AQ Monitoring Results:
Crockett: Lead at John Swett

This page last reviewed September 27, 2010


Lead is a bluish-gray metal that occurs naturally in the earth's crust, and it exists in many compounds. Ambient lead no longer poses a problem in California, as levels are below the established state standard throughout California. Through breathing and swallowing lead dust, lead (including metal lead and its compounds) can cause adverse health effects, such as fatigue, headaches, and sleeping difficulty; more seriously, loss of short-term memory, depression, and many others. Lead can cause developmental and reproductive harm. Moreover, determined by California under Proposition 65, lead can cause cancer. Lead is more harmful to children since they absorb lead more readily and their developing nervous system puts them at increased risk. Exposures to small amounts of lead over a long time can slowly accumulate to reach harmful levels for children without warning.

Current lead emissions to outdoor air are small compared with twenty years ago. Lead in the ambient air has decreased significantly since the mid-1970s due to the phase-out of leaded gasoline. Lead is included in some paints, lead batteries, and some aircraft fuel. It is also used in other industrial activities. The major identified source of outdoor air lead emissions in California is aircraft fuel combustion. ARB adopted in 1993 an air toxic control measure for non-ferrous metal melting operations, which is expected to reduce lead emission by 45 percent.

However, harm can come from many years' deposition and accumulation of lead in soil. Research suggests that the primary sources of lead exposure for most children are deteriorating lead-based paint, lead contaminated dust, and lead contaminated residential soil. Many homes built before 1978 have lead-based paint. However, the federal government banned lead-based paint from housing in 1978, further reducing the exposure to lead.

Ambient Monitoring Results

Ambient levels of lead are routinely monitored at approximately twenty sites in the California air toxics monitoring network. The statewide average concentration of lead during 1998-2000 was 11 ng/m3 (nanograms per cubic meter), with values ranging from 2 ng/m3 to 570 ng/m3. These values are lower than the 30-day average state standard of 1500 ng/m3 based on a different monitoring method. The current routine monitor closest to Crockett is in Fremont. Relative to the statewide average, the Fremont region was 39% lower, with an average concentration of 7 ng/m3 for the same time period.

The ambient monitoring results at John Swett are provided here:

  • A graph comparing the monthly summaries of lead at the community with historical statewide and regional levels
  • A table of summary statistics
  • Raw data in Excel format

Cancer Risk

Cancer risk is the number of excess cancer cases among a million people if the people are exposed to levels of a toxic air pollutant over 70 years. Lead is equivalent to less than 1% of the potential cancer risk of the nine measured compounds and the estimated diesel particulate matter.