Assessment of Health Risk and Elemental Concentrations in Minjingu Vegetables and Soils by Wavelength Dispersive X-ray Fluorescence

Abstract

The samples of soil and selected species of vegetables (cowpea leaves, spinach, sweet potato leaves, Ethiopian mustard and Chinese cabbages) were randomly collected from four sites, Idara ya maji, Nkaiti, Mbulungu and Mkwajuni of Minjingu village of Manyara in Tanzania. The samples were analyzed by means of wavelength dispersive x-ray fluorescence (WDXRF) spectrometry to determine the heavy metal concentrations in soils and vegetables of the field study with emphasis on their health risk index (HRI) assessment. The results indicate that soils have concentration range of 142-1547 for Ca, 737-2515 for K, 2396-4748 for Si, 0-121 for P, 0-181 for Mg, 0-36 for S, 0-68 for Na, 561-942 for Al, 121-4748 for Fe, 0-80 for Mn, 0-53 for Sr, 0-37 for Cs and 0-11 for Ni in mg/kg which was above the maximum tolerable limits(MTL). Elements detected in vegetables were in the range of 2123-6122 for Ca, 747-8005 for K, 65-996 for Si, 40-348 for Mg, for Mn, 85-584 for P, 22-705 for S, 0-218 for Na, 70-835 for Fe, 23-286 for Al, 0-98 for Cs, 84-1076 for Cl and 0-13 for Ni in mg/kg. The highest heavy metal retention capability was exhibited in Cowpea leaves, Spinach and Chinese cabbages but sweet potato leaves and Ethiopian mustard has shown lower concentrations. Control site recorded the least concentration values. The HRI values for Sr, Ni and Fe in vegetables exceeded the maximum threshold limits (HRI>1) set by United States Environmental Protection Agency (USEPA). The findings of this work indicates that soils and vegetables grown, particularly cowpea leaves, spinach and Chinese cabbages were extremely contaminated at levels able to pose detrimental health effects to the consumers. Therefore the consumption of cowpea leaves, spinach and Chinese cabbages should be reduced to the maximum if not abandoned. But limited quantities of Ethiopian mustard and sweet potato leaves can be taken while immediate steps are taken to reduce anthropogenic activities at the polluting site. This situation makes the regular monitoring of the grown vegetables a compulsory act.