Rising levels of domestic wastes in urban communities as a result of rapid industrialization marked by huge developmental strides prompted the need to study heavy metal contamination levels in river sediments which have become a global worriment and have earned ample attention due to the lethal and persistent nature of heavy metals in marine and freshwater systems (Sun et al., 2019; Ali et al., 2019). Stream deposits store and transport considerable volumes of heavy metals (Guo et al., 2018; Li et al., 2020). Heavy metals are elements with a specific density of 5.0 or higher and are toxic to organisms and the environment when their concentration levels exceed the permissible limit. They are resistant bio-accumulative contaminants in the environment, and their toxicity is due to their metal structure (Patel et al., 2018). Heavy metals, similar to other metals in stream sediments, are sourced from the breakdown of bedrock, pesticides and fertilizers from agricultural runoff, combustion of fossil fuels, sewage disposal, irrigation of wastewater, industrial and municipal wastes, mining activities, ore smelting, emissions from vehicles and deposition from the atmosphere (Guo et al., 2018; Li et al. 2020).

Heavy metals pose a health threat to living organisms or human consumers once they enter the food chain (Strady et al., 2017; Raut et al., 2017; Xu et al., 2017; Patel et al., 2018). Thus, understanding their concentration levels in stream sediments is vital for assessing river system protection (Li et al., 2020). In terrestrial ecosystems, soils are the major recipient of heavy metals. In contrast, sediments are the primary sink for metals in the aquatic ecosystem; thus, various media are analysed to monitor, assess, and control metal pollution in the environment (Kruopiene, 2007). In the hydrological cycle, 99% of contaminants are stored in sediments, with just 1% dispersed in water (Paramasivam et al., 2015). The bulk of contaminants that are stored in sediments over time will sink and become major pollutants in the aquatic environment (Paramasivam et al., 2015; Nazneen & Patel, 2016; Patel et al., 2018). Hence the analysis of sedimentary deposits from the river system is of significant interest in aquatics system study. Sedimentary deposits indicate the present quality of the aquatic system and also provide relevant clues on the impact of contamination sources. River sediments studies have been performed internationally to comprehend the source, carrier and accretion of heavy metals in aquatic systems (Malvandi et al., 2017; Xu et al., 2017; Nawab et al., 2018; Vu et al., 2018; Patel et al., 2018; Chen et al., 2018; Omwene et al., 2018; Zhang et al., 2019; Li et al., 2020). Various tools have been advanced to appraise the potential risk to the environment and organisms as a result of the presence of heavy metals in stream deposits (Li et al., 2020), and these help in aquatic and environmental management (Vu et al., 2018; Patel et al., 2018; Ji et al., 2019).

Amudo Ezza is situated in Ezza South Local Government Area of Ebonyi province, southeastern Nigeria, within the Lower Benue Trough Basin Figure 1. The study area is known for Lead-Zinc mineralization and also the occurrence of Galena and Sphalerite (Igwe et al., 2015; Obiora et al., 2016); thus, this has led to the increase in artisanal mining accompanied by an associated rise in environmental and health challenges (Dondeyne et al., 2009; Huang et al., 2010; Dooyema et al., 2012; Plumlee et al., 2013; Bello et al., 2016; Yabe et al., 2018; Tabelin et al., al., 2020). Entrepreneurship, mining activities and small to large-scale farming are the primary sources of livelihood in the Ebonyi province of the eastern region of Nigeria (Obiora et al., 2016; Okolo & Oyedotun, 2018). Due to the poor management and regulation of the mining sector in Nigeria, most mining activities are prompted by artisanal and small-scale miners, who make up about 95% of miners in Nigeria (Lawal, 2002; Oramah et al., 2015). Oramah et al. (2015) reported that over 500,000 people are directly employed by artisanal and small-scale mining in Nigeria. Hitherto, the economic benefits that come from creating jobs, the risk that artisanal, open cast and small-scale mining poses are great due to the challenges tangled with the coordination and adequate monitoring of such enterprises (Twerefou, 2009; Ochieng et al., 2010; Oramah et

al., 2015). Surface runoff can carry heavy metals associated with pesticides, fertilizers from agricultural activities and toxic metals associated with mining-related activities and deposit these poisonous metals into tributary and stream sediments. Therefore, this could lead to heavy metal contamination, affecting the ecosystem and human health in Ebonyi province (Okolo & Oyedotun, 2018).

The pollution and contamination of Pb, Cd, Zn, and Cu in soils around Enyigba have been studied, but there is a paucity of research on the stream sediments of Amudo-Ezza (Chukuma, 1994; Ezeh, 2007). Heavy metal pollution in Abakaliki Ebonyi province has led to persistent cardiovascular diseases in inhabitants around Lead-Zinc mineralization areas where mining activities are the primary source of livelihood (Okogbue & Ukpai, 2013). Contamination of water bodies by heavy metals in Enyigba, Abakaliki Ebonyi province has been reported by Ezeh & Anike, 2009; Nnabo, 2016; Igwe et al., 2015; Okolo & Oyedotun, 2018; Aloke et al., 2019; Obiora et al., 2019. Other researchers have observed higher than acceptable concentration limits of Pb, Cd and Ni in agricultural soils in the regions around the study area. At the same time, traces of heavy metals have also been observed in bouillon cubes and food condiments in some eastern states in Nigeria (Orisakwe et al., 2012, Obiora et al., 2016). Ogbodo (2011) accessed the soil fertility of the Iyiudene floodplain, Iyiokwu floodplain, Ebonyi river basin and upland areas in Abakaliki, eastern Nigeria. The research revealed low soil fertility for agricultural purposes. Also, Ali et al. (2019) posited that heavy metals could disturb metabolic processes and genetic makeup while also affecting foetal development, eventually leading to cancer and other developmental anomalies observed in some children. Hence there is a pertinent need to study the stream sediments in the study area owing to the fact the streams serve as a source of survival for residents of the area. Opencast mining is suggested to be the main contributor to heavy metal pollution in the eastern region of Nigeria (Okogbue & Ukpai, 2013; Okolo et al., 2015; Nnabo, 2016; Okolo & Oyedotun, 2018). Recently, Egbueri et al. (2020) reported heavy metal pollution of As, Cd, Co, Ni, Pb and Se in hand-dug wells and boreholes in Ameka district Ezza south local government area Ebonyi state. Onu-umpku ufie, Ndende, Onuebonyi and Ogbachi in Amudo-Ezza are vital tributaries in Ebonyi province in southeastern Nigeria and serve as the sources of surface water resources to over 150,000 people (NPC, 2007). These toxic metals that get attached to surface particles of the stream deposits can easily be released into the stream water and thus will be eventually ingested by the inhabitants who rely on surface water for domestic purposes and aquatic organisms. Therefore, there is a need to provide new insights into the contamination levels of stream sediments in the River Iyiudene Amudo-Ezza in southeastern Nigeria.

Based on a literature search of the present study area, no published work assessed the contamination status of stream sediments of River Iyiudene and the effects of these selected toxic metals on the ecosystem and humans. Therefore, in the present research, stream sediments were collected from Rivers Onu-umpku ufie, Ndende, Onuebonyi and Ogbachi in Amudo-Ezza, southeastern Nigeria and were analysed to (I) decipher the dispersion levels of heavy metals (lead, zinc, copper, cadmium, arsenic and nickel) (II), assess the contamination levels of the selected heavy metals using different techniques, Single pollution index (PI), Geo-accumulation index (Igeo), and Correlation matrix and (III) decipher the potential sources of the heavy metals in Amudo-Ezza stream deposits and how they affect the environment and its residents. Heavy metal assessment in River Iyiudene stream sediments would provide insights into the quality of the ecosystem.

The study area Amudo-Ezzai is situated in Ebonyi county, eastern Nigeria, which is bounded by coordinate readings 6˚03'N and 6˚08'N and Longitude 7˚58'E and 8˚03'E covering a total area of about 81 km² (Figure 1). Amudo-Ezza is within the Abakaliki Shale of the Asu River Group. Geologically the study area consists of Cretaceous deposits of the Asu river group belonging to the Benue Trough. The Benue Trough was developed due to the break-up of the South American continent from the African continent in the Early Cretaceous (Obaje et al., 2004). The Asu River group comprises shales, mudstones and sandstones.

The study area comprises shales, and mudstones, which appeared brown to dark grey, weathered, fissile and jointed. Also, the shales and mudrocks are embedded by the vein mineralization of lead-zinc and baked shales that are intrusive along veins (Nnabo et al., 2011). The lead-zinc vein mineralization is accommodated inside the grey to dark grey shales (Nnabo et al., 2011). The general trends of the beds were in the NE-SW direction, which corresponds to the significant trend in the Benue trough. The wet (i.e. rainy), and dry seasons are the two distinct seasonal intervals in the study area. The rainy season commences in early March and stops around October, while the dry season runs from October to February. The two seasons are controlled by the two prevalent winds, which blow over the nation in separate year periods (Odoh et al., 2012). The dry harmattan wind which blows from the Sahara Desert occurs in the dry seasonal period.

In contrast, during the rainy season, the significant wind is the marine wind which blows from the Atlantic Ocean (Odoh et al., 2012). The average temperatures during the dry seasonal period are between 20˚C to 38˚C, and during the rainy seasonal period is from 16˚C to 28˚C (Odoh et al., 2012). The normal monthly precipitation ranges from 3.1 mm in January and 270 mm in July. The average yearly precipitation varies from 1750 mm to 2250 mm (Aghamelu et al., 2011; Odoh et al., 2012).

Five main rivers (Onu-umpku ufie, Ndende, Onuebonyi, Ogbachi and Cross River) form the tributaries that drain the geological units and transport a large amount of sediments within the ecosystem in Ebonyi, eastern Nigeria. The geochemistry of stream sediments of Amudo-Ezza is less studied; thus, this research will provide new information on the heavy metal dispersion levels in eastern Nigeria.

A topographic map was used to locate the various streams and river channels for the fieldwork and sample collection. A Global positioning system (GPS) was used to read the latitude and longitude coordinates of the sampling points. Also, a hand trowel, a scoop, and sample bags were used to collect the stream sediments. Stream sediment sampling was conducted during the dry season. The sampling interval was 400m along the stream channels. A total of 20 samples were taken from the centre of the river channel at separate points. To avoid surface contaminants, the samples were scooped from the 10 - 15 cm depth range. The stream sediments from the fieldwork and sampling were air-dried at room temperatures for a week. They were subsequently crushed and sieved through 177-μ sieve size fractions using nylon screens. Nitric acid (HNO3), Hydrochloric acid (HCl), deionised water, beakers and volumetric flasks were employed in the elemental decomposition (digestion) stage. Finally, an atomic absorption spectrophotometer (AAS) was used in the elemental analysis of six heavy metals: Pb, Zn, As, Cd, Cu and Ni.

Heavy metal dispersion and concentration levels of the analyzed six heavy metals in the stream sediments are shown in Table 1. The concentration values are reported in mg/kg. The distribution pattern of the heavy metals shows wide variation pattern; the values in mg/kg are Pb: 1.3 - 9.4, Zn: 11.1 - 38.5, Cu 0.1 - 13.3, As: 0.1 - 0.6, Cd: 0.1 - 9.7 and Ni: 0.1 - 7.8 (Figure 2). Statistical data of the stream sediments is presented in Table 2. The mean contents of these heavy metals in the stream sediments took the order Zn > Cu > Pb > Cd > Ni > As, which is similar to the concentration levels reported in stream sediments of River Orle, Nigeria (Adepoju & Adekoya, 2014). The concentration levels of the heavy metals were low when correlated with sediments from Imo River, southeastern Nigeria (Ekwere et al., 2013), Gulf of California sediments (Brumsack, 1986), upper continental crust (UCC) (Taylor & McLennan, 1985), Average shale and surface horizons worldwide (Kabata-Pendias, 2010) and excluding Cd, which was available at higher concentration than in Imo river and UCC.

Several authors have argued that the increasing spate of cardiovascular diseases in eastern Nigeria can be blamed on the open-cast mining practices in the region; hence the need to assess the heavy metal concentration in sediments recovered from the study area was the main motivator for this research. Stream sediments were sampled from the River Iyiudene, Abakaliki, south-eastern Nigeria, and assessed to determine the concentration and contamination levels of six heavy metals, including Pb, Zn, Cu, As, Cd and Ni. The results delineated a wide contrast in the concentration levels of the heavy metals, with the mean contents in the order Zn > Cu > Pb > Cd > Ni > As. The heavy metal concentration levels in River Iyiudene were low compared with sediments from Imo River, Gulf of California, Upper continental crust, Average shale and surface horizons, excluding Cd, which showed high concentration levels than the other reference studies. The concentration of Pb, Zn, Cu, As and Ni in all the sampled locations was below the ERM and ERL limits; thus, their concentration levels are below the toxic limit and pose no threat to the ecosystem. In contrast, the Cd concentration in Nine (9) sample locations was above the ERL limits, and one sample location was above the ERM limits. Therefore, the Cd concentration in this study poses a plausible biological risk to the ecosystem.

Multiple approaches were applied to determine the heavy metallic contamination of the stream sediments. The single pollution index showed no pollution from heavy metals of Pb, Zn, Cu, As, and Ni, whereas Cd revealed no pollution to strongly polluted sediments. The geo-accumulation index revealed no pollution from Pb, Zn, Cu, As, and Ni. In contrast, the Igeo values for Cd indicate no pollution through moderate to high pollution. Correlation analysis showed a moderate positive correlation exists between Zn and Pb alone. Our findings revealed Cd pollution in the study area, which needs to be monitored due to the toxic effect of Cd on the ecosystem and Humans. High Cd concentration in the stream sediments of River Iyiudene is sourced from the geological background of the river basin and anthropogenic processes. It is noteworthy that there are other avenues through which pollution can occur, including hydrophobic organic contaminants; hence we recommend that other works be designed to investigate this and other contaminants present in the sediments.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

The authors declare no conflicts of interest regarding the publication of this paper.

Nwazue, E. U., Omietimi, E. J., Mienye, E., Imarhiagbe, O. J., Adeosun, O. A., & Nnabo, P. N. (2022). Heavy Metal Dispersion in Stream Sediments in River Iyiudene, Abakaliki South-Eastern Nigeria: Source, Distribution Pattern, and Contamination Assessment. Journal of Geoscience and Environment Protection, 10, 48-69. https://doi.org/10.4236/gep.2022.107004