Partitioning of chlorpyrifos to soil and plants in vegetated agricultural drainage ditches.

Constructed wetlands and vegetated agricultural drainage ditches (VADD) have been proposed as structural best management practices for the mitigation of chlorpyrifos contamination in agriculturally dominated watersheds. Sorption to soil and submergent aquatic plants has been measured as an important sink for chlorpyrifos; however, sorption to emergent plants has not been well characterized. Sorption isotherms for two soils and five emergent plants were determined by batch equilibrium technique. Sorption to whole plant stems (K(d)=570-1300 L kg(-1)) was more than 10 times higher than to soil (K(d)=40-71 L kg(-1)). Chopped plant material had K(d) values 7.6-96.2% greater than whole stems. Wetland plants with high internal surface area due to porous tissues had greater linear partitioning coefficients than terrestrial plants with a hollow structure. Chlorpyrifos sorption reached pseudo-equilibrium rapidly, indicating that partitioning will be an important mechanism in vegetated natural treatment systems for mitigating peak concentrations in surface waters and allowing time for attenuation by slower degradation reactions.