What is the reported toxic daily dose of lead?

• A. 0.5 mg/day
• B. 5 mg/day
• C. 0.5 g/day
• D. 5 g/day

Answer: (A)

Lead toxicity can arise from very small daily intakes because lead accumulates in bone and other tissues over time, so even modest ongoing exposure can build a harmful body burden. The amount traditionally cited as a toxic daily intake is about half a milligram per day. This reflects the level at which chronic exposure begins to produce adverse effects, given lead’s long biological half-life and tendency to persist in the body.

The other options represent much larger daily amounts—several milligrams to grams per day—which would be far more likely to cause acute poisoning rather than reflect the typical threshold used to define a toxic daily dose.