Hazard Quotient Tool Calculator

Inputs

Concentration (C)

mg/L

Enter concentration in mg/L.

Example: dissolved contaminant concentration in drinking water.

Intake rate (IR)

L/day

Enter a positive intake rate.

Typical adult drinking water value is often near 2 L/day.

Exposure frequency (EF)

days/year

Use 1-366 days/year.

Accounts for seasonal exposure or intermittent contact.

Exposure duration (ED)

years

Enter a positive duration in years.

Time period the receptor is exposed to the chemical.

Body weight (BW)

Enter body weight in kg.

Used to normalize intake to mg/kg-day.

Reference dose (RfD)

mg/kg-day

Enter a positive reference dose.

Use an authoritative non-cancer RfD for the chemical.

Averaging time mode

Averaging time affects intake smoothing across time.

Averaging time (AT)

years

Enter a positive averaging time.

Enabled only for custom mode.

Quick presets

Presets adjust typical values; edit as needed.

Reset

Required fields. Outputs are educational; confirm inputs for compliance work.

Example data table

These examples show how changing assumptions shifts HQ. They are not regulatory defaults.

Scenario	C (mg/L)	IR (L/day)	EF (days/year)	ED (years)	BW (kg)	RfD (mg/kg-day)	Notes
Adult, steady exposure	0.05	2.0	350	30	70	0.003	Common ingestion-style assumptions.
Child, higher intake per kg	0.05	1.0	350	6	15	0.003	Lower BW increases CDI and HQ.
Seasonal exposure	0.05	2.0	120	10	70	0.003	Lower EF reduces CDI proportionally.

Formula used

This tool estimates non-cancer risk using the ingestion pathway. It first computes the chronic daily intake (CDI), then divides by the reference dose (RfD).

CDI (mg/kg-day) = (C × IR × EF × ED) / (BW × AT)
HQ = CDI / RfD
Cmax (for HQ = 1) = (RfD × BW × AT) / (IR × EF × ED)

C is concentration (mg/L), IR is intake (L/day), EF is days/year, ED is years, BW is kg, and AT is averaging time in days.

How to use this calculator

Enter the chemical concentration and the intake rate.
Set exposure frequency and duration for your scenario.
Provide body weight and an authoritative reference dose.
Use non-cancer averaging time, or choose custom.
Click Calculate, then export results as CSV or PDF.

Exposure inputs should match the route

Hazard quotient screening is only as reliable as its exposure story. For drinking-water ingestion, concentration in mg/L pairs naturally with intake in L/day. If you are evaluating food, soil, or air, convert to a compatible concentration unit and intake rate before using the same structure. Document the pathway, receptor, and any dilution or treatment assumptions.

Chronic daily intake explains the scaling

The calculator computes chronic daily intake by multiplying concentration, intake rate, exposure frequency, and exposure duration, then dividing by body weight and averaging time. This structure makes the sensitivity intuitive: doubling concentration doubles intake; halving body weight doubles intake. Averaging time smooths exposure across days, which is why non-cancer assessments commonly align averaging time to exposure duration.

Reference dose selection drives the benchmark

RfD is the toxicity benchmark used in the denominator, so it should come from an authoritative source and match the exposure route and duration. When multiple values exist, select the one applicable to chronic exposure and note any uncertainty factors. Using an inappropriate RfD can understate or overstate risk more than any reasonable exposure adjustment.

Interpreting HQ values for decisions

HQ is unitless. Values below one are typically interpreted as unlikely to pose non-cancer adverse effects for the modeled receptor, while values above one suggest potential concern and a need for refinement. Refinement may include better sampling data, receptor-specific intake estimates, alternative exposure frequencies, or the addition of site controls that reduce concentration or contact.

Using the target concentration output wisely

The tool also back-calculates a target concentration that would yield HQ equal to one for the same assumptions. This is useful for setting provisional screening levels, comparing treatment goals, or communicating “what-if” reductions. Because the target depends on every input, treat it as scenario-specific and always report the full parameter set alongside the target value.

To support audits, store the calculation date, chemical identifier, and units used. If you evaluate several chemicals, compute a hazard index by summing HQs for common target organs. Pair results with confidence notes: sampling variability, detection limits, and conservative defaults. This transparency helps reviewers understand why a value materially changed between iterations over time.

FAQs

What does HQ represent in this tool?

HQ compares estimated chronic intake to a reference dose. It is a screening indicator for non-cancer effects and helps prioritize whether an exposure scenario needs refinement or mitigation.

Why can HQ increase when body weight decreases?

CDI is normalized by body weight. With the same concentration and intake, a smaller body weight yields a higher mg/kg-day dose, so HQ rises proportionally.

Should averaging time always equal exposure duration?

For many non-cancer chronic assessments, averaging time is set to exposure duration. Use a custom averaging time when guidance or study design requires a different averaging window.

How do I handle intermittent or seasonal exposure?

Adjust exposure frequency to reflect days per year of contact. Keep the same concentration unit and intake rate for the pathway, then recalculate to see how HQ changes with EF.

What if I have multiple chemicals in the same sample?

Calculate HQ for each chemical using its own reference dose. If they affect the same target organ or endpoint, sum the HQ values to estimate a simple hazard index for screening.

Is HQ below 1 always safe?

Not always. HQ depends on assumptions, data quality, and the selected reference dose. Treat HQ below 1 as lower concern, then confirm with better measurements, site context, and applicable guidance.