Health Effects and Characteristics of Lead-Based Paint Hazards
What lead does in the body
Lead is a cumulative toxicant with no known safe blood level. It enters by inhalation of dust and fume and by ingestion (hand-to-mouth, food, cigarettes, contaminated clothing). Absorbed lead binds red cells and moves into soft tissue and bone, where it is stored and released over decades. It inhibits ALAD and ferrochelatase, producing microcytic anemia, disrupts calcium signaling in nerve cells, and damages proximal renal tubules. Adults show peripheral neuropathy (wrist drop), hypertension, kidney effects, gout and reproductive harm. Children under six are most vulnerable because of pica, a higher absorption fraction, and a developing nervous system; effects include IQ decrement, attention and behavior problems and hearing loss, with encephalopathy, seizures and death at high exposure. CDC's current blood lead reference value is 3.5 µg/dL; OSHA's adult triggers are 40 µg/dL (return to work) and 50 µg/dL (medical removal).
Hazard versus mere presence
Lead-based paint means paint containing 1 mg/cm² or 0.5% lead by weight. The 0.06% CPSA figure is the limit for consumer paint sold after 1978 - it is not the abatement definition. Intact paint on a surface no one chews and nothing rubs is not itself a hazard. Hazards are: deteriorated paint, paint on friction, impact and chewable surfaces, dust-lead, and soil-lead. Current EPA dust-lead hazard standards are 5 µg/ft² on floors, 40 µg/ft² on interior sills and 100 µg/ft² in window troughs; soil-lead is 400 ppm in play areas and 1200 ppm averaged elsewhere.
Rule of thumb
In a pre-1978 house with no test data, assume lead-based paint and treat paint as a hazard wherever it is deteriorating, on a friction or impact surface, or within a child's reach. Expect questions contrasting hazard with paint presence and asking you to recognize the blood-lead numbers.