1,2,3Department of Science Laboratory Technology, LAUTECH Ogbomoso
4Department of Pure and Applied Chemistry, LAUTECH Ogbomoso
Water pollution remains a significant global challenge, worsened by the discharge of untreated wastewater from domestic, industrial, and agricultural sources. Abattoirs, integral to meat production, are major contributors to environmental degradation due to improper wastewater disposal. This study examines various physicochemical parameters and the concentration of polycyclic aromatic hydrocarbons (PAHs) in wastewater from the New Atenda Abattoir in Ogbomoso, Southwestern Nigeria, focusing on its environmental impact. Wastewater samples were collected from three distinct locations within the facility, and physicochemical parameters were analyzed using standard methods. The concentrations of 15 USEPA priority PAHs were quantified via Gas Chromatography-Mass Spectrometry (GC-MS). The physicochemical parameters, including pH (6.3–7.2), electrical conductivity (EC, 230–580 µS/cm), biochemical oxygen demand (BOD, 92–156 mg/L), and turbidity (68–126 NTU), indicated high levels of both organic and inorganic contamination. PAH concentrations ranged from 0.28- 8485 µg/L with naphthalene being the most abundant compound. Diagnostic ratios, such as Fluorene/Pyrene (Fl/Pyr = 1.51) and Chrysene/Benzo(a)anthracene (Chr/Baa = 0.83) LMW/HMW (683.8) revealed a mix of pyrogenic and petrogenic contamination sources with major contribution from petrogenic sources (petroleum products). Comparison with regulatory limits showed that PAH levels exceeded permissible thresholds, indicating significant environmental and public health risks. This study underscores the urgent need for improved wastewater treatment and management practices to mitigate the detrimental effects of abattoir effluents on local ecosystems and public health.
Water pollution, exacerbated by untreated wastewater from domestic, industrial, and agricultural activities, poses a significant global challenge [1]. Abattoirs, essential for meat production, are key contributors to environmental degradation, particularly through the improper discharge of wastewater. These industrial facilities generate large volumes of waste from processes such as animal slaughter and meat processing, and when untreated, this wastewater contaminates surrounding ecosystems, impacting both surface water quality and public health [2]. In Nigeria, both urban and rural abattoirs discharge wastewater without adequate treatment, leading to severe environmental and health risks [3]. The abattoir sector plays a critical role in Nigeria’s livestock industry, supplying meat to over 150 million people and providing employment opportunities [4]. However, most facilities in developing nations, such as Nigeria, lack the infrastructure for proper wastewater management [4]. The effluent from abattoirs contains various contaminants, including suspended particles, inorganic substances, and organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), which are primarily produced during meat processing and other operations [5]. PAHs are persistent organic pollutants composed of fused benzene rings, and they are notorious for their toxicity and environmental persistence [6,7]. These contaminants, primarily originating from incomplete combustion of organic materials, pose serious risks to human health and the environment, particularly due to their mutagenic, carcinogenic, and toxic properties [8,9].. This study aims to investigate the physicochemical parameters and concentrations of PAHs in wastewater from the New Atenda Abattoir in Ogbomoso, Nigeria. Additionally, the study will examine the sources of these pollutants and their impact on the receiving water bodies.
Experimental Methods
Sampling was carried out at the New Ogbomoso Central Abattoir, located along the Ilorin/Ogbomoso Expressway, Ogbomoso, Oyo State, Nigeria. The abattoir is situated in the Ogbomoso North Local Government Area, with geographical coordinates of 8.1655828° N and 4.259556° E. This facility processes approximately 100 cows daily, making it a significant source of wastewater. Wastewater samples were collected from three distinct locations within the abattoir and mixed together to form one composite sample : wastewater . Wastewater samples were collected in previously washed and dried amber glass bottles to minimize contamination. Immediately after collection, the samples were placed in ice packs and transported to the laboratory for analysis.
The physicochemical parameters of the wastewater samples were analyzed using standard methods as outlined by the American Public Health Association [10].
Biochemical Oxygen Demand (BOD5) was determined following the Azide Modification method (APHA, 1995). The procedure involved the incubation of wastewater samples in the dark at 20°C for five days. The DO (dissolved oxygen) was measured at the start (DO?) and after five days (DOf). The BOD was calculated using the formula:
???????????? (????????/????) =????????0 – ????????f %????????????????????????????????
Where;
D0 = DO of the sample immediately after saturation with air (initial DO)
Df = DO of the sample after 5 days’ incubation (final DO)
Sample Extraction and Analysis for PAHs
The extraction of polycyclic aromatic hydrocarbons (PAHs) was performed using the liquid-liquid extraction method. A 500 mL sample was measured into a separatory funnel, and 10 g of NaCl was added to saturate the sample, preventing emulsion formation during extraction. To extract the organic pollutants, 25 mL of dichloromethane (DCM) was added. The mixture was agitated for two minutes while periodically venting to release pressure and facilitate the transfer of organic contaminants into the DCM phase. After agitation, the sample was allowed to settle, and the water and DCM phases separated based on their differing densities. The DCM phase, which formed the bottom layer, was collected in a clean, dry conical flask. The extraction process was repeated twice, each time with 25 mL of DCM, to improve extraction efficiency. After extraction, 10 mL of 0.1M sodium carbonate solution was added to the DCM eluate to neutralize any dissolved fats. The extract was then dried with anhydrous sodium sulfate to remove any residual water. To further purify the extract, the sample was fractionated using a silica gel column. The saturate and aromatic fractions were eluted using 25 mL of n-hexane and a mixture of 25 mL of n-hexane and DCM (1:9), respectively. These fractions were collected separately and analyzed for PAH concentrations.
Analysis of PAHs by Gas Chromatography-Mass Spectrometry (GC-MS)
The aromatic fractions were analyzed for PAH concentrations using a Gas Chromatograph-Mass Spectrometer (GC-MS). The GC conditions, including temperature programming, column type, and carrier gas flow rate, were optimized for PAH analysis. The instrument was calibrated using a standard PAH mixture, and the concentration of each PAH compound was determined based on the peak areas, with appropriate corrections for dilution factors.
Quality Control and Assurance
To ensure the reliability of the analytical results, duplicate samples were collected from each sampling point, and all analyses were carried out in triplicate. Procedural blanks and spiked samples were also included to check for contamination and extraction efficiency. Calibration standards were used to ensure the accuracy of the GC-MS analysis, and recovery rates for PAHs were determined to validate the extraction process. All chemicals used in the study, including NaCl, DCM, sodium carbonate, and anhydrous sodium sulfate, were of analytical grade, and their handling followed standard laboratory safety protocols.
RESULTS AND DISCUSSION:
Physicochemical Characteristics of Atenda Abattoir Wastewater
The physicochemical characteristics (Table 1) of the Atenda Abattoir wastewater were assessed to evaluate its potential environmental impact. The findings revealed several parameters that significantly deviate from the permissible limits, suggesting a poor quality of effluent. The average pH of the wastewater was 8.5, which falls within the USEPA permissible range of 7.5–9.0, indicating that the effluent is slightly alkaline. This elevated pH could be attributed to the extensive use of soaps and detergents in the abattoir for cleaning purposes, such as washing slaughtered cattle. The pH level of water plays a critical role in the availability of heavy metals and nutrients, as it affects the solubility and bioavailability of these substances. A pH outside the optimal range can disrupt the acid-base balance of the water, negatively impacting aquatic life and altering the solubility of chemical contaminants [12, 13]. The temperature of the wastewater was measured at 32°C, which is within the World Health Organization (WHO) and Federal Ministry of Environment (FMEnv) permissible limit of <40>
The dissolved oxygen (DO) concentration was notably low at 1.42 mg/L, significantly below the National Environmental Standards and Regulations Enforcement Agency (NESREA) standard of 4.0 mg/L and well below the 5.0 mg/L threshold required to sustain most aquatic organisms [14]. This low DO value is indicative of severe oxygen depletion in the receiving water body, likely resulting in stress or even death of aquatic organisms. The low DO concentration also suggests that the wastewater has a high organic load, which depletes oxygen through microbial activity. In comparison, studies by Ayodele et al. (2024) and Adeyemi-Ale (2014) found similar poor DO values in abattoir wastewater, reinforcing the poor quality of this effluent.
Table 1: Physicochemical parameters of abattoir wastewater
|
Parameter |
Value |
Maximum permissible limit (WHO 2016) |
|
Temperature ºC |
32 |
20-33 |
|
pH |
8.52 |
6-8 |
|
DO mg/L |
1.42 |
Greater than 5 |
|
BOD mg/L |
129 |
100 |
|
Turbidity NTU |
640 |
500 |
|
Conductivity µS/cm |
3721 |
1000 |
|
TDS mg/L |
1843 |
500 |
The biochemical oxygen demand (BOD) of the wastewater was 129 mg/L, which far exceeds the 100 mg/L limit for direct discharge. High BOD values indicate the presence of significant amounts of biodegradable organic matter, which consumes large amounts of oxygen during decomposition. This not only depletes oxygen in the water but also leads to eutrophication, a condition that can cause the death of aquatic organisms and degrade water quality over time [17, 18]. The BOD values in this study are higher than those reported by Adeyemi-Ale (2014) and Ijah et al. (2022), underscoring the necessity of effective wastewater treatment. The turbidity of the wastewater was recorded at 348 NTU, which is above the WHO limit of 500 NTU. High turbidity in water is often caused by suspended particles, which can indicate contamination. Elevated turbidity not only reduces water quality but also poses a risk to public health, as it provides a medium for pathogens, which could lead to waterborne diseases. This finding aligns with the results of Ayodele et al. (2024), who also reported high turbidity values in industrial wastewater. Conductivity, which measures the water's ability to conduct electricity due to dissolved ions, was found to be 3721 µS/cm, significantly higher than the permissible limit of 1000 µS/cm. The high conductivity value suggests that the wastewater contains elevated levels of dissolved salts and other ionic substances, likely from detergents, waste products, and other contaminants. High conductivity levels can affect the water's mineralization and salinity, which may have harmful effects on aquatic ecosystems [15]. The total dissolved solids (TDS) in the wastewater were 1843 mg/L, surpassing the threshold of 500 mg/L, above which water is generally considered polluted. TDS levels higher than 1000 mg/L are considered unacceptable for discharge. This high TDS concentration indicates that the wastewater contains a mixture of dissolved organic and inorganic substances, such as salts, detergents, and waste residues, which can degrade water quality and harm aquatic organisms [15]. When compared to other studies, the Atenda Abattoir wastewater consistently demonstrates poor quality. For instance, a DO concentration of 3.85 mg/L in industrial wastewater [15], and a DO of 1.89 mg/L from another abattoir [16]. The 1.42 mg/L DO value in this study is comparable, further emphasizing the wastewater’s detrimental effect on water quality. Additionally, the high BOD (129 mg/L) in this study surpasses those found by Adeyemi-Ale (2014) and Ijah et al. (2022), reinforcing the need for stringent wastewater management practices. The environmental and public health implications of these findings are far-reaching. The high turbidity, BOD, and TDS levels, combined with the low DO concentration, suggest that the Atenda Abattoir wastewater poses significant risks to aquatic life and human health. The elevated turbidity may increase the potential for waterborne diseases, while the high BOD and low DO levels indicate severe oxygen depletion, threatening aquatic ecosystems. The high conductivity and TDS levels further suggest the presence of harmful pollutants, such as salts and heavy metals, which could contaminate both surface water and groundwater resources if not treated.
Polycyclic Aromatic Hydrocarbons (PAHs) in Atenda Abattoir Wastewater
The raw wastewater from Atenda Abattoir was analyzed for a total of fifteen PAHs (Table 2; Figure 1), including Naphthalene, Acenaphthylene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benz(a)anthracene, Chrysene, Benzo(j)fluoranthene, Benzo(k)fluoranthene, Benz(a)pyrene, Indeno(1,2,3-cd)pyrene, and Benzo(g,h,i)perylene (Figure 1). The PAH composition in the Atenda Abattoir wastewater was categorized based on the number of rings (2-3 rings, 4 rings, and 5-6 rings), or molecular weight, distinguishing between Low Molecular Weight (LMW) PAHs (2-3 ring PAHs) and High Molecular Weight (HMW) PAHs (4-6 ring PAHs). The distribution of these PAHs is summarized in Table 1. LMW PAHs were found to be more abundant than HMW PAHs in the wastewater.
Figure 1: PAH Chromarogram of Atenda Abattoir wastewater
Table 2: Concentration of PAHs in raw abattoir wastewater
|
PAH |
Concentration (µg/L) |
limit for individual PAH (USEPA 2015) |
|
Naphthalene* |
8485 |
20 |
|
Acenaphthylene* |
5.7 |
20 |
|
Fluorene* |
288.55 |
50 |
|
Phenanthrene* |
20.85 |
28 |
|
Fluoranthene* |
4.61 |
20 |
|
Pyrene* |
3.05 |
20 |
|
Benz(a)anthracene# |
1.48 |
0.038 |
|
Chrysene# |
1.24 |
0.0038 |
|
Benzo(j)fluoranthene# |
0.60 |
0.0038 |
|
Benzo(k)fluoranthene# |
0.60 |
0.038 |
|
Benz(a)pyrene# |
0.67 |
0.038 |
|
Indeno(1,2,3-cd)pyrene# |
0.28 |
0.0038 |
|
Benzo(g,h,i)perylene |
0.34 |
0.038 |
|
? LMW PAH |
8800 |
? Recommended GRP I PAH 10 |
|
? HMW PAH |
12.87 |
? Recommended GRP II PAH 100 |
|
? Total PAH |
8812 |
|
#Group I PAH (Carcinogenic) *Group II PAHs (Non-Carcinogenic)
Naphthalene and Fluorene exhibited the highest concentrations, with 8485 µg/L and 288 µg/L, respectively, in the raw wastewater. Other LMW PAHs, such as Acenaphthylene and Phenanthrene, were found at concentrations of 5.7 and 20.85 µg/L. In terms of HMW PAHs, Fluoranthene, Pyrene, Benz(a)anthracene, and Chrysene were detected at concentrations of 4.61, 3.05, 1.48, and 1.24 µg/L, respectively. The remaining HMW PAHs, including Benzo(j)fluoranthene, Benzo(k)fluoranthene, Benz(a)pyrene, Indeno(1,2,3-cd)pyrene, and Benzo(g,h,i)perylene, were detected at relatively lower concentrations (0.60, 0.60, 0.67, 0.28, and 0.34 µg/L, respectively). The total concentration of PAHs with 2 rings was 8485 µg/L, while the 3-4 ring PAHs and 5-6 ring PAHs had concentrations of 316.81 µg/L and 6.21 µg/L, respectively. The LMW PAHs (2-3 rings) accounted for 99.8% of the total PAHs, amounting to 8800 µg/L, while HMW PAHs (4-6 rings) represented only 12.87 µg/L. The total PAH concentration in the raw wastewater was 8812 µg/L, which exceeds the permissible discharge limit of 550 µg/L set by the National Standards for Water Quality (NSDWQ, 2008). The PAH concentrations in this study are higher than those reported by Amaechi-Onyerimma and Onugha (2016), who recorded a maximum total PAH value of 1160 µg/L in selected abattoir effluents in Rivers State, Nigeria. The elevated concentrations of PAHs in Atenda Abattoir wastewater are primarily attributed to a mix of petrogenic and pyrogenic sources, such as the use of petroleum products for burning cattle and other waste materials. This study corroborates previous findings by Ihunwo et al. (2019) and Ganiyu et al. (2024), which identified similar sources of PAH contamination in effluents from industrial activities. The discharge of wastewater containing high levels of PAHs, particularly carcinogenic Group I PAHs, poses a serious environmental and public health risk. The presence of these toxic compounds can lead to long-term detrimental effects on aquatic ecosystems and human health, particularly in vulnerable populations such as pregnant women and children.
Pollution Indices of PAHs in Atenda Abattoir Wastewater
Pollution indices provide a measure of the severity of pollutant contamination. The pollution index (PI) for each PAH was calculated using the following formula:
PI =Measured concentrationPermissible concentration
Naphthalene exhibited the highest pollution index of 424, indicating it was the most polluting PAH. Other PAHs with high pollution indices included Chrysene, Benzo(j)fluoranthene, Indeno(1,2,3-cd)pyrene, Benz(a)anthracene, and Benz(a)pyrene, with pollution indices of 326, 157, 73, 38, and 17.63, respectively. Benzo(k)fluoranthene, Dibenz(a,h)anthracene, Benzo(g,h,i)perylene, and Fluorene also showed significant pollution indices of 15.78, 12.10, 8.94, and 2.88, respectively, while others had low pollution indices, indicating they were less polluting. The high pollution indices observed suggest that the receiving water body is at significant risk of contamination, rendering it unsuitable for domestic and agricultural activities.
The presence of Group I PAHs, which are classified as carcinogenic by USEPA, further underscores the potential health risks posed by exposure to the wastewater. The exposure to PAHs can disrupt reproductive mechanisms, affecting enzyme activities in males and inducing oxidative stress and mitochondrial dysfunction in females, leading to testicular apoptosis [21].
Source Diagnosis of PAHs in Atenda Abattoir
The presence of both LMW and HMW PAHs in wastewater shows the influence of both petroleum and the presence of combustion products from low-temperature pyrolytic processes and/or petrogenic sources [20]. This results followed a similar trend with study by Ganiyu et al. (2024) which assessed the influence of the oil storage depot discharges on proximate water sources in Ibadan, Southwest Nigeria, they observed ring wise distribution pattern of the PAHs in collected water samples follows the order: 2–3 rings >5–6 rings >4 – ring PAHs and low molecular weight (LMW) PAHs accounted for 90.73% relative to HMW (9.27%). The predominance of two and three rings PAHs (>40%) in water indicates that the major source of pollution in the water comes from petroleum [22]. Other sources may come from the burning in the abattoir which releases sooth into the atmosphere and leads to direct air-water exchange. LMWs/HMWs > 1.0 proposes petrogenic sources of PAHs, and LMWs/HMWs <1> 0.5 is pyrolytic, and the ratios of Fla./(Fla + Pyr) > 0.5 suggests wood, grass and/or coal combustion [7]. In this study, sources indicated both pyrolytic and petrogenic, (Table 2). LMW/HMW gave value of 683 which indicate that the source is highly petrogenic, Flu / Pyr gave value of 1.51 which established that petrogenic sources, burnings as well contributed to the PAH present in the wastewater. Chr/BaA gave value of 0.83 which is as well an indication of pyrolytic sources. Flu/ Flu + pyr as well gave 0.6, a value indicating pyrolytic sources. For diagnosis using Ant/Ant +Phe, values less than 0.1 indicated petrogenic or natural sources while values greater than 0.1 showed pyrogenic or anthropogenic sources [23]. From the values obtained in this research, it is evident that pyrogenic sources are major contributors to the PAH in atenda abattoir waste water. For the 5-6 member rings, the ratio between BaA/ (BaA + Chr) gave values of 0.54, when the values from this ratio is about 0.2, the origin of the PAHs are from petrogenic sources, while values navigating above 0.35 shows pyrogenic sources of PAHs [24]. The implication of the observation made with respect to BaA/ (BaA + Chr) ratio implies that PAHs of the wastewater had pyrogenic sources.
Table 3: Source Diagnosis of PAHs in New Atenda Abattoir, Ogbomoso
|
Indices |
Value |
Source [6) |
|
LMWHMW
|
683 |
Petrogenic
|
|
ChrBaA
|
0.83 |
Pyrolytic
|
|
FluPyr
|
1.51 |
Petrogenic
|
|
FluFlu+Pyr
|
0.60 |
Pyrolytic |
The elevated concentrations of PAHs in the present work possibly originated from burning of cattles and usage of other products such as woods and polythene to enhance burning and use of petroleum products such as kerosene and petrol for burning. This observation corroborates the findings of Ihunwo et al., (2019) and that of Ganiyu et al. (2024), that established that petrogenic and pyrolytic sources are major route of PAH sources in effluents which however depends on respective industrial activities and PAH concentrations. Discharge of this water which contains all the categories of PAHs at appreciable level directly into the environment poses threat to receiving water body, surrounding underground water and surrounding soil. Intake of such receiving water or underground water can be injurious to pregnant women and infants. It can inflict behavioural disorder, impair intelligent quotient, cause asthmatic breathing, and other health abnormalities in both adults and children [24].
CONCLUSION
The physicochemical characteristics and polycyclic aromatic hydrocarbon (PAH) concentrations in the Atenda Abattoir wastewater indicate significant environmental and public health concerns. The wastewater exhibited high turbidity, biochemical oxygen demand (BOD), and total dissolved solids (TDS), coupled with low dissolved oxygen (DO) levels, all of which suggest severe pollution. These characteristics imply that the effluent may cause oxygen depletion, eutrophication, and contamination of aquatic life, posing risks to both environmental ecosystems and human health. Furthermore, the analysis of PAHs revealed elevated concentrations of both low molecular weight (LMW) and high molecular weight (HMW) compounds, with LMW PAHs being more abundant. These high concentrations surpass the permissible limits for discharge, with naphthalene and fluorene showing the highest levels. The presence of carcinogenic PAHs, especially in significant quantities, underscores the long-term threat to aquatic ecosystems and human health, particularly for vulnerable populations. The pollution indices of the PAHs indicate a significant risk of contamination to the receiving water body, rendering it unsuitable for agricultural and domestic purposes. Source diagnostic indices suggest a predominance of petroleum-derived, petrogenic sources of PAHs, with potential pyrogenic contributions from low-temperature pyrolysis processes. This study underscores the urgent need for proper treatment and management of abattoir wastewater to mitigate its adverse impacts on the environment and public health
REFERENCE
Ogunmoroti E. A.1, Adedosu H. O.*2, Ayoola P. B.3, Adedosu T. A.4, Assessment of Physicochemical Properties and Polycyclic Aromatic Hydrocarbons (PAHs) in Wastewater from New Atenda Abattoir, Ogbomoso and its Environmental Impacts, Int. J. Sci. R. Tech., 2025, 2 (1), 360-367. https://doi.org/10.5281/zenodo.14729463
10.5281/zenodo.14729463
