**2.4 Exposure assessment (Estimated Daily Intake (EDI))**

The Estimated Daily Intake (EDI) via consumption of heavy metal contaminated periwinkle was evaluated using Eq. 1 [13].

$$\text{Estimated Daily Intake} \left(EDI\right) = \frac{\text{EFXEDXFIRXG} \text{fXCM}}{\text{BWXTA} \left(EFXED\right)} \tag{1}$$

where EF = Exposure frequency ED = Exposure duration FIR = Fish ingestion rate CF = conversion factor Cm = heavy metal concentration in periwinkle (μg/g d-w), BW = Adult body weight 70 kg [14, 15]. TA (EF × ED) = average exposure time [5, 6].

#### **2.5 Assessment of non-carcinogenic health risks**

The target hazard quotient (THQ ) was used to evaluate the non-carcinogenic health risks associated with consumption of periwinkles contaminated with heavy metals. THQ was expressed in Eq. 2 [5, 6, 13].

$$\text{Target hazard Quantit} \left( THQ \right) = \frac{EDI}{RFD} \tag{2}$$

where EDI = Estimated Daily Intake. RFD = Reference Oral Dose of metal.

#### **2.6 Assessment of carcinogenic health risks**

Assessment of Carcinogenic health risks with hazard quotient was done using Eq. 3.

Hazard quotient (carcinogenic) [16].

$$\text{Incremental Lifetime Change Risk} \left( \text{ILCR} \right) = CDI \,\text{X SF} \tag{3}$$

$$\text{where } \text{CDI} = \text{Chromatic daily intake (CDI)} = \frac{\text{EDIXEFXED}}{ATn} \tag{4}$$

SF = slope factor EDI = Estimated Daily Intake EF = Exposure frequency ED = Exposure duration ATn = Average life span.

#### **2.7 Hazard index (HI)**

In view of the fact that contaminants do not act in seclusion in the environment, the HI was used to assess the total risk from various contaminant pathways. This is the sum of the target hazard quotients for all heavy metals, calculated using Eq. 5 [5, 6, 17]. HQ and HI values less than 1 were considered safe [18].

$$
\Delta H = \sum HQ = HQ\_{\mathcal{M}} + HQ\_{\mathcal{CM}} + HQ\_{\mathcal{Gr}} + HQ\_{\mathcal{Cu}} + HQ\_{\mathcal{Pb}} + HQ\_{\mathcal{Zn}} \tag{5}
$$

#### **2.8 Data analysis**

Significant difference in metal concentrations between periods (months) was tested with ANOVA (General Linear Model) using the software Minitab 16. The standard deviation was calculated as the positive square root of the sample variance with number of observations as six (6) and expressed in the Eq. 6 as.

$$\mathbf{S}\_{\mathbf{X}} = \sqrt{\frac{\sum\_{i=1}^{n} \left(\mathbf{X}\_{i} - \overline{\mathbf{X}}\right)^{2}}{n - 1}}\tag{6}$$

#### **3. Result and discussion**

#### **3.1 Concentration of heavy metals in tissues of bivalves**

The concentration of heavy metals in tissues of *Tympanotonus fuscatus* is presented in **Figure 2a**–**f** while **Table 1** compared the metal concentrations with permissible limits. Heavy metal toxicity is a major global concern due to human health risk associated with consumption of contaminated sea food, hence the need for evaluation. Mean metal concentrations (mgkg−1) in the soft tissues of

*Consumption Safety in Relation to Bioaccumulation of Heavy Metals in Periwinkles… DOI: http://dx.doi.org/10.5772/intechopen.94057*

**Figure 2.** *(a–f) Temporal variations of heavy metal concentrations in the study area.*


#### **Table 1.**

*Heavy metal concentrations and permissible limits.*

periwinkles (*Tympanotonus fuscatus*) examined was in the order of Zn (5.36 ± 4.5) > Pb (4.88 ± 1.67) > Cu (2.61 ± 1.13) > Cr (1.94 ± 1.04) > Ni (1.36 ± 0.64) > Cd (0.66 ± 0.3). Variation in metal concentrations was significantly different (p < 0.05). This implies differential bioaccumulation in the concentrations of the heavy metals in gastropod tissues with respect to time, particularly those metals with elevated concentrations above regulatory limits. Consumers of periwinkle from the study area are therefore, exposed to significantly higher concentrations of heavy metals. Moslen and Miebaka [1] had reported that fish could accumulate elevated levels of heavy metals in their tissues over time without physical signs of distress but this may constitute potential health harm to consumers of such fish from presumed polluted areas. Mean values of Cr, Cu and Zn observed in this study were below their respective recommended limits of 12–13 [21, 22] , and 30 (FAO/ [20]) while mean values of Ni, Cd and Pb exceeded their recommended limits of 0.2 [20], 0.1 [23] and 0.5 [19]. In other studies, Akinrotimi et al. [24] reported heavy metal concentrations (mgkg−1) as follows Ni (1.17 ± 0.05), Cd (0.06 ± 0.01), Cr (2.44 ± 0.01), Pb (0.29 ± 0.06), Zn (5.57 ± 0.61) in bivalve Mollusks while Moslen et al. [11] reported thus Cd (0.02), Cr (1.57), Pb (0.01) and Zn (24.42) in gastropod Mollucs.
