Source of Lead in Soil

THE PROBLEM:

Soil samples that were taken from the area under San Francisco’s famed Golden Gate Bridge showed high lead content. Leaded gasoline and rust proofing paint from the bridge were suspected as possible sources.

Identifying lead in soil using light and electron microscopy

THE ANALYSES:

During a thorough examination of the soil, MVA Scientific Consultants discovered numerous paint particles, which appeared as rust-colored specks among grains of sand and particles of rounded quartz.

Several of these specks were carefully isolated and cross sections were prepared for further analysis.

THE OUTCOME:

MVA’s analysis by scanning electron microscopy (SEM), coupled with energy dispersive x-ray spectrometry (EDS), showed that the specks were layered paint chips, and that all of the layers contained lead. Many also contained lead chromate.

Microscopic comparison of the sequence of paint layers in the paint chips with paint chips isolated directly from the bridge showed the same sequence of colors, strongly implicating the bridge as the source of the lead in this soil.