Which of the following is an example of a biomarker of exposure?

• A. Blood lead level.
• B. DNA adducts.
• C. Enzyme changes.
• D. Chromosome aberrations.

Answer: (A)

Biomarkers of exposure measure the amount of chemical that has entered and circulated in the body, reflecting the internal dose. Blood lead level is the clearest example because it directly quantifies the lead present in the bloodstream, giving a straightforward readout of recent and absorbed exposure.

DNA adducts show that a reactive chemical has interacted with DNA, which signals exposure to a genotoxic agent and can indicate potential early effects, but it’s more about molecular interaction and risk rather than a simple measure of how much chemical is in the body. Enzyme changes reveal the body's response to exposure and can indicate effects or mechanisms, not just how much chemical is present. Chromosome aberrations reflect genetic damage from exposure and are biomarkers of effect, not exposure dose. So the blood lead level best represents an exposure biomarker because it directly measures the internal dose.