Expanding the applicability of multimedia fate models to polar organic chemicals

Reliable estimates of environmental phase partitioning are
essential for accurate predictions of the environmental
fate of organic chemicals. Current fate and transport models
use single-parameter linear free energy relationships (SPLFERs)
to quantify equilibrium phase partitioning. The
applicability of such SP-LFERs is limited because no single
parameter is able to describe appropriately all the
molecular interactions that contribute to environmental
phase distribution processes. Environmental partitioning
coefficients predicted by SP-LFERs may thus have errors
of up to an order of magnitude. Ranges for several
environmental partitioning equilibria are identified, where
such errors can result in significantly different fate predictions
for individual bulk model compartments. We propose
that it is possible to reduce such errors and uncertainties
by implementing polyparametric LFER (PP-LFER) approaches
in multimedia fate models. A level III fugacity model was
modified such that the partitioning properties of chemicals
are characterized by five linear solvation energy parameters
rather than vapor pressure, water solubility, and octanolwater partition coefficient. A comparison of modified and unmodified models for a set of organic chemicals shows that the approach chosen to simulate environmental phase partitioning can have a large impact on model results, including long-range transport potential, overall persistence, and concentrations in various media. It is argued that PPLFER based environmental fate models are applicable to a much wider range of organic substances, in particular those with polar functional groups. Obstacles to the full implementation of PP-LFER in multimedia fate models are currently the lack of solute descriptors for some chemicals of environmental concern and suitable regression equations for some important environmental phase equilibria, in particular for the partitioning between gas and particle phase in the atmosphere.