Dig into your yard in New Orleans and you’re likely to find more than dirt: bricks, oyster shells, rusted nails, chunks of concrete, even the occasional talismanic jar. The same holds true in just about any Louisiana city old enough to carry layers of history, where the ground may hide remnants of old homes, debris from demolished buildings, or earth added to raise the land above flood levels.
What’s less visible are the contaminants that may be lurking in that soil. That concern has grown as more Louisianans take up backyard gardening.
Home gardening exploded during the COVID-19 pandemic. The LSU AgCenter’s 2023 report estimates there are more than 625,000 home gardens in the state.
According to Joe Willis, a horticulture extension agent with the AgCenter, pandemic demand spurred the creation of a free 10-week online gardening course. Step one in the course: soil.
“If you take care of your soil, and your soil is in good condition, and of course, your garden is located in the right place, your plants are going to grow,” Willis said.
But gardeners should also make sure their soil is safe for humans. Urban soil can carry invisible hazards, particularly in areas with a history of industrial or commercial use.
Pepper plants grow as students tend their raised gardening beds at LSU’s Hill Farm, which is a 5-acre sliver of the agricultural land on the east side of the campus, Monday Nov. 8, 2021, in Baton Rouge, La. LSU created the community garden for students to grow vegetables and herbs. Kiki Fontenot and Ed Bush are the LSU faculty overseeing this garden.
“Especially in older neighborhoods, we recommend people do a soil test,” Willis said.
For about $11, the AgCenter’s test can measure pH, nutrients and levels of heavy metals like lead, mercury and cadmium. Lead is the most common contaminant in soil.
“The soil from those lead paints 50, 60 or more years ago, it’s still in that top 1- to 2-inch layer of soil,” Willis said. “It is persistent.”
Soil is likely to contain high levels of lead if it is near any structure built before 1978, when lead-based paint was taken off the market, or if an old building was demolished on the site. Pesticides containing lead were often used on fruit trees, so land close to old orchards is also of concern. Soils near heavily trafficked roadways can also be laced with contaminants. Yards near old dry cleaners, which used harmful chemicals and any site with industrial fill or construction debris may also pose a risk.
The primary concern with gardening in contaminated soil is exposure by stirring it up, said Willis. But food grown in the soil may also absorb it.
Vegetables vary in how much they absorb metals. Plants like sunflowers are known to draw lead from soil and are sometimes used to clean up contaminated areas. Fruiting crops like tomatoes, peppers and squash tend to be safe in mildly contaminated soil.
But root vegetables and leafy greens carry a higher risk. Roots can absorb lead from the soil, and leafy greens are easily contaminated by soil splashing or contact during gardening.
Results from the AgCenter’s soil test can be used with guidance from the Environmental Protection Agency to decide what kind of plants are safe to grow there.
Container beds are typically safer, and can also offer the benefit of controlling the quality of soil and the amount of water your plants get, Willis said. But what kind of container you use also matters, said Melissa Gonzales, an exposure scientist and chair of environmental health sciences at Tulane University.
Raised beds should be at least 12 inches deep and contain a good quality topsoil or garden soil mix.
Gonzales once stopped to warn to a neighbor who was building raised beds out of old railroad ties, which are commonly treated with chemicals to prevent decay.
“I just had to stop and tell him,” Gonzales said. “I told him, ‘Please, don’t eat those vegetables.’”
When in doubt, both Gonzales and Willis recommend raised beds constructed from materials such as plastic wood, metal or lumber you know has not been treated with harmful chemicals. It should also be filled with soil you know is free from contaminants.
“You don’t want to have chronic, low-level lead exposure, even if it’s below detectable, for children, pregnant women, anybody really,” Gonzales said.
The AgCenter recommends a minimum of 8 inches of soil in raised beds to prevent roots from growing into the native soil below. For most vegetables, 12 inches is more ideal, and 18 inches is what Willis recommends for root vegetables.
发表回复