Lead is a heavy metal that normally occurs in low levels in all soils and often has natural concentrations that range from 20 TO 30 parts per million (ppm); but when you consider that some recent studies have shown that lead content of some urban soils may range from 100 ppm to over 1000 ppm several questions come to mind including but not limited to: How does lead get into the soil? What are the hazards associated with lead? Will plants grow in lead contaminated soil? Is it safe to eat plants that have been grown in lead contaminated soils and if so, what precautions should be taken? How can you reduce or remove the lead in the soil?
When Dr. Arthur Graigmill, University of California Cooperative Extension Environmental Toxicology Specialists at UC Davis and Dr. Ali Harivandi, University of California Extension Environmental; Horticulture Advisor, San Francisco Bay Area conducted research that resulted in the publication of “Home Gardens and Lead … What You Should Know about Growing Plants in Lead-Contaminated Soil”
they made some interesting observations regarding the problem and solution in those areas that score high in soil lead content.
For example, in answer to the question, why do some urban areas have soil with elevated lead levels, Graigmill and Harivandi concluded the answer is often directly related to their proximity to highly travelled roads and older buildings painted with lead-based paints.
They also state that houses close to freeways and other highly used roads, or houses located in industrial zones may have concentrations of lead in excess of 1,000 ppm.
Lead-based paint that is flaking or has been scraped or blasted, can cause soil lead concentrations to exceed 3,000 ppm. Being that lead is toxic to humans and poisoning can occur either through ingestion of lead or by breathing in lead dust one important question is, how can you minimize exposure to the soil dust which results in exposure to lead in soil? One of the recommendations presented by Graigmill and Harivandi is to grow ground cover over lead-contaminated soil to reduce the amount of lead-laden soil dust that can become airborne with windblown soil. They recommend natural turfgrass or other ground cover vegetation such as low growing ceanothus, bearberry, or lantana.
Graigmill and Harivandi acknowledge that it’s not easy to remove or dilute lead concentrations from the soil. They also suggest that if the soil has not been disturbed the highest concentration of lead will be in the upper few inches.
By maintaining a dense stand of ground cover, such as lawns that cover the soil entirely, dust and mud problems can be minimized and the risk of lead inhalation can be significantly reduced.
A PDF copy of Home Gardens and Lead … What You Should Know about Growing Plants in Lead-Contaminated Soil can be accessed FREE at the following link: http://anrcatalog.ucdavis.edu/pdf/8424.pdf