The Potential of Arrowroots (Colocasia esculanta) in Phytoremediation of Heavy Metals in the Meru Region

Abstract

Potential health hazard implications of heavy metals in taro/arrowroot (Colocasia esculenta) are imminent especially if taro is cultivated in heavily polluted water bodies due to the fact that taro plant bio-accumulate heavy metals. Determination of heavy metals in food crops is important in order to establish their concentration levels. This study sought to investigate the presence and concentration of heavy metals: Cadmium, Chromium, Copper, Mercury, Manganese, Lead and Zinc in the leaves and corms of the taro/arrowroot plant and the corresponding water and sediments from Gachioma and Karumanthi rivers in Meru Town of Meru County. The concentration levels of these heavy metals in the plant were determined to assess whether taro can accumulate them to toxic levels. Taro corms and leaves together with water and sediment samples were collected along the two rivers. The solid samples were first dried in the sun then in an oven and ashed in the muffle furnace. The residue was leached from the vessel using hot concentrated hydrochloric acid then digested using a mixture of nitric, perchloric and sulphuric acids in a volume ratio of 3:1:1. The samples were analyzed at JKUAT Chemistry laboratories using the Buck Scientific Atomic Absorption Spectrophotometer (AAS) model 210 VGP. Microsoft Excel Computer Software was used to analyze the data. Analysis showed that concentration of mercury was below detection limits in all the analytes from the two rivers. Cadmium concentration levels in water from the two rivers were below detection limits. The study showed that concentration of chromium was highest in Gachioma River with a mean of 0.162 ± 0.003 ppm while the concentration for all xviii other metals in the two rivers was below 0.12 ppm. In the sediments, the metal with the highest concentration was manganese in Gachioma River sediments which ranged between 4.755 and 11.000 ppm with a mean of 7.824 ± 0.172 ppm. The metal with lowest concentration in the sediments was cadmium in Gachioma River which ranged between 0.036 and 0.054 ppm with a mean of 0.048 ± 0.002 ppm. Zinc had the highest concentration in corms collected from Karumanthi River whose range was between 0.498 and 1.726 ppm with a mean of 0.88 ± 0.014 ppm. The metal with lowest concentration in corms was lead with a mean of 0.02 ± 0.0002 ppm and ranged between 0.008 and 0.026 ppm. The heavy metal with highest concentration in the leaves was manganese in the leaves of corms collected from Karumanthi River which ranged between1.730 and 3.776 and a mean of 2.68 ± 0.022 ppm. Lead had the lowest concentration in the leaves of taro collected from Gachioma River which ranged between 0.010 and 0.150 ppm and a mean of 0.012 ± 0.00 Statistical analysis indicated that both leaves and corms bio-accumulated heavy metals. Results indicate that the plant can accumulate heavy metals if grown in heavily polluted water bodies. These results showed that the amounts of heavy metals in the two rivers were very low and did not pose any potential health hazard to consumers as they were below the and National Environmental Management Authority (NEMA) permitted levels. The potential use of the plant in water treatment is worth further investigation.