Dermal Flux
Calculate signed steady concentration-gradient dermal flux and net transfer; depletion, lag time, finite-dose skin storage and metabolism are excluded.
Description
Calculate signed dermal diffusion flux and net transferred mass for a fixed concentration gradient.
A permeability coefficient relates a concentration difference across a barrier to a steady diffusion flux. For a dermal scenario, the coefficient depends on the chemical, vehicle, and barrier conditions. A constant-gradient calculation is a simplified transfer model rather than a complete skin-absorption history.1
This tool multiplies a supplied permeability in cm/hour by donor minus receiver concentration in mg/cm³. The output flux is mg/cm²/hour. Multiplying by area in cm² and exposure hours gives signed net transferred mg.
Positive means transfer in the donor-to-receiver direction; a larger receiver concentration produces negative flux and mass. The sign is retained. Concentration units matter: mg/cm³ equals mg/mL, so mg/L values must be divided by 1,000 before entry.
When to use Dermal Flux
Use it to inspect a constant-gradient transfer scenario with a known or separately estimated permeability, including a nonzero receiver concentration.
How to use Dermal Flux and interpret its calculation
- Enter positive permeabilityCmPerHour and nonnegative donorConcentrationMgPerCubicCm and receiverConcentrationMgPerCubicCm.
- Enter nonnegative areaSquareCm and exposureHours, then run the calculation.
- Read signedFluxMgPerSquareCmHour and netTransferredMassMg with their direction and units. Check whether the assumed concentrations stay approximately constant over the interval.
J = permeability × (Cdonor − Creceiver); net mass = J × area × hours A zero receiver represents a sink boundary in this simple model. Flux is a signed amount per area per time.
The implementation preserves negative concentration differences and does not clamp reverse transfer to zero. Area and duration affect mass but not the calculated flux.
{
"input": {
"permeabilityCmPerHour": 0.1,
"donorConcentrationMgPerCubicCm": 2,
"receiverConcentrationMgPerCubicCm": 0.5,
"areaSquareCm": 10,
"exposureHours": 2
},
"output": {
"signedFluxMgPerSquareCmHour": 0.15,
"netTransferredMassMg": 3
}
}Equal donor and receiver concentrations give zero flux and mass. Zero area or zero duration gives zero mass while retaining the gradient-derived flux. Zero permeability is rejected rather than modeled as an impermeable barrier.
Limitations and assumptions
The model assumes constant permeability and boundary concentrations. It does not handle finite donor depletion, receiver buildup, lag time, changing skin condition, or multiple barrier layers. The predicted mass is not capped by the amount available.
No permeability is fitted or retrieved, and no systemic dose, body-mass normalization, bioavailability, or biological effect is calculated. Signed transfer is not automatically a positive absorbed exposure dose.
Alternative or Complementary methods
A calibrated permeability equation may provide a model input after its applicability is checked. For an available contact loading and absorbed fraction rather than a constant concentration gradient, use contact-dose arithmetic.
References
-
Exposure Assessment Tools by Routes — Dermal — U.S. Environmental Protection Agency
Similar or alternative tools
- Skin Permeability Coefficient
Evaluate a supplied permeability model from partitioning, molecular weight, and coefficients.
- Dermal Absorption Dose
Calculate absorbed mass from supplied contact loading, area, and absorption fractions.