HEAVY METAL CONTENTS OF SELECTED VEGETABLES HARVESTED FROM CRUDE OIL-PRODUCING RIVERS STATE AND NON OIL-PRODUCING ENUGU STATE IN NIGERIA: COMPARATIVE ASSESSMENT

Abstract

The aim of this study was to investigate the heavy metal (HM) content of selected vegetables harvested from crude oil-producing Rivers State and non oil-producing Enugu State in Nigeria: comparative assessment. Four vegetables; Telfaria occidentialis, Talinum triangulare, Ocimium gratissimum, and Murraya koenigii, were harvested where available from local farms in local government areas (LGAs) purposively selected, each from the 3 senatorial zones in each state. A total of 26 vegetables were harvested and studied; 12 vegetables of 4 kinds from Enugu State and 14 vegetables of 4 kinds from Rivers State. The study used an experimental design. The chemical analysis in mg/100g of the vitamin, mineral and heavy metals (HMs) were conducted using standard methods. Data obtained were analyzed using Statistical Product for Service Solution (SPSS) version 21 and data collected was presented using descriptive statistics (mean, and standard deviation). Means were separated using t-test (between 2 locations) and Analysis of Variance, while Duncan's new multiple range test was used to compare means. The acceptance level of significance was p < 0.05 for all the results. Significant (p < 0.05) differences were recorded in the levels of the HMs in all the locations. The mean highest values varied in descending order; lead (Pb) > cadmium (Cd) > mercury (Hg) in mg/100g. Vegetable samples harvested from Rivers State had the highest toxicity level for both Pb (0.19 to 0.34) and Hg (0.01 to 0.03), while samples harvested from Enugu State had the highest toxicity level for Cd (0.07 to 0.25). The mean Pb contents for Ocimium gratissimum (0.27) and Talinum triangulare (0.26), harvested from Rivers States were significantly (p < 0.05) higher than their counterparts harvested from Enugu State (0.19 & 0.21, respectively). On the other hand, Cd had significantly (p < 0.05) higher values, 0.22 mg/100g, 0.20 mg/100g, and 0.15 mg/100g, in Ocimium gratissimum, Talinum triangulare and Telfaria occidentialis respectively, in Enugu State. Mercury had the least mean value than Pb & Cd in all the locations. Although, a significantly (p < 0.05) higher mean value of 0.02 mg/100g in both Murraya koenigii and Telfaria occidentiali was obtained in Rivers State. All the vegetables from all the localities in this study had toxic levels of HM much above the FAO/WHO acceptable limits; 0.03 mg/100g for Pb, and 0.02 mg/100g for Cd in foods and 0.0001 mg/100g for Hg in natural mineral water. Vegetable harvested from Rivers State had the highest values for vitamins C, E, and B1, except for vitamin B2 which had the highest value in the samples harvested from Enugu State. Vitamin C had the highest value, 63.3 mg/100g in Talinum triangulare harvested from Ogba/Egbema/Ndomi and Eleme, while, vitamin E had the highest value of 0.40 IU in both Ocimium gratissimum and Telfaria occidentialis harvested from Ogba/Egbema/Ndomi. On the other hand, vitamin B1 had the highest value of 1.58 mg/100g in both Ocimium gratissimum and Telfaria occidentialis harvested from Ogu/Bolo and in Murraya koenigii harvested from Etche in Rivers State while, vitamin B2 had the highest value of 0.36 mg/100g in Telfaria occidentialis harvested from Nsukka in Enugu State. The minerals; calcium (Ca), iron (Fe), and zinc (Zn) were highest in vegetable harvested from Rivers State, except for selenium (Se) which had the highest value in vegetables harvested from Enugu State. Calcium was 56.59 mg/100g in Ocimium gratissimum from Etche, while, Fe was 28.57 mg/100g in Talinum triangulare from Ogu/Bollo, and Zn was 23.26 mg/100g in Murraya koenigii from Ogu/Bollo in Rivers State. On the other hand, Se was 0.18 mg/100g in both Ocimium gratissimum and Telfaria occidentialis harvested from Nsukka and Enugu-East, respectively, in Enugu State. This study showed that the vegetable samples are good sources of vitamin C, B1, B2, Fe, Zn, and Se for an adequate diet. It can therefore be said that the public health importance for increased consumption of vegetables may equally mean increased HM consumption and bioaccumulation for the population in Rivers and Enugu States.