Study: Tomatoes grown in lead-contaminated soil appear safe to eat

For city dwellers, growing your own fruits and vegetables can be a tricky venture. A terrace or backyard garden can be a great way of getting easy access to fresh and healthy foods. But is that food still safe to eat if it’s grown in lead-contaminated soil?

A new study says there’s reason to be hopeful. Researchers at the University of Illinois Urbana-Champaign found that tomatoes grown in untreated, lead-contaminated soils accumulated a startlingly low amount of lead from the soil – performing similarly to soils treated for lead contamination. This two-year experiment started out by growing Roma tomatoes in three Chicago neighborhoods with average soil lead levels over 350 parts per million – almost 17 times more than normal background level for lead in soil, and often surpassing the limits for inhalation risk in Illinois. 

Researchers tested the lead levels of plants grown with various  phosphate-based fertilizers (often used to mitigate soil lead levels) and  with no fertilizer at all.

Both with and without the phosphate-based fertilizers, the tomatoes had lead levels well below recommended consumption levels.

“There was so little lead accumulation in the fruits, we estimate the average adult male would have to eat almost 400 pounds of tomatoes per week to reach toxic levels,” said Andrew Margenot, one of the co-authors of the study. He added that a child of about 60 pounds “would need to eat ‘only’ 80 pounds of tomatoes per week – still quite a bit, but a lower threshold of consumption.”

The findings represent good news for local produce lovers in cities like Chicago, which has historically been plagued by pollution. Chicago’s industrial history – centered on smelting and steel manufacturing – has laced the city’s soil with dangerous levels of lead. Median soil lead concentrations in Chicago are ten times greater than expected background lead concentrations. This exposure is also an environmental justice issue, as much of the contaminated soil is located in predominantly Black neighborhoods on the South Side of Chicago.

“A lot of Black Americans were forced to live in highly industrialized areas of the city which typically had high levels of contaminants in soil, water, and air,” said Margenot.

There are over 4,600 urban gardens throughout Chicago, and some of these projects have been targeted specifically to help communities of color throughout the city. While it’s good to know that fruits like tomatoes may be safe to eat even if the soil itself is quite contaminated, lead-contaminated soil still represents a substantial public health threat to those who live, work, or play near industrial sites.

The authors of the study also cautioned that food grown in heavily leaded soil should be carefully monitored. While tomatoes in both years of the study were technically safe to eat, there was a ten-fold jump in lead concentrations between the first year of planting and the second. This result baffled the researchers. Margenot explained that more research needs to be done because “there’s a very poor correlation between total soil lead and lead uptake.”

Additionally, previous research has found that while fruits may not bioaccumulate lead, leaves and roots might.

Finally, while these tomatoes may be safe to eat, working in lead-laced soil is still incredibly hazardous.

“If you magically have no exposure to contaminated soils to get to the fruit stage, or if you mulch the heck out of the soil and wear a suit and respirator, you’re golden,” Margenot said. “But, of course, we all know it doesn’t happen that way.”

For city dwellers, growing your own fruits and vegetables can be a tricky venture. A terrace or backyard garden can be a great way of getting easy access to fresh and healthy foods. But is that food still safe to eat if it’s grown in lead-contaminated soil?

A new study says there’s reason to be hopeful. Researchers at the University of Illinois Urbana-Champaign found that tomatoes grown in untreated, lead-contaminated soils accumulated a startlingly low amount of lead from the soil – performing similarly to soils treated for lead contamination. This two-year experiment started out by growing Roma tomatoes in three Chicago neighborhoods with average soil lead levels over 350 parts per million – almost 17 times more than normal background level for lead in soil, and often surpassing the limits for inhalation risk in Illinois. 

Researchers tested the lead levels of plants grown with various  phosphate-based fertilizers (often used to mitigate soil lead levels) and  with no fertilizer at all.

Both with and without the phosphate-based fertilizers, the tomatoes had lead levels well below recommended consumption levels.

“There was so little lead accumulation in the fruits, we estimate the average adult male would have to eat almost 400 pounds of tomatoes per week to reach toxic levels,” said Andrew Margenot, one of the co-authors of the study. He added that a child of about 60 pounds “would need to eat ‘only’ 80 pounds of tomatoes per week – still quite a bit, but a lower threshold of consumption.”

The findings represent good news for local produce lovers in cities like Chicago, which has historically been plagued by pollution. Chicago’s industrial history – centered on smelting and steel manufacturing – has laced the city’s soil with dangerous levels of lead. Median soil lead concentrations in Chicago are ten times greater than expected background lead concentrations. This exposure is also an environmental justice issue, as much of the contaminated soil is located in predominantly Black neighborhoods on the South Side of Chicago.

“A lot of Black Americans were forced to live in highly industrialized areas of the city which typically had high levels of contaminants in soil, water, and air,” said Margenot.

There are over 4,600 urban gardens throughout Chicago, and some of these projects have been targeted specifically to help communities of color throughout the city. While it’s good to know that fruits like tomatoes may be safe to eat even if the soil itself is quite contaminated, lead-contaminated soil still represents a substantial public health threat to those who live, work, or play near industrial sites.

The authors of the study also cautioned that food grown in heavily leaded soil should be carefully monitored. While tomatoes in both years of the study were technically safe to eat, there was a ten-fold jump in lead concentrations between the first year of planting and the second. This result baffled the researchers. Margenot explained that more research needs to be done because “there’s a very poor correlation between total soil lead and lead uptake.”

Additionally, previous research has found that while fruits may not bioaccumulate lead, leaves and roots might.

Finally, while these tomatoes may be safe to eat, working in lead-laced soil is still incredibly hazardous.

“If you magically have no exposure to contaminated soils to get to the fruit stage, or if you mulch the heck out of the soil and wear a suit and respirator, you’re golden,” Margenot said. “But, of course, we all know it doesn’t happen that way.”

This story was originally published by Grist with the headline Study: Tomatoes grown in lead-contaminated soil appear safe to eat on Jul 25, 2022.