Wednesday, August 22, 2012

Lead Contaminated Soil - A Hidden Danger

Miss B beneath a mammoth cucumber vine which was a "volunteer" this year.
A while back I shared that I had received the results of our soil lead scan and one of the garden beds I had tested came back highly contaminated, while the other two beds I had tested came back mildly contaminated. I gave up any hope of eating the cukes and squash from the highly contaminated bed, and have held off on consumption of the gorgeous patty pan squash from the third bed until I the quantitative results come back...while waiting I have done a fair amount of learning about lead contaminated soil.

Where does lead come from?

Paint - lead was in paint prior to 1978. So if your house is older than that you could expect to find lead around the house where paint was scraped off for repainting at some point.

Leaded gasoline - this was phased out in the starting in the 70's but if you are on an old main road (like we are) you could pretty much guarantee your soil is contaminated with lead along the road.

Old Orchards - lead arsenate was in heavy use until WWII

Scrap metal - discarded roof flashing, lead pipes etc.

Numbers what they mean
I've found differing breakdowns on the numbers but the consensus seems to be this.

Less than 50 ppm = Normal/Background
No steps needed

50-300 ppm = Slight Contamination
Wash all vegetables.  Wash and peel root crops.
Move play areas to an uncontaminated site.

300-500 ppm = Moderate Contamination
Grow fruiting vegetables only.  Avoid leafy vegetables. Avoid root crops. Wash vegetables thoroughly.  Keep soil pH 6.5-7.0 (this prevents the lead from being taken up by the plants).  Add manure/compost each year.
Move play areas to uncontaminated site.  Have blood lead level tested.

More than 500 ppm = Heavy Contamination
Avoid breathing dust during cultivation.  Mulch or maintain grass cover to keep down dust/rain spatter.  Move edible garden to uncontaminated are or bring in clean soil to build new garden.
Move play areas to uncontaminated site.  Have blood lead level tested.

Our soil results and what I will be doing now
Our front side garden (near the house and road) came in at 1000 ppm!  Yikes!  I had already torn up the squash and cukes I had growing there.  Most of this is lawn, and then some lovely giant snowball hydrangeas.  When I cut the hydrangeas back this fall I'll bag them and dispose of them at the transfer station (will check with the folks there to see if this is the proper way to handle).  The small strip of sod I'd torn up and thrashed to make a bed for the cukes and squash (the dust was flying - and of course I was inhaling it - agh...) I will heavily mulch and any weeds pulled from this bed will go to the transfer station as well (again with their permission).  No edibles in this bed unless I put down a membrane impermeable to roots and create a new raised bed there.  Hydrangeas for now!

Miss B's flower garden came in at 130 ppm.  Not too bad.  Fortunately, I did most of the planting while she has done most of the cutting.  Long term I would like to build an arbor over this area with grapes and wisteria, and a little cobblestone patio of I'm not going to take action, just continue to limit Miss B's "helping" to cutting, and add compost and whatnot.

The back garden where I have strawberries, elderberries, blueberries (planted by the previous owners), squash, black beans, and tomatoes is 100 ppm.  Again, not too bad.  My plan for this bed is to add compost and manure to increase the organic matter,  continue to wash everything from this bed thoroughly and to abstain from planting leafy greens, or tubers.

All in all I breathe a sigh of relief.  As I continue to develop a plan for our yard, with heavy emphasis on the edibles, I will definitely be doing additional soil testing.  Our composting program will also be going ahead full throttle.  Must make more new "clean" soil.

I also found some research is being done on growing specific plants to take up the lead and then when the plants are removed the lead (or some of it the hope is) is taken too.  Will be doing more research this winter.  Who knows, maybe I'll get involved in such a study : )

I feel there is so much interest in urban gardening right now, and I've seen very little information outlining the importance of testing for lead in the soil.  I hate to be a negative nelly, but won't you please help me spread the word?  Maybe I/we can come up with a striking poster or button or something and place it on the side of this blog, or around town next spring.  If you know of anyone gardening nearby an old home, or along an old heavily trafficked road, please ask them if they've tested for lead.  It's terrible to find out you have lead contaminated soil, but would be so much worse not to ever find out and be breathing the dust and eating contaminated food.

Not contaminated.  These beauties are heading to the freezer!
So the verdict is in on the Patty Pans and now I can blanch and freeze, and feel good about it.  These sure will make lovely soups and stir fries this winter.  With a bit of coconut milk, onion and curry powder - delicious.  And I will rest easy knowing for a fact they are safe.  One of the big benefits of a home garden is increased health right?

Won't you please help me spread the word?


  1. Wow!! I have a small garden and have thought about getting the soil tested, now I know I need to! That's too bad about all your plants - it would kill me to not be able to eat those veggies! I'll post this on my FB page. Thanks for the info!

  2. Thanks Tonya! It did feel kind of crazy pulling up zucchini and squash plants (complete with little baby edibles on them). But fortunately all my tomatoes and greens were already in raised beds, and some squash too! So the majority of our veggies are still good to go, but it totally could have been the other way around. That's what I find so mind boggling/disturbing about lead...I mean, the soil looked fine, the plants were thriving. There's really just know way to know unless you test. Thanks for posting to FB.