Evaluation of the levels of selected heavy metals in leafy vegetables from irrigation farming sites in Jos, Plateau, Nigeria

Leafy vegetables are used in making soups, local salads and diverse forms of foods for human consumption is common in Africa. These vegetables include Brassica oleracea (cabbage), Phaseolus vulgaris (green beans) and Solanum lycopersicum (tomatoes). The area of study is famous for agriculture and mining activities; Farmers cultivate them on degraded farmlands polluted with metals; these vegetables absorb these metals thereby making them enter the food chain. During dry season, water from mining ponds is used for irrigation. Industrial waste water is also used. Levels of cadmium (Cd), Arsenic (As), copper (Cu), and lead (Pb), were assessed using Inductively Coupled Plasma Optically Emitting Spectrophotometer (ICP-OES) equipment. Five samples of each vegetable were collected randomly from different irrigation farms situated at Bassa, Bisichi and Zaramaganda. Graph pad prism-7 multiple comparison tests in a one-way ANOVA was used to compare variations in metal concentrations at 95% confidence limit. Pb, As and Cd were not detected in water samples from Bisichi but mean level of Cd and Pb in water from Bassa and Zaramaganda were 0.932 mg/L (P=0.05) and 1.242 mg/L (P=0.05); 0.84 mg/L (P=0.05) and 16.338 mg/L (P=0.05), respectively relative the FAO/WHO safe limits. Water samples from Bassa contained Cu whose level was above (P=0.05) safe limits; only one was below the standard (P>0.05). Samples from Zaramaganda contained highest levels of the metals. cabbage and green beans from Zaramaganda and Bisichi contained Pb, Cu above (P=0.05) the FAO/WHO limit. Mean Pb content in cabbage and green beans from Bisichi was 2.099 and 0.189 mg/kg respectively. From Bassa, Pb content in tomatoes and green beans were 0.086 and 491.31 mg/kg respectively. From Zaramaganda, Pb content in green beans and tomatoes were 12.31 and 14.522 mg/kg; level of Cd in green beans 0.481 mg/kg. Considering Cu, tomato from Bassa contained highest level, 64.310 mg/kg (P=0.05), green beans from Zarmaganda was 48.251 mg/kg (P=0.05), tomato from Bisichi contained 38.541(P=0.05) relative safe limits. In conclusion, the significant concentrations of Cd, Pb and Cu in the vegetables in the area of study, which are routinely used in making soups, portage and local salads, predispose consumers to, cancer, cardiovascular diseases, inhibition of the heme biosynthesis pathway, hemolysis and febrile reactions due to their respective toxicities.