Page 1 of 10
European Journal of Applied Sciences – Vol. 10, No. 4
Publication Date: August 25, 2022
DOI:10.14738/aivp.104.12661. Anikwe, U. F., Okenwa, E. J., Ona, J. S. E., Anikwe, C. H., & Oparaji, E. H. (2022). Risk Assessment of Heavy Metal Toxicity and Stress
Marker Enzyme in Waste Water from Municipal Dam Site around Enugu Metropolis, Enugu State. European Journal of Applied
Sciences, 10(4). 716-725.
Services for Science and Education – United Kingdom
Risk Assessment of Heavy Metal Toxicity and Stress Marker
Enzyme in Waste Water from Municipal Dam Site around Enugu
Metropolis, Enugu State
Anikwe, Uchenna, Fredrick
Department of Applied Biology and Biotechnology
Enugu State University of Science and Technology
Okenwa, Ezinne Jennifer
Department of Applied Biology and Biotechnology
Enugu State University of Science and Technology
Ona, Jekwu, S. E.
CSDP, Enugu state
Anikwe, Chidera, Henry
Department of Civil Engineering, Institute of Management and
Technology, Enugu state
Oparaji, Emeka H.
Department of Biochemistry, University of Nigeria
Nsukka, Enugu state
ABSTRACT
Impact of waste water toxicity from collection ditches within Enugu metropolis,
Enugu state was assessed in the present study. Risk impact of heavy metal
recalcitrant was also determined in the present study as the waste water from the
ditch were used by subsistence farmers around for irrigation purposes.
Physicochemical analysis of the soil irrigation with the domestic waste water was
carried and revealed the following: pH 6.65, conductivity 792 respectively.
Dissolved mineral contents were found in the following order:
Cl>Ca>Fe>SO4>Mg>Cu>K>Pb>PO3 while heavy metals of Hg, As and Cd were found
at below detectable limit range (BDL). Total organic carbon (TOC) and total organic
matter (TOM) contents were found at 179.93 and 221 mg/kg in the various
treatments. These varied significantly from the control treatment. Physicochemical
properties of the domestic waste water were equally analyzed. Soil enzymes
showed the activity of the lipase, urease, peroxidase and catalase with an increased
of lipase, urease and peroxidase after the irrigation with OD of 0.610, 0.677 and
0.712 respectively catalase activity was reduced downwardly. Health risks to
human through utilization of the waste water by human were assessed by:
estimated dietary intake (EDI), estimated weekly intake (EWI) and Target hazard
quotient (THQ). EDI for the heavy metals of Pb, Cu and Fe were 3.98 x 10-3, 1.22 x 10-
2 and 1.2 x 10-2 mg/g, respectively estimated while EDI of 1.36 x 10-3, 8.33 x 10-3 and
9.52 x 10-3 mg/g were obtained for Pb, Cu and Fe from the control experiments. EWI
Page 2 of 10
717
Anikwe, U. F., Okenwa, E. J., Ona, J. S. E., Anikwe, C. H., & Oparaji, E. H. (2022). Risk Assessment of Heavy Metal Toxicity and Stress Marker Enzyme
in Waste Water from Municipal Dam Site around Enugu Metropolis, Enugu State. European Journal of Applied Sciences, 10(4). 716-725.
URL: http://dx.doi.org/10.14738/aivp.104.12661
for heavy metals of Pb, Cu and Fe were 9.52 x 10-3, 583 x 10-2 and 6.7 x 10-2 mg/g,
respectively. The results showed that the THQ for Fe and Cu were less than 1 while
that of Pb was greater than 1. THQ were less than 1in all the analysed metals from
the control experiment. The findings from this study show that there is a
considerable health risks connected with utilization of waste water from our study
locale and these waste water bioaccumulate heavy metal levels which are
potentially poisonous to humans who consume them.
Key words: waste water, heavy metals, enzymes, risk-assessment.
INTRODUCTION
The use of municipal waste water and effluent of domestic constituents on agricultural soil have
provided a salvage pathway for waste disposal through utilization of the recyclable constituents
in the waste water for optimized agricultural produce (Khalid et al., 2017).
Wastewater production sources include different human activities, such as: Industrial,
commercial, and domestic activities (Alobaidy et al., 2010). Municipal wastewater is also
sometimes distinguished into urban, rural, and agricultural areas and sources. With the rapid
expansion of human population, cities, industries, and the domestic water supply, the quantity
of wastewater production is increasing at the same proportion (Khalid et al., 2017). The average
volume of wastewater generated daily by human activities depends on the availability of the
water quantity in the house, the cultural level and type, the cost of the water, and the economic
conditions (Alobaidy et al., 2010).
Agriculture is the most common area in which untreated wastewater is reused. According to an
estimate in 2004, approximately 20 million ha is irrigated with wastewater in fifty countries
worldwide (Chen et al., 2013). The use of wastewater for crop irrigation has further increased
in recent years. The municipal wastewater demand corresponds to 11% of the water
withdrawal globally (Thebo et al., 2017). About 3% of the municipal wastewater demand is
consumed and the remaining 8% is being discharged as wastewater; that is, 330 km3 of
wastewater per year, which is potentially irrigating almost 40 million ha (approximately 8000
m3 per ha) or 15% of all irrigated lands (Chen et al., 2013).
Wastewater usage for crop irrigation has certain advantages such as providing the essential
nutrients and organic matter, saving water and nutrients, and reducing water contamination
(Huibers et al., 2005). It has been reported that quite sufficient quantities of macronutrients (N,
P, and K) are supplied to soil and plants via wastewater application (Huibers et al., 2005).
Therefore, it is a great temptation for poor farmers to irrigate crops with wastewater as it can
reduce the crop production cost, with the cost of crop production decreasing by 10%–20%
when irrigated using wastewater (WHO, 2006).
The fundamental problem facing our country Nigeria is inadequate machinery in waste
management. This is to an extent due to the bridge of policies, inadequate infrastructure and
economic challenges. This has hampered the nation’s economic developments in agriculture,
industrial and other otherwise (Emeka, 2008). Agriculture still stands out as a major fulcrum
in our country’s major developmental stride for the achievements of her dream 2020. Over the
Page 3 of 10
718
European Journal of Applied Sciences (EJAS) Vol. 10, Issue 4, August-2022
Services for Science and Education – United Kingdom
years, records from ecological impact assessments have shown how various wastes from
different sources have impacted on the various ecological niches/properties of our biosphere.
These records have kept mouth shattering of the sustainability our environment (soil) which is
the centre for various earthly activities (Ajanaku, 2007). Sustainability of the agricultural sector
in our developing country Nigeria cannot be over emphasized; assessment of quality markers
of soil for efficient agricultural practices give a view of the level of recalcitrant present in the
soil. Agricultural practices and its bountifulness can only improve when the integrity of the
surrounding soil is not compromised. The present study provides information on the impact of
domestic waste water from a cafeteria irrigated on agricultural soil on soil physicochemical
properties and soil quality marker enzymes.
MATERIALS AND METHODS
Materials
All the reagents, equipment used in the present study were of analytical grade and products of
BDh, May and Baker, Sigma Aldrich. The equipments are calibrated at each use.
Collection of the Experimental Samples
Samples Collection
Arable soil sediments and waste water were collected from four municipal dam for domestic
waste collection located within Enugu metropolis, Enugu state (Long.140N, SE 4) as described
by Ezenwelu et al. (2022). The samples were collected in clean sterile sample containers and
was taken to the lab for further experiments
Determination of physicochemical properties of the soil and waste water
Soil and waste water physicochemical properties were determined as described in the journal
of ATSDR, 2009. Physicochemical properties: pH, conductivity, dissolved minerals (Cl, Mg, Ca,
K, PO3, TS, TDS, TSS, DO, BOD, heavy metals (As, Cd, Cr, Hg, Pb, Cu) were assessed.
Health Risk Assessment of Heavy Metals
The health risks connected with the association of the waste water analyzed in this study were
assessed based on the Target hazard quotient (THQ), estimated daily intake (EDI), estimated
weekly intake (EWI) and carcinogenic risk (CR) of the heavy metals.
Estimated Daily Intake (EDI)
Estimated Daily Intake (EDI) of heavy metals depend both on waste water concentration of the
particular metals and average consumption of the water samples.
EDI is calculated using the equation below:
EDI = Concentration of metals × Daily water intake
Average Body weight ................................. eqn 1
Where: EDI is Estimated Daily Intake
Estimated Weekly Intake (EWI)
The chronic toxicity of the metals was calculated as the Estimated Weekly Intake (EWI).
Tolerable intakes are expressed on a weekly basis because the contaminants given this
designation may accumulate within the body over a period of time (Herrman and Younes, 1999)
The EWI (μg/kg bw) was determined using the following equation as reported by (Copat et al.,
2012).
Page 4 of 10
719
Anikwe, U. F., Okenwa, E. J., Ona, J. S. E., Anikwe, C. H., & Oparaji, E. H. (2022). Risk Assessment of Heavy Metal Toxicity and Stress Marker Enzyme
in Waste Water from Municipal Dam Site around Enugu Metropolis, Enugu State. European Journal of Applied Sciences, 10(4). 716-725.
URL: http://dx.doi.org/10.14738/aivp.104.12661
EWI= Cm X IRw
BW ..............................................................................eqn 2
Where: EWI is Estimated Weekly Intake
Cm: the metal concentration in plantain
IRw: is the weekly ingestion rate (seven times the daily ingestion rate) (Renieri et al., 2014).
BW: Body weight.
Target Hazard Quotient
Target Hazard Quotient (THQ) is the ratio between exposure and reference oral dose (RfDing)
and it is normally used to express the risk of non-carcinogenic effects. According to this ratio,
exposed populations are prone to experience health risks if the value is equal to or greater than
1. Values less than 1 consequently indicate no health risk for those metals for the exposed
population.
THQ was calculated based on the equation below:
THQ = Concentration of metals × Daily water intake
RfD × Average Body weight ..................................eqn3
Where: THQ is target hazard quotient
RfD is reference oral dose
Soil Enzyme Assessment
Soil quality marker enzymes were determined using standard assay protocols, enzyme such as:
Lipase, catalase, urease and peroxidase were assayed as described by Ezenwelu et al. (2022),
Latha (2013), Douglas and Bremner (1971) respectively.
Statistical Analysis
One way analysis of variance (ANOVA) and statistical micro word excel was used in the analysis
of the data. T-student test was used in comparism of the data significances
RESULTS
Table one shows the physicochemical properties of the waste water from municipal ditch
characterized with cafeteria effluent. The results showed very much in contrast the properties
of the waste water from the control experiment.
Table two shows the physicochemical properties of the waste water from municipal ditch
characterized with cafeteria effluent. The results showed very much in contrast the properties
of the waste water from the control experiment.
Page 5 of 10
720
European Journal of Applied Sciences (EJAS) Vol. 10, Issue 4, August-2022
Services for Science and Education – United Kingdom
Table 1: Physicochemical Properties of the Waste Water
Physiochemical Parameters Control Water
Sample
Waste Water Sample
pH 7.20 5.30
Water Conductivity (Ω-1cm-1) 782 913
Chloride ion (Mg/L) 7123 1203.42
Dissolved oxygen (Mg/L) 7.02 5.76
Magnesium (Mg/L) 16.24 24.21
Potassium (Mg/L) 1.02 8.18
Calcium (Mg/L) 32.33 39.76
B0D5 0.93 4.02
Total Organic Carbon (TOC)
(mg/L)
38.40 184.41
Total Organic Matter (mg/L) 46.74 226.82
N=2
Table 2: Heavy Metal Profile of the Municipal Ditch within Enugu Metropolis
Heavy metals control sample waste water
Iron (Mg/L) 1.25 22.29
Cadmium (Mg/L) BDL BDL
Mercury (Mg/L) BDL BDL
Arsenic (Mg/L) BDL BDL
Lead (Mg/L) BDL 10.32
Copper (Mg/L) 1.14 17.22
Page 6 of 10
721
Anikwe, U. F., Okenwa, E. J., Ona, J. S. E., Anikwe, C. H., & Oparaji, E. H. (2022). Risk Assessment of Heavy Metal Toxicity and Stress Marker Enzyme
in Waste Water from Municipal Dam Site around Enugu Metropolis, Enugu State. European Journal of Applied Sciences, 10(4). 716-725.
URL: http://dx.doi.org/10.14738/aivp.104.12661
Table 3: Physicochemical Properties of the Soil Sediments
Physiochemical parameters Control experiment Soil sample
pH 7.6 4.24
Soil Conductance 610 433
Chloride ion (Mg/g) 433 1151.614
Phosphorus (Mg/g) 1.78 1.23
Magnesium (Mg/g) 6.27 11.27
Potassium (Mg/g) 7.22 11.52
Calcium (Mg/g) 18.23 19.34
Total petroleum hydrocarbon
(TPH)(Mg/g)
0.34 1014.93
Total Organic Carbon (TOC)
(Mg/g)
10.45 78.64
Total Organic Matter (TOM)
(mg/g)
12.85 196.73
Table 4: Heavy metal concentrations in the soil sediments from the municipal ditch
Heavy metals Control experiment Test sample
Iron(Mg/g) 3.52 38.7
Cadmium(Mg/g) BDL 0.015
Mercury(Mg/g) BDL BDL
Arsenic(Mg/g) BDL BDL
Lead(Mg/g) BDL 1.73
Copper(Mg/g) 1.08 25.49
Page 7 of 10
722
European Journal of Applied Sciences (EJAS) Vol. 10, Issue 4, August-2022
Services for Science and Education – United Kingdom
Table 2 Estimated Dietary Intake (EDI) OF Heavy Metals
Heavy metals (mg/g) Control experiment Bodoh sample
Lead 1.36 x 10-3 3.98 x 10-3
Iron 9.5 x 10-3 1.2 x 10-2
Arsenic BDL BDL
Copper 8.33 x 10-3 1.22 x 10-2
Cadmium BDL BDL
Mercury BDL BDL
N=2 * BDL= Below detectable limits
Table 3 Estimated Weekly Intake (EWI) OF Heavy Metals
Heavy metals (mg/g) Control experiment Bodoh sample
Lead 9.52 x 10-3 2.8 x 10-2
Iron 6.0 x 10-2 8.0 x 10-2
Arsenic BDL BDL
Copper 5.83 x 10-2 8.6 x 10-2
Cadmium BDL BDL
Mercury BDL BDL
N=2 * BDL= Below detectable limits
Table 3 Estimated Weekly Intake (EWI) OF Heavy Metals
Heavy metals (mg/g) Control experiment Bodoh sample
Lead 9.52 x 10-3 2.8 x 10-2
Iron 6.0 x 10-2 8.0 x 10-2
Arsenic BDL BDL
Copper 5.83 x 10-2 8.6 x 10-2
Cadmium BDL BDL
Mercury BDL BDL
N=2 * BDL= Below detectable limits
Table 4 Target Hazard Quotient of Heavy Metals.
Heavy metals (mg/g) Control experiment Bodoh sample
Lead 3.4 x 10-3 1.01
Iron 5.3 x 10-3 4.03 x 10-2
Arsenic BDL BDL
Copper 2.3 x 10-4 3.9 x 10-3
Cadmium BDL BDL
Mercury BDL BDL
N=2 * BDL= Below detectable limits
Fig one shows the activity of the identified soil quality marker enzymes from the agricultural
soil contaminated with the municipal waste water and the control experiment.
Page 8 of 10
723
Anikwe, U. F., Okenwa, E. J., Ona, J. S. E., Anikwe, C. H., & Oparaji, E. H. (2022). Risk Assessment of Heavy Metal Toxicity and Stress Marker Enzyme
in Waste Water from Municipal Dam Site around Enugu Metropolis, Enugu State. European Journal of Applied Sciences, 10(4). 716-725.
URL: http://dx.doi.org/10.14738/aivp.104.12661
Fig. 1. Activity of soil enzymes from the waste water polluted soil.
DISCUSSION
The use of municipal waste water and effluent of domestic constituents on agricultural soil have
provided a salvage pathway for waste disposal through utilization of the recyclable constituents
in the waste water for optimized agricultural produce. Besides these benefits, a number of
drawbacks are associated with the use of wastewater for crop irrigation (WHO, 2006).
Wastewater contains potentially toxic elements (PTEs) such as zinc, chromium, copper,
cadmium, nickel, lead, mercury, and parasitic worms, which can induce severe risks to the
human health and the environment.
This study looked at assessing the health risk factor associated with heavy metal toxicity in a
municipal ditch within Enugu metropolis on soil physicochemical properties and quality
marker enzyme activity. Physicochemical analysis of the soil showed the presence of the
following: pH 7.4 and 6.65, conductivity 488 and 792 respectively. This can be attributed to the
nature of the contaminant in the soil such as oil and other kitchen condiments which can
contain higher acidic contents (oleic, benzoic acids) as stated in the proceedings of the ASTDR,
2009. Dissolved mineral contents were found in the following order:
Cl>Ca>Fe>SO4>Mg>Cu>K>Pb>PO3 while heavy metals of Hg, As and Cd were found at below
detectable limit range (BDL) in both the soil samples. Total organic matter (TOM) and total
organic carbon (TOC) contents were found at 91.66, 22.05 and 76.85, 179.93 in the various
treatments. Chikere et al., 2006 in their study at Eleme petrochemical jetting port site reported
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
LIPASE UREASE PEROXIDASE CATALASE
OD nM
Soil Enzymes
control
Test sample
Page 9 of 10
724
European Journal of Applied Sciences (EJAS) Vol. 10, Issue 4, August-2022
Services for Science and Education – United Kingdom
a similar correlation of ions concentrations in the contaminated Eleme port soil. They revealed
a higher concentration of the mineral ions in the following order 2.28, 1.84, 5.22 and 1789.22
mg/g respectively for K, nitrate, magnesium and chloride ions. Khalid et al., 2017 in their
assessment study on soil pollution and Lead (Pb) accumulation revealed higher quotients of
heavy metals like Fe, Pb and Cu in the soil while heavy metals of Hg, As, Cd were found below
detectable limits in the soil. The same trend was found in the waste water as the BOD5 quotients
was found at 5.2mg/ml with initial dissolved oxygen concentrations at 6.2 mg/ml. Vallero 2010
stated that dissolved oxygen concentration (DO) is said to have reciprocal relationship with the
biochemical oxygen demand (BOD) in water, he went on to state that the presence of organic
matter in water bodies increases biochemical activities of aquatic flora and fauna and such
leads to their exponential multiplications (Bloom) and demand for oxygen for biochemical
activities (oxidation, respiration etc). Dissolved mineral concentrations such as Cl, Ca, Mg, PO3,
Cu, Fe and SO4 were found richly in abundance. Heavy metals such as Pb was found in trace
quantity were as Cd, As and Hg were found in non detectable range. TDS, TSS and TS were
recorded at 23036, 396.5 and 23433.
This as reported in the proceedings of ASTDR, 2009 that every exposed water body are
characterized by the presence of solid particles which may be suspended within the costal
water axis or dissolved in the olefiers of the water bed.
The proceedings went further to state that these solid particles constituents of the water can
be as a result of rock weathering, human activities such as querrying, volcanic eruption in the
water bed and water bodies eutrophications.
Analysis of soil enzymes showed the activity of the lipase, urease, peroxidase and catalase with
corresponding OD reading of 0.403, 0.611, 0.652 and 0.817 respectively. There was an increase
of lipase, urease and peroxidase after the irrigation with the waste with OD of 0.610, 0.677 and
0.712 respectively while catalase activity was reduced. Vallero 2010 reported the activities of
quality marker soil enzymes in the presence of recalcitrants; most constitutive enzymes are
said to be mark qualities of soil otherwise House-keeping enzymes whose activities are
activated in the presence/influx of recalcitrants to a particular ecological nich(es). Lipases are
activated in the presence of triacylglyceride while peroxidase and catalse activity is stimulated
in the presence of peroxide and other superoxides; urease activity is activated in the presence
of organic matter urea.
CONCLUSION
The results from the present study have shown the vulnerability of agricultural soil to effluent
from domestic sources used for irrigation and its impact on agricultural productivity. Despite
the agronomical potentials of the waste water in composite such as abundant dissolved mineral
contents (Cl, Ca, Mg, Cu, Fe), high conductivity among other benefits, there exist a reasonable
amount of potential toxic element (PTE) they contain such as Pb.
Page 10 of 10
725
Anikwe, U. F., Okenwa, E. J., Ona, J. S. E., Anikwe, C. H., & Oparaji, E. H. (2022). Risk Assessment of Heavy Metal Toxicity and Stress Marker Enzyme
in Waste Water from Municipal Dam Site around Enugu Metropolis, Enugu State. European Journal of Applied Sciences, 10(4). 716-725.
URL: http://dx.doi.org/10.14738/aivp.104.12661
References
Agency for Toxic Substance Development and Disease Registry (ATSDR) (2003). Documentary on toxicological
profile of total petroleum hydrocarbon contaminations. Agency for toxic substance and disease registry, division
of toxicology and toxicology information branch, Atlanta Georgia.
Agency for Toxic Substance Development and Disease Registry (ATSDR) (2009). Documentary on toxicological
profile of total petroleum hydrocarbon contaminations. Agency for toxic substance and disease registry, division
of toxicology and toxicology information branch, Atlanta Georgia.
Ajanaku, L. (2007). Battling with Darkness. TELL (Special Edition). May 21, pp: 31-33.
Alobaidy, A., Abid, H. and Maulood B. (2010). Application of water quality index for assessment of Dokan lake
ecosystem, Kurdistan region, Iraq. Journal of Water Resources, 2:792.
Chen, Z., Ngo, H. and Guo, W. (2013). A critical review on the end uses of recycled water. Critical Review on
Environal Science and Technology, 43:1446–1516.
Chukwu, M. and Adams, E. (2016). Effect of Generator (Exhaust) Fumes on the Growth and Development of
Lycopersicum esculentus (Tomato). Journal of Applied Environmental Science and Management, 20 (2) 335– 340
Douglas, D. and Bremner, E. (1971). A rapid method of evaluating different compounds as inhibitors of urease
activity in soil. Soil Biology and Biochemistry, 3:309-315.
Emeka, E. (2008). Development crisis of power supply and implications for industrial sector in Nigeria. Students
Tribes Tribalism, 6(2): 83-92.
Ejedegba O., Onyeneke, E. and Oviasogie, P. (2007). Characterisation of lipase isolated from coconut seed under
different nutrient conditions. African Journal of Biotechnology, 6: 723-727.
Ezeonu, M., Okafor, J. and Ogbonna, J. (2013). Laboratory Exercise in Microbiology. Ist edn. Ephrata Publishing
and Printing Company, Nsukka.Pp. 100-117.
Kathirvelan, P. and Kalaiselvan, P. (2007). Groundnut (Arachis hypogaea L.) Leaf Area Estimation Using
Allometric Model. Research Journal on Agriculture and Biological Sciences, 3(1): 59-61
Khalid, S., Shahid, M., Dumat, C., Niazi, N., Bibi, I., Gul Bakhat, H., Abbas, G., Murtaza, B. and Javeed, H. (2017).
Influence of groundwater and wastewater irrigation on lead accumulation in soil and vegetables: Implications for
health risk assessment and phytoremediation. International Journal Phytoremediation, 19:1037–1046.