SPMD-Water Partition Coefficients

Literature values of SPMD-water partition coefficients (iifswS) should be used with caution. Different units of Ks are generated when the concentrations in SPMD and water are expressed on a mass basis (e.g., ng g ) or a volume basis (e.g., ng mL ). Depending on the choice of concentration units, values will have units of g g mL mL or mL g or Ksv, values are given as dimensionless numbers in the former two cases. Care should be taken to distinguish between the different versions of Ksv,. Preferably, mL mL units should be used, because most of the equations for SPMD uptake kinetics use the volume of an SPMD rather than its mass. The two most frequently used versions of Ks are interrelated by 

In Tables A.1 through A.3, all Ksv, values were converted to mL mL units where applicable. In the literature sources where the units were not explicitly mentioned, these were inferred from the model equations used. To avoid possible ambiguity in the future, authors are urged to specify the units of their reported Ks values. 

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When the k and SPMD-water partition coefficient of the PRC are known, its Rs can be calculated from Eq. 3.20. More precisely, we assume that the PRC is representative of the in situ sampling rates of target compounds with similar physicochemical properties as the PRC. Various approaches have been used to estimate sampling rates for all analytes from the PRC-derived sampling rates (see Section 3.6.). 

Figure 3.3 SPMD-water partition coefficients (ml mL units) as a function of log Kqw for PAHs—filled circles Huckins et al. (1999), filled triangles Huckins et al. (2004) phenanthrene, PCB 52, and p,p -DDE—open triangles Huckins et al. (2002a) chlorobenzenes, PAHs, and PCBs—squares Booij et al. (2003a) pesticides—filled diamonds Sabaliunas and Sodergren (1997) and HCHs—open diamonds Vrana and Schiiurmann (2002). Additional kjw data were calculated for PCBs (asterisks) and alkylated benzenes (crosses) using the fCmw data from Lefkovitz et al. (1996) and Reynolds et al. (1990), and the data from Chiou (1985).

Herein, we examine several eqnations which are nsed to determine BCF% and BAFs, SPMD-water partition coefficients (Ksv,s), and the more complex exchange processes of some BMOs. Hopeffilly, the formulation and the assumptions behind these equations further clarify some of commonalities and differences between residue accumulation in BMOs and SPMDs. 

Table A.1 SPMD-Water Partition Coefficients (K s, mL mL M of Mono-Aromatic and Polycyclic Aromatic Hydrocarbons...

Table A.2 SPMD-Water Partition Coefficients K s, ml mL ) of Chlorobenzenes and PCBs...

Table A.3 SPMD-Water Partition Coefficients (/CwS, rnL ml M of Organochlorine Pesticides...

Einally, LDPE SPMDs with grass carp lipid were exposed for 21 d to 14C-2,2, 5,5 -TCB, 14c-3,3, 4,4 -TCB, i c-mirex and i c-fenvalerate, whereas SPMDs with triolein or lecithin were exposed to only " C-2,2, 5,5 -TCB. After 21 d, the largest mass fraction of these test chemicals ( " C-mirex was an exception) was in the triolein. The C-2,2, 5,5 -TCB log triolein-water partition coefficient was 6.01, whereas the " C-2,2, 5,5 -TCB partition coefficients for the grass carp lipid-water and lecithin-water systems were 30% and 35% lower, respectively. Comparison of these data to literature log AlowS of 2,2, 5,5 -TCB showed that the partition coefficients for the grass-carp lipid and the lecithin were not significantly different from median values reported for the log ATow of " C-2,2, 5,5 -TCB. However, the partition coefficient of 2,2, 5,5 -TCB in triolein and water in direct... 

Huckins et al.29 reported a 20-70% impedance in the uptake of PAHs in cases of severe biofouling on the surface of SPMDs. Their model describing the mass transfer in a biofilm indicated that it behaved like an immobilized water layer with a resistance that is independent of the biofilm/water partition coefficient. This would result in a similar mobility of compounds in the biofilm since this is independent of their hydrophobicity.19 Similarly, Richardson et al.47 observed that biofouling caused a reduction of up to 50% in the uptake of PAHs and organochlorine pesticides by SPMDs. It has been suggested by several authors that PRCs can be used to correct biofouling during deployment,42,47 but more experimental evidence is needed. 

When equilibrium is attained, the concentration of the compound in the SPMD is equal to the concentration in water multiplied by ratio of compound uptake and release rate constants. The ratio describes partition coefficient between SPMD and water, Ksw. Equilibrium for some chemicals with high fugacities may occur in less than one month. 

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