Study of Phytochemical Contents and Antioxidant Properties of Fresh Vegetables in relation to the Essential and Toxic Metals and their Health Risk Assessment

Abstract

Vegetables, soil and irrigation water samples were collected form the sub-urban areas of Rawalpindi and the samples were processed for metal analysis using flame atomic absorption spectrometer. Digestion of soil and vegetables samples was done according to the reported method for complete digestion. Vegetable samples were processed to find out the essential and toxic metals along with their phytochemical contents and the antioxidant properties. For phytochemical contents and the antioxidant properties dried, powdered vegetable samples were extracted by sequential method using water and acetone respectively as extracting medium. Total polyphenols, flavonoids, flavonols, and ascorbic acid contents were determined along side DPPH radical scavenging activity, hydroxyl. radical scavenging activity, ferrous ion chelating activity, ferric reducing antioxidant power and phosphomolybdenum complex assay were also evaluated. Among major essential metals, Ca showed highest concentration in all the vegetable samples followed by Mg, K and Na whereas in case of minor essential metals, Fe showed highest concentration and among trace metals, Cr showed the highest concentration in almost all the vegetable samples. On average basis, minor essential and trace metals showed random distribution in vegetable samples. Very strong and significant correlations were observed in most of the cases and quartile distribution pattern showed that metals were more dispersed and asymmetrically distributed in vegetables and water samples as compared to the soil samples. Among phytochemicals, water extracts of most of the vegetables showed exceedingly high polyphenol and ascorbic acid contents than acetone extracts and random pattern in case of flavonols and flavonoid contents. DPPH, FRAP and PMA were almost comparable in both the water and the acetone extracts of the vegetable samples whereas OH was notably high for acetone extracts and Fe2+ was significantly higher in water extracts. Health risk assessment for selected metals in vegetables showed that hazard quotient and cancer risk indicated values much below the limit values (unity and 1 x 10-4, respectively) indicating no long term non-carcinogenic as well as carcinogenic health risks are associated with the consumption of these vegetables. Among selected metals, Na, Mg, K and Cd showed significant translocation in different vegetables, notably high in leafy vegetables. Soil contamination factor and enrichment factor showed that soil was highly contaminated with Cd, Pb, Ca and Cu indicating the anthropogenic contribution of metals in the soil.