Introduction

Before you can say whether the cadmium in rice or the lead in fish is a health concern, you need one number: how much of the element a person actually takes in per day, per kilogram of body weight. That number is the Estimated Daily Intake (EDI), and it is the entry point to every human-health risk assessment for dietary trace elements — Target Hazard Quotient (THQ), Hazard Index (HI) and carcinogenic risk all build on it.

This guide walks through the formula, the input values, a worked example, and the mistakes that most often distort the result.

The EDI formula

The simple, most commonly used form is:

EDI = (C × IR) / BW

C  = element concentration in the food (mg/kg, wet or dry weight — state which)
IR = ingestion rate of that food (kg/day)
BW = body weight (kg)

The result is in mg per kg body weight per day (mg/kg/day).

For chronic exposure assessments, the USEPA-style extended form adds exposure frequency and duration:

EDI = (C × IR × EF × ED) / (BW × AT)

EF = exposure frequency (days/year)
ED = exposure duration (years)
AT = averaging time (days) — ED × 365 for non-carcinogenic effects

If you assume daily consumption over the whole exposure duration, the extended form collapses back to the simple one.

Where the input values come from

Concentration (C). From your own measurements (ICP-MS, AAS) or literature. Be explicit about whether the value is on a wet-weight or dry-weight basis — mixing the two is one of the most common errors, and dry-weight values can be several times higher.

Ingestion rate (IR). This is where most assessments go wrong. National food-consumption surveys and many reference tables report intake per year or per capita per year, while the formula needs kg per day. If your source says a population eats 7.3 kg of fish per year, the daily rate is:

IR = 7.3 / 365 = 0.02 kg/day

Forgetting this conversion overestimates the intake — and every downstream risk metric — by a factor of 365.

Body weight (BW). Common defaults: 70 kg for adults, 15–30 kg for children depending on age group. Always state the value you used; risk estimates for children are higher precisely because BW is smaller.

Worked example

Measured mercury in fish: 0.12 mg/kg (wet weight). Consumption: 20 g of fish per day (0.02 kg/day). Adult body weight: 70 kg.

EDI = (0.12 × 0.02) / 70
    = 0.0024 / 70
    = 3.43e-5 mg/kg/day

On its own this number says little — it becomes meaningful when divided by the reference dose (RfD) to give the THQ. For methylmercury, the USEPA RfD is 1.0e-4 mg/kg/day:

THQ = EDI / RfD = 3.43e-5 / 1.0e-4 = 0.34

A THQ below 1 suggests the exposure is unlikely to cause adverse non-carcinogenic effects. For the full THQ workflow, see our guide to Target Hazard Quotient for heavy metals in food.

Common mistakes to avoid

Unit mismatch between C and IR. If C is in mg/kg, IR must be in kg/day — not g/day. Convert grams to kilograms first (divide by 1000).
Yearly vs daily ingestion rates. Check the units of every consumption figure before you type it in; convert kg/year to kg/day by dividing by 365.
Wet vs dry weight. Report which basis you used and convert if your reference doses assume a different one.
Averaging across foods. EDI is per food item. For total exposure, calculate EDI for each food and sum them per element.
Silent zeros for below-detection samples. Do not substitute 0 for values below the limit of detection; use LOD/2 and state that you did.

Doing this in Labreador

The Ecotoxicology Risk Assessment module computes EDI, THQ, Hazard Index and carcinogenic risk in one pass. It ships with built-in RfD and CSF defaults for 23 trace elements, accepts the ingestion rate in kg/day or kg/year (converted automatically), supports batch mode for many samples at once, and adds Monte Carlo probabilistic analysis and a THQ heatmap. Everything runs in your browser — no data is uploaded.

For the formulas behind every module, see the methods reference.

Conclusion

EDI is a simple multiplication, but the result is only as good as the units behind it: concentration basis, daily (not yearly) ingestion rate, and a stated body weight. Get those three right, and THQ, HI and cancer risk follow mechanically.

If you use Labreador in your research, please cite: Helczman, M. (2026). Labreador - Bioassay Analysis Platform (Version 1.6.0) [Computer software]. Zenodo. https://doi.org/10.5281/zenodo.21676846