N-15 tracer studies on the effect of airborne bromoxynil on the nitrogen metabolism of plants

In wind tunnel experiments the effect of airborne Bromoxynil on the nitroge n metabolism of young tomato and sunflower plants was studied using the N-1 5-tracer technique. Bromoxynil concentrations from 0-3,420 ng/m(3) were tes ted in 48 h exposure experiments. No observable effect concentrations (NOEC ) were derived from the obtained dose-response relationships. Very low bromoxynil concentrations (2 ng/m(3)) lead to a stimulation of the N-15-incorporation. Only concentrations >1,000 ng/m(3) caused a decrease i n the N-15-incorporation of the non-protein and protein fraction. The deriv ed NOECs for tomato were 2.6 ng/m(3) for the non-protein and 1.1 ng/m(3) fo r the protein fraction, respectively. For sunflower, the respective NOECs w ere 1.6 ng/m(3) and 1.7 ng/m(3). Measurements with tomato plants seven days after Bromoxynil exposure result ed in four times higher NOEC values compared to right after the 48 h exposu re. This demonstrates the ability of the plants to recover from low concent rations. At 2 ng/m(3) tomatoes recovered completely after the 7 days, while higher concentrations lead to a lasting effect.