Lead & figs?

Asked July 6, 2018, 2:57 PM EDT

Hi. I'd like to plant 2 fig trees and am wondering what, if anything, to do about lead in our soil: 519 ppm. My vague understanding is that fruit tends to pick it up less than vegetables (especially leafy greens), but particularly with a toddler as a primary fig eater, "less than" isn't completely reassuring. And, replacing the top 6-8" of soil doesn't even seem like it would make much difference to a tree. Thanks for any advice!

Baltimore Maryland soil lead contamination

1 Response

You are correct that research shows that across a wide range of edible crops lead (Pb) is less likely to accumulate in fruits (tomato, pepper, bean, etc.)
Crops differ greatly in Pb accumulation in edible plant tissue:

•Low growing leafy vegetables accumulate Pb from soil and soil-Pb is splashed onto leaves (lettuce, spinach, chard, herbs)
•Root vegetables (enlarged hypocotyls) can accumulate Pb within their xylem tissue (carrot, beet, turnip, radish)
•Tubers are phloem fed and very low in Pb (potato)
•Fruit and seed crops are very low in Pb even when grown in high Pb soils

So what is a safe soil lead level? All government and university thresholds and recommendations are for guidance only (and they vary!) There are too many variables at play to develop an agreed upon universal standard.

Page 6 of a 2014 U.S. EPA document gives you a summary of their most recent deliberations on the subject. Potential risk increases with total soil lead levels. Planting fruiting crops in lieu of leafy greens and root crops is recommended for lead levels of 400-1200 ppm.

The following is the recommendation of Rufus Chaney, Ph.D. a retired USDA scientist and expert on heavy metals in soil:

•Soil < 500 mg total Pb/kg dry weight:

Grow any crop you want; wash before cooking or eating fresh.

•Soil 500 to 1500 mg Pb/kg dry weight:

No lettuce, spinach, chard, herbs (collards, kale, cabbage okay)

Use raised beds; limit storage root crops (potato safe if washed well)

There is no need to remove your soil. You can best reduce health risks by maintaining high organic matter levels (3-5%), and keeping soil covered with plants and/or mulch. Take common-sense precautions to reduce exposure to the soil and movement of soil particles and dust to hands, shoes, tools, and and mouths.

We think the potential health risk of growing figs in your soil is fairly low. Large containers filled with purchased soil is another option, although the fig roots could grow through drainage holes into the existing soil. jt