What do I need to know about lead before planting vegetables?
In situations where heavy metals may be high in the soil, selecting certain vegetables to grow can lower the risk of heavy metal exposure.
Vegetable gardening can bring health benefits by growing and consuming fresh vegetables. However, in situations where vegetables are grown in soils or irrigated with water high in heavy metals, such as lead or arsenic, certain crops can actually concentrate these metals in their tissues. When humans consume them, we further concentrate these chemicals, causing us harm.
Much research has been done looking at various crops’ relative abilities to accumulate heavy metals while growing. Two studies, “Variability of Bioaccessible Lead in Urban Garden Soils” and “Field evaluations on soil plant transfer of lead from an urban garden soil,” seem to show that adding compost to soil may decrease the concentration of lead in the harvested product. Certain vegetables are less likely to accumulate harmful levels of heavy metals than others. In general, heavy metals tend to accumulate in root, leaf and stem tissue. Those vegetables that arise from flowers and are botanically considered fruits, like tomatoes, peppers and cucumbers, are less likely to have harmful levels of heavy metals than leaf, stem or root crops like kale, broccoli and carrots.
This could also be related to the amount of soil that sticks to those produce items as shown in two studies, “Concentrations of lead, cadmium and barium in urban garden-grown vegetables: The impact of soil variables” and “Phytoavailability of Lead for Vegetables in Urban Garden Soils.” In areas where heavy metals like lead are a concern in both soil and water, it is important to keep these things in mind when creating garden plans and selecting seeds.
The lists below outline vegetables that are the best choice for situations where heavy metals are a problem, and ones to avoid. Findings are from “Lead levels of edibles grown in contaminated residential soils: a field survey,” published in the Science of the Total Environment. For more information regarding safe growing practices in urban environments, contact your local Michigan State University Extension county office.
Lead can last in the soil for years, but choosing carefully what you grow and how you grow your garden can reduce its impact on the produce you harvest.
Low risk vegetables*
Moderate risk vegetables
High risk vegetables
*Assuming they are washed well with a food grade detergent and potable water before consumption. Findings from Finster et al. 2003.