PLASTICS IN THE OCEANS - Plastics and Environmental Sustainability - page 458

POPstoorganismsingestingmicroparticlesandhowserioustheconsequent
adverse impacts might be at species and population levels.
The term partition coefficient refers to the equilibrium distribution of a
solute between two phases separated by a boundary. In this case, the two
phases are the solid plastic and seawater. Any compound (such as a POP)
in seawater will readily diffuse into the hydrophobic plastic as well resulting
in an equilibrium concentration of the compound in the plastic will be
very much higher than that in seawater (Ogata et al., 2009). The partition
coefficient K P/W is the ratio of the concentrations, and in the case of plastics
in seawater can be expressed as follows:
where q e and C e are the equilibrium concentrations of the POP compound
in the plastic and in water. 4 The higher the K P/W value, the more efficient
is the plastic in concentrating the POP from seawater. Typical values of
K P/W for some common organic pollutants are given in Table 10.5 . As seen
from the table, the values are large and plastic-specific. Rochman et al.
found PS to sorb higher equilibrium concentrations of polycyclic aromatic
hydrocarbons (PAH) compared to PP, PET, or PVC and about the same
as for high density polyethylene and LDPE (Rochman et al., 2013c). The
relatively higher available free volume and aromaticity of PS were probably
responsible for the enhanced solubility.