Modifications to persistent organic pollutant bioaccumulation metrics for poly‐ and perfluoroalkyl substances
| 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, liver fatty acid binding protein) 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)a 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 |
| 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, liver fatty acid binding protein) 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)a 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 |
Emerging approach: activity‐based metrics. See section PFAS bioaccumulation modeling.
PFAS = poly‐ and perfluoroalkyl substances.
Modifications to persistent organic pollutant bioaccumulation metrics for poly‐ and perfluoroalkyl substances
| 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, liver fatty acid binding protein) 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)a 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 |
| 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, liver fatty acid binding protein) 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)a 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 |
Emerging approach: activity‐based metrics. See section PFAS bioaccumulation modeling.
PFAS = poly‐ and perfluoroalkyl substances.
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