Assessing the Toxicity of Colocassia Esculenta (Cocoyam Plant) Grown on Mercury Contaminated Soil

The unsafe disposal of heavy metals is a serious environmental problem all over the world as it has devastating effects on plant biodiversity as well as animal and human health. Contamination can be caused by effluents from industries and exposure of rocks containing metalloid or heavy metals such as arsenic (As), lead (Pb), and mercury (Hg). Several techniques have been used to clean up soil and water bodies contaminated with these heavy metals or metalloid. Phytoremediation is one of the emerging methods which has proven to be ecofriendly and efficient. Plants such as Colocasia esculenta have been reported to be a hyperaccumulator. However, there are concerns regarding the excessive metal uptake by the plant when grown on mercury-contaminated sites, since high Hg levels can cause toxicity in human beings. This study was thus carried out to ascertain the toxicity of C. esculenta plants cultivated in 10 ppm Hg-induced soil sample for four weeks. The concentration of mercury in soil, water and cocoyam samples decreased after 28 days of planting. Accumulation of Hg in plant tissues was measured, and Translocation Factor (TF) was calculated. TF was in the order of Root-Stem (0.60) > Root-Leaves (0.56) > Soil-Root (0.23).  The results indicated that Cocoyam plants have an excellent ability to remove Hg from contaminated soils and further accumulate it in their tissues. With the threshold level of Hg at 0.0016 mg/kg body weight (FAO/WHO), the results obtained suggest that cocoyam plants grown in such contaminated areas may pose health threats to humans.