Evaluation of human health and ecological risk of heavy metals in water, sediment and shellfishes in typical artisanal oil mining areas of Nigeria

Heavy metal contamination in water and sediment is a serious concern in nations that depend heavily on natural resources such as Nigeria. In most coastal communities around oil mining areas in Nigeria, drinking water quality, staple food, and livelihoods are primarily dependent on ecological systems and marine resources (e.g., fish). Thus, humans and other receptors are exposed to heavy metal risks through ingestion and dermal contact. This research evaluated the potential ecological risks of heavy metals including Cadmium (Cd), Chromium (Cr), Nickel (Ni), and Lead (Pb) in water, sediments, and shellfishes (Callinectes amnicola, Uca tangeri, Tympanotonus fuscatus, Peneaus monodon) along the Opuroama Creek in Niger Delta, Nigeria. The concentrations of heavy metals were measured in three stations using the Atomic Absorption Spectrophotometer and their relative ecological (geo-accumulation index and contamination factor) and human health risk (hazard index and hazard quotient) analysed. The toxicity response indices of the heavy metals indicate that the sediments pose significant ecological risk particularly with Cd. None of the three exposure pathways to heavy metals in the shellfish muscles and age groups pose a non-carcinogenic risk. Total Cancer Risk values for Cd and Cr exceeded the acceptable range (10−6 to 10−4) established by USEPA in children and adults, raising concerns of potential cancer risks following exposure to these metals in the area. This established a significant possibility of heavy metal risks to public health and marine organisms. The study recommends conducting in-depth health analysis and reducing oil spills while providing sustainable livelihoods to the local population.


Introduction
The most critical challenges the sustainable development goals aspire to address include public health and environmental safety. Heavy metal contamination undermines environmental safety and causes harm to public health and the global environment (CDCP 2022). Thus, it is a focal point of new research and drives efforts to achieve One Health objectives. Heavy metals are metallic elements with atomic weights and densities that exceed those of water and occur naturally (Ahmed et al. 2022). In developing countries where suitable pollution control measures are yet to be implemented (Sam et al. 2022), environmental media contain numerous toxic compounds, including heavy metals from multiple sources (Priya et al. 2014). As a result, heavy metal pollution contributes to the disease burden and causes various non-communicable and infectious diseases.
Nigeria is a natural resources-dependent economy in Sub-Saharan Africa. The Niger Delta region of the country is the hub of oil exploration and exploitation. With a population of over 45 million people and a landmass of 70,000 km 2 , the Niger Delta hosts several oil infrastructures, onshore and offshore, and accounts for over 95% of Nigeria's foreign exchange. In the last six decades, oil exploration activities 1 3 have resulted in the contamination of over 5000 sites in the region (Nwozor 2019), degrading an extensive expanse of mangroves, farmlands and water bodies (Onyena and Sam 2020;Sam et al. 2022). As a result, farming activities have reduced significantly and affected the local economy (Sam and Zabbey 2018).
Sediment and water contamination in Nigeria are mainly caused by anthropogenic activities. The unregulated use of agrochemicals (including pesticides, herbicides and fertilizers) in agriculture contributes to the burden of contamination in the aquatic ecosystem. Surface runoff from land-based waste sites, including indiscriminate dumping of mixed waste (including chemical waste), and solid wastes in the aquatic environment also contribute to hazardous waste in the marine environment (Weldeslassie et al. 2018;Akhtar et al. 2021). Most importantly, the unregulated discharge of effluent from the oil industry (Sam et al. 2015), oil spills from mining activities (including artisanal and conventional oil operators), smelters, and black carbon have been described as the primary source of hazardous heavy metal pollution in the Niger Delta region of Nigeria (Sankhla et al. 2016;Weldeslassie et al. 2018;Sonone et al. 2020).
Recently, increased hydrocarbon contamination, has significantly reduced livelihood opportunities such as seafood harvesting, and has affected fish breeding areas and increased fish deaths (Trathan et al. 2015;Fentiman and Zabbey 2015). This has limited local communities' access to marine resources and exposed them to potential public health risk factors and associated socio-economic burdens. However, considering the dependence of the local population on the ecosystem to create employment, improve livelihood (Sam and Zabbey 2018;Onyena and Sam 2020), and the need to meet these essential needs, they now engage in artisanal oil mining and refining activities (Naanen 2019), with limited capacity to handle hazardous hydrocarbon waste (e.g., waste oil) arising from the process. These artisanal oil mining activities are undertaken in the creeks and mangrove ecosystems, where stolen hydrocarbon is heated at various temperatures to derive petrol, diesel and kerosene. In the process, significant hazardous wastes are released into environmental media with varying levels of socio-economic, environmental and public health risks (Whyte et al. 2020;Sam et al. 2017;Zabbey et al. 2021).
In the last decades, several studies have reported high levels of heavy metals in soil (Okereke et al. 2016;Agbai and Efenudu 2022), sediment (Babatunde et al. 2015;Nwipie et al. 2019), and water bodies (Marcus and Edori 2016;Sagbara et al. 2020) in different coastal communities in the Niger Delta region. Hazardous heavy metals (e.g., Hg, Pb, Cr, Cu, Zn, Cd, Mn, Ni, and Ag) are metallic, toxic in low quantities, and persistent (Emeka and Emeka 2020), which makes eliminating them from the environment difficult . They can successfully exert their toxicity through variable means including dermal contact, inhalation and ingestion pathways from sediments and water, and negatively impact human health. Once they bioaccumulate in the human body, they have the capacity to affect brain function, irritate the digestive system, damage lipids and protein synthesis and enhance osteoporosis . As they interfere with the food chain, aquatic animals may die due to nutrient pollution (e.g., phosphates and nitrogen) contained in toxic algae (Zohdi and Abbaspour 2019;Madhav et al. 2020). Considering these ecological and environmental contaminants and the likelihood of exposure of the local population (as they are present in water and seafood), this study evaluates the presence of four heavy metals in water, sediment and shellfish to assess the potential ecological and public health risks of heavy metals to the local population.

Study area
The study was carried out along the Opuroama Creek located in Asari-Toru Local Government Area of Rivers State (Fig. 1), in the Niger Delta region of Nigeria. The creek is a joint tributary of the Sombrero Estuary, one of the 21 estuaries in the Niger Delta geomorphic unit of Nigeria's extensive (approximately 853 km) coastline, and located Southeast of the Niger Delta between longitude N04° 48′ 14.0″ and latitude E06° 50′ 16. The creek consists of the main channel and associated feeder creeks linking other communities like Te-ama, Sangama, Abalaama, Degema, Krakrama and other riparian communities. The creek hosts massive oil infrastructure including oil pipelines, well heads and stations and are prone to artisanal and conventional oil spills. The local population are mainly farmers and fisherfolks, involved in periwinkle picking (Tympanotonus fuscatus), and the distribution of seafood locally and regionally to the tourism industry, as a livelihood measure for economic stability.
The tidal influence is frequent and vigorous such that pollutants from various sources are presumed to be evenly dispersed in the environment. The Lutjanidae, Clupeidae, Cichlidae and Claroteidae are among the main fish families in this ecosystem but the most common are the Claroteidae (the silver catfish and tilapias) (Davies and Ekperusi 2021), which are critical staple foods in the area. The tidal mudflat species include gobies, periwinkles, crabs, and mudskippers, which are traded daily for subsistence and sustenance in the region.
The mangrove vegetation of the area comprises Rhizophora racemosa, R. mangle and R. harrisonii (red mangrove), Avicennia germinans (white mangrove), Laguncularia racemosa (black mangrove) and Conocarpus erectus (buttonwood). There is a contiguous presence of mangrove associates such as Acrostichum aureum (mangrove fern) and Paspalum vaginatum (mangrove sedge). In terms of relative species abundance, the mangrove is typical of the broader Niger Delta mangrove composition, characterized by the dominance of R. racemosa. Sediments of the studied sites were uniformly consolidated spongy and highly fibrous "chicoco" peaty mud characteristic of many mangrove swamps of the Niger Delta . The study area is also characterized by human threats to this mangrove swamp. Threats include illegal refining and bunkering activities, sand dredging and deliberate cutting of juvenile mangroves. The section of the river studied lies within Station 1 (longitude 04°48′14.8″ N-06°50′17.9″ E latitude), Station 2 (longitude 04° 48′14.2″ N-E06°50′17.1″ E latitude) and Station 3 (longitude 04°48′13.2″ N-E006° 50′16.9″ E latitude) (Fig. 1).

Sampling procedure
A total of three stations were chosen and were at least 1 km apart along Opuroama creek (Fig. 1). The three selected sample stations were based on the peculiarities and characteristics of the creek such as proximity to the oil refining sites, depository of spilt oil, and anthropogenic activities around the location. Samples collected for analysis include water, sediment and biota (Shellfishes), as shown in Fig. 2 Panels A, B, C, and D. While the biota sampling process which involves the collection of the different shellfish from Opuroama creek and the nets used is represented in Panel E, F, G, and H. All sites were geo-referenced using a handheld global positioning system (GPS) receiver unit (Magellan GPS 315) to generate geographic coordinates of the sampling area.

Water sample
To obtain interstitial water, three pits were dug randomly at each sample station's intertidal flat to a specified depth range (3-5 cm). The interstitial water samples were collected by

Sediment sample
A grab bottom sediments samples were collected once a month in composite from three different stations using an Ekman grab sampler (EG 15) which has a volume of 3L and sampling area 15 × 15 cm, weight of 3 kg and a closed size (height × width × depth) 330 × 190 × 200 mm (Muli 2005) and kept in a plastic container previously treated with 10% nitric acid for 24 h and rinsed with de-ionized water to prevent absorption of heavy metals through the walls of the container (Sankhla et al. 2019). It was dried, sieved and weighed before it was taken to the laboratory for analysis.

Shell fish
The swimming crabs (Callinectes amnicola) were caught using a dragnet while the Mudflat crab (Uca tangeri) were collected randomly from their hideout in the mud using a crab trap. Periwinkles (Tympanotonus fuscatus) were handpicked from the mud flat, while the Tiger shrimps (Penaeus monodon) were caught using a dragnet. The average shell length and weight of periwinkles are 5.4 ± 2.5 cm and 9.75 ± 0.02 g while the average carapace length and weight of swimming crabs are 9.1 ± 2.6 cm and 334 ± 2.3 g respectively. The average carapace length of the Mudflat crab is 4.71 ± 0.11 cm and the weight is 38.3 ± 2.5 g while the average carapace length and body weight of the Tiger shrimps was 8.4 ± 2.09 cm and 26.9 ± 0.28 g. Sampling was conducted monthly from January 2018 to December 2018 at the three sample stations. The samples collected were persevered in an ice pack before being transported to the Centre for Marine Pollution Monitoring and Seafood Safety Laboratory (CMPM & SSL), University of Port Harcourt, Rivers state, Nigeria for heavy metal concentration analysis using Atomic Absorption Spectrometer (AAS) method as recommended by APHA (1999) standards.

Pre-processing of samples
The samples were transported each month directly from the sampling location to the CMPM & SSL laboratory in Port Harcourt, Nigeria (approximately 50 km). The processing of samples were carried out monthly after each sampling before taking to the laboratory. In the laboratory, all organisms were transferred to 30 L aerated tanks with simulated brackish water (20 g/L NaCl) and living/dead organisms were counted. The sampled species were identified using the FAO species identification guide for fishery purposes (Carpenter and Niem 2001). All living organisms were depurated without feed for 18-24 h. Organisms from each sampling sub-site were stored in dedicated tanks for the entire period of depuration. Following the depuration period, all the muscles of shell fish species were dissected and stored in refrigerators at 4 °C. The temperature (4 ± 0.3 °C) of the refrigerators was monitored and recorded twice daily.

Determination of heavy metals
The elements Cadmium (Cd), Chromium (Cr), Nickel (Ni) and Lead (Pb) were determined at standard wavelength using the Atomic Absorption Spectrophotometer (AAS) method as recommended by APHA (1999) standards. The samples were digested using concentrated Analar nitric acid according to Zhang (2007). The Atomic Absorption Spectrophotometer (Model PYE UNICAM SP9; Philips Pye Unicam Ltd., York Str., Cambridge CBl 2PX, England) with acetylene-air fame was used for the determination of heavy metals.

Quality assurance/quality control (QA/QC) and statistical analysis
The current study used stringent QA/QC standards. The dissecting tools and sampling containers were cleaned by soaking in 15% HNO 3 (w/w) for at least 24 h prior to usage. They were then rinsed with distilled water and dried. Sterile lab gloves and nasal masks were worn throughout the experiment to prevent sample contamination. To reduce errors, each reading was recorded in triplicates. Method blanks were used in the experiment for quality control, and standard sediment reference materials were used to evaluate the experimental accuracy and precision. Analytical-grade reagents were used for all of the experimental reagents.

Statistical analysis
A one-way Analysis of Variance (ANOVA) test was conducted to evaluate the difference between the means of temporal and spatial variations in metal concentrations. Tukey Pairwise test was used to determine significant differences. The potential ecological risk index (PERI), the geo-accumulation index (I geo ), the Contamination Factor (C f ) and the Degree of Contamination (DC) were calculated to assess the contamination risks and adverse effects of heavy metals on aquatic organisms. Human health risk assessments were conducted to determine carcinogenic and hazard index values related to ingestion, inhalation, and skin contact with organisms.

Potential Ecological Risk Index (PERI)
The index is calculated using the Hakanson (1980) formula (1) outlined below: where n = the number of heavy metals and E r = single index of the ecological risk factor calculated using the following formula (2) below: The Tr is "toxic-response" and C f is contamination factor for a given metal; Ni = 5, Cd = 30, Cr = 2, Cu = 5, Zn = 1 and Pb = 5 (Hakanson 1980). The potential ecological risk classification is given as low risk (< 110), moderate risk (< 110 ≤ RI < 200), considerable risk (200 ≤ RI < 400), and severe Risk (> 400).

Geo-accumulation index (Igeo)
The index of geo-accumulation has been widely used for the assessment of sediment contamination (Islam et al. 2014). There are seven grades of the index, ranging from 0 to 6, with each grade having its unique number of points (Uncontaminated to extremely contaminated). It is calculated using the formula (3) below: where, C n is the mean concentration of the heavy metal in the water samples analysed. B n is the reference value.

Contamination factor (C f )
The Contamination factor (C f ) is expressed as the ratio between the content of each metal to the background value (Hakanson 1980). The Contamination factor (C f ) was calculated using the following formula (4); where C metal is the mean metal content in sample sediment, and C background is the mean natural background value of the metal. The heavy metal standards were used as natural background values. The ratio of the measured concentration to the natural abundance of a given metal had been proposed as the index. C f is classified into four grades for monitoring the pollution of a single metal over a period of time (Ali et al. 2016). These four grades include low degree (C F < 1), moderate degree (1 ≤ C F < 3), considerable degree (3 ≤ C F < 6), and very high degree (C F > 6).

Degree of contamination (DC)
The degree of contamination has been used by Essien et al. (2019) to calculate the risk of heavy metals in municipal solid waste dumpsites. The equation is given by where Cf 1 is the contamination factor of metal. DC greater than 24 is considered a very high degree of contamination while DC ≤ 6 is a low degree of contamination.

Human health risk assessment
Heavy metals have been classified by the International Agency for Research on Cancer (IARC) based on their ability to induce carcinogenesis. Elements including Cd, Cr, Pb, and As have been categorised as carcinogenic, whereas Cu, Zn, Fe, Ni, Mn, and Co have been classified as non-carcinogenic. There are three pathways including ingestion, inhalation (accidental and intentional), and skin absorption (Luo et al. 2012), through which heavy metals can penetrate the human body and potentially cause harm. Chronic daily intake (CDI) helps in assessing the health risk caused by exposure to heavy metals through different pathways. CDI is calculated using Eqs. (6), (7), (8), below: where CDI ing CDI der and CDI inh (mg/kg/d) represent the chronic daily intake of heavy metals through ingestion, dermal contact and inhalation respectively. C is the heavy metal concentration in the target sample. IR ing (mg/d) and IR inh (m 3 /d) are ingestion and inhalation rates of the target sample; EF is the exposure frequency (day/year); ED is the exposure duration (year); SA is the posed surface area of the skin (cm 2 ); AF is the adherence factor (kg/m 2 /day); ABS is the dermal absorption factor; PEF is the particle emission factor (m 3 /kg); BW is the body weight (kg); AT is the average time (day). The values used are represented in Table 1.

The hazard index (HI)
It is the sum of the hazard quotient (HQ) and is used to assess the overall potential non-carcinogenic risk posed by measured heavy metals. It represents the cumulative non-carcinogenic risk. It is the sum of HQs for similar toxic effects and all pathways. It is calculated using Eqs. (9) and (10): where RfD denotes the reference dose, based on the guidelines of the US Environmental Protection Agency for health risk assessment calculation. If HI is greater than one (1), non-carcinogenic effects of heavy metals on an exposed individual may occur. If the HI is below one, the exposed (8) CDI inh = C I xIR inh xEFxED PEFxBWxAT

Carcinogenic risk assessment (CR)
The carcinogenic risk is calculated as individual lifetime cancer risk by multiplying chronic daily intake doses (CDI) with cancer slope factor (CSF) (mg/kg/day). The carcinogenic risk (CR) was calculated using the formula below;

Results and discussion
The heavy metal concentrations in the water, sediment and biota from Opuroama Creek are presented in Table 4.

Concentrations of the heavy metals in the water
The levels of Cd, Ni, Pb, and Cr in the water followed the sequence: Pb > Cr > Ni > Cd with Pb recording the highest value of 0.595 ± 0.45 mg/L, followed by Cr (0.085 ± 0.08 mg/L), and the least value was reported in Cd (Table 4) (2016) reported a concentration of up to 3 mg/L of Cr in the Oginigba River. The levels of Cd, Ni, Pb, and Cr in the water samples collected from the Niger Delta region showed significant variability, with some exceeding the recommended limits set by the NESREA and World Health Organization (2017). These findings underscore the importance of regular monitoring and implementation of effective management strategies to prevent further contamination and ensure the safety of water resources for both human consumption and environmental sustainability.

Concentrations of the heavy metals in the sediments
The levels of Cd, Ni, Pb, and Cr in the sediment followed the sequence: Cd, Ni, Pb, and Cr > Cd > Pb > Ni with Cr recording the highest value (0.506 ± 0.31 mg/kg) followed by Cd (0.224 ± 0.22 mg/kg), and the least value was Pb (0.260 ± 0.23 mg/kg). These concentrations were below the intervention levels of Cd (12 mg/kg), Ni (210 mg/kg), and Cr (380 mg/kg) established by the Environmental Guidelines and Standards for the Petroleum Industry in Nigeria (EGASPIN) (DPR 2002). The levels of the heavy metals in sediment from Opuroama Creek were above the studies of Aghoghovwia et al. (2018) and Aigberua et al. (2020).
Some studies in the Niger Delta have observed heavy metal concentrations in the sediment higher than the current study. For example, a study conducted by Ekelemu et al. (2019) on sediments recorded concentrations of Cd, Ni, Pb, and Cr to be 0.14-0.96 mg/kg, 3.67-56.1 mg/kg, 2.03-51.7 mg/kg, and 10.7-151.8 mg/kg, respectively. Also, Oyoo-Okoth et al. (2016) reported concentrations of Cd, Ni, Pb, and Cr in sediment samples collected from Bonny River, Niger Delta, to be in the range of 0.12-1.01 mg/kg, 3.33-37.25 mg/kg, 0.82-34.16 mg/kg, and 0.52-26.01 mg/ kg, respectively.
The elevated levels of heavy metals on the sediments from other Niger Delta region of Nigeria is dependent on their location and extent of pollution. The USEPA identifies that heavy metal concentration, even in minute quantity, tends to cause health risk effects. The result of the current study on the sediments from Opuroama Creek suggests a relatively low risk to human health and the environment.

Concentrations of the heavy metals in the shellfishes
The highest concentrations of Cd were recorded in C. amnicola (0.168 ± 0.17 mg/kg) while the least was in P. monodon and T. fuscatus (0.001 ± 0.01 mg/kg). The concentrations of Cd were not significantly different (p < 0.05) in T. fuscatus, and P. monodon. No significant (p > 0.05) difference was also observed in U. tangeri, and C. Amnicola. Nickel recorded the highest concentrations in U. tangeri (0.004 ± 0.01 mg/kg) while the least was in P. monodon and T. fuscatus (0.001 ± 0.01 mg/kg). The highest concentrations of Pb (0.321 ± 0.29 mg/kg) were recorded in P. monodon while the least was in C. amnicola (0.002 ± 0.01 mg/kg). There were significant difference (p > 0.05) between C. amnicola, T. fuscatus, P. monodon and U. tangeri respectively. These values were below the 0.5 mg/kg maximum acceptable limit set by Food Standards Australia and New Zealand (FSANZ 2008). The highest concentration of Cr was recorded in U. tangeri (0.612 ± 0.47 mg/kg) while the least was in P. monodon (0.004 ± 0.00 mg/kg). The concentration of Cr in U. tangeri and T. fuscatus was not significantly different (p < 0.05) although C. amnicola and P. monodon differ significantly (p < 0.05).
The levels of heavy metals detected in the shellfish in this study were lower than those previously reported in other Niger Delta locations. For example, cadmium and lead concentrations measured in T. fuscatus var. radula samples collected from Brass Island River, recorded values 0.042 mg/ kg and 0.36 mg/kg, respectively (Obasi et al. 2015). While the muscles of C. amnicola samples collected from Bodo Creek recorded Cd concentrations of 0.03 ± 0.03 mg/kg and Pb concentrations of 0.62 ± 0.02 mg/kg (Abu and Nwokoma 2016). Patrick-Iwuanyanwu et al. (2020) reported that the average levels of heavy metal concentrations in seafood samples collected from three markets (Swali, Mbiama, and Kpansha) for Pb ranged from 0.02 to 0.74 mg/kg, while Cd concentrations ranged from 0.04 to 0.39 mg/kg, Ni concentrations ranged from 0.43 to 2.28 mg/kg, and Cr concentrations ranged from 1.50 to 4.94 mg/kg. According to Abdolahpur Monikh et al. (2013), the concentrations of heavy metals present in shellfish can vary based on factors such as their age, size, and the type of sediment they inhabit. Since shellfish filter significant amounts of water, they tend to accumulate toxins from their surrounding environment (Baki et al. 2018). These toxins can then be passed up the food chain, potentially leading to higher levels of heavy metals in shellfish. Consuming seafood contaminated with heavy metals can result in severe long-term health effects for the Niger Delta population. Despite lower concentrations being detected in shellfish from Opuroama Creek, there is still a possibility of these organisms accumulating more pollutants, thereby increasing the risk of adverse health effects. Exposure to heavy metals like lead, cadmium, nickel, and chromium through consumption of contaminated seafood are associated with various health issues, including impaired immune system, damage to the liver, kidneys, and nervous system, as well as an elevated risk of cancer (Tchounwou et al. 2012;Balali-Mood et al. 2021).

Potential Ecological Risk Index and Geo-accumulation index in sediment from Opuroma Creek
Sediments are sinks for environmental pollutants and have been shown to have accumulated higher levels of heavy metals. The potential ecological risk indices and geo-accumulation index in the sediment samples recorded in this study are listed in Table 5. The potential ecological risk indices (PERI) for single regulators indicated that the severity of pollution of the four heavy metals decreased in the following sequence: Cd > Pb > Cr > Ni. The high ecological risks of Cd and Pb in the individual samples result from their high toxic-response factors. The potential toxicity response indices for the heavy metals showed that sediments are of severe ecological risk. The geo-accumulation index described the degree of contamination by heavy metal the sediment samples (Table 5). The sediments were extremely contaminated (Class 6) with Cd and Pb, Cr was moderate to heavily contaminated. As indicated in Table 5, Cd posed a severe ecological risk in sediments compared to other metals, Cr and Ni showed lower ecological risks in all the samples. The single heavy metal contamination index highlights the risk that Cd and Pb pose to the ecosystem.

Degree of contamination (DC) in the various environmental samples
In the present study, the degree of contamination (DC) was defined as the sum of all contamination factors (Cf) in the samples from Opuroama creek ( Table 6).
As indicated in Table 6, DC ranged from 14.12 to 110.84. A degree of contamination greater than 24 is considered very high (Lacatusu 2000). All the samples except T. fuscatus recorded a high degree of contamination, indicating serious anthropogenic pollution in the study area which could be attributed to the illegal crude oil effluent contamination and the associated activities found on the surface sediments.
A study conducted in Nigeria found high levels of contamination in fish species from the Niger Delta region, which is also known for illegal oil activities (Allison et al. 2018;Osuagwu and Olaifa 2018;Babatunde et al. 2019;Ofori et al. 2021). These studies found that the concentrations of heavy metals in the fish species exceeded the maximum permissible limits set by international regulatory agencies, indicating a significant health risk to local populations. Similar issues of anthropogenic pollution have been reported in other countries, such as China, where rapid industrialization and urbanization have led to severe contamination of aquatic ecosystems (Sodango et al. 2018).
Organisms leaving in such contaminated substratum are capable of accumulating heavy metal concentrations for extended periods of time thus posing health risks (Fig. 3). The findings of this study reveal a high degree of contamination in the study area, which raises concerns about the potential health risks associated with consuming contaminated fish and other aquatic organisms.

Non-carcinogenic risk (HI) from the consumption of shellfishes from Opuroama Creek
The assessment of potential health risks associated with shellfish involves evaluating the concentration of heavy metals in the organisms and the pathways of human exposure to these metals. In this study, parameters such as CDI (chronic daily intake), HQ (hazard quotient), and HI (hazard index) were used to estimate non-carcinogenic risks. The study also examined which exposure routes, including ingestion, inhalation, and dermal absorption, posed non-carcinogenic risks. The findings of this study indicate that the HI values for the shellfish are all below 1 (Table 7). According to the United States Environmental Protection Agency (USEPA 2012), metals with HI values greater than 1 are considered to have a higher potential to cause cancer, while those with HI values below 1 are deemed to have no carcinogenic risk. Based on the criteria set forth by the USEPA, the results of this study indicate that none of the three exposure pathways to heavy metals, as assessed in the fishes and age groups, pose a non-carcinogenic risk. However, the study indicated higher health risks in children compared to adults. The US EPA studied the non-carcinogenic health risk assessment in children and the adult population and revealed HI values to be greater in children than in adults (USEPA 2011). The estimated HI values in this study highlight the importance of the ingesting pathway in the risks posed, followed by the dermal and inhalation pathways.

Carcinogenic risk from the consumption of shellfishes from Opuroama Creek
Similarly, in this study, the reference dose (RfD) and cancer slope factor (CSF) values for Cd, Pb, and Cr were utilized to estimate the potential cancer risks associated with the three exposure pathways (Table 8). The Lifetime Cancer Risk (LCR) was calculated, and the results showed that the LCR values were all below 1, indicating that there were no significant cancer risks identified for both adults and children in the studied shellfishes. However, the Total Cancer Risk (TCR) associated with Cd and Cr was notably higher compared to that of Pb in C. amnicola and U. tangeri, indicating a possibly higher cancer-causing potential in both children and adults within the study area. Additionally, the TCR value for Cr was found to be the highest among all the heavy metals assessed in T. fuscatus across different age groups. The TCR values for Cd and Cr were observed to exceed the acceptable range (10 −6 to 10 −4 ) established by the USEPA in both children and adults, raising concerns about the potential cancer risks associated with exposure to these metals in the studied population who consume fishes harvested from Opuroama creek. Cadmium (Cd), a highly hazardous element, can cause cancer and organ toxicity, including hepatic, pulmonary, renal, skeletal, and reproductive toxicity. Cd biomagnifies and has a high carcinogenic potential (Arisekar et al. 2020). Chromium (Cr) has two main oxidation states, Cr +3 and Cr +6 , which are present in water; Cr +6 is extremely harmful to humans. Nickel (Ni) is a significant heavy metal due to its importance in the biological functions of all organisms (Sule et al. 2022). Lead (Pb) is a heavy metal derived from fossil fuels and leaded gasoline that is highly soluble and easily absorbed by organic matter. It is toxic to aquatic organisms, particularly fish (Ali and Khan 2019). It has numerous negative health effects, including neurotoxicity, nephrotoxicity, anaemia, encephalopathy, abdominal discomfort, nausea, and constipation (Arisekar et al. 2020;Anandabaskar 2019). The abundance of Cr and Ni in food is significant due to their importance in lipid and insulin metabolism (Sule et al. 2020;Ahmed et al. 2016). Differences in metal composition in seafood from different rivers are caused by regional industrial and organic pollution and absorption by sediments and water (Ihunwo et al. 2020;Abarshi et al. 2017). The levels Fig. 3 Health effects of heavy metals on human organs and systems. The consumption of heavy metals contaminated tiger prawns and shellfish constitute the pathways through which Cd, Cr, Ni and Pb affect human health and other marine receptors of Cd, Pb, and Cr reported in this study are consistent with levels reported in other areas with similar anthropogenic activities, such as industrial or mining activities (Anyanwu and Davies 2023).
The potential health risk associated with heavy metal exposure is a global issue that affects various countries around the world. There have been several reported incidences of heavy metal contamination in seafood in various countries around the world, including India, Bangladesh, Pakistan, and America (Acharya et al. 2023;Siddiqui and Saher 2022;Dehghani et al. 2021;Sarkar et al. 2016). For instance, a study conducted in Chilika lagoon, India found that Penaeus monodon was safe for consumption, with no potential human health risks identified (Acharya et al. 2023). In contrast, high levels of heavy metals were found in fiddler crabs (Austruca iranica) from Pakistan, indicating severe accumulation of metals that may amplify through the food chain (Siddiqui and Saher 2022). A risk assessment of heavy metal concentrations in Penaeus vannamei found that consumption of shrimp cultured in the region did not pose a carcinogenic (lifetime cancer risk (LCR) < 10 −4 ) or non-carcinogenic health risk for both Indians and Americans. The study also suggested that dermal absorption of P. vannamei may not be a concern for local fishermen and marine fish/shrimp farmworkers in India and America (Arisekar et al. 2022). According to Dehghani et al. (2021), Penaeus merguiensis from the northern Persian Gulf contained concentrations of Zn and Ni that exceeded the recommended limits set by FAO/WHO, with the carcinogenic risk of Ni also exceeding acceptable levels. In Khulna, Bangladesh, P. monodon from Rupsa and Paikgacha contained Cr concentrations above the recommended limit, with a target hazard quotient above 1 and a higher hazard index, indicating a potential human health risk (Biswas et al. 2021). Heavy metals in various seafood, including crabs and shrimps from Pulicat Lake, India, were highest in the liver, but concentrations in the muscle were within permissible levels and safe for consumption (Batvari et al. 2016). However, Macrobrachium rosenbergii and P. monodon from the Khulna-Satkhira region in Bangladesh contained Pb, Cd, and Cr concentrations that exceeded recommended limits, posing potential health risks (Sarkar et al. 2016).
The findings of the study highlight the potential health risks associated with the consumption of seafood from Opuroama Creek. The results of this study suggest that the ingestion pathway is the most critical route of exposure to heavy metals. Furthermore, the higher health risk observed in children than adults emphasizes the need to pay special attention to vulnerable populations, particularly children, who are more susceptible to the adverse effects of heavy metals. Thus, given the potential health risks associated with heavy metal pollution there is a need for additional research to better understand the sources, pathways, and fate of heavy metals in artisanal mining sites and develop efficient riskmitigation techniques. Continued monitoring of the levels of these heavy metals in various environmental media is necessary to ensure that they remain within safe levels.

Conclusion
This study establishes that toxic exposure to heavy metals represents a substantial hazard to both human health and the ecological integrity of these locations. Heavy metal levels observed in the water, sediment, and shellfish above the permissible limits indicate a potential risk to human health from consuming contaminated shellfish and negative effects on the aquatic ecosystem. Cadmium, chromium and lead accumulated higher concentrations in the samples studied, however, only the total cancer risk values for Cd and Cr were observed to exceed the acceptable threshold established by the USEPA in both children and adults. Given the potential health risks associated with heavy metal pollution, it is crucial to find alternative sources of food for the local population. Policymakers should prioritize strategies to reduce heavy metal pollution in the creek. Therefore, a multi-faceted approach that includes alternative income and food sources, pollution reduction strategies, which include enforcing regulations to prevent illegal crude oil effluent contamination, promoting cleaner production practices in industries, investing in wastewater treatment facilities education and awareness, and monitoring and evaluation could help improve the situation in Opuroama Creek. Coordinated efforts are required to reduce the risks posed by heavy metal contamination and safeguard the safety of both human populations and the environment in these places.