Is my soil contaminated?
I recently moved in to a new house with many fruit trees and vegetable beds. The space around all the trees and beds have tarps, and the beds themselves have black plastic, as weed control over the ground. Both have started to degrade and small pieces of plastic are now mixed in the soil. Should I test the soil for any chemical contamination before I plant food crops or eat any fruit this year?
Clackamas County Oregon
Thank you for contacting Ask an Expert with your soil question.
Your concern over plastics in soil is shared by the wider agricultural community, as well as others. Plastics of all kinds are widely use on both organic and conventional agriculture. However, sources of plastic in soil can also be traced, through both water and aerial routes, to the washing of clothing with synthetic fibers, losses from artificial turf and other sports surfaces, tire wear, irrigation pipes and tubes, as well as the humble plastic pot.
In the past, concerns focused primarily on the marine ecosystem. The investigation into the issue of micro plastics and soil has increased only recently and, though a few observations have been made, no conclusions are available.
I do not believe that chemical/soil testing will assist you. As any material breaks down over time, different products are formed. It would be difficult for a laboratory to know exactly what compounds to test for.
With so little evidence available, I cannot provide a definitive answer to your question. Were it my own garden (and I have used plastic sheeting for weed control in the past), I would clean up what I could, dispose of it as your garbage collection requires, and find new ways to accomplish your gardening goals.
Straw is great for keeping weeds down and soil moisture in. Close spacing of garden plants deprives weeds of the light they need. In orchards, a grass or clover cover crop can compete weeds away. The Oregon Extension Service publication Growing Your Own has lots of great advice. (See it here: https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9027.pdf)
Have a good gardening year,