Pollution Evaluation of Industrial Effluents from Consolidated Breweries: A Case Study from Benue State, Nigeria

Abstract

Industrial effluent discharged into surface water is an environmental concern, as it affects the esthetics, water quality as well as microbial and aquatic flora. Brewery effluents were analyzed for physicochemical parameters (pH, temperature, conductivity, turbidity, total dissolved solids (TDS), dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), nitrate, and sulfate, chloride) and heavy metals (As, Cd, Co, Cr, Fe, Mn, Ni, Pb, and Zn). Atomic absorption spectrophotometer was used to characterize heavy metals using standard analytical methods and compared with WHO standards. The result showed that pH (6.2–6.98), conductivity (137–273 μS/cm), chloride (31–53 mg/l), nitrate (7.53–10.72 mg/l), BOD, and DO were within the WHO limit. However, turbidity, sulfate, and phosphate were above the WHO limit. Heavy metal concentrations Cr, Ni, Pb, Mn, As, and Cd were higher than the WHO limit and vice versa for Fe, Zn, and Co. Ecological risk assessment revealed that effluent samples pose low to moderate ecological risk, for As, Pb, and Ni. Therefore, there is a need for proper treatment and continual monitoring before discharge into the environment.

1. Introduction

Due to an increase in industrial activities, environmental pollution is one of the most critical problems in developing countries. More challenging is the unsafe disposal of solid wastes/industrial wastes into the ambient environment. Industries that use large amounts of water in their processes include chemical manufacturing, steel plants, metal processors, etc. Effluents and most products from industries create serious pollution to water bodies and soils. Water bodies especially freshwater reservoirs, and rivers are the most affected. This has rendered underground and surface waters unsafe for human, recreational, and agricultural use. Biotic life is destroyed and natural ecosystems are infected. Human life is at risk and the principle of sustainable development is compromised [1].

Moderately or untreated industrial effluents may contain high levels of pollutants which in water body systems cause an increase in BOD, COD, Total Dissolved Solids (TDS), Total Suspended Solids (TSS), toxic metals such as Cd, As, Cr, Ni, and Pb, and fecal coliform. Hence make such water unsuitable for drinking, irrigation, and aquatic life support. Industrial wastewater impacts include high BOD from biodegradable wastes such as those from human sewage, pulp and paper industries, slaughterhouses, tanneries, and chemical industries [2, 3, 4].

Brewery wastewater effluent is highly variable in quality and composition. The products of the brewery operations include large volumes of wastewater from liquors pressed from grains and yeast recovery, from the Clean-in-place system located in the brewing house, cellar house, and bottling house, which is discharged into the nearby River. These industrial wastewaters are the main source of heavy metals since nearly all industrial by-products consist of some level of heavy metals [5].

Wastewater shows different degrees of environmental nuisance and contamination hazards due to its chemical and microbiological characteristics. Excessive nutrients (primarily, nitrogen and phosphorus) in wastewater, sludge, and excreta may contaminate surface waters and cause eutrophication, which affects the esthetics of water bodies (lakes, rivers), and results in odor and appearance problems, which was evident in the physiochemical evaluation of brewery effluents in Enugu State [6] and Edo State [7] both in Nigeria.

Previous research has shown that the release of untreated effluents has the potential to negatively impact aquatic organisms, by decreasing pH to acid level, increasing conductivity, temperature turbidity, and total solids in such an environment leading to a decrease in dissolved oxygen with microbial bloom from rich nutrients (nitro-groups, sulfur-groups, and phosphors) [8, 9, 10, 11, 12].

Heavy metals are also released from these effluents. Studies have shown that long-term exposure to low concentrations of some heavy metallic anions can result in the development of sub-chronic to chronic illnesses and diseases in a given population, usually between 1 in 1000 to 1 in 1,000,000 as institutionalized by the US. Environmental Protection Agency (EPA) [13, 14].

The forms in which metal pollutants exist in wastewater discharges determine their release into the aquatic ecosystem. Some metals become bio-available when soluble airborne solids are dissolved by weak acids such as carbonic acid. Their concentration became enhanced by the abundance of metals in road dust and tire residues [15].

The physicochemical properties and selected heavy metals of industrial effluents from consolidated Breweries in Benue State, Nigeria were studied. Therefore, the study aimed to assess the concentration levels, and ecological and health risks of industrial effluents discharged daily into the nearby River, a primary source of fishing activity and domestic purposes in the neighboring community. Information from the present study will be helpful to the relevant government agencies and policymakers in preparing preventive action to control the direct discharge of effluents from chemical industries, agro-based activities, and domestic waste to the rivers and the sea.

2. Materials and method

2.1 Location/study area

Consolidated breweries plc Makurdi, Benue state is located at kilometer 5 Gboko Road, pm 102,339 Makurdi, Benue State, Nigeria. The locality is predominantly an agrarian community where farming and animal husbandry takes place with a few industrials such as small and medium scale enterprise (mechanic workshop, local markets, construction, and mining) activities. Figure 1 shows the map of the study location.

Figure 1.

Study map showing the study locations.

2.2 Sample collection and preparation

Four samples of effluent were collected with a cleaned plastic container at a different location in the brewery. The plastic containers used were carefully washed with 1% HNO₃ acid, rinsed with tap water, and then distilled water. The samples were labeled appropriately; Sample A-untreated effluent, B- treated effluent, C- contact point of the treated effluent with the river, and D- 10 kilometers away from the contact point. These samples were transported to the laboratory for analysis in an ice-packs container and protected from direct sunlight. They were stored in the refrigerator at 20°C.

2.3 Physicochemical analysis

2.3.1 pH

The pH values of the samples were determined at the point of sampling using a portable pH meter after calibrating against buffer solution (pH 4.7 and 9.2).

2.3.2 Turbidity

The turbidity of the samples was determined using the turbidity meter (Labtech digital model), and EPA 180 was selected as the measurement mode.

2.3.3 Total dissolved solids (TDS)

TDS was determined by an electrometric method using a TDS meter (Jenway, model 4076).

2.3.4 Dissolved oxygen (DO)

DO is the amount of gaseous oxygen dissolved in the water. It was determined using a dissolved oxygen meter (Model H1 9146, HANNA) as described by AOAC [16].

2.3.5 Biological oxygen demand (BOD)

BOD measures the amount of dissolved oxygen used by microorganisms in the oxidation of organic matter in a water sample. The BOD was determined by collecting the water sample in a sealed bottle, incubating for a standard period in the dark (usually 5 days at 200°C), and determining the residual oxygen in the water at the end of incubation (Model H1 9146, HANNA). BOD was determined using the following formula as described by AOAC [16].

$$\mathrm{BOD}=\left({\mathrm{DO}}_1–{\mathrm{DO}}_5\right)\mathrm{mg}/\mathrm{l}$$E1

Where:

DO₁ = Sample before incubation.

DO₅ = Sample after 5 days of incubation.

2.3.6 Chemical oxygen demand (COD)

COD is the amount of oxygen consumed under specified conditions of organic and oxidizable inorganic matter in water and wastewater. The COD is determined first by pipetting 10 ml of the water sample into a conical flask and adding 5 ml of 0.025 N potassium dichromate (K₂Cr₂0₇). 15 ml of sulfuric acid (H₂S0₄) was added to it, and the solution was diluted with 40 ml of distilled water to get a 70 ml solution. Seven drops of phenolphthalein ferrous sulfate indicator were added, and the solution was allowed to cool. The solution was titrated with 0.025 N ferrous ammonium sulfate. A blank solution was also titrated. COD was determined by using the following formula:

$$\frac{\left(T_1-T_2\right)\times N\times 8000\times C}{\mathit{\text{Volume of water sample used}}}\left(\mathrm{mg}/\mathrm{l}\right)$$E2

Where:

T₁ = Titer value for blank.

T₂ = Titer value for effluent sample.

N = Normality of the ferrous ammonium Sulfate used is 0.025.

C = Chloride correction which is in Milligram per liter of chloride × 0.03.

8000 = Milliequivalent weight of oxygen x 1000 mL/L.

2.3.7 Chloride

Ten ml of the water sample was pipetted into a conical flask with 3 drops of potassium chromate (K₂Cr0₂) and the solution was titrated with 0.1 N silver nitrate (AgNO₃). Chloride was determined by using the following formula:

$$\frac{\left({\mathrm{T}}_v\mathrm{x}0.003546\mathrm{x}105\right)\mathrm{mg}}{\mathrm{l}}$$E3

Where:

Tv = Titer value of sample.

0.003546 = equivalent weight of chloride

2.3.8 Sulfate

Ten ml of water sample was pipetted into a conical flask plus 5 ml of 2 N HCl and 0.05 N BaCl₂. The solution was boiled for 5 minutes and allowed to cool. Two ml of ammonium (NH₄⁺) and 5 ml of 0.01 N EDTA were added to the solution and boiled for 5 minutes. Five ml of pH buffer 10 and 3 drops of Eriochrome black) indicators were added. The solution was titrated with 0.01 N MgCl₂. Sulfate was determined by using the following formula:

$$\left(\frac{10-\left({\mathrm{T}}_v\times 0.93\right)\times 96.01484}{10}\right)\mathrm{mg}/\mathrm{l}$$E4

Where:

Tv = Titrate value of the sample.

96.01484 = molecular weight of sulfate.

0.93 = Constant.

10 = Volume of water sample used.

2.3.9 Analysis of effluent samples for heavy metals concentration

An effluent sample of 200 mL was measured into a 500 mL beaker, and 5 mL of concentrated nitric acid was carefully added. This solution was concentrated to 20 mL by heating in a water bath for a few hours. The concentrated extract was cooled and transferred into a 50 mL standard flask, then made up to mark with distilled water. Heavy metal (Pb, Cd, Zn, As, Cr, Fe, Mn, Co, and Ni) contents of the samples were determined using atomic absorption spectrophotometer (Spectra AA Varian 400 plus) involving direct aspiration of the aqueous solution into air-acetylene flame. A reagent blank was prepared and analyzed. Heavy metal concentrations of a series of standards were determined and a calibration graph was developed. From the graph, the concentrations of heavy metals in the sample were calculated as described by Braid et al. [17].

2.4 Ecological risk assessment

2.4.1 Contamination factor (CF)

CF is the extent of pollution of the contaminant of interest, it is expressed:

$$\mathrm{CF}=\frac{\text{chemical contaminant of interest}}{\text{background value using}\mathrm{WHO}\text{standard}}$$E5

The following terminology was used to describe the contamination factor:

1. CF < 1: low contamination factor;

2. 1 ≤ CF < 3: moderate contamination factor;

3. 3 ≤ CF < 6: considerable contamination factor;

4. CF ≥ 6 _ very high contamination factor.

2.4.2 Degree of contamination (Cdeg)

This is the summation of the contamination factor of all chemical contaminants in the study site. It is calculated as follows:

$${\mathrm{C}}_{\mathit{deg}}=\sum \left(\mathrm{CF}\right)={\mathrm{CF}}_1+{\mathrm{CF}}_2+{\mathrm{CF}}_3+\bullet \bullet \bullet +{\mathrm{CF}}_n$$E6

For the description of contamination degree (Cdeg), the following terminologies have been used:

1. Cdeg <8: low degree of contamination;

2. 8 ≤ Cdeg <16: moderate degree of contamination;

3. 16 ≤ Cdeg <32: considerable degree of contamination;

4. Cdeg ≥32: very high degree of contamination.

2.4.3 Modified degree of contamination (mCdeg)

This is the average effect of all chemical contaminants of interest, the advantage of mCdeg is that it quantifies the chemical contaminants into a composite aggregate to derive salient information about the study site using the formula:

$$m{\mathrm{C}}_{\mathit{deg}}=\frac{1}{n}\sum \left(\mathrm{CF}\right)$$E7

Where: n is the total chemical contaminant and CF is the contamination factor. mCdeg is classified as:

1. mCdeg <4: low moderate contamination;

2. 4 ≤ mCdeg <16: medium moderate contamination;

3. 12 ≤ mCdeg <20: high moderate contamination;

4. mCdeg ≥20: extreme moderate contamination.

2.4.4 Pollution load index (PLI)

This is the geometric mean of CF value to the nth number of chemical contaminants of interest, it is given as described by Tomlinson et al. [18]:

$$\mathrm{PLI}={\left({\mathrm{CF}}_1\times {\mathrm{CF}}_2\times {\mathrm{CF}}_3\times \bullet \bullet \bullet \times {\mathrm{CF}}_{\mathrm{n}}\right)}^{1/\mathrm{n}}$$E8

Where:

n is the total chemical contaminant.

CF is the contamination factor.

The PLI gives the level of pollution classified as:

1. PLI < 1: no pollution;

2. 1 < PLI < 2: modest pollution;

3. 2 < PLI < 3: high pollution;

4. 3 < PLI: extremely high pollution.

2.4.5 Potential ecological risk index (PERI)

Assesses the toxicity factor of a particular chemical contaminant of interest, where the definite contamination status is evaluated concerning the ecosystem. It is expressed as shown in Eq. (9) and (10). A methodology to assess ecological risks for aquatic pollution was developed by Hakanson [19]. The ecological risk index (R_I) is calculated as a sum of eight elements of heavy metals (As, Cd, Cr, Ni, Mn, Pb, Co, and Zn).

$$\text{PERI}=\sum {\mathrm{E}}_{\mathrm{r}}=\mathrm{TF}\times \mathrm{CF}$$E9

$${\mathrm{R}}_{\mathrm{i}}=\sum {\mathrm{E}}_{\mathrm{r}}$$E10

Where:

Er is the ecological risk index of different chemical contaminants,

TF is the toxicity factor of each chemical contaminant of interest as described by Hussain et al. [20] and Umeh et al. [21].

CF is the contamination factor in Eq. (5),

RI is the risk index calculated as the sum of the potential ecological risk factors for heavy metals in the wastewater.

Er and RI values are categorized using:

1. Er <40 and RI <150: low ecological risk;

2. 40 < Er ≤80 and 150 < RI <300: moderate ecological risk;

3. 80 < Er ≤160, appreciable ecological risk;

4. 160 < Er ≤320 and 300 < RI <600: high ecological risk;

5. Er > 320 and RI ≥ 600: extremely high ecological risk.

3. Results

The values of the physical and chemical parameters of effluent samples from the Brewery are presented in Table 1 and Figure 2 respectively. The pH values were 6.98, 6.20, 6.48, and 6.72 for sampling points A, C, D, and E respectively. In all sampling locations, the highest pH value of 6.98 was obtained at sampling point A and the lowest value of 6.20 was obtained at sampling point C.

Parameters	Sample A	Sample B	Sample C	Sample D	WHO
pH	6.20	6.98	6.48	6.72	6.50–8.50
Turbidity (NTU)	102.70	115.00	39.90	30.70	50. 00
TDS (mg/l)	48.00	4.00	16.00	10.00	500.00
Conductivity (μS/cm)	272.00	273.00	178.00	187.00	1000.00

Table 1.

Physical parameters of the studied effluents.

*A-un treated effluent, B- treated effluent, C- contact point of the treated effluent with the river and D- 10 kilometers away from the contact point.

Figure 2.

Chemical parameters from the studied effluents. DO: Dissolved oxygen; BOD: Biological oxygen demand; COD: Chemical oxygen demand.

The TDS values in the present work ranged from 4.0 to 48.0 mg/l. Dissolved oxygen values ranged from 4.70 to 23.60 mg/l for all sampling points. The highest (15.90) and lowest (0.40) biological oxygen demand values were recorded at sampling points C and A, respectively. The chemical oxygen demand in the present work ranged from 18.88 to 19.24.32 mg/l. The values of nitrate varied between 1.28–1.95 mg L-1. The highest (7.16) phosphate value was recorded at sampling point C and the lowest (6.93) at sampling point A. Sulfate values ranged from 31.69 to 35.39 mg/l for all sampling points. Chloride values ranged from 28.00 to 53.00 mg/l for all sampling points.

Figure 3 shows the results of heavy metals concentration analyses of effluent samples across the study area. Among the 9 elements studied, concentrations of As, Pb, and Ni were higher than WHO recommended limits. In contrast, lower concentrations of Co, Mn, and Zn were observed in the different sampling locations. Elements displayed wide variations in their distribution, suggesting control of anthropogenic activities on water chemistry. Overall, concentration of the study elements followed the order: As >Fe > Mn > Zn > Ni > Pb > Cr > Co > Cd. The sampling site C recorded the highest concentration of Fe and As.

Figure 3.

Heavy metal concentrations.

4. Discussion

Water quality in an aquatic environment is very important for the survival of its flora and fauna. Water pH can affect aquatic organisms as their metabolic activities are pH-dependent [22, 23]. The pH across the sampling points ranges from 6.20 in sample A to 6.98 in sample B, indicating slight acidity. A significant (P ≤ 0.05) difference was observed between the pH values for each sampling point, although, B and D were within the WHO [24] guideline regulatory limit of 6.5–8.5 set for drinking water, while samples A and C were a little below the standard limit. The slight acidity could be attributed to the chemicals used in the treatment processes and the water may serve as a sink for various wastes and chemical preservatives used in the brewery such as oxides of sulfur, nitro, carbon, and phosphor in turn form sulfuric, nitric, carbonic and phosphoric acid on reaction with water leading to microbial bloom from rich nutrients source thereby causing reduction in dissolved oxygen, increase turbidity, conductivity, odor and diminish aquatic esthetic respectively. Water pH helps to control metal solubility, and water hardness and serves as an indicator of water pollution [7, 9].

Nitrate in the present study was all below-recommended limit when compared to the WHO [24] standard for safe drinking water. Nitrate is alleged to be an indicator of pollution in the public water supply [25]. It is the stable form of nitrogen that plays a significant role in the process of eutrophication. The conductivity range of the various sampling points varied considerably across the study area. Point B showed the highest value and, therefore, decreased along with the sampling points, most likely due to the effect of dilution and removal of soluble salts by biological utilization.

The biological oxygen demand (BOD) and chemical oxygen demand (COD) are useful parameters in water quality analysis. The highest and lowest BOD values were recorded at sampling points A and B, respectively. Biological oxygen demand is the amount of oxygen required by aerobic microorganisms to stabilize the organic material of wastewater at a standardized temperature (20°C) and time of incubation (usually 5 days). It is used to indicate the organic strength of water. When BOD is less than 4 mg/l, water is deemed to be reasonably clean and unpolluted, while a BOD level greater than 10 mg/l indicates pollution [26].

Chemical oxygen demand is a measure of organic contamination in water. It is the amount of dissolved oxygen required to cause chemical oxidation of the organic material in water and is a key indicator of the environmental health of surface water [18]. There was a gradual increase in chemical oxygen demand from point B to point D. Chemical oxygen demand values were below the WHO recommended value of 200 mg/l [24]. High chemical oxygen demand COD values indicate pollution due to oxidizable organic matter [27].

Phosphate concentration was high in all sampling points and greater than the WHO recommended value of 2.0 mg/l. Phosphate is known as a limiting nutrient in the aquatic ecosystem [28]. There is little variation in dissolved oxygen values of effluent samples across the study areas. The dissolved oxygen concentration is a function of temperature, pressure, salinity, and biological activities in the water body. The tropical aquatic ecosystem should have a dissolved oxygen concentration of at least 5 mg/l in other to support diversified biota, including fish [29, 30, 31, 32]. The level of 4.70 mg/l for point B was within the WHO, [24] standard value of 5 mg/l necessary for aquatic productivity, while other points were above the standard limit of 5 mg/l.

The highest value of sulfate was observed in point C (35.39 mg/l). This value is far below the permissible limit stipulated by World Health Organization WHO, [24]. The present work was in line with the work of Alao [30], who also reported low sulfate levels in the water receiving brewery effluent in Majawe Ibadan.

The values of chloride and iron obtained from point B, C, and D falls below the WHO permissible limit, while point C was within the 1 mg/l desirable level from WHO. The result of chloride agrees with Imoobe and Koye [33], who reported the value of chloride in Eruvbi Stream to be below the permissible limit stipulated by the World Health Organization [24]. The discharge of industrial effluents into receiving water bodies invariably results in the presence of a high concentration of pollutants in the water and sediments.

The pollutants are present in concentrations that may be toxic to different organisms [34, 35, 36]. The concentration of Cadmium across the study area ranged from 0.001 at sampling points B and D to 0.007 at sampling point C. The values recorded were lower than (0.043 mg/l) and (0.072 mg/l) in the water reported by Oguzie and Okhagbuzo [37]. The value of all samples assessed was above the permissible limit of 0.003 ppm set by WHO [24] for drinking water except for sampling points B and D. High concentrations of Cadmium (Cd) have been reported to inhibit the bio-uptake of Phosphorus and Potassium by plants [38].

Specific industries involved in electroplating, pigments production, chemicals, and alloy processing are sources of cadmium to the urban environment. Chromium (Cr) levels in the effluents were relatively low across the different sampling points. The concentrations of chromium in effluents were below the 0.050 mg/l value recommended by the World Health Organization (WHO) [24] in industrial effluents except for sampling point B.

A high concentration of nickel (Ni) was recorded in the effluent samples ranging from 0.114 ppm in point D to 0.246 ppm in point A. The concentrations of nickel in effluents are higher than the <1 mg/l value recommended by the WHO [24] in industrial effluents. Ni has wide applications in the manufacture of batteries, fertilizer, welding products, electroplating, and household appliances and has essential functions in every area of industrial activity [2].

Lead (Pb) and Arsenic (As), a major environmental pollutant is a multi-organ poison that, in addition to well-known toxic effects, depresses immune status and causes damage to the central nervous system, kidney, and reproductive system [39]. The lead (Pb) values were quite low in all the sampling points except in point E where it was not detected. All the points showed a lead value above the maximum acceptable concentration.

4.1 Contamination factor/pollution index

The contamination factor (CF) values were revealed in Table 2. Arsenic (As) can be categorized as a very high contamination factor across all the sampling locations. The highest values of CF of As at location C (48.46) and the lowest at location B (33.12), indicating severe anthropogenic contribution to the contamination load of rivers at this site. The CF of Cd (Cadmium) can be categorized as low to moderate. Two locations (B and D) can be categorized as having low CF of Cd, and two locations (A and C) can be categorized as having moderate CF of Cd. Lead (Pb) can be categorized as a very high CF across all the sampling locations. The highest values of CF of Pb at location A (32) and the lowest at location B (12.1). The CF of Ni (Nickel) can be categorized as considerable to very high contamination. Two locations (C and D) can be categorized as having considerable CF of Ni, and two locations (A and B) can be categorized as having very high CF of Ni. The CF of cobalt and Zinc can be categorized as low contamination factors of Co and Zn, respectively. Other elements such as Cr (0.26–2.48), Mn (0.29–1.035), and Fe (0.62–3.42) can be categorized as low to moderate CF. The result indicates that contamination of effluents from Nigeria Brewery contributed to As and Pb [21].

Sample locations/elements	A	B	C	D
Arsenic (As)	48.26	33.12	48.46	45.20
Cadmium (Cd)	1.67	0.33	2.33	0.33
Cobalt (Co)	0.00	0.085	0.10	0.00
Chromium (Cr)	0.64	2.48	0.26	0.38
Iron (Fe)	3.42	0.624	0.83	0.53
Manganese (Mn)	0.51	1.035	0.73	0.30
Nickel (Ni)	8.20	7.17	4.96	3.80
Lead (Pb)	32.00	12.1	13.8	0.00
Zinc (Zn)	0.063	0.038	0.033	0.012
PLI	2.10	1.25	1.16	0.70
C.deg	94.7	25.14	71.50	50.55
M-C.deg	40.17	21.05	29.56	5.616

Table 2.

Contamination factor, pollution index and contamination index.

*A-un treated effluent, B- treated effluent, C- contact point of the treated effluent with the river and D- 10 kilometers away from the contact point. PLI: pollution load index; C.deg.: degree of contamination; M-C.deg.: modified degree of contamination.

The pollution Load Index (PLI) is a resourceful tool to measure and compare contamination. Analyzed effluents samples discharged into rivers at locations A (2.1), B (1.25), and C (1.16) displayed higher PLI values (PLI > 1) and progressive deterioration in quality. Location D was observed to have a low pollution index value of 0.7. The order for PLI was A > B > C > D. Higher PLI values in rivers demonstrated substantial anthropogenic impacts on the river quality signifying the need for immediate intervention to prevent pollution. In contrast, lower PLI values pointed to no considerable anthropogenic activities, signifying no need for intervention but requiring constant monitoring [31].

Degrees of contamination (Cdeg) values of effluents from Nigeria’s brewery are revealed in Table 2. The degree of contamination across the sampling locations can be categorized into four categories according to the Patil et al. [28] classification. Sampling locations A, C, and D can be categorized as having a very high degree of contamination (Cd value = 94.7, 71.50, and 50.54, respectively), this indicates very severe anthropogenic pollution at these sampling sites. Location B indicates a considerable degree of contamination with a Cd value of 25.137. The present study revealed Pb and Ni as the most severe component causing moderate to very high river contamination. A similar pattern was noted for contamination degree (Cdeg), where sampling locations having dominant anthropogenic activities displayed a high Contamination degree. Regular monitoring of the river for the presence of trace elements, especially Arsenic, lead, and nickel, is required [34].

4.2 Potential ecological risk index method

The evaluation results on the potential ecological risk factor (Eir) and the potential ecological risk index (RI) are summarized in Table 3. The order of potential ecological risk coefficient (Eir) of heavy metals in discharge effluents was As > Pb > Cd > Ni > Cr > Mn > Co > Zn. The mean potential ecological risk coefficient of Cd, Cr, Mn, Ni, Co, and Zn were all lower than 40, which is low ecological risk. At the same time, the mean potential ecological risk coefficient of Pb and As were greater than 80 and 320, respectively, which indicates moderate to extremely high ecological risk. All the sampling locations were at High to very high-risk levels where the RI values were much greater than 600. However, because most samples are contaminated with As, Pb, and Ni, their impact on the ERI became very obvious and predominant. Therefore, the present study indicates that As, Pb, and Ni were the major heavy metal posing an ecological risk in the study area [21, 31, 35].

Sample Locations/Elements	A	B	C	D	Mean
Arsenic (As)	482.6	331.2	484.6	452	437.6
Cadmium (Cd)	50.1	9.9	69.9	9.9	34.9
Cobalt (Co)	0	0.425	0.5	0	0.231
Chromium (Cr)	3.2	12.4	1.3	0.76	4.42
Manganese (Mn)	2.55	5.175	3.65	1.475	3.212
Nickel (Ni)	41	35.83	24.8	19	30.15
Lead (Pb)	160	60.5	69	0	72.37
Zinc (Zn)	0.038	0.063	0.0326	0.012	0.036
Risk index	739.48	455.5	653.78	483.14	582.9
Risk grade	Extremely High	High	Extremely High	High	High

Table 3.

Potential ecological risk index.

A- un treated effluent, B- treated effluent, C- contact point of the treated effluent with the river and D-10 kilometers away from the contact point.

5. Conclusion

The laboratory analysis results of the effluent samples indicated that metals and other contaminants from the effluents have compromised the River quality. The results of the physicochemical analysis showed that sulfate, phosphate, COD, and heavy metals such as Cr, Ni, Pb, Mn, As, and Cd were slightly higher than WHO and FEPA standards for drinking water, while the pH, Chloride, Nitrate, Nitrite, TDS, Conductivity, BOD, COD and some heavy metals such as Fe, Zn, Co were within the standard of WHO and FEPA, set for drinking water. The study, however, showed that some contaminants sampled were within statutory limits. It was also observed that sample A (Untreated effluent) and sample B (Treated effluent) had lower mean differences than sample C and sample D. Contamination factors follow a similar trend in metal contamination. At the same time, PLI index models confirmed that the effluents from the different sampled locations were polluted, except for location D, which is unpolluted. The mean anthropogenic input for the sampled effluents for the individual metals followed the order As> Fe > Mn > Zn > Ni > Pb > Zn > Cr > Co > Cd. The ecological risk assessments for the heavy metals were at high ecological risk. Furthermore, the potential ecological index depicts As at extremely high risk, Pb at appreciable risk, Ni at moderate risk, and Cr, Mn, Co, Zn, and Cd at a low ecological risk level. Hence any significant increase would persuade environmental challenges. However, the present study recommends proper treatment of effluents before discharging to reduce their mean difference from the WHO standard and protect the health of the local population.

Acknowledgments

The authors acknowledge and extend their sincere gratitude to all who assisted in realizing this present work.

Conflict of interest

All the authors declare no conflict of interest regarding this manuscript.

Notes/thanks/other declarations

We are thankful for the invitation to contribute to River Basin Management and other anonymous reviewers for their assistance. This research work was self-funded, as the authors declare no conflict of interest.