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Background on Lead

Lead is a metal that naturally occurs in the Earth’s crust. For centuries, lead was added to paint as a pigment, and was used in water pipes, fixtures, and solder. It was first added to gasoline to improve octane ratings in the 1920s. After scientists realized the harms posed by lead, especially for children and their development, the substance was successively taken out of new household paint, automobile gasoline, and new plumbing in the U.S.[9]

Today, the paint in older housing can be hazardous to young children, especially if the paint is in disrepair. From the most recent national estimate, in 2005-2006, out of the 37 million homes with lead-based paint (35% of homes in the U.S.), 34 million were built before 1978 and 23 million had hazards such as deteriorating paint or lead in the dust or surrounding soil at levels above federal thresholds.[10] Children under 6 lived in 3.6 million of the homes with lead-based paint hazards.[11] Soil can contain high levels of lead, a legacy from exterior leaded paint, leaded gasoline, and industrial sources. The Flint crisis has shown the danger of lead pipes when the water flowing through them is corrosive. One study found that children exposed to lead in dust, water, and soil were associated with having 36%, 20%, and 11-16% higher blood lead levels (BLLs), respectively, than those not exposed.[12]

Large quantities of lead can be extremely dangerous for children and adults, leading to kidney damage and brain damage. Even the smaller amounts found in soil or household dust from deteriorated paint may still be harmful, without symptoms that are immediately apparent.[13] There is no safe amount of exposure or safe level of lead in a child’s blood.[14] Low levels have been strongly associated with “intellectual deficits, diminished academic abilities, attention deficits, and problem behaviors.”[15]

It’s important to act quickly to measure BLLs after suspected exposure. Once lead enters the body, it travels to soft tissues and different organs via the blood, and most of it moves into the bones and teeth in a matter of weeks, where it can stay for decades. The rest is excreted. “About 73% of the lead in children’s blood is stored in their bones.”[16] When the lead exposure happens over a shorter timeframe, elevated levels in the blood “will decline within a few weeks to months,” but if exposure happens over an extended period of time, “the decline in BLL can take much longer.”[17] Although it is much better to prevent the exposure to lead in the first place, catching elevated blood lead levels (EBLLs) early through regular blood testing can help prevent further adverse impacts once the source of lead is addressed and can provide an opportunity for interventions that may mitigate the impacts.[18]

Generally, studies have shown that BLLs start to increase “in late infancy” and peak at 18-36 months.[19] This is because of “normal mouthing behaviors and increasing mobility,” as well as the fact that lead is absorbed more efficiently by younger children.[20] Routine testing timeframes of around ages 1 and 2 are based on this BLL trend.