ACCUMULATION OF ARSENIC IN THE SHOOTS OF SUDAN GRASS AND BUSH BEAN

Abstract

When Sudan grass (Sorghum vulgare var. sudanense) and bush bean (Phaseolus vulgaris var. humilis) were grown for varying lengths of time in nutrient solutions containing various concentrations of NaAsO/sub 2/, it was found that concentrations of arsenic up to 0.5 to 0.6 ppM had no effect on the growth of either plant as measured by increases in dry weight. Growth was effectively suppressed, however, by concentrations of 1.2 and 12.0 ppM of As for bean and Sudan grass, respectively. Addition of arsenic to the solutions caused an immediate plasmolysis of the roots and wilting of the leaves followed by discoloration of roots and necrosis of leaf tips and margins, indicating that the arsenic effected a sudden decrease in the movement of water into the plants. The concentrations of arsenic in the plant tops and in each of their parts except the reproductive structures were found to be proportional to the concentrations in the nutrient solutions. The magnitudes of these concentrations were more or less constant during the experimental periods, the longest of which was nine weeks. The leaves were highest, the stem tissues intermediate, and the reproductive structures lowest in concentration of arsenic. Within a narrow range of concentrations of more » arsenic in the nutrient medium both plants grew successfully; but they contained concentrations of arsenic in the plant tops in excess of the tolerance limit (1.08 ppM of As) established by law for the arsenic content of foods. For equal relative reductions in yield the more resistant species (Sudan grass) contained several times the concentration of arsenic in the sensitive species (bean). Accumulated arsenical residues in soils as a result of insect and weed control practices are discussed as a source of arsenic contamination in foods through absorption by plants. « less