The benefits of growing food in cities (nutrition, exposure to nature) outweigh the very low risks of lead contamination. This is the conclusion of a recent University of Washington study:
It is highly unlikely that urban agriculture will increase incidences of elevated blood Pb for children in urban areas. This is due to the high likelihood that agriculture will improve soils in urban areas, resulting in reduced bioavailability of soil Pb and reduced fugitive dust. Plant uptake of Pb is also typically very low. The exceptions are low-growing leafy crops where soil-splash particle contamination is more likely and expaneded hypocotyl root vegetalbes (e.g. carrot). However even with higher bioaccumulation factors, it is not clear that the Pb in root vegetables or any other crop will be absorbed after eating.
The paper outlines a set of best practices for dealing with contaminated soils. You should always:
- Wash fruits and vegetables from your garden. Also wash your hands and don’t wear shoes in the house.
- Compost, compost, compost! Compost dilutes the overall amount of lead in soil and encourages healthy plant growth which also dilutes the (usually small) amount of lead a plant will uptake. Apply compost annually since it breaks down over time.
- Plant away from painted surfaces of old (lead paint era) buildings.
Some other things to consider especially if you garden with children under 5 years old:
- Don’t eat a lot of carrots, radishes, redbeets or turnips grown in contaminated soil. The edible portion of these plants consist of xylem tissue that traps lead (potatoes are OK since they are phloem fed). That said, you’d have to eat a lot of contaminated root vegetables to elevate lead levels in your blood.
- Adding phosphorus fertilizers will decrease the bioavailability of lead.
- In general root vegetables uptake the most lead, leafy greens less and fruit almost none.
- The most conservative approach is to grow in raised beds.
The main concern is for children under 5 years old. If your soil tests high in lead and you have young ones you should consider doing your edible gardening in raised beds and limit their exposure to garden soils to a few times a month. Mulch and ground covers will also decrease lead exposure in the other parts of your yard.
The paper concludes that for older children and adults, “There is little indication that growing or eating food from urban gardens will result in high Pb (lead) exposure.”