Removal of Chlorpyrifos by Water Lettuce (Pistia stratiotes L.) and Duckweed (Lemna minor L.)

Abstract

The potential of water lettuce (Pistia stratiotes L.) and duckweed (Lemna minor L.) to remove chlorpyrifos in water was investigated under laboratory greenhouse conditions. At initial chlorpyrifos concentrations of 0.0, 0.1 and 0.5 mg/L, the relative growth rates (RGR) of L. minor and P. stratiotes were not significantly different. In contrast, in the presence of 1 mg/L chlorpyrifos the RGR was significantly inhibited, giving an observed fresh weight based RGR_FW for P. stratiotes and L. minor from day 0 to 7 of −0.036 and −0.023 mg/g/day, respectively. The maximum removal of chlorpyrifos by P. stratiotes and L. minor, when chlorpyrifos was at an initial culture concentration of 0.5 mg/L, was 82% and 87%, respectively, with disappearance rate constants under these conditions of 2.94, 10.21 and 12.14 μg h⁻¹ for the control (no plants), and with P. stratiotes and L. minor, respectively, giving actual corrected plant removal rate constants of 7.27 and 9.20 μg h⁻¹ for P. stratiotes and L. minor, respectively. The bioconcentration factor (BCF) of L. minor was significantly greater than that for P. stratiotes and therefore, at least under these greenhouse-based conditions, L. minor was more efficient than P. stratiotes for the accelerated removal of chlorpyrifos from water.

KEY WORDS:

• chlorpyrifos
• water lettuce
• duckweed
• phytoremediation

ACKNOWLEDGMENTS

The authors gratefully acknowledge Dr. Robert Butcher, PCU, Faculty of Science, Chulalongkorn University, for his invaluable comments and review, and to two anonymous reviewers whose comments on an earlier version improved this manuscript. This research was in part supported by the Inter-Department of Environmental Science, Chulalongkorn University.