This week I thought I’d do a series of posts about soil and heavy metals beginning with a few more details about the possible lead contamination situation in our backyard.
Two weeks ago Darren Butler, who is teaching a vegetable gardening series at our house, led a class project where we took four samples from different locations in the backyard, mixed them together and sent them off to Wallace Laboratories, a local soil testing lab with an international reputation. The results came back showing plant available lead levels at 112 parts per million. Note that “plant available” is different than the total amount of lead in the soil. The total amount would be about ten times higher or 1,120 ppm. According to the University of Minnesota Extension Service,
Generally, it has been considered safe to use garden produce grown in soils with total lead levels less than 300 ppm. The risk of lead poisoning through the food chain increases as the soil lead level rises above this concentration. Even at soil levels above 300 ppm, most of the risk is from lead contaminated soil or dust deposits on the plants rather than from uptake of lead by the plant.
If the Wallace Labs report is correct, we’ve got a serious problem. It is possible that, in sampling and averaging multiple locations, we hit a “hot” spot where someone may have dumped paint or paint chips. Clearly, we’ll have to set up a grid of tests to see if the problem is isolated.
I re-did the first test, trying as best I could to take samples from the same locations and sent this second test off to the less expensive UMass soil testing service. The results came back with substantially lower lead levels: 220 ppm, in the “low” range according to most experts, but still higher than I would like. Except for the soil pH, all the other numbers were completely different.
The next step will be to test the testing services. I’m going to take one sample and split it into three parts, sending one to Wallace, another to UMass and the third to Timberleaf Soil Testing. I hope that two of the testing services agree on something!
In subsequent posts I’m going to discuss what we’re going to do, phytoremediation (spoiler alert: I don’t think it’s practical in residential situations), and my issues with the real estate industry.
This week the Center for Disease Control and Prevention is promoting their National Lead Poisoning Prevention Week. Especially if you have kids, get your soil and the interior of your house tested.