Internal Dose Monitoring

Exposure Verification · Exposure Verification overview

Internal dose monitoring quantifies the chemical that has actually crossed the body's barriers and entered systemic circulation. It is the most direct evidence that a control regime is or is not working.

Absorbed dose vs airborne exposure

Airborne exposure is a hazard; absorbed dose is the harm-relevant quantity. Two workplaces with identical air concentrations can produce very different absorbed doses depending on RPE fit, dermal contact, work rate and breathing pattern. Internal dose monitoring measures the consequence, not the cause.

For skin-notated substances — most solvents, isocyanate amines, organophosphate pesticides — airborne measurement systematically underestimates exposure because dermal uptake is invisible to a pump and tube.

Matrices used

Urine is the dominant matrix for water-soluble metabolites. Blood is used where the parent substance binds plasma proteins (lead, mercury, cadmium) or where short-half-life parent compound measurement is informative (carbon monoxide as carboxyhaemoglobin). Exhaled air is used for some volatile parent compounds — for example benzene at very low ppb levels.

Reporting against reference values

Internal dose is reported against HSE BMGVs (where available) or ACGIH BEIs. Both reference sets are health-based, derived from the dose-response relationship between biomarker level and effect, and benchmarked to roughly the airborne occupational exposure limit absorbed only by inhalation.