According to [1], heavy metals are generally understood to be metals with relatively high densities, atomic weights, or atomic numbers. Arsenic, chromium, lead, mercury, iron, copper, nickel, and zinc are a few examples of heavy metals.

Food products are thought to be the major source from which the general population is exposed to heavy metals, and these heavy metals have toxicological consequences for humans. Chronic exposure to nickel and nickel compounds can accumulate in the body and have a number of harmful impacts on human health, including renal and cardiovascular illness, lung fibrosis, and respiratory tract cancer (Genchi et al., 2020). Lead, on the other hand, adversely affects the hematopoietic, renal, cardiovascular, reproductive, and skeletal systems [2].

Whelk (Buccinum undatum), also known as Ngolo, is a subtidal marine neo-gastropod that belongs to the Buccinidae family [3]. Whelk has a small amount of fat as well as providing vitamins, proteins, and minerals. It can be effective for weight loss since it has few calories. It helps improve brain function, slows the aging process, maintains hair health, and prevents its damage. Despite the several advantages of Buccinum undatum, its sustainability is endangered by human activities that introduce heavy metals into its habitat [4].

Periwinkle, also called Tympanotonus fascatus, is a brackish gastropod belonging to the Potamididae family [5]. It is found in the mangrove soil within the intertidal zone and is indigenous to Nigeria and West Africa [6]. Periwinkle is a relatively affordable source of animal protein, vitamins, and minerals. Due to its iodine concentration as well as calcium, phosphate, and iron content, it is particularly beneficial for conditions such as endemic goiter (Asunkwari and Archibong, 2011). Periwinkle has major commercial and economic significance in the Niger Delta region of Nigeria, and it is extensively distributed in the mangrove swamps and intertidal areas of the estuarine and marine waters of this region [5]. Periwinkles are bio-indicators of heavy metal and hydrocarbon contamination in the aquatic environment, as well as deposit feeders. This implies that the organism can bio accumulate heavy metals in their tissues while engaging in the deposit feeding process [7].

According to Nwoko et al. (2014), the toxicity and accumulative behavior of heavy metals have caused serious levels of pollution in the aquatic ecosystem. The presence of heavy metals at high concentrations in varying aquatic species such as Tympanotonus fuscastus and Baccinum undatum poses a serious threat to human health, water quality, the survival of these species, and the aquatic environment. Hence, the assessment of the heavy metal content in these species is therefore required.

Study Area

Okuru-Ama is a community located in Rivers State, Nigeria. Its coordinates lie within latitude 4.788337 and longitude 7.037956. It has a prominent river known as the Okuru-Ama River. The Okuru-Ama-Amaer is a coastal environment in the Okuru-Ama community in the Niger Delta region that harbors a rich collection of biotopes and is also part of the mangrove forest [8].

Sample Collection

Tympanotonus fuscatus and Baccinum undatum samples were bought from fishermen, who brought the samples from the Okuru-Ama River in the Okuru-Ama community, Port Harcourt. The samples were properly washed before being placed in separate labeled cellophane bags and kept in an ice-cooled box. The samples were then stored in the freezer prior to analysis.

Sample Preparation

The shells of periwinkle and ngolo were cracked to obtain the soft fleshy part. To obtain the dry tissue, the weight of the soft fleshy parts of the two samples was measured using a weighing balance before being placed on foil paper and dried at 80⁰ C for 24 hours. The dry tissue was ground into fine powder using a mortar and pestle and sieved to obtain a consistent particle size using a 2 mm mesh size. They were then preserved in well-labeled plastic bottles.

Digestion Procedures

Dry samples of the Periwinkle and Ngolo were digested with 0.5 ml of concentrated nitric acid (HNO₃). The digestion was carried out in a fume cupboard, and a water bath was used to stabilize and attain a temperature of 100^o C. The fully digested samples were filtered using Whatman filter paper and diluted with distilled water to a level of 100 mL in a standard volumetric flask.

Metal Determination

The resulting solution was analyzed for heavy metals using an atomic absorption spectrophotometer.

Data Analysis

Data collected from the experiment was expressed as mean± standard deviation and subjected to one-way analysis of variance. Statistical significance was defined as a probability ≤0.05.

Table 1: Heavy Metals Concentration (mg/kg) in Periwinkle Flesh from Okuru-Ama River.

BDL- Below Detection Limit

Values are expressed as mean ± standard deviation

*mean difference is significant at 0.05 when comparing station 1 to 2 & 3

a,b is significant at 0.05 when comparing station 2 with 1 & 3

c,d is significant when comparing station 3 with 1 & 2

Table 2: Heavy Metals Concentrations (mg/kg) in Tympanotonus fuscatus Shell from Okuru-Ama River.

BDL- Below Detection Limit

Values are expressed as mean ± standard deviation

*mean difference is significant at 0.05 when comparing station 1 to 2 & 3

a,b is significant at 0.05 when comparing station 2 with 1 & 3

c,d is significant when comparing station 3 with 1 & 2

Table 3: Heavy Metals Concentration (mg/kg) in Baccinum undatum from Okuru-Ama River.

BDL- Below Detection Limit

Values are expressed as mean ± standard deviation

*mean difference is significant at 0.05 when comparing station 1 to 2 & 3

a,b is significant at 0.05 when comparing station 2 with 1 & 3

c,d is significant when comparing station 3 with 1 & 2

The levels of heavy metals found in Tympanotonus fuscatus flesh and Tympanotonus fuscatus shell collected from different stations in the Okuru-Ama Rivers are displayed on Tables 1 and 2, respectively. The concentrations of zinc and iron in Tympanotonus fuscatus flesh and shell for stations 1, 2, and 3 were in the order station 3 > station 2 > station 1. In contrast, that of Baccinum undatum was in the order station 1>station 3>station 2.

Zinc is a vital trace mineral that is also crucial for cell division, DNA and protein synthesis, and the metabolic function of 300 of the body’s enzymes (these enzymes regulate the metabolism of proteins, carbohydrates, fats, and alcohol). Zinc is essential for wound healing and tissue growth, immune system function, connective tissue growth and maintenance, embryonic growth, bone mineralization, and sperm production [18]. A deficiency of zinc can lead to decreased nerve conduction, decreased wound healing, infertility, and retarded growth. Excess zinc exposure leads to lethargy, focal neuronal deficits, and an elevated risk of prostate cancer [9]. Therefore, high intakes of Tympanotonus fuscatus, which is zinc-concentrated in the Okuru-Ama River, can pose serious health hazards.

The concentration of zinc for Tympanotonus fuscatus flesh, Tympanotonus fuscatus shell, and Baccinum undatum was higher than that of Benson and Etesin (2007), who had a value of 0.49 mg/kg. The values obtained from this study are higher than the permissible limit of 0.10 mg/kg [10,11].

The iron content recorded for all samples was significantly higher than the recommended standard limit of 0.5 mg/kg for periwinkle and fish [5,10]. The concentration of iron in this study was higher than that of [16], who had a range value of 3.08–3.35 mg/kg. Iron is an essential metal that is required in a range of metabolic activities such as electron transport, DNA synthesis, and the transfer of oxygen. It can create free radicals, so its concentration in the body needs to be closely controlled because excessive amounts can cause tissue damage, and deficiency can also lead to anemia [12]. Iron is therefore a necessary heavy metal, but when aquatic species from the Okuru-Ama River are consumed in excess, it has the potential to become toxic. The high concentration of iron in Tympanotonus fuscatus from the Okuru-Ama River can be attributed to the fact that this metal is naturally abundant in Nigerian soils and is leached into the sediment of water bodies eventually where the fauna feeds [13].

The concentration of copper in Tympanotonus fuscatus flesh and shell for stations 1, 2, and 3 was in the order of station 2>station 3>station 1. While those of Baccinum undatum were in the order station 3>station 1>station 2, These values were higher than those of [6], who had a value of 1.70 ± 0.50 mg/kg in their study, except for those of stations 1 and 2 for Tympanotonus fuscatus flesh and Baccinum undatum, respectively. Copper is one of the metals that is crucial for maintaining human health. In addition to being required for the synthesis of hemoglobin, it interacts with specific proteins to produce enzymes that serve as catalysts for the body’s functions [6]. However, the copper concentration of Tympanotonus fuscatus and Baccinum undatum from the Okuru-Ama River was higher than the permissible limit of 2.00 mg/kg [10,11], except for those from stations 1 and 2 for Tympanotonus fuscatus flesh and Baccinum undatum, respectively, and this could pose health hazards. Oil exploration and refining, which might introduce this metal into the water body and subsequently the sediment from which the fauna feeds, may be responsible for the concentration of copper in these samples.

The concentrations of lead (Pb) and nickel (Ni) in the samples were below the detectable limit and therefore may not pose serious health consequences to consumers at the moment.

According to the study, there has been an accumulation of heavy metals in Tympanotonus fuscatus flesh, Tympanotonus fuscatus shell, and Baccinum undatum from the Okuru-Ama River. The concentration of zinc, iron, and copper present in Tympanotonus fuscatus and Baccinum undatum showed bioaccumulation of some of these metals, which were above the permissible limit of the Federal Environmental Protection Agency, showing that long-term consumption of aquatic resources from the Okuru-Ama River might be hazardous. The findings of this study highlight the importance of routinely monitoring water bodies, particularly those that receive effluent, in order to prevent and lessen the cumulative impacts of metals that may result in sub-lethal implications for aquatic life and subsequent poisoning of human life.

1. Khlifi R. and Hamza–Chaffai A. Head and Neck Cancer Due to Heavy Metal Exposure via Tobacco Smoking and Professional Exposure, a Review. Toxicolology and Applied Pharmacy. 2010; 248: 71-88.
2. Barchiesi F, Branciari R, Latini M, Roila R, Lediani G, Filippini G, et al. Heavy metals contamination in shellfish: benefit-risk evaluation in central Italy. Foods. 2020; 9: 1720.
3. Hildur M. The Common whelk (Buccinum undatum L.): Life History Traits and Population Structure. Evolution and Regulation of Colour Polymorphism in the Subtidal Gastropod, Buccinum undatum. University of Iceland. 2010: 53.
4. Snorre B, Sylvia F. Regional Occurrence of Heavy Metals in the Common Whelk (Buccinum undatum) - Implications for an evolving industry in Norway. 2011.
5. Abiaobo N, Asuquo IAE. Assessment of heavy metal concentration in prewinkle (Tympanotonus fuscatus) samples from Uta Ewa creek, Imo River Estuary, South Eastern Nigeria. Journal of Agriculture & Marine Biology. 2020; 9: 32-35.
6. Nsikak O, Idopise A. Assessment of Heavy Metal Concentrations in Periwinkle (Tympanotonus fuscatus) Samples from Uta Ewa Creek, Imo River Estuary, South Eastern Nigeria. Journal of Aquaculture and Marine Biology. 2020; 9: 32-35.
7. Moslen M, Ekweozor KEI, Nwoka N. Assessment of heavy metals and bioaccumulation in prewinkle (Tympanotonus fuscatus) var. radula (L) obtained from the upper reaches of Bonny River Estuary, Nigeria. Journal of Heavy Metal Toxicity and Diseases. 2017; 2: 1-5.
8. Onome D. Communal conflicts- the case of Abuloma and Okuru-Ama, Niger Delta Nigeria. 2010.
9. Plum MC, Rink L, Haase H. The essential toxin: impact of zinc on human health. International Journal of Environmental Research & Public Health. 2010; 7: 1342-1365.
10. E.P.A. (Federal Environmental Protection Agency) (2003): Guidelines and Standards for Environmental Pollution Control in Nigeria.238 P.
11. Guidelines for drinking water quality (4th edition). Geneva World Health Organization. World Health Organization (WHO). 2011: 224-229.
12. Abbaspour N, Hurell R, Kelishadi R. Review on iron and its importance for human health. Journal of Research in Medical Sciences. 2014; 19: 164-174.
13. Ademoroti C. Environmental Chemistry and Toxicology. First edition, Foludex press limited, Ibadan. 1996.
14. Chioma DL, Okechukwu DN, Reminus O. Determination of heavy metals in salt water periwinkle and fresh water periwinkle in Port Harcourt, Rivers State. Scholars International Journal of Chemistry & material Science. 2021; 4: 1-5.
15. CLIMA: Changes in Fish Distribution and Species Composition as a Result of Climatic Changes in the East Greenland Ecosystem: Implications for Fisheries and Management Norwegian. 41st WEFTA Meeting, Gothenburg. 2016.
16. Don-Lawson C, Nweneka DO, Oka R. Determination of Heavy Metals in Salt Water Periwinkle and Fresh Water Periwinkle in Port-Harcourt, Rivers-State. Scholars International Journal of Chemistry and Material Sciences. 2021; 4: 1-5.
17. Etesin MU, Benson UB. Cadmium, Copper, Lead and Zinc Tissue Levels in Bonga Shad (Ethmalosa fimbriata) and Tlapia (Tilapia guineensis) caught from Imo River, American Journal of Food Technology. 2007; 2: 48-54.
18. Kumar V, Kumar A, Singh SK, Tripathi SK, Kumar D, Singh R, et al. Zinc Deficiency and Its Effect on the Brain: An update. International Journal of Molecular Genetics and Gene Therapy. 2016; 1.