Temperature and pH Effects on Plant Uptake of Benzotriazoles by Sunflowers in Hydroponic Culture

ABSTRACT

This article describes a systematic approach to understanding the effect of environmental variables on plant uptake (phyto-uptake) of organic contaminants. Uptake (and possibly phytotransformation) of xenobiotics is a complex process that may differ from nutrient uptake. A specific group of xenobiotics (benzotriazoles) were studied using sunflowers grown hydroponically with changes of environmental conditions including solution volume, temperature, pH, and mixing. The response of plants to these stimuli was evaluated and compared using physiological changes (biomass production and water uptake) and estimated uptake rates (influx into plants), which define the uptake characteristics for the xenobiotic. Stirring of the hydroponic solution had a significant impact on plant growth and water uptake. Plants were healthier, probably because of a combination of factors such as improved aeration and increase in temperature. Uptake and possibly phytotransformation of benzotriazoles was increased accordingly. Experiments at different temperatures allowed us to estimate an activation energy for the reaction leading to triazole disappearance from the solution. The estimated activation energy was 43 kJ/mol, which indicates that the uptake process is kinetically limited. Culturing plants in triazole-amended hydroponic solutions at different pH values did not strongly affect the biomass production, water uptake, and benzotriazole uptake characteristics. The sunflowers showed an unexpected capacity to buffer the solution pH.

Keywords:

• benzotriazoles
• corrosion inhibitors
• plant uptake
• phytotransformation
• activation energy

ACKNOWLEDGMENTS

The research described in this article is contribution No. 04-128-J of the Kansas Agricultural Experiment Station and has been partially supported by the U.S. EPA and the U.S. Air Force under assistance agreements R-819653, R-825549, and R-825550 to the Great Plains–Rocky Mountain Hazardous Substance Research Center for regions 7 and 8 under project numbers 94-27 and 98-3. The Center for Hazardous Substance Research at Kansas State University also provided partial funding.

Notes

^a USEPA, 1977.

^b Hart et al., 2004.

^c Greater than 500 mg/L.

¹ Standard Hoagland's solution contains KNO₃ (404 mg/L), KH₂PO₄ (109 mg/L), MgSO₄·7H₂O (394 mg/L), Ca(NO₃)₂·4H₂O (1476 mg/L), FeSO₄·7H₂O (6 mg/L), EDTA Na₂ (8 mg/L), H₃BO₃ (3 mg/L), MnCl₂·4H₂O (2 mg/L), ZnSO₄·7H₂O (0.2 mg/L), CuSO₄· 5H₂O (0.2 mg/L), and H₂MoO₄· H₂O (0.2 mg/L).

^a In Experiment 3, each plant was its own control (see text for details).