Dietary Exposure and Non-Carcinogenic Health Risk Assessment of Heavy Metals in Edible African Giant Snails from Southern Nigeria

dose of the metal (mg/kg/d), which is defined as the maximum tolerable daily intake of metal with no adverse effect. 2.5.3. Hazard Index (HI): The hazard index (HI) was calculated to determine the overall health risk of exposure to all the heavy metals via the ingestion of a RTE snail described by (USEPA, 2002). The hazard index (HI) was calculated as the summation of the hazard quotient (HQ) arising from all the metals examined. HI = ?HQ The hazard index value correlates with the toxicity level of the ingested snail. HI > 1 signifies that the anticipated exposure may present possible health hazards. 2.5. Statistical analysis: Data were evaluated with one-way ANOVA and independent sample T-test in IBM SPSS version 25. Tukey’s HSD Post Hoc test was employed to ascertain differences among means. P < 0.05 signifies substantial differences between groups. 3.0. Results The results of the mean concentrations of heavy metals in tissues of both species of snails are shown in Tables 1 and 2 while Species-wise comparison of heavy metals concentrations (?g g?1 dry weight) in African giant snails collected from Ugbolu-Afor market is contained in Table 3. Table 1: Mean concentrations (?g g?1 dry weight) of heavy metals in tissues of Achatina achatina collected from Ugbolu-Afor Market Heavy Metal Shell (?g g?1) Foot (?g g?1) Digestive Tract (?g g?1) Digestive Gland (?g g?1) As 0.075 ± 0.020a 0.207 ± 0.292a 0.053 ± 0.023a 1.195 ± 1.010b Zn 0.564 ± 0.312a 0.139 ± 0.046a 0.102 ± 0.036a 0.766 ± 0.965b Cu 0.428 ± 0.392ab 0.147 ± 0.034ab 0.085 ± 0.013a 0.129 ± 0.067b Pb 0.159 ± 0.037a 0.396 ± 0.459ab 0.155 ± 0.043b 0.515 ± 0.682c Cd 0.003 ± 0.002a 0.030 ± 0.049a 0.572 ± 0.513b 0.650 ± 0.939b Cr 0.147 ± 0.044a 0.134 ± 0.025a 0.130 ± 0.095a 0.159 ± 0.139a Fe 1.706 ± 0.404b 1.405 ± 0.505b 0.293 ± 0.246a 0.419 ± 0.512a Values are expressed as mean ± standard deviation (SD) of triplicate determinations (n = 3). Different superscript letters within a row indicate significant differences among tissues based on one-way ANOVA followed by Tukey’s HSD post hoc test (P < 0.05). As = Arsenic; Zn = Zinc; Cu = Copper; Pb = Lead; Cd = Cadmium; Cr = Chromium; Fe = Iron. Table 2: Mean concentrations (?g g?1 dry weight) of heavy metals in tissues of Archachatina marginata collected from Ugbolu-Afor Market Heavy Metal Shell (?g g?1) Foot (?g g?1) Digestive Tract (?g g?1) Digestive Gland (?g g?1) As 0.664 ± 0.475a 0.310 ± 0.143a 0.492 ± 0.708b 0.050 ± 0.050a Zn 0.105 ± 0.038a 0.115 ± 0.051a 0.368 ± 0.566b 0.791 ± 0.643c Cu 1.488 ± 0.476b 1.132 ± 0.672ab 1.043 ± 0.072a 1.043 ± 0.768b Pb 0.105 ± 0.078a 0.052 ± 0.036a 0.670 ± 0.536b 0.064 ± 0.035a Cd 0.668 ± 0.860a 0.760 ± 0.589b 0.626 ± 0.487b 1.576 ± 0.395c Cr 0.818 ± 0.694a 0.111 ± 0.074a 0.051 ± 0.031a 0.382 ± 0.582a Fe 0.494 ± 0.416a 0.156 ± 0.037a 0.865 ± 0.856b 0.834 ± 0.650b Values are expressed as mean ± standard deviation (SD) of triplicate determinations (n = 3). Different superscript letters within a row indicate significant differences among tissues based on one-way ANOVA followed by Tukey’s HSD post hoc test (P < 0.05). As = Arsenic; Zn = Zinc; Cu = Copper; Pb = Lead; Cd = Cadmium; Cr = Chromium; Fe = Iron. Table 3: Species-wise comparison of heavy metal concentrations (?g g?1 dry weight) in African giant snails collected from Ugbolu-Afor Market Heavy Metal Achatina achatina (Mean ± SD) Archachatina marginata (Mean ± SD) Test statistic P-value Significance As 0.420 ± 0.575 0.379 ± 0.462 t = 0.21 > 0.05 NS Zn 0.428 ± 0.616 0.345 ± 0.498 t = 0.37 > 0.05 NS Cu 0.197 ± 0.195 1.177 ± 0.540 t = ?4.62 < 0.05 S Pb 0.306 ± 0.516 0.223 ± 0.327 t = 0.44 > 0.05 NS Values represent species-wide mean ± standard deviation (SD) pooled across tissues (n = 12 per species). Independent-samples t-test was used to compare metal concentrations between species. S = significant (P < 0.05); NS = not significant (P > 0.05). Figure 1: Species-wise comparison of mean heavy metal concentrations (?g g?1 dry weight) in edible African giant snails (Achatina achatina and Archachatina marginata) collected from Ugbolu-Afor Market. 3.1. Estimated Daily Intake (mg kg?1 day?1) The estimated daily intake of heavy metals through consumption of snail digestive gland tissues by adults (70 kg body weight) varied among metals and between species (Table 4). For Achatina achatina, EDI values ranged from 3.69 × 10?5 mg kg?1 day?1 for Cu to 3.41 × 10?4 mg kg?1 day?1 for As. In contrast, Archachatina marginata exhibited EDI values ranging from 1.83 × 10?5 mg kg?1 day?1 for Pb to 4.50 × 10?4 mg kg?1 day?1 for Cd. Among the assessed metals, arsenic (As) and cadmium (Cd) consistently showed higher EDI values relative to other elements in both species. Zinc (Zn), copper (Cu), chromium (Cr), and iron (Fe) exhibited comparatively lower EDI values, reflecting their lower concentrations and/or higher reference dose thresholds. Table 4: Estimated daily intake for heavy metals associated with adult consumption of snail digestive gland tissues from Ugbolu-Afor Market (body weight = 70 kg). Metal Achatina achatina Archachatina marginata As 3.41×10?4 1.43×10?5 Zn 2.19×10?4 2.26×10?4 Cu 3.69×10?5 2.98×10?4 Pb 1.47×10?4 1.83×10?5 Cd 1.86×10?4 4.50×10?4 Cr 4.54×10?5 1.09×10?4 Fe 1.20×10?4 2.38×10?4 Figure 2: Estimated daily intake (EDI; mg kg?1 day?1) of selected heavy metals through consumption of snail digestive gland tissues by adult consumers (70 kg body weight). 3.2. Hazard Quotient The calculated hazard quotient (HQ) values for individual metals indicated marked differences in non-carcinogenic risk potential (Table 5). For Achatina achatina, HQ values ranged from 1.71 × 10?4 for Fe to 1.14 for As. Notably, arsenic was the only metal with an HQ exceeding the safety threshold of unity in this species. In Archachatina marginata, HQ values ranged from 3.40 × 10?4 for Fe to 0.45 for Cd. All individual HQ values for this species remained below unity, although cadmium contributed the highest HQ among the assessed metals. As and Cd were the dominant contributors to HQ values across both snail species, whereas Zn, Cu, Cr, and Fe posed minimal non-carcinogenic risk based on their HQ values. Table 5: Hazard quotient (HQ) for heavy metals associated with adult consumption of snail digestive gland tissues from Ugbolu-Afor Market (body weight = 70 kg). Metal HQ (A. achatina) HQ (A. marginata) As 1.14 0.05 Zn 0.0007 0.0008 Cu 0.0009 0.0075 Pb 0.04 0.01 Cd 0.19 0.45 Cr 0.02 0.04 Fe 0.0002 0.0003 Figure 3: Hazard quotient (HQ) values for individual heavy metals associated with adult consumption of snail digestive gland tissues. 3.3. Hazard Index (HI) The cumulative non-carcinogenic risk, expressed as the hazard index (HI), differed substantially between the two snail species (Table 6). The HI for Achatina achatina was 1.38, exceeding the recommended safety limit of 1. In contrast, the HI for Archachatina marginata was 0.55, remaining below the threshold for potential concern. The elevated HI observed for Achatina achatina was largely attributable to arsenic, with additional contributions from cadmium and lead, whereas the lower HI for Archachatina marginata reflected generally lower HQ values across all metals. Table 6: Hazard index (HI) for heavy metals associated with adult consumption of snail digestive gland tissues from Ugbolu-Afor Market (body weight = 70 kg). Species Hazard Index (HI) Achatina achatina 1.38 Archachatina marginata 0.55 Figure 4: Cumulative non-carcinogenic risk expressed as hazard index (HI) for adult consumers of edible African giant snails. Table 7: Estimated Daily Intake , Hazard Quotient (HQ), and Hazard Index (HI) for heavy metals through consumption of snail digestive gland by adults (70 kg body weight) Metal RfD (mg kg?1 day?1) EDI (A. achatina) (mg kg?1 day?1) HQ (A. achatina) EDI (A. marginata) (mg kg?1 day?1) HQ (A. marginata) As 3.0×10?4 3.41×10?4 1.14 1.43×10?5 0.05 Zn 3.0×10?1 2.19×10?4 7.30×10?4 2.26×10?4 7.53×10?4 Cu 4.0×10?2 3.69×10?5 9.21×10?4 2.98×10?4 7.45×10?3