Assessment of Heavy Metals in Guinea Sorrel (Hibiscus sabdariffa) Cultivated on Fadama Soils in Maiduguri, Nigeria

River Ngadda is one of the main sources of water used by the resident of Maiduguri Metropolis The proximity of the people to the river encourages a lot of irrigation farming along the river bank during the dry season especially vegetables therefore, concentration values of heavy metals namely Aluminum, Cobalt, Iron, Lanthanum, Manganese, Chromium, Rubidium, Scandium, Samarium, Thorium, Vanadium and Zinc were determined in Guinea Sorrel (Hibiscus sabdariffa) vegetable samples obtained at six different locations on different dry season farming (Fadama) sites along the bank of river Ngadda and Alau dam in Maiduguri, Nigeria. Instrumental neutron activation analysis (INAA) technique which is a sensitive method for determination of major, minor and trace element in a matrix was used to assessed the heavy metal accumulation levels in Guinea Sorrel with the aim to establish the food safety status from heavy metals concentration levels for guinea sorrel cultivated along the bank of river Ngadda and Alau dam and consumed on a daily basis as compared to WHO/FAO recommended maximum permissible limit (MPL) for edible vegetables. The result obtained showed that the concentration values of Al ranged from 932 ± 18 to 3369 ± 54 ppm, Co 0 .12 ± 0.03 to 40 ± 4 ppm, La 1.00 ± 0.03 ppm to 38 ± 4 ppm, Manganese 112 ± 0.4 to 176 ± 1 ppm, Rubidium 4 ± 0.5 to 21 ± 1ppm, Sc 0.10 ± 0.007 to 27 ± 1 ppm Sm 0.106 ± 0.004 to 17.2 ± 0.4 ppm, V 1.10 ± 0.3 to 4 ± 1 ppm and Zn 17 ± 3 to 63 ± 4 ppm, and Fe 379 ± 33 ppm to 2316 ± 65 ppm. This result indicates that the maximum concentrations of Fe, Cr, Mn and Co, in guinea sorrel from most of the sites were above the acceptable limits given by FAO/WHO for edible vegetables. Therefore, it is certain that there is the health risk associated with the continuous consumption of guinea sorrel vegetables cultivated from the study site and authors of this work hereby recommends that investigation of this kind should be carried out from time to time so as to know the buildup or otherwise of heavy metals in guinea sorrel cultivated in the study sites.