Environment Pollution and Climate Change
Open Access

Heavy metal; Bottom sediments; Effluents; Upstream; Downstream; Ubeji River

Introduction

Industrialization is one of the main indices of global and national development that brings about development and obvious benefits. But more often than not, industrialization has been a mixed blessing to mankind; while it enhances the quality of life, comfort and national gross domestic production, it may also poses a serious threat to the natural ecosystems and the security of public health. Scientific evidence have shown that uncontrolled industrial practices have led to unacceptable high levels of harmful and toxic substances discharged in the air, water bodies and on soils with significant environmental consequences.

Many water bodies in the world are known to flow through major cities and towns to serve as a potential source of water for domestic and industrial use. Such water bodies’ flowing through major towns and cities includes River Ubeji in Warri South Local Government Area of Delta State, Nigeria which supports a wide diversity of both flora and fauna. Some of these water bodies have residential and industrial establishments situated along their course and due to institutional failures discharge their waste into the water causing water pollution and river sediments pollution.

Sediments can be transported by the flowing river water and eventually deposited as layers of soil particles on the bed or bottom of water bodies. These sediments in rivers act as an intermediary between aquatic and terrestrial ecosystems. Sediments act as a carrier and sink for contaminants reflecting the history of pollution and providing a record of catchment input into aquatic ecosystem. When effluents with high heavy metal concentrations are discharged into receiving rivers they may settle down in the sediments and pose imminent danger to the food chains and becomes a potential health risks to humans owing to their toxicity and carcinogenicity.

Due to the ineffectiveness of purification systems, effluents may become seriously dangerous, leading to the accumulation of heavy metals in receiving water bodies and sediments with potentially serious consequences on the ecosystem. This study focuses on the presence of heavy metals from petroleum hydrocarbon in sediments which has been a major source of concern [1].

Description of study area

River Ubeji is located in Ubeji Community, Warri South Local Government Area of the Niger Delta region of Delta State of Nigeria. Ubeji community lies between latitudes 5°34’29” and 5°34’21 north of the Equator and longitudes 5°41’30” and 5°42’02” east of the Greenwich meridian. It covers a land area of about 16 km2. The Ubeji River takes its source from a spring at Ekpan and flows for over 20 km to empty into Escravos River. The Ubeji River serves as the terminal point for storm runoff in the Ubeji community. The inhabitants of Ubeji community and surrounding villages rely on the Ubeji River for some of their domestic water supply, fishing, sand mining and intervillage transportation. The banks of the Ubeji River area is traversed by numerous small dentric drainage pattern draining into Ubeji River. This flat and low relief area often encourage flooding after rain especially during the wet season, mainly because of the heavy rainfall, high groundwater table and the flat-floored valley. The projected population figures by 2022 at 2.8% geometric growth rate was estimated as 28, 168 comprising of Urhobos, Ijaws and the Itsekiris as the largest ethnic group.

Materials and Methods

Bottom sediments from Ubeji River were collected with a Van-veen grab sampler on a weekly basis for a period of 5 months April-August). The sediments were collected in the top layer where the deposition of the suspended material and accumulation of heavy metals occurs. Three samples were collected and mixed together to obtain a representative sample of each sample location. The sediments were labeled S1 (200 m Upstream from point of effluent discharge) S2 (point of effluents discharge) and S3 (200 m Downstream from point of effluent discharge) along the river. The samples were air dried and stored until analyzed for zinc, iron, manganese, lead, chromium, cadmium, and mercury. Table 1 shows the location of the sampling points.

Table 1: Coordinates of sampling points.

Results and Discussion

Tables 2 shows the summary of results of the mean concentration of the heavy metals investigated in Ubeji River sediments at 200 m upstream from point of effluent discharge, at the point of effluent discharge and at 200 m downstream from point of effluent discharge.

Zinc (Zn)

From Tables 2-4 the results shows that the concentration of zinc in the sediments at the upstream ranged from 16.12 mg/Kg to 18.08 mg/Kg with a mean value 17.14 ± 0.89 mg/Kg. At the point of effluent discharge the concentration of zinc ranged from 69.41 mg/Kg to 85.21 mg/Kg with an average concentration of 77.05 ± 6.29 mg/Kg. Similarly at the downstream the zinc concentration ranged from 60.33 mg/Kg to 64.81 mg/Kg. Within the 3 sampling points, the point of effluent discharge recorded 85.21 mg/Kg and 16.12 mg/Kg at the upstream as the highest and lowest concentration of zinc respectively. From the results obtained and when compared to the DPR quality guidelines in estuarine sediments. The 3 sampling points were found to be less than the 90 mg/Kg permissible limits specified and thus safe for benthic organisms [2].

Table 2: Mean and standard deviation of the concentration of heavy metals in Ubeji River sediments at 200m upstream from point of effluent disposal.

Table 3: Mean and standard deviation of the concentration of heavy metals in Ubeji River sediments at point of effluent disposal.

Table 4: Mean and standard deviation of the concentration of heavy metals in Ubeji River sediments at 200 m downstream from point of effluent disposal.

Iron (Fe)

From Tables 2-4 the results show the iron concentration in the sediments. At the upstream the iron concentration ranged from 2.94 mg/Kg to 3.58 mg/Kg with a mean concentration of 3.26 ± 0.28 mg/ Kg. At the point of effluent discharge the iron concentration ranged from 10.79 mg/Kg to 12.58 mg/Kg, with a mean concentration of 11.68 ± 0.73 mg/Kg. Similarly the iron concentration downstream from the point of effluent discharge ranged from 9.84 mg/Kg to 12.58 mg/Kg, with a mean value of 10.77 ± 1.11 mg/Kg. Within the 3 sampling points, the point of effluent discharge recorded 12.58 mg/Kg and upstream recorded 2.94 mg/Kg as the highest and lowest concentrations of iron respectively. From the results obtained and when compared to DPR (2002) sediment quality guidelines in estuarine. The results revealed that all 3 sampling points were less than the 20 mg/Kg permissible limits specified and thus safe to support benthic organisms.

Manganese (Mn)

From Tables 2-4 the results show the manganese concentration in the sediments. From the results obtained, the concentration of manganese in the sediments at the upstream ranged from 19.06 mg/Kg to 21.28 mg/Kg, with a mean concentration of 20.28 ± 0.91 mg/Kg. At the point of effluent discharge the concentration of manganese ranged from 50.49 mg/Kg to 55.56 mg/Kg, with a mean concentration of 52.65 ± 2.14 mg/Kg. The concentration of manganese downstream from the point of effluent discharge ranged from 40.45 mg/Kg to 43.68 mg/Kg with a mean concentration of 41.68 ± 1.23 mg/Kg. From the results obtained and when compared to the DPR sediment quality guidelines in estuarine sediments. The values in sediments sampled at upstream and downstream from the point of effluent discharge were below the permissible limits 46 mg/Kg, except for the point of effluent discharge that recorded an mean value of 52.65 ± 2.14 mg/Kg which is above the specified limits and likely to cause harm to benthic organisms.

Lead (Pb)

From Tables 2-4 the results shows the lead concentration in the sediments at the upstream ranged from 10.42 mg/Kg to 11.06 mg/ Kg with a mean value of 10.69 ± 0.24 mg/Kg. At the point of effluent discharge the lead concentration ranged from 41.10 mg/Kg to 60.06 mg/ Kg, with a mean concentration of 47.04 ± 7.86 mg/Kg. Similarly at the downstream the lead concentration ranged from 10.06 mg/Kg to 10.26 mg/Kg, with a mean concentration of 10.12 ± 0.08 mg/Kg. Within the 3 sampling points, the highest and lowest values where recorded as 60.06 mg/Kg and 10.06 mg/Kg at the point of effluent disposal and at the downstream respectively. From the results obtained the concentration of lead in sediments at the upstream and downstream were below the permissible limits of 31 mg/Kg by DPR (2002) for sediment quality guidelines in estuarine sediments. However the point of effluent discharge recorded an average value of 47.04 ± 7.86 mg/Kg which is above the specified limits to support benthic organisms.

Chromium (Cr)

From the results obtained as presented in Tables 2-4 the concentration of chromium in the sediments at the upstream ranged from 28.0 mg/Kg to 40.59 mg/Kg, with a mean value of 36.14 ± 5.21 mg/ Kg. At the point of effluent discharge the concentration of chromium ranged from 52.66 mg/Kg to 62.99 mg/Kg, with a mean concentration of 56.87 ± 4.32 mg/Kg. The concentration of chromium at the downstream ranged from 35.91 mg/Kg to 47.17 mg/Kg, with a mean concentration of 43.39 ± 6.87 mg/Kg. From the results obtained and when compared to the DPR sediment quality guidelines in estuarine sediments. The concentration of chromium in sediments sampled at the point of effluent discharge and at the downstream were both above the permissible limits of 40 mg/Kg, except at the upstream from the point of effluent discharge that recorded an average concentration level of 36.14 ± 5.21 mg/Kg which is below the specified limits and thus safe to support benthic organisms.

Cadmium (Cd)

From the results presented in Tables 2-4, the concentration of cadmium in the sediments at the upstream ranged between 1.43 mg/ Kg to 1.92 mg/Kg with a mean concentration 1.69 ± 0.19 mg/Kg. At the point of effluent discharge the concentration of cadmium ranged between 2.41 mg/Kg to 3.05 mg/Kg with a mean concentration of 2.77 ± 0.26 mg/Kg. The concentration of cadmium downstream from the point of effluent discharge ranged from 1.62 mg/Kg to 2.25 mg/ Kg with a mean concentration of 1.92 ± 0.26 mg/Kg. From the results obtained and when compared to the DPR sediment quality guidelines in estuarine sediments, the concentration of cadmium in sediments sampled at all sampling point were all above the permissible safe limits of 0.60 mg/Kg and thus not safe to support benthic organisms [3].

Mercury (Hg)

From the results presented in Tables 2-4, the concentration of mercury in the sediments at the upstream ranged from 0.02 mg/Kg to 0.06 mg/Kg with a mean concentration of 0.05 ± 0.02 mg/Kg. At the point of effluent discharge the concentration of mercury ranged from 0.16 mg/Kg to 0.29 mg/Kg with a mean concentration of 0.21 ± 0.05 mg/Kg. The concentration of mercury at downstream from the point of effluent discharge ranged from 0.04 mg/Kg to 0.29 mg/ Kg with a mean concentration of 0.18 ± 0.10 mg/Kg. From the results obtained and when compared to the DPR sediment quality guidelines in estuarine sediments. The average concentration of mercury sampled at all sampling point were below the permissible safe limits 0.20 mg/ Kg, except for the point of effluent discharge that recorded an average concentration of 0.21 ± 0.05 mg/Kg which is above the specified safe limits to support benthic organisms (Figure 1).

Figure 1: Mean concentration of heavy metals at sampling points.

Summary of Findings

A lot of researchers have used water from natural water bodies as pollution indicator, but sediment have been known to provide a better and more accurate insight into long-term pollution state of aquatic environment (Ogbeibu, et al 2014., Yau and Gray 2005). Sediments have been described as sink of pollutants whereby they accumulate various levels of pollution. This study revealed that the sediments sampled from the Ubeji River recorded the following mean concentrations, at 200 m upstream from the point of effluent discharge. Zinc (17.14 mg/Kg), iron (3.26 mg/Kg), manganese (20.28 mg/Kg), lead (10.68 mg/Kg), chromium (36.14 mg/Kg), cadmium (1.69 mg/Kg), and mercury (0.05 mg/Kg). The results obtained shows that all the heavy metals investigated at the upstream fell within the DPR (2002) limits for the survival of aquatic organisms except for cadmium. At the point of effluent discharge, the mean concentrations were zinc (77.05 mg/ Kg), iron (11.68 mg/Kg), manganese (52.65 mg/Kg), lead (47.04 mg/ Kg), chromium (56.87 mg/Kg), cadmium (2.77 mg/Kg), and mercury (0.21 mg/Kg). The result shows that lead, manganese, chromium and cadmium were above the DPR (2002) limits for the survival of aquatic organisms. Analysis by ANOVA showed that there was no significant impact of refinery effluent on the quality of Ubeji River sediments at the sampling stations under investigation at 5% significant value.

Recommendations

In the light of the research findings the following recommendations were made:

The Warri Refinery and Petrochemical Company and other companies operating in the catchment area of Ubeji River need to maximize the treatment of their effluents, as some parameters investigated were found to be above the WHO and DPR acceptable limits.

Land use planning should form the basis of management planning for Ubeji River water quality control and protection since the land cover within the Ubeji community area is characterized by increase in settlements, which include urban developments, sewage and industrial effluents which are threats to the Ubeji River water quality. The growth rate of urbanization should also be slowed down within the Ubeji area and be extended to other areas.

The Federal Environmental Protection Agency (FEPA) need to intensify monitoring and mitigation exercises of Ubeji River as it serves as source of water, fish supply and livelihood to the community along the river course.

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