Reference Concentration

Apply caller continuous-exposure and dosimetric adjustments plus assessment factors to an inhalation POD; gas/particle-specific dosimetry and authoritative RfC derivation are not performed.

Description

Apply a supplied exposure schedule, dosimetric multiplier, and assessment factors to an inhalation point of departure.

An inhalation reference concentration assessment starts from evidence relevant to a chemical and endpoint, adjusts exposure and dosimetry as appropriate, and accounts for uncertainty. Continuous exposure and species-related dosimetry are separate parts of that assessment.^[1]

This tool first adjusts an animal point-of-departure concentration by hours per exposure day and exposure days per week. It then multiplies by your dosimetric adjustment and divides by the product of your assessment factors.

Both concentration outputs use mg/m³. The continuousEquivalentMgPerCubicMeter output includes the schedule adjustment only, before dosimetry and factors. The derived reference concentration is a candidate under supplied assumptions rather than an authoritative limit.

When to use Reference Concentration

Use it to document a chosen sequence of duration, dosimetric, and factor adjustments, or compare arithmetic scenarios with an independently justified point of departure.

How to use Reference Concentration and interpret its calculation

Enter positive animalPointOfDepartureMgPerCubicMeter, hoursPerExposureDay no greater than 24, and exposureDaysPerWeek no greater than 7.
Enter positive dosimetricAdjustment and a nonempty assessmentFactors list with each factor at least one.
Run the calculation and review the schedule-only continuous equivalent before the derived reference concentration. Record why the adjustment assumptions apply to the endpoint.

Ccontinuous = POD × (hours/24) × (days/7); candidate RfC = Ccontinuous × dosimetric adjustment / product(factors)

The dosimetric input multiplies the adjusted concentration; it is not automatically limited to one.

The implementation allows positive fractional hours and exposure days to represent an average schedule. It does not infer a dosimetric factor, select assessment factors, or verify whether a simple concentration-time adjustment is biologically suitable.

json

{
  "input": {
    "animalPointOfDepartureMgPerCubicMeter": 10,
    "hoursPerExposureDay": 6,
    "exposureDaysPerWeek": 5,
    "dosimetricAdjustment": 0.5,
    "assessmentFactors": [
      10,
      3
    ]
  },
  "output": {
    "continuousEquivalentMgPerCubicMeter": 1.7857142857142858,
    "derivedReferenceConcentrationMgPerCubicMeter": 0.02976190476190476
  }
}

A 24-hour, 7-day schedule leaves the schedule-only concentration equal to the POD. Multiplier one and factors [1] leave that concentration unchanged in the final output. Zero schedule values, schedules exceeding a day or week, and empty factors are rejected.

Limitations and assumptions

A linear duration adjustment can be inappropriate for an endpoint driven by peak concentration or different kinetics. The tool does not determine applicability, choose animal-to-human dosimetry, review a critical study, or retrieve official RfCs.

It does not convert air concentration to a retained mg/kg amount or make a route-to-route extrapolation. A candidate result is not a clinical or occupational exposure recommendation.

Alternative or Complementary methods

For a retained inhaled mass, use a separate ventilation-and-retention model. A dose-based NOAEL-to-RfD calculation uses different units and must not be substituted for a concentration-based assessment.

References

Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry (1994) — U.S. Environmental Protection Agency

Similar or alternative tools

Inhalation Dose
Calculate retained mass and a body-mass-normalized amount from interval exposures.
NOAEL to RfD Converter
Apply factors to a supplied daily dose point of departure on its own dose basis.