Bio-accumulation of Potentially Toxic Trace Elements in Vegetables in Sri Lanka

Potentially toxic trace elements (PTEs) from natural and anthropogenic sources, particularly in agriculture, may accumulate in soils and enter the food chain, posing health risks. Only a portion of these elements is bioavailable for plant uptake, which is strongly influenced by soil properties. This study quantified bioaccumulation factors (BAFs) to assess the uptake of Cd, Pb, As, Cu, and Zn by different vegetables, identified the soil properties influencing the bioavailability and accumulation, and evaluated whether Mehlich 3 extractable PTEs concentrations could serve as indicators of plant-available PTEs. Surface soil (0-15 cm) and corresponding vegetables were collected from two different cropping systems and soil types: vegetable-only Ultisol (Nuwara Eliya) and coarse-textured Entisol (Kalpitiya), and vegetable paddy rotation Ultisol (Badulla). PTE concentrations in soil and vegetables were measured using an Inductively Coupled Plasma Optical Emission Spectrometer. Total concentrations (mg/kg) of Cd (0.88), Pb (15), As (14.6), Cu (53.5), and Zn (136.7), Mehlich 3 extractable Cd (0.245), Pb (3.6), Cu (5.55), and Zn (19.1) were higher in Ultisol in Nuwara Eliya, while the highest As (0.245) concentration was observed in the Entisol of Kalpitiya. Elevated BAF values were observed for Cd (0.53) in carrots, Zn (0.64) in beetroot from Nuwara Eliya, and Zn in carrots (0.75), beetroot (1.69), cabbages (0.67), beans (0.97), and red onions (0.68) in Badulla, and Zn in beetroots (2.7) and red onions (4.22), Cu in beetroots (0.50), and red onions (1.13), and Cd in red onions (0.79), from Kalpitiya showing the highest accumulation. BAFs of Pb (0.01-0.06) and As (0.01 -0.08) relative to low across three locations. Soils in Kalpitiya contained very low organic carbon (<2%) and clay (<3%), while soils from Nuwara Eliya and Badulla had higher organic carbon (>2%) and clay (>20%). Higher organic carbon and clay levels reduced the mobility of potentially toxic elements (PTEs).