Elucidation of heavy metal content, phenolic profiles, and antioxidant activities of kale (Brassica oleracea L. var. acephala) and arugula (Brassica eruca L.) grown in urban gardens in Istanbul

Abstract

This study was conducted to evaluate the effect of two distances: close (0–10 m) and far (60 m) from the heavy traffic roadside, at three different cultivation sites (MS: Mevlanakapi–Silivrikapi, SB: Silivrikapi–Belgradkapi, and BY: Belgradkapi–Yedikule kapi) along the road line. First, the phenolic compounds, antioxidant activity, and physicochemical properties in kale and arugula vegetables were examined. Second, heavy metal concentrations in vegetables, soil, and irrigated water were investigated. In both vegetables, the highest total phenolic content was detected in samples obtained from far distance in SB site (3880.3 mg/kg) for kale and in BY site (1459.9 mg/kg) for arugula, whereas the lowest content was found at the close distance in MS site for both kale (448.5 mg/kg) and arugula (586.4 mg/kg). The antioxidant activity values [mg Trolox/kg (dw)] ranged from 366.74 to 586.10 and 2349.00 to 3757.4 for kale and from 520.00 to 945.60 and 3323.00 to 5814.70 for arugula in 2,2′‐azino‐bis (3‐ethylbenzothiazoline‐6‐sulfonic acid) and 2,2‐diphenyl‐1‐picrylhydrazyl methods, respectively. The levels of Cd and Hg in kale and arugula and Fe content in arugula exceeded FAO/WHO permissible limits, making them unsafe for human consumption. Meanwhile, the Pb content in kale and arugula and Fe content in kale were observed to be within acceptable limits set by FAO/WHO. In the irrigated water, the Pb value was below the permissible limit, whereas the Cd value was above it and no Hg and Fe were detected. In the soil samples, the Pb and Fe values were below the limit, whereas the Cd and Hg values were higher.