The Q&A Archives: Perlite and Lead

Question: A geologist friend told me that perlite contains traces of lead. Are you aware of any risk in using perlite in potting soils or soil amendments? Would the lead remain inert in the soil or could acids, such as nitric acid, cause it to become a problem? We are planning to put a great quantity of potting soil containing perlite in a community garden but would not want to do this if there was any risk of heavy metal contamination. Any assistance you can provide us in this matter will be greatly appreciated.

Answer: I'm sorry for the delay with my response. You aren't at risk from lead toxicity from perlite. It doesn't decay or deteriorate in the soil. You are wise to be cautious though, since history shows that substances we have traditionally though of as harmless turn out to be dangerous. Just to give you a benchmark, research on sewage sludge, which is used on cropland in some areas, shows that (by 1977 standards), sludge containing 500 ppm (parts per million) of lead were considered safe, concurrent with soil testing to monitor for buildup of lead in the soil. I'm sure the traces of lead in perlite are far lower.

That said, there are other less expensive alternatives for improving soil texture and drainage than applying commercial soil mixes. Have you explored other options? If you'd like, send us another question through the Q&A system describing what you're trying to acheive, and we'll be happy to help. Please do not use the "reply" function in your email application to submit a follow-up questions -- it will get lost. Enjoy your gardening season!

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