In 1990, lead levels exceeded 10ug/dL in US children aged 6 and under by ____.

The correct answer is based on historical data regarding childhood lead exposure in the United States. In the early 1990s, significant public health concerns were raised regarding lead poisoning in children, particularly those aged six and younger. It is documented that millions of children had lead levels exceeding 10 micrograms per deciliter (µg/dL), a threshold considered to indicate lead poison.

The figure of 3 million represents a substantial portion of the child population that was affected by lead exposure due to various environmental sources, including lead-based paints in older homes, contaminated soil, and lead in plumbing systems. Public health interventions in subsequent years, including the removal of lead from gasoline and regulations on lead-based paint, contributed to reducing these levels significantly.

Understanding the magnitude of the issue is essential for recognizing the historical context of lead exposure and the importance of ongoing monitoring and prevention strategies for childhood lead poisoning. The other figures do not accurately reflect the estimated prevalence of elevated lead levels in that time frame.