Phytoremediation of moderately contaminated soil

Asked May 5, 2020, 4:55 PM EDT

Hello. I just got my soil test back and the lead results are 510 ppm. This is a small city yard, and I will probably go to raised beds for my herb and veggie growing. However, I have a 12' square plot that I'd like to experiment with, to see if I can improve the soil. I'm reading up on planting mustard greens to take up lead from the soil and wondered if you had any advice on that. I dug the bed mainly to have a mini bee pasture for my honeybees, but I think it would be a worthy project to try to lower the lead contamination. I appreciate any help you can offer.

Baltimore Maryland

5 Responses

Hi- we don't have a solid, research-based recommendation for planting mustard species (known Pb hyperaccumulators) in Maryland soils to remove lead. As you've seen there are many online research articles on this subject, although there does not seem to be much recent research. If you move forward with the project how will you dispose of the plants? Some researchers suggest using the plants as a bioenergy source (biodiesel) which would not be practical for you. Also, it seems that most of the lead taken up is in the root system so you'd need to dig up as much soil as possible to remove the roots which would increase the risk of lead exposure.
Two of the more recent, general articles we found:
https://www.mdpi.com/1422-0067/12/11/7760/htm
https://www.hindawi.com/journals/ijce/2011/939161/

Another option is to grow non-food crops in the 12 sq. ft. area. By maintaining a soil pH of 6.0 to 7.0, increasing soil organic matter, and keeping the soil covered with plants and/or mulches you will reduce the risk of Pb moving off-site or being transported on shoes and tools inside your home.
Jon


Thank you for your response. If I do this, my plan would be to dig up the plants, roots and all, bag it, and put it out in the trash. I realize this means the lead will end up in a landfill, but I assume the landfills are already contaminated. My other option is to only grow flowers in the spot. Right now I am growing a green manure that I planted before my soil test came back. My plan was to improve the texture and fertility of the soil. It's hard to know what is best to do.

Yes, it is a challenge to deal with the consequences of human activity.

If kids will not be playing/working in the garden you could still decide to grow vegetables in the area where you the 512 ppm level was recorded. If you regularly add organic matter to the area, maintain a 6.0-7.0 soil pH, keep the soil covered at all times, and thoroughly wash harvested produce you will greatly reduce the risk of lead ingestion or inhalation.

We would recommend avoiding carrot as Pb can be taken up by roots and move through the xylem transport vessels in the storage root:
https://www.researchgate.net/publication/271820973_Accumulation_of_Lead_and_Arsenic_by_Carrots_Grown_on_Lead-Arsenate_Contaminated_Orchard_Soils

https://extension.umd.edu/hgic/topics/lead-garden-soils

https://extension.oregonstate.edu/food/safety-storage/should-i-worry-about-heavy-metals-my-garden-soil
Jon


Thanks again for your help. I've read a little more on phytoremediation and while the idea is intriguing it doesn't seem like the best approach for me. I will leave the current bed to just flowers for the bees and next year the veggie and herb plot will be a raised bed. If I can't remove the lead, at least I can sequester it underground. Thanks!