Biochar addition to an arsenic contaminated soil increases arsenic concentrations in the pore water but reduces uptake to tomato plants (Solanum lycopersicum L.)

► The consequences of adding biochar to an arsenic contaminated soil-plant system were studied. ► Arsenic was mobilised into soil pore water rapidly following biochar addition. ► Transfer of arsenic from soil to roots and aerial plant parts was reduced by biochar. ► Fruit arsenic concentrations were very low, so toxicity risk was negligible. ► Biochar did not affect biomass yield and reduced germination without nutrient supplement.