The most recent lead test for the White House garden came in very low at 14 parts per million — a score similar to those found in places where there are no automobiles. (Amazing for Washington, D.C.!) This was a great improvement from the 93 ppm that resulted from the first test done many months ago. (This number was still way below the 400 ppm considered hazardous by the Environmental Protection Agency, but was not as stringent as, say, The Netherlands guidelines of 40 ppm.) Here's how they got the lead content to go down...
First of all, it seems that the 93 ppm of lead was attributed to long-term use of sludge as a lawn fertilizer. It was only in 1994 that President Bill Clinton directed the government agencies to start using environmentally friendly practices for landscaping government grounds, gradually reducing the use of toxic chemicals.
For the Obamas' garden, once they had the soil tested they started to make adjustments:
[They added] lime, green sand and crab meal as well as organic matter in the form of compost made by the National Park Service. The pH was adjusted to between 6.5 and 7. When the pH is in that range, lead is unavailable to the plants.
Gardening experts say that good sources of organic matter also include composted leaves, nonacid peat, and well-rotted manure. If soils have high levels of lead, one-third by volume of organic matter should be added to reduce lead availability.
Read the whole article at The New York Times.
Image via The White House