Arsenic in leafy vegetable plants grown on mine water-contaminated soils: Uptake, human health risk and remedial effects of biochar

Abstract

Field investigation and microcosm experiment were conducted to examine the uptake of arsenic by vegetable plants grown on the soils contaminated by acidic mine water and evaluate the human health risk from consuming the vegetables. Plant uptake of arsenic was related to the ratio of phosphorus to arsenic in soil solution for the same vegetable species. Bioaccumulation coefficient (BAC) of arsenic was highly variable amongst the different vegetable species with water spinach (white stem) and sweet potato leaf being identified as major vegetable species with high BAC. There was a reasonably good relationship between the gastric phase-bioaccessible arsenic and the gastrointestinal phase-bioaccessible arsenic. Consumption of the vegetables grown in the investigated area poses a significantly potential human health risk with a hazard quotient (HQ) of 2.7. Application of biochar significantly inhibited the uptake of arsenic by the vegetable plant due to protonation of biochar surfaces under acidic conditions, which favoured adsorption of arsenic. The bioaccessibity of arsenic in the edible part of vegetable was also reduced due to biochar application. The HQ of the test vegetable plant (Gynura cusimbua) after soil amendment by biochar was reduced to 2 from 6 for the unamended soil.

Keywords: Acidic mine water; Arsenic; Biochar; Human health risk; Leafy vegetable.