A lot of attention has been given recently to developing
fugacity-based, multi-compartment models for
the bioconcentration of volatile organic chemicals in vegitation. The basic approach was
first developed by Riederer (Environ. Sci.
Technol., 1990, 24, 829-837). Polder et al (Environ. Toxicol. Chem., 1998, 17,
962-968), in a literature study, compared Riederers model with a simple
one-compartment model suggested by Trapp and
Mattheis (Environ.Sci.Technol., 1995, 29, 2333-2338).
The Trapp-Mattheis model is implemented in the European Union Uniform System
for the Evaluation of Substances (EUSES). For
herbaceous plants, both models gave acceptable results.
Haitt (Anal. Chem., 1998, 70, 851-856), working with eight different plant species, obtained satisfactory results with all plant species using a four-compartment model; air, water, lipid and terpenoid compartments. Haitt recommends using:
where:
BCF = bioconcentration factor
Va = volume fraction of air in plant leaf
Vw = volume fraction of water in plant leaf
Kaw = air-water (Henrys law) partition coefficient
Vl = volume fraction of lipid in plant leaf
Koa = octanol-air partition coefficient = Kow/Kaw
Kow = octanol-water partition coefficient
Vt = volume fraction of terpenoid in plant leaf
Kta = terpenoid-air partition coefficient
Typically, Va = 0.19, Vw = 0.7, and Vl =0.05. Haitt suggests that PKoa can be substituted for VtKta in the above relationship, where P is the product of Vt and the ratio of the chemicals activity in octanol and in terpenoid phase. The average value of P ranged from 6 in juniper to 0.08 in grass.