15.195 | 16.733 | 16.636 | 16.645 | 13.612 | 18.021 | 23.200 | 17.672 | 14.763 |
Pd | 13.806 | 11.872 | 13.222 | 16.268 | 13.135 | 15.091 | 13.118 | 14.554 | 15.113 | 14.092 | 12.032 |
Rh | 40.931 | 34.133 | 37.080 | 54.136 | 36.365 | 41.810 | 33.376 | 39.850 | 51.084 | 45.576 | 38.837 |
Cd | 27.483 | 19.529 | 23.694 | 28.078 | 19.209 | 23.890 | 21.477 | 25.906 | 32.407 | 31.182 | 22.683 |
Zn | 4.224 | 6.651 | 2.321 | 4.996 | 7.171 | 4.072 | 7.667 | 6.513 | 3.128 | 5.532 | 1.971 |
In | 23.380 | 18.550 | 21.254 | 29.581 | 24.070 | 25.284 | 17.710 | 27.051 | 33.129 | 30.214 | 24.920 |
Sn | 25.223 | 17.107 | 22.236 | 24.218 | 18.836 | 22.741 | 15.781 | 24.830 | 29.497 | 21.245 | 6.368 |
Cu | 4.292 | — | — | — | — | — | — | 8.456 | — | 6.115 | — |
Mn | — | — | — | 6.111 | — | — | 4.692 | — | — | 4.591 | — |
Ti | 59.967 | 39.830 | 77.145 | 61.716 | 57.692 | 66.638 | 61.716 | 56.232 | 81.337 | 68.712 | 30.264 |
Ru | 7.618 | 5.887 | 6.287 | 9.127 | 6.617 | 7.552 | 5.705 | 7.911 | 8.987 | 11.168 | 6.728 |
Elements | μg m−3 (103) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SS 1 | SS 2 | SS 3 | SS 4 | SS 5 | SS 6 | SS 7 | SS 8 | SS 9 | SS 10 | Control | |
a SS: sampling spot. | |||||||||||
Fe | 65.216 | 117.369 | 64.907 | 58.841 | 75.845 | 66.117 | 74.814 | 78.882 | 71.591 | 64.873 | 40.775 |
Ag | 14.816 | 14.256 | 14.600 | 13.793 | 10.712 | 13.141 | 15.124 | 17.355 | 20.912 | 16.879 | 5.779 |
Pd | 10.055 | 10.950 | 10.548 | 10.336 | 13.027 | 12.984 | 13.966 | 16.090 | 12.858 | 13.546 | 4.257 |
Rh | 39.296 | 40.073 | 49.705 | 50.420 | 43.516 | 43.390 | 42.053 | 40.784 | 41.675 | 47.632 | 23.215 |
Cd | 30.775 | 36.293 | 31.515 | 38.002 | 34.670 | 35.813 | 33.801 | 29.326 | 34.528 | 40.658 | 16.512 |
Zn | 7.383 | 7.062 | 7.972 | 7.569 | 8.256 | 7.113 | 7.147 | 8.439 | 9.575 | 9.060 | 4.076 |
In | 30.951 | 31.533 | 32.937 | 33.979 | 39.602 | 35.213 | 39.011 | 39.964 | 37.513 | 36.509 | 14.767 |
Sn | 30.449 | 28.356 | 28.885 | 32.747 | 33.616 | 34.408 | 35.851 | 33.131 | 38.872 | 36.832 | 23.892 |
W | — | 39.939 | — | — | — | — | — | 45.297 | — | — | — |
Cu | 4.799 | — | — | 7.552 | — | 4.987 | — | 8.456 | 7.351 | — | — |
Ti | 66.240 | 59.111 | 85.865 | 79.968 | 74.118 | 50.451 | 44.101 | 82.033 | 66.369 | 59.150 | 38.833 |
Ru | 10.644 | 8.711 | 7.989 | 10.640 | 7.425 | 9.737 | 11.510 | 8.323 | 10.376 | 10.764 | 3.780 |
S | 9.903 | 8.922 | — | — | 9.555 | — | 7.871 | — | 8.141 | 7.539 | — |
Gold (Au) was detected at two sampling spots only in the wet season, SS 6 (4.849 × 103 ± 2.396 × 103 μg m−3) and SS 9 (4.615 × 103 ± 2.2843 × 103 μg m−3). The concentration values of Au were higher than the stipulated values by USEPA and WHO. Au was not detected in the dry season.
Silver (Ag) was characterized in the wet samples with the highest concentration (23.200 × 103 ± 3.112 × 103 μg m−3) at SS 9, while the lowest concentration of (11.554 × 103 ± 2.204 × 103 μg m−3) was observed at SS 2. On the other hand, the concentration (20.912 × 103 ± 2.962 × 103 μg m−3) at SS 9 also gave the highest in the dry season, while the lowest (10.712 × 103 ± 2.689 × 103 μg m−3) was found at SS 5. The concentrations at all locations were higher than the USEPA and WHO set standard of 35 μg m−3 and 25 μg m−3 respectively.
The highest concentration of palladium (Pd) 16.268 × 103 ± 2.237 × 103 μg m−3 in the characterized samples, in the wet season, was observed at SS 4, while the lowest concentration (11.872 × 103 ± 1.692 × 103 μg m−3) was recorded at SS2. Similarly, the highest (16.090 × 103 ± 3.132 × 103 μg m−3) concentration of Pd was obtained at SS 8 in the dry season, while SS 1 has the lowest (10.055 × 103 ± 0.991 × 103 μg m−3). The values obtained in the two seasons were higher than the USEPA and WHO standards.
Rhodium (Rh) was characterized in the wet samples with the highest concentration (54.136 × 103 ± 2.712 × 103 μg m−3) at SS 4, while the lowest concentration of (33.376 × 103 ± 1.959 × 103 μg m−3) was observed at SS 7. On the other hand, the concentration (50.420 × 103 ± 1.303 × 103 μg m−3) at SS 4 also gave the highest in the dry season, while the lowest (39.296 × 103 ± 2.821 × 103 μg m−3) was found at SS 1. The concentrations at all locations were higher than the USEPA and WHO set standards of 35 μg m−3 and 25 μg m−3, respectively.
The highest concentration (32.407 × 103 ± 4.160 × 103 μg m−3) of cadmium (Cd) characterized in the wet samples was collected at SS 9, while the lowest (19.209 × 103 ± 3.419 × 103 μg m−3) was found in the samples collected at SS 5. Analysis of particulates deposited in the dry season indicated the highest concentration (40.658 × 103 ± 2.441 × 103 μg m−3) at SS 10, while the lowest (29.321 × 103 ± 2.770 × 103 μg m−3) was recorded at SS 8. These values were higher than the USEPA and WHO standards. They were all higher than (1 × 10−2 μg m−3) wet season and (3.9 × 10−2 μg m−3) dry season values reported by Kumar et al. (2018), as well as 0.5 × 10−2 μg m−3 (ref. 44) and 9.18 μg m−3.33
Zinc (Zn) recorded the highest concentration (7.667 × 103 ± 1.067 × 103 μg m−3) in the wet season at SS 7, while the lowest concentration (2.321 × 103 ± 0.849 × 103 μg m−3) was detected at SS 3. The highest concentration (9.575 × 103 ± 1.411 × 103 μg m−3) was found at SS 9 in the dry season, while the lowest (7.062 × 103 ± 1.624 × 103 μg m−3) was recorded at SS 2. The concentrations at all locations in the wet and dry seasons were higher than the USEPA and WHO standards. They were also higher than (0.941 μg m−3) wet season and (2.48 μg m−3) dry season values by Kumar et al.43 and 22.2 × 10−3 μg m−3 reported by Antisari et al.44
The highest concentration (33.129 × 103 ± 5.168 × 103 μg m−3) for indium (In) was observed in the wet samples at SS 9, while the lowest (17.710 × 103 ± 2.807 × 103 μg m−3) was recorded at SS 7. The highest concentration (39.964 × 103 ± 2.347 × 103 μg m−3) in the dry season was observed at SS 8, while the lowest (30.951 × 103 ± 3.511 × 103 μg m−3) was recorded at SS 1. All the characterized concentrations were higher than the recommended USEPA (35 μg m−3) and WHO (25 μg m−3) standards.
Tin (Sn) was detected in the characterized samples collected for both seasons. The highest concentration (29.497 × 103 ± 6.353 × 103 μg m−3) was recorded at SS 9, while the lowest concentration (15.781 × 103 ± 3.473 × 103 μg m−3) was recorded at SS 7 in the wet season. The highest concentration (38.872 × 103 ± 6.853 × 103 μg m−3) in the dry season was also recorded at SS 9, while the lowest concentration (28.356 × 103 ± 5.814 × 103 μg m−3) was found at SS 2 in the dry season. The concentrations at all SS in the wet and dry seasons were higher than USEPA and WHO standards. Their concentrations were equally higher than (4.1 × 10−2 μg m−3) wet season and (14.8 × 10−2 μg m−3) dry season values given by Kumar et al.43
In the dry season, tungsten (W) was detected at two sampling spots, SS 2 (39.939 × 103 ± 1.412 × 103 μg m−3) and SS 8 (45.297 × 103 ± 4.634 × 103 μg m−3). The concentration values of W were higher than the stipulated values by USEPA and WHO. Tungsten was not detected in the wet season.
The highest concentration (8.456 × 103 ± 1.763 × 103 μg m−3) of copper (Cu) was found at SS 8, while the lowest (4.292 × 103 ± 2.103 × 103 μg m−3) was recorded at SS 1 in the wet season. The highest of the dry season characterized concentration (7.552 × 103 ± 2.307 × 103 μg m−3) was found at SS 4, while the lowest concentration (4.799 × 103 ± 2.040 × 103 μg m−3) was also recorded at SS 1. The values were higher than the stipulated USEPA (35 μg m−3) and WHO (25 μg m−3) standards. The characterized concentrations of Cu were also higher than (16.9 × 10−2 μg m−3) wet season and (49.4 × 10−2 μg m−3) dry season values reported by Kumar et al.,43 as well as (21.3 × 10−3 μg m−3) by Antisari et al.44
The highest concentration of manganese (Mn) (6.111 × 103 ± 2.433 × 103 μg m−3) was detected at SS 4 in the wet season while the lowest concentration (4.591 × 103 ± 1.776 × 103 μg m−3) was found at SS 10. The concentration values were higher than the recommended standards by USEPA and WHO, and they are also much higher than (28.6 × 10−3 μg m−3) that reported by Antisari et al.44 Manganese was not detected in the dry season.
The highest concentration (81.337 × 103 ± 9.861 × 103 μg m−3) of titanium (Ti) was found at SS 9, while the lowest (39.830 × 103 ± 4.759 × 103 μg m−3) was recorded at SS 2 in the wet season. The highest of the dry season characterized concentration (85.865 × 103 ± 6.698 × 103 μg m−3) was found at SS 3, while the lowest concentration (44.101 × 103 ± 6.512 × 103 μg m−3) was also recorded at SS 7. The values were higher than the stipulated USEPA (35 μg m−3) and WHO (25 μg m−3) standards.
Ruthenium (Ru) was detected in the characterized samples. The concentration (11.168 × 103 ± 0.787 × 103 μg m−3) was highest at SS 10, while the lowest concentration (5.705 × 103 ± 0.577 × 103 μg m−3) was found at SS 7 in the wet season. The dry season analysis shows that the highest concentration (11.510 × 103 ± 1.278 × 103 μg m−3) was found at SS 7, while the lowest concentration (7.425 × 103 ± 1.690 × 103 μg m−3) was found at SS 5. The characterized results for ruthenium were higher in concentration when compared with the standard values by USEPA and WHO.
The concentration (9.903 × 103 ± 0.694 × 103 μg m−3) of sulphur (S) in the characterized dry samples was highest at SS 1, while the lowest concentration (7.539 × 103 ± 0.933 × 103 μg m−3) was found at SS 10. The concentration values were higher than the stipulated values by USEPA and WHO. Sulphur was not detected in the wet season. In the wet season, Fe had the highest concentration of 72.569 × 103 μg m−3 in SS 1, while Zn had the lowest concentration of 4.224 × 103 μg m−3; the metal concentrations were in the following order Fe > Ti > Rh > Cd > Sn > In > Ag > Pd > Ru > Cu > Zn. In the dry season, Ti had the highest concentration of 66.24 × 103 μg m−3 in SS 1, while Cu had the lowest concentration of 4.799 × 103 μg m−3; the metal concentrations followed the order as Ti > Fe > Rh > In > Cd > Sn > Ag > Ru > Pd > S > Zn > Cu. Fe also had the highest concentration of 111.65 × 103 μg m−3 and 117.369 × 103 μg m−3 in the wet and dry seasons respectively at SS 2, while Ru had the lowest concentration of 5.887 × 103 μg m−3 in the wet season, also Zn had the lowest concentration of 7.062 × 103 μg m−3 in the dry season.
The trend of the metal concentration Fe > Ti > Rh > Cd > In > Sn > Pd > Ag > Zn > Ru was observed in the wet season, while the concentration of metals was in the order Fe > Ti > Rh > W > Cd > In > Sn > Ag > Pd > S > Ru > Zn.
In the wet season, from SS 3 and SS 4 respectively, Ti had the highest concentration of 77.145 × 103 μg m−3 and 61.716 × 103 μg m−3 while Zn had the lowest concentration of 2.321 × 103 μg m−3 and 4.996 × 103 μg m−3 with the following order Ti > Fe > Rh > Cd > Sn > In > Ag > Pd > Ru > Zn and Ti > Fe > Rh > In > Cd > Sn > Ag > Pd > Ru > Mn > Zn respectively from SS 3 and SS 4. In the dry season, from SS 3 and SS 4 respectively, Ti also had the highest concentration of 85.865 × 103 μg m−3 and 79.968 × 103 μg m−3 while Zn and Cu had the lowest concentration of 7.972 × 103 μg m−3 and 7.552 × 103 μg m−3; the metal concentration followed the order as Ti > Fe > Rh > In > Cd > Sn > Ag > Pd > Ru > Zn and Ti > Fe > Rh > Cd > In > Sn > Ag > Ru > Pd > Zn > Cu at SS 3 and SS 4 respectively.
Fe had the highest concentration of 81.104 × 103 μg m−3 in the wet season at SS 5, while Ru had the lowest concentration of 6.617 × 103 μg m−3 in the following order Fe > Ti > Rh > In > Cd > Sn > Ag > Pd > Zn > Ru. Similarly in the dry season, Fe had the highest concentration of 75.845 × 103 μg m−3 at SS 5, while Ru also had the lowest concentration of 7.425 × 103 μg m−3; the concentration of metals was in the order Fe > Ti > Rh > In > Cd > Sn > Pd > Ag > S > Zn > Ru. In SS 6, Ti had the highest concentration of 66.638 × 103 μg m−3 in the wet season, with Zn having the lowest concentration of 4.072 × 103 μg m−3 in the following order Ti > Fe > Rh > In > Cd > Sn > Ag > Pd > Ru > Au > Zn. In the dry season, the concentration of Fe was the highest with 66.117 × 103 μg m−3 with Cu having the lowest concentration of 4.799 × 103 μg m−3 in the following order Fe > Ti > Rh > Cd > In > Sn > Ag > Pd > Ru > Zn > Cu. In the wet season, Fe had the highest concentration at both SS 7 and SS 8 with 77.941 × 103 μg m−3 and 69.061 × 103 μg m−3; the metal concentration followed the order as Fe > Ti > Rh > Cd > In > Sn > Ag > Pd > Zn > Ru > Mn and Fe > Ti > Rh > In > Cd > Sn > Ag > Pd > Cu > Ru > Zn respectively.
Meanwhile in the dry season, Fe also had the highest concentration of 74.814 × 103 μg m−3 at SS 7 while the concentration of Zn was the lowest with 7.147 × 103 μg m−3 in the following order Fe > Ti > Rh > In > Sn > Cd > Ag > Pd > Ru > S > Zn. At SS 8, Ti had the highest concentration of 78.882 × 103 μg m−3 while Ru had the lowest concentration of 8.323 × 103 μg m−3; the metal concentration followed the order Ti > Fe > W > Rh > In > Sn > Cd > Ag > Pd > Zn > Ru.
At SS 9 and SS 10, in the wet season, Ti had the highest concentration of 81.337 × 103 μg m−3 and 68.712 × 103 μg m−3 respectively. The concentration of Zn was the lowest 3.128 × 103 μg m−3 at SS 9, and Mn also had the lowest concentration of 4.591 × 103 μg m−3 at SS 10. The metal concentration followed the order as Ti > Rh > In > Cd > Fe > Sn > Ag > Pd > Ru > Au > Zn and Ti > Fe > Rh > Cd > In > Sn > Ag > Pd > Ru > Cu > Zn > Mn at SS 9 and SS 10, respectively. In the dry season at SS 9 and SS 10, Fe had the highest concentration of 71.591 × 103 μg m−3 and 64.873 × 103 μg m−3. The metal concentration followed the order Fe > Ti > Rh > Sn > In > Cd > Ag > Pd > Ru > Zn > S > Cu and Fe > Ti > Rh > Cd > Sn > In > Ag > Pd > Ru > Zn > S, respectively. The concentration of Cu was the lowest (7.351 × 103 μg m−3) at SS 9, while S had the lowest concentration of 7.539 × 103 μg m−3 at SS 10.
As discussed in this section, all the heavy metals characterized are exponentially higher than the stipulated standard. The result obtained showed that heavy metals are being released through the open burning of solid wastes, and the emission has a significant influence on the concentration of the heavy metals in the particulate samples collected, which is in accordance with Kumar et al.,43 and combustion of solid waste releases high number of particulates and metals into the environment. Some of these heavy metals trigger human poisoning (acute/chronic) after being exposed through food or air. Their accumulation in the human body causes harmful effects on organs and tissues, such as deoxyribonucleic acid (DNA) and membrane damage, neurotoxicity, skin toxicity, cancer, cardio-vascular toxicity among others.45,46 Globally, heavy metal contamination is gradually turning into a critical issue of concern as a result of the release of air emissions from human activities such as open burning of solid waste.47,48
SS | Wet season | Dry season | ||
---|---|---|---|---|
(g per m2 per month) | (g m−2 s−1) 10−6 | (g per m2 per month) | (g m−2 s−1) 10−5 | |
a Average flux in the wet season = 3.57 × 10−6 (g m−2 s−1). Average flux in the dry season = 2.28 × 10−5 (g m−2 s−1). | ||||
1 | 9.55 | 3.68 | 41.37 | 1.60 |
2 | 10.82 | 4.17 | 48.7 | 1.88 |
3 | 8.59 | 3.31 | 38.83 | 1.50 |
4 | 11.46 | 4.42 | 64.61 | 2.50 |
5 | 7.32 | 2.82 | 60.47 | 2.33 |
6 | 10.18 | 3.93 | 71.93 | 2.78 |
7 | 7.96 | 3.07 | 52.51 | 2.03 |
8 | 9.87 | 3.81 | 42.97 | 1.66 |
9 | 9.23 | 3.56 | 88.80 | 3.43 |
10 | 7.64 | 2.95 | 79.89 | 3.08 |
Control | 0.95 | 0.37 | 33.74 | 1.30 |
Trace metals | Trace metal concentration in ppt (μg m−3) | Deposition velocity (m s−1) | |
---|---|---|---|
Wet season | Dry season | ||
Fe | 67512.8 | 0.00005288 | 0.0003377 |
Au | 4732 | 0.00075444 | 0.0048183 |
Ag | 16445.9 | 0.00021708 | 0.0013864 |
Pd | 14027.1 | 0.00025451 | 0.0016254 |
Rh | 41434.1 | 0.00008616 | 0.0005503 |
Cd | 25285.5 | 0.00014119 | 0.0009017 |
Zn | 5227.5 | 0.00068293 | 0.0043615 |
In | 25032.3 | 0.00014262 | 0.0009108 |
Sn | 22171.4 | 0.00016102 | 0.0010284 |
Cu | 6287.7 | 0.00056778 | 0.0036261 |
Mn | 5131.3 | 0.00069573 | 0.0044433 |
Ti | 63098.5 | 0.00005658 | 0.0003613 |
Ru | 7685.9 | 0.00046449 | 0.0029665 |
Authors | Year | Range |
---|---|---|
Mamun et al. | 2022 | 0.081–0.112 |
Yan et al. | 2014 | 0.0019–0.0817 |
Zhang et al. | 2012 | 0.0015–0.0331 |
Qi et al. | 2005 | 0.008–1 |
Lestari et al. | 2003 | 0.0021–0.893 |
Yun et al. | 2002 | 0.0011–0.004 |
The results of the scavenging ratio in the wet season (Table 9) revealed that Cu, Ti, Mn and Fe had the highest scavenging ratios, which were estimated to be 3.96, 3.39, 1.89 and 1.46 respectively. Meanwhile Zn, Ag, Sn and Cd were characterized with lower scavenging ratios of 0.66, 0.74, 0.77 and 0.95 respectively. Also, in the dry season, the scavenging ratio (Table 10) shows that Cu, Ti, Fe and In had the highest scavenging ratios, which were estimated to be 2.1, 1.57, 1.57 and 1.12 respectively. However, Ag, Pd, Zn and Ru were characterized with lower scavenging ratios of 0.61, 0.75, 0.82 and 0.89 respectively. As a result, Cu, Ti, Mn, and Fe may be better removed in the atmosphere near solid waste combustion sites via wet deposition. Wet deposition may influence the lifetime of Cu, Ti, Mn, and Fe in the environment, whereas dry deposition governs the lifetime of Zn, Ag, Sn, Au, and Cd. The contribution of scavenging particulate trace metals to the deposition flux was calculated using trace metal scavenging ratios, which are the concentrations of trace metals in precipitation divided by their concentrations in air.
Trace metals | Trace metal concentration in air (6 hours) (μg m−3) | Trace metal concentration in ppt (720 hours) (μg m−3) | Scavenging ratio |
---|---|---|---|
Fe | 46208 | 67512.8 | 1.46 |
Au | 5107 | 4732 | 0.93 |
Ag | 22228 | 16445.9 | 0.74 |
Pd | 14643 | 14027.1 | 0.96 |
Rh | 38794 | 41434.1 | 1.07 |
Cd | 26605 | 25285.5 | 0.95 |
Zn | 7980 | 5227.5 | 0.66 |
In | 26531 | 25032.3 | 0.94 |
Sn | 28790 | 22171.4 | 0.77 |
Cu | 1588 | 6287.7 | 3.96 |
Mn | 2746 | 5131.3 | 1.89 |
Ti | 18672 | 63098.5 | 3.39 |
Ru | 7190 | 7685.9 | 1.07 |
Trace metals | Trace metal concentration in air (6 hours) (μg m−3) | Trace metal concentration in ppt (720 hours) (μg m−3) | Scavenging ratio |
---|---|---|---|
Fe | 47097 | 73845.5 | 1.57 |
Au | 8440 | — | — |
Ag | 24793 | 15158.8 | 0.61 |
Pd | 16544 | 12436 | 0.75 |
Rh | 44620 | 43854.4 | 0.98 |
Cd | 32443 | 34538.1 | 1.06 |
Zn | 9648 | 7957.6 | 0.82 |
In | 31955 | 35721.2 | 1.12 |
Sn | 35998 | 33314.7 | 0.93 |
W | — | 42618 | — |
Cu | 2946 | 6172.3 | 2.10 |
Mn | 3932 | — | — |
Ti | 42641 | 66740.6 | 1.57 |
In this study, the estimated value of the highest deposition velocity was found to be that of Au (0.0048183 m s−1) which is lower than the values reported by Yan et al.,49 Zhang et al.50 and Qi et al.51 but higher than the result of Jimoda et al.33 The lowest value corresponds to that of Fe (0.0003377 m s−1) which is lower to those reported by previous studies.49,51,52 The highest deposition velocity from trace metals in the Sokoto Aiyekale dump site, Ilorin was found to be almost the same when compared with the work of Yun et al.,53 which obtained a deposition velocity of 0.004 m s−1. The estimated scavenging ratio for the trace metals in the government approved dump site, Ilorin was in the range 0.61–3.96, which is comparable to the one estimated by Alamu et al.54 A series of reviewed literature studies showed that there is paucity of information on dispersion modelling of pollutants from open burning of municipal solid waste. Researchers like Adeniran et al.,55 Ipeaiyeda and Falusi,56 Fakinle et al.,57 Daffi et al.58 and Pansuk et al.59 assessed the air pollution from household and local open burning of solid wastes in dump sites along the road/across the streets using handheld gas analyzers without modelling the gases to evaluate the dynamics of the pollutants as they travel to receptor communities. Meanwhile, this study considered Ilorin as a state capital (with over 1 million population), which is the only state capital in Nigeria with one government approved dumpsite in the city. Thus, with the magnitude of waste being burned daily on a 600 plot (390000 sqm) Sokoto-Aiyekale dump site in Ilorin metropolis with 130 burning points, the receptor communities, workers and the environment could be at risk of release of hazardous cocktail of emissions. There is hence the need for forward trajectory modelling with an American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) dispersion model to assess and evaluate the impact on air quality in the receptor communities surrounding the Sokoto-Aiyekale dump site.
Year | PM | VOCs |
---|---|---|
2016 | 69.8 | 187.5 |
2017 | 72.0 | 193.3 |
2018 | 74.1 | 199.1 |
2019 | 76.4 | 205.2 |
2020 | 78.7 | 211.4 |
Average | 74.2 | 199.3 |
VOCs affect the air quality more, due to their higher predicted concentrations as contained in Tables 12 and 13.
Receptor | Predicted concentration (μg m−3) | Annual | % Recommended in FMEnV | % Recommended limit in WHO | |||
---|---|---|---|---|---|---|---|
1 h | 8 h | 24 h | 1 h (600 μg m−3) | 24 h (150 μg m−3) | Annual (40–60 μg m−3) | ||
Sokoto | 15300 | 5229 | 2537 | 359 | 25.50 | 16.91 | 8.98 |
Aiyekale | 15300 | 4257 | — | — | 25.50 | — | — |
Abe-Emi | 50800 | 14200 | 4500 | 650 | 84.67 | 30 | 16.25 |
Wara | 20800 | 5229 | 2537 | 217 | 34.67 | 16.91 | 5.43 |
Airport | 15300 | — | — | 25.50 | — | — | |
Olorunsogo | 15300 | 4257 | — | — | 25.50 | — | — |
Osere | 9800 | — | — | — | 16.33 | — | — |
Oko Erin | 8841 | — | — | — | 14.74 | — | — |
Asa-Dam | 8841 | — | — | — | 14.74 | — | — |
Egbejila | 8841 | — | — | — | 14.74 | — | — |
Orisumibare | 9800 | — | — | — | 16.33 | — | — |
Receptor | Predicted concentration (μg m−3) | Annual | % Recommended in FMEnV | ||
---|---|---|---|---|---|
1 h | 8 h | 24 h | 24 h (160 μg m−3) | ||
Sokoto | 20500 | 5600 | 2700 | 368 | 16.88 |
Aiyekale | 20500 | 4602 | — | — | — |
Abe-Emi | 80500 | 14600 | 5700 | 650 | 35.63 |
Wara | 20500 | 5600 | 2700 | 235 | 16.88 |
Airport | 20500 | — | — | — | — |
Olorunsogo | 20500 | 4602 | — | — | — |
Osere | 9511 | — | — | — | — |
Oko Erin | 9511 | — | — | — | — |
Asa-Dam | 9511 | — | — | — | — |
Egbejila | 8521 | — | — | — | — |
Orisumibare | 10500 | — | — | — | — |
From the results obtained, the following were the conclusion of the study.
(i) The emission inventory for PM and VOCs was in the range 2200.5–2481.1 and 5913.9–6668.0 tons per annum between 2016 and 2020, respectively.
(ii) Particulate characterization shows that Fe had the highest concentration of 67512.8 and 73845.5 μg m−3 in the wet and dry seasons respectively. The wet and dry deposition fluxes ranged from 7.32 to 11.46 and 38.83 to 88.8 g per m2 per month, respectively. Deposition velocities of the trace metals were in the range 0.0000528–0.00075444 m s−1 and 0.0003377–0.0048183 m s−1 in the wet and dry seasons respectively. The scavenging ratio ranged from 0.66 to 3.96 and 0.54 to 2.13 in the wet and dry seasons respectively.
(iii) The daily quality of air was within the Federal Ministry of Environment's (FMEnV) guidelines. Nevertheless, the 1 hour, 24 hour, and annual PM air quality for all receptor communities exceeded the FMEnV and World Bank standards.
(iv) Abe-Emi, Sokoto and Wara communities are at risk of VOC emissions. Also, all the receptor communities are negatively affected by PM emissions.
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