Table 3.
Modifications to persistent organic pollutant bioaccumulation metrics for PFAS.
| Metric | Traditional Indicator | PFAS-Specific Recommendation |
|---|---|---|
| KOW, KOA | Used as surrogates for equilibrium partitioning of neutral organic chemicals to lipid tissues of aquatic and air-breathing organisms. | DOW: Octanol-water distribution ratio (takes degree of ionization into account); DMW: Membrane-water partition ratio; Chemical activity ratios; KPW: Protein-water partition coefficient; KA, KD: Equilibrium association and dissociation constants for specific proteins (e.g. albumin, LFABP) Key gap: relevant metric for air-breathing organisms. |
| BCF: bioconcentration factor (waterborne or airborne exposure only) BAF: bioaccumulation factor (waterborne/airborne and/or dietary exposure) |
Concentration in organism (whole body, lipid-normalized)/concentration in water (freely dissolved) | Concentration (chemical activity)1 in serum/ concentration in water; Concentration in liver/ concentration in water; Concentration in organism (whole body)/concentration in water. Key gap: (1) Selecting appropriate tissue to represent accumulation in organism. (2) Accounting for contributions of precursors to field based BAFs. |
| BMF: biomagnification factor TMF: trophic magnification factor |
Concentration in predator (whole body, lipid-normalized)/concentration in prey (whole body, lipid-normalized) | Concentration in predator liver /concentration in prey liver; Concentration in predator (whole body) / concentration in prey (whole body); Key gaps: Selecting appropriate predator and prey tissues across food webs. |
1
Emerging approach: activity-based metrics. See section 6.4.