Evaluation of Heavy Metal Content and Human Health Risk Assessment of Water Leaf (Talinum triangulare) Grown on Arsenic Spiked Soils

AIM: This study investigated the concentration of heavy metal (Arsenic), taken up by waterleaf plant cultivated in three contaminated soil type namely; sandy, loamy and clay. The health risk associated in exposing the waterleaf plants was accessed from the different soil types at different treatment levels of 40mg/kg (low) and 80mg/kg (high) of arsenic.

Methods: Three soil types namely; sandy, loamy and clay were spiked with 40 mg/kg and 80 mg/kg of arsenic. The waterleaf plant was grown on the spiked soil samples for the period of 2, 4, 6 and 8 weeks. Each soil sample was taken before the spiking of the soil to serve as the basal control soil sample. This will determine the content of arsenic in the soil. After the stipulated growth period, the soil sample was collected into a clean sample bottle likewise the waterleaf plant which was harvested, washed, oven dried and ground into a powdered form which was acid digested. The heavy metal content in both the plant and soils were determined by atomic absorption spectroscopy.

Results: The results of arsenic concentration in waterleaf from loamy soil at 40 mg/kg were 0.118 mg/kg, 0.189 mg/kg, 0.295 mg/kg, and 0.332 mg/kg at weeks 2, 4, 6, and 8 respectively. At 80 mg/kg, arsenic concentrations in loamy soil were 0.200 mg/kg, 0.388 mg/kg, 0.612 mg/kg and 0.693 mg/kg respectively. For sandy soil, the concentration of arsenic in the waterleaf plant treated at 40 mg/kg were 0.083 mg/kg, 0.219 mg/kg, 0.279 mg/kg, and 0.310 mg/kg for weeks 2, 4, 6 and 8 respectively and 0.159 mg/kg, 0.400mg/kg, 0.572 mg/kg, 0.632 mg/kg at 80 mg/kg respectively while in clay soil, the arsenic concentration was 0.079 mg/kg and 0.167 mg/kg for weeks 2 and 4 at 40 mg/kg and 0.190 mg/kg and 0.320mg/kg for 80 mg/kg for weeks 2 and 4 respectively. No growth was recorded in weeks 6 and 8. The mean values of the arsenic concentration in the plant spiked with 40 mg/kg and 80 mg/kg respectively were significantly different (p<0.05)from each other but that for the loamy soil at 40 mg/kg was not significantly different (p>0.05).The Estimated Daily Intake for arsenic was <1, Target Hazard Quotient was < 1 and the Health Risk Index for adults that would be exposed to arsenic was <1 except for the loamy soil which was ≥ 1 at week 4 and 6 for treatment level 80 mg/kg.

Conclusion: Arsenic concentration increases in the plant with increasing period of growth, while in the soil, the reverse occurs. The result shows that the waterleaf plant absorbed heavy metal (Arsenic) from the contaminated soils but at concentrations that do not pose any health risk within the experimental period of exposure. However, it is possible that with extended duration of exposure, consumption of plants exposed to contaminated soils with heavy metals could be hazardous.