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

Consumption of contaminated periwinkles (*Tympanotonus fuscatus*) is a key exposure route for human health risk. Estimated daily intake (EDI) was used for exposure assessment via consumption of contaminated periwinkles. EDI values (mgkg−1) of this study ranged from 0.1 x 10−3 (Cd) – 0.84 x 10−3 (Zn) (**Figure 3**). Different researchers have reported variations in EDI values. Anaero-Nweke et al. [25] in a study of bioaccumulation of heavy metals in tissues of *Tympanotonus fuscatus* had reported EDI range of 6.57–8.81 mgkg−1 above FAO/WHO [26] permission tolerable daily intake of 0.25 mgkg−1 for Pb and EDI values of 0.01–0.07 mgkg−1 within FAO/WHO [26] permissible tolerable daily intake of 0.07 mgkg−1 for Cd. Tongo and Ezemonye [18], had reported EDI values of 0.138–0.200 mgkg−1 in fish from the Niger Delta region while Moslen [11] also reported EDI values of fish

**Figure 3.** *Estimated daily intake of the periwinkles is presented in the study area.*

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

tissue as follows: Cd (5.5 x 10−5), Cu (6.9 x10−4), Ni (3.0 x 10−4), Pb (4.5 x 10−4) and Ag (1.9 x 10−4). The EDI values of all metals examined in the present study were less than their respective reference oral doses (RFD) implying minimal health risk due to consumption of contaminated periwinkles in the study area. However, [13] stated that RfD represents an estimation of the daily exposure of a contaminant to which the human population may be continually exposed over a lifetime without an appreciable risk of harmful effects. It is important to mention that among the different metals examined Pb, Cd, Cr and Ni are classified as chemical hazards [27, 28] meaning they could impair body functions at certain concentrations.

#### **3.3 Target Hazard Quotient**

Assessment of risk is very important because it has to do with evaluation of the amount of a substance that could lead to negative health impact for exposed persons over a particular duration. The health risk assessment of each contaminant is often based on the evaluation of the risk level and is classified as carcinogenic or non-carcinogenic health hazards [29]. The target hazard quotient was used to assess the non-carcinogenic risk. In the present study, THQ (non-carcinogenic) values ranged from 0.01 (Cu) - 0.22 (Pb) (**Figure 4**). The values of THQ (noncarcinogenic) in the present study were all <1suggeting low risk of exposure for consumers of periwinkles. Researchers have reported that THQ >1 potent risk of non-carcinogenic effect to consumers of such sea foods [5, 6, 30]. However, Khan et al. [31] stated that THQ builds some degree of alarm for carefulness but does not assess risk regarding exposure to contaminants. The THQ of the present study were also in tandem with values reported by Moslen and Miebaka [32]. Dee et al. [33] also found THQ for Cd, Cu, Mn, Pb, and Zn as 0.12, 0.06, 0.04, 0.41, and 0.03, respectively. The values of hazard quotient carcinogenic (HQ ) of the present study ranged from 10−6 – 10−4 (**Figure 5**). Such values indicated low to moderate values of carcinogenic risk [34].

Metals in the environment may not act singly. The sum of the THQ (hazard index - HI) was calculated to give an indication of the total potential non-carcinogenic health impacts that could result from exposure to a mixture of heavy metals in periwinkles consumed, following EPA guidelines for health risk assessment [35, 36]. The HI value (0.56) of the present study was <1 depicting low risk of exposure for consumers of periwinkles. The HI value of the present study is less than that

**Figure 4.** *The target hazard quotient non-carcinogenic of heavy metals.*

#### **Figure 5.**

*The hazard quotient (carcinogenic) of heavy metals.*

(1.60–5.06) reported by Denil et al. [37] for four different clams but agrees with that (0.45) in fish reported in the Niger Delta region [38]. The percentage make-up of the HI was in the order Pb > Cr > Cd> > Zn > Ni > Cu indicating the elevated input of Pb, Cr and Cd concentrations in the periwinkles examined.
