TITLE:
A Quantitative LC-MS/MS Study of the Partitioning, Transport, and Fate of Pesticide Residues on Soil
AUTHORS:
Heather A. Gamble, Donald S. Gamble
KEYWORDS:
Pesticide-Soil Interactions, Sorption Kinetics, LC-MS/MS Fast Polarity Switching, Predictive Modeling
JOURNAL NAME:
Journal of Environmental Protection,
Vol.7 No.3,
February
26,
2016
ABSTRACT:
Titration of pesticides onto sorption sites
can determine sorption capacities on soils. Previous studies have tracked the
sorption capacities and detailed kinetics of the uptake of atrazine and its
decomposition byproduct hydroxyatrazine on different soils, including
measurements made using LC-MS/MS. These studies have now been extended to
explore sorption-desorption equilibria for a mixture of pesticides from soil
using LC-MS/MS. Desorption of sorbed pesticide residues has environmental
regulatory implications for pesticide levels in runoff, or for longer term
sequestration, partitioning, and transport. The uptake of pesticides by the
soil at equilibrium was measured for a number of different concentrations, and
sorption capacities were estimated. Pesticide-soil interaction studies were
conducted by exposing standard stock solutions of pesticide mixtures to a
characterized Nova Scotia soil. The mixture contained atrazine and dicamba.
Initial aqueous mixture concentrations ranging from 5 × 10-9 to 10-5 M or greater were exposed to 25 mg aliquots of
soil and allowed to reach equilibrium. The total uptake of each pesticide was
measured indirectly, by measuring the concentration remaining in solution using
an IONICS 3Q 120 triple quadrupole mass spectrometer. These sorption capacities
have been supplemented by studies examining equilibrium recovery rates from
soil aliquots with different initial uptakes. This gives insight into the
fraction of easily recoverable (reversibly sorbed) pesticides on the soil.
Proper quantification of equilibrium constants and kinetic rate coefficients
using high performance LC-MS/MS facilitates the construction of accurate,
predictive models. Predictive kinetic models can successfully mimic the
experimental results for solution concentration, labile sorption, and
intra-particle diffusion, and could be used to guide regulatory practices.