Assessment on bio-accumulation of metals in Zea mays (maize) plants grown in a polluted wetland in Harare, Zimbabwe.
TITLE :Assessment on bio-accumulation of metals in Zea mays (maize) plants grown in a polluted wetland in Harare, Zimbabwe. This study investigated bio-accumulation of eight metals; Iron, Zinc, Manganese, Lead, Copper, Cobalt, Cadmium, and Nickel in the soil and in maize grown in a wetland polluted by sewage effluent in Harare, Zimbabwe. Thirty maize plants growing in the wetland were randomly selected and from each plant, the leaf, stem, root and seed were analyzed for presence and levels of the eight metals using the Atomic Absorption Spectrophotometer method. Soil samples were also taken around the rhizosphere of each sample plant and analyzed for levels of the metals. Data were analyzed using One-way Analysis of Variance. Results showed significant differences (p<0.05) in metal levels in the soil and plant samples. The soil had the highest levels of all metals except for Zinc, Cadmium and Lead which were highest in the plant tissues. Bio-accumulation Factor (BAF) for Cadmium and Lead was >1 in all plant tissues. BAF for Zinc was also >1 in the leaf and seed. However, measured amounts for Cadmium and Lead in the seed did not exceed the World Health Organization limits, suggesting that the maize fruit was safe for human consumption, although there was concern of bio-magnification of the metals if pollution in the wetland persisted. Metal contaminants enter the human body mostly via food and drinking water (Khan, Malik and Mahammad 2013). Metal consumption by humans through food chains has been reported in many countries (Islam, Yang and Mahmood 2007). While some studies have been carried out on bio-accumulation of metals in crops (Khairiah et al. 2002; Ismail, Farihah and Khairiah 2005; Islam, Yang and Mahmood 2007; Zeng, Li and Mei 2008; Khan, Malik and Mahammad 2013; Alia et al. 2015), research on contamination of food crops by metals is scant in Zimbabwe, particularly in polluted wetlands. This study was therefore carried out to generate empirical data that could contribute towards filling of this research gap. The study was carried out in Marlborough Wetland which was polluted by sewage effluent, in Zimbabwe's capital city, Harare. The study investigated bio-accumulation of metals in maize plants cultivated in Marlborough Wetland in order to assess suitability of the cereal crop for human consumption. The main objective of the study was to determine the level of bio-accumulation of eight metals; Iron (Fe), Zinc (Zn), Manganese (Mn), Lead (Pb), Copper (Cu), Cobalt (Co), Cadmium (Cd), and Nickel (Ni) in the soil and in the root, stem, leaf and fruit of maize plants grown in the polluted wetland.