Arsenic toxicity and accumulation in turnip as affected by arsenic chemical speciation

Arsenic (As) uptake by turnip, growing under soilless culture conditions, w as studied. A 4 x 3 factorial experiment was conducted with four As species [arsenite, arsenate, methylarsonic acid (MMAA), dimethylarsinic acid (DMAA )] and three As concentrations (1.0, 2.0, and 5.0 mg L-1). Arsenic phytoava ilability and phytotoxicity were primarily determined by As speciation. Org anic arsenicals, especially MMAA, were clearly phytotoxic to this turnip cu ltivar. Plant As concentrations significantly increased with increasing As application rates. Both organic arsenicals showed a higher upward transloca tion than their inorganic counterparts, contributing to the greater phytoto xicity and lower dry matter productions of these organic treatments. Both i nner root and outer root skin As concentrations were above the maximum limi t set for As content in food crops (1.0 mg kg(-1)). If turnip plants are ex posed to a large pulse of As, as growth on contaminated nutrient solutions, they will accumulate residues at levels that are unacceptable for animal a nd human consumption.