The amount of lead exposure considered dangerous varies, but there is no known safe blood lead concentration. For children, blood lead levels of 3.5 micrograms per deciliter (μg/dL) or higher are concerning and may be associated with decreased IQ and neurodevelopmental harm. For adults, the Centers for Disease Control and Prevention (CDC) considers blood lead levels of 10 μg/dL as an upper limit, with symptoms more likely above 40 μg/dL. Serious health effects in adults typically begin at blood lead levels above 40 μg/dL, and at very high levels (over 100 μg/dL), severe neurological symptoms and even death can occur. Children generally start showing symptoms around 60 μg/dL.

Lead exposure accumulates over time, so repeated small exposures can also be harmful. The US EPA states that the maximum contaminant level goal (MCLG) for lead in drinking water is zero, reflecting that no level of lead exposure is truly safe.

In summary:

• Children: Blood lead level ≥3.5 μg/dL is dangerous
• Adults: Blood lead levels ≥10 μg/dL warrant concern; symptoms often above 40 μg/dL
• No safe level of lead exposure has been found
• Long-term repeated exposure, even at low levels, is harmful