Water Toxicity Calculator

Inputs

Enter exposure assumptions and one or more contaminants. Use the “Add row” button for additional chemicals.

Exposure settings

Concentration units

µg/L values are converted to mg/L internally.

Daily ingestion rate (L/day)

Enter ingestion rate.

Body weight (kg)

Enter body weight.

Exposure frequency (days/year)

Enter exposure frequency.

Exposure duration (years)

Enter exposure duration.

Averaging time (days)

Common default for non-cancer: AT = ED × 365.

Enter averaging time.

Contaminants

Concentration	Guideline (mg/L)	Reference dose (RfD)	Slope factor (optional)
In chosen units above.	Used only for ratio.	Required for HQ.	Enables cancer risk.
In chosen units above.	Used only for ratio.	Required for HQ.	Enables cancer risk.
In chosen units above.	Used only for ratio.	Required for HQ.	Enables cancer risk.

Tip: If you only have a guideline value (mg/L), you can still compute C/Guideline. For HQ, provide a reference dose (RfD).

Example data table

Sample inputs to demonstrate calculations. Replace with your lab results and preferred toxicity factors.

Contaminant	C (mg/L)	Guideline (mg/L)	RfD (mg/kg-day)	Slope factor	Typical use
Lead (Pb)	0.010	0.010	0.0035	0.0085	Demonstrates metal screening with both HQ and risk.
Arsenic (As)	0.005	0.010	0.0003	1.5	Shows sensitivity when RfD is very small.
Nitrate (NO₃⁻)	10.0	50.0	1.6	—	Illustrates a common ion with low HQ at typical levels.

Formula used

Screening calculations commonly used in exposure and risk assessment.

Chronic Daily Intake (CDI)

CDI = (C × IR × EF × ED) / (BW × AT)

C: concentration (mg/L), IR: ingestion (L/day), EF: days/year, ED: years, BW: kg, AT: days. Output: mg/kg-day.

Hazard Quotient (HQ)

HQ = CDI / RfD

RfD is the reference dose (mg/kg-day). HQ > 1 suggests potential non-cancer concern under the selected assumptions.

Cancer Risk (optional)

CR = CDI × SF

SF is the slope factor ((mg/kg-day)⁻¹). Total risk sums CR across contaminants with SF values.

Combined index

Hazard Index (HI) is the sum of HQ values. It is a conservative screening metric for mixtures when endpoints are assumed additive.

How to use this calculator

Choose concentration units and enter exposure settings (IR, BW, EF, ED, AT).
Add each contaminant as a row and enter its concentration from lab results.
Optionally enter a guideline (mg/L) to compute the C/Guideline ratio.
Enter a reference dose (RfD) to compute HQ; add a slope factor to compute cancer risk.
Press Submit. Results appear above the form and can be exported.

Professional overview

Why screening calculations matter

Water monitoring often produces analyte lists, yet decisions still need a single picture of potential exposure. This calculator converts measured concentrations into dose indicators comparable across chemicals. It supports mixture screening by summing hazard quotients into a hazard index, highlighting where cumulative non-cancer concern may be plausible under selected assumptions very clearly.

Key exposure drivers you can test

Chronic Daily Intake scales linearly with concentration and ingestion rate, and inversely with body weight and averaging time. Doubling daily ingestion from 2 to 4 L/day doubles CDI, HQ, and risk. Reducing body weight from 70 to 35 kg doubles dose metrics, which is why child scenarios often yield higher indices for the same result.

How hazard quotients translate into a hazard index

Each contaminant with a reference dose produces an HQ = CDI/RfD. Summing HQ values gives HI, a conservative screening statistic for mixtures when effects are assumed additive. If three chemicals have HQ values of 0.3, 0.4, and 0.6, then HI = 1.3, meaning the combined benchmark is exceeded even though two HQ values are below one.

Using guideline ratios alongside toxicity factors

Guidelines are practical for quick comparison, but they can differ by jurisdiction and endpoint. The C/Guideline ratio helps prioritize follow-up sampling when toxicity factors are unavailable. A ratio of 1.2 means the concentration is 20% above the selected guideline. Pairing ratios with HQ clarifies whether an exceedance also translates into a dose concern under your exposure inputs.

Optional cancer risk for chemicals with slope factors

When a slope factor is provided, the calculator estimates individual excess lifetime cancer risk as CR = CDI × SF and sums across applicable chemicals. A total risk of 2×10⁻⁵ implies about two additional cases per 100,000 exposed people under modeled conditions. Because slope factors are chemical-specific and updated, document sources and versions when reporting results.

Reporting results with transparency

Exported tables include exposure assumptions, contaminant inputs, and derived metrics, enabling reproducibility. For professional reporting, note units, detection limits, and whether non-detects were treated as zero or a substitution value. Use sensitivity checks by varying ingestion rate, body weight, and averaging time to bound uncertainty and guide next actions such as treatment evaluation or confirmatory sampling.

FAQs

What does a hazard quotient above 1 mean?

HQ above 1 means the estimated daily dose exceeds the selected reference dose under your inputs. It is a screening flag, not a diagnosis. Review assumptions, data quality, and whether the reference dose matches the relevant exposure route and population.

Why is hazard index used for mixtures?

HI sums hazard quotients to provide a conservative mixture screen when effects are treated as additive. It helps identify cumulative concern even when individual HQ values are below one. Use chemical grouping and endpoint knowledge when interpreting combined results.

Do I need both guideline and reference dose?

No. Guideline enables a simple C/Guideline ratio. Reference dose enables HQ and HI. If you have both, you can compare a regulatory benchmark with a dose-based screen in the same output table for better prioritization.

How should I handle non-detect laboratory results?

Common options include treating non-detects as zero, half the detection limit, or the detection limit. Each choice affects CDI and downstream metrics. Document your approach and, if possible, run sensitivity scenarios to see how much conclusions change.

When is cancer risk calculated?

Cancer risk is calculated only for rows with a positive slope factor. The calculator multiplies CDI by the slope factor and sums across those contaminants. If no slope factors are entered, cancer risk outputs remain blank and only non-cancer metrics are summarized.

Can I model children or high-consumption scenarios?

Yes. Adjust body weight and ingestion rate to represent the target group. Lower body weight and higher ingestion generally increase CDI, HQ, and risk. Keep exposure frequency, duration, and averaging time consistent with your scenario definition and reporting needs.