Environmental Risk Assesment of Heavy Metals Content of Municipal Solid Waste Used as Organic Fertilizer in Vegetable Gardens on the Jos Plateau, Nigeria

Abstract

This study was conducted on vegetable gardens in and around Jos on the Jos Plateau, North central Nigeria; a city which has had strong European influence as a result of a long history of tin mining activity in the area. The study seeks to assess the degree of accumulation and/or contamination of the heavy metals in compost from municipal solid waste due for application as organic fertilizer in vegetable gardens as well as the potential human health risk associated with the consumption of vegetables grown with such organic fertilizer. Three waste dumpsites in Jos and gardens were selected where vegetables cultivation (cabbage, lettuce, spinach, turnip, carrot, radish, beet root, tomato and spring onions) are practiced. The representative samples of compost material, agricultural soil and vegetables were collected and analyzed for heavy metals such as: As, Cd, Co, Cr, Ni, Pb, Cu, Zn, Sb and Se. Geochemical results show that the concentrations of these elements in the compost are higher (in decreasing order of As>Cd>Zn>Pb>Cu>Cr) compared to that in the soils yet to be applied the organic fertilizer. The degree of contamination of the soils and the compost, the transfer factor (TF) from the agricultural soil to vegetables and its health risk index (HRI) were calculated. Results show that in general, the agricultural soils are severely contaminated by As, Cd, Zn and Pb (CF= 10-25). Other elements such as Cr, Cu and Ni have moderately contaminated the soil. All the vegetables seem to have been severely contaminated by Se and As (Se>As>Zn) and therefore are good accumulators of these toxic metals. The leafy and the root vegetables appear to be the major accumulator of Se and As respectively. The TF of As in all the different varieties of vegetables is >1, indicating that this element is readily absorbed by these plants. The HRI value for As, Pb and Zn is >1 for the all the vegetables and therefore is unsafe posing serious human health risks.