Jumat, 16 November 2018

Building better, safer soils

Urban farming can help families in interior cities enjoy more fruits and vegetables. Community gardens also help many people get exercise and bring neighbors together. But there’s one big trouble. Soils in many cities have high levels of lead. That toxic heavy metal harms the brain and nervous system, leading to health problems, especially in children. But scientists have simply announced some achievement in setting up safer soils.

Yes, building them. Sara Perl Egendorf is a soils scientist with Brooklyn College or university of the City University of New York and the New York Metropolis (NYC) Urban Soils Institute. She and her team worked with the Mayor’s workplace and city parks section to fix some local soils.

They started by collecting sediment dug up from building sites. Glaciers remaining this sediment throughout the area towards the end of the previous ice age. It was much like what happens when dirty snow banks melt - only much larger. Plants can increase in glacial sediments. But it’s hard for plant life to get needed nutrients from it, such as nitrogen and phosphorus. So Egendorf’s workforce added compost. That’s mainly decayed plant materials, rich in nutrients. It came from the Gowanus Canal Conservancy in Brooklyn, N.Y.

Both the compost and the sediment from setting up sites “are components that would otherwise be entering the waste stream,” says Egendorf. “Thus, we diverted them from landfills.” They’re now providing a service as soil.

The team tested different mixtures of sediment and compost. One mixture had an equal, 50-50 mix. Another added one component compost to two parts of sediment. Another blend used one portion compost to four parts sediment.

Team members prepared raised garden beds (ones built atop the normal soil) for every single soil mixture at two community sites. Each backyard also had a raised bed filled with topsoil from a local store. The researchers planted basil, kale, eggplant, onions, peppers and tomatoes in each bed.

In the first year, the 50-50 mix produced whole lot more crops than did the store-bought topsoil. Scientists remain working to check the crops for business lead and other metals. However, the earliest lab effects for that 1st harvest advise the produce is harmless to eat. 

Testing the crops is definitely “a real strength of Egendorf’s job,” notes Dan Brabander. As a geoscientist at Wellesley School in Massachusetts, he deals with geology, chemistry, health and the environment.

Brabander also likes the fact that the New York City group ran handled tests. By growing crops side-by-side under the same conditions, the researchers could largely rule out that anything other than the soil type afflicted the results.

Making soil safer
Brabander and his colleagues also study ways to reduce risks from lead in urban gardens. One of his projects has looked at how compost might help community gardens near Boston, Mass. 

High school students had worked with The Food Job of Lincoln, Mass., to build raised back garden beds. At first, gardeners stuffed the beds with compost. Over several years, though, neighborhood soils settled or got mixed into the beds.

The Massachusetts group examined the fine particles in the beds’ soils. These are the bits of dirt that “people are more most likely to come in contact with,” explains Rosalie Sharp of Wellsley College. They can get flung in to the air. Those bits can also stick to hands.

Tests showed that these very fine contaminants probably originated from the neighborhood soil. And they acquired 10 times further lead in them than similar-size particles that came generally from compost!

The team also tested for different forms of lead in the soil. Some designs are less likely to be taken up by crops and would be less damaging if eaten as part of a plant.

Types of lead varied widely from location to place, the study found. One purpose could be how the business lead ended up in the soil, say Sharp and Brabander. In some spots, most lead very likely came from old house paint that contained the steel. Soil in other places had additional residues of the emissions from automobiles that burned leaded gasoline (up until the 1970s or so). Organisms frequently consider up the gasoline’s lead more easily compared to the lead from aged paints.

The chemistry of the soil itself probably also concerns, Sharp and Brabander say. For example, higher levels of compounds with carbon might produce the lead less dangerous. Other factors may also play a role. Additional acidic soil can leach lead from soil, for example.

Egendorf likes the fact that the Massachusetts group tested great contaminants both from the compost and the local soils. “Documenting the distinctions between these components is essential,” she says. She also likes the way the group has been probing the effects of different types of lead. The task helps show how the chemical substance make-up of compost can make soil safer.

Testing for lead
Other get the job done by the Massachusetts squad uses easily transportable equipment for fast, on-the-spot soil sampling. In one round of checks, the group found that lead levels in most places were under 400 parts per million (ppm). The U.S. Environmental Security Agency considers that an acceptable amount.

Some soil “hot areas,” however, had lead degrees of up to 700 ppm. “So testing in one spot in a back garden doesn’t necessarily offer you a [good gauge] for the whole garden,” Sharp says. Sooner or later, portable testing results could pinpoint where extra compost or other treatments may be needed to cut lead risks. Testing could also guide selections on where to plant crops that are most likely to have up metals into their edible parts.

The teams shared their findings here at the twelve-monthly meeting of the Geological Society of America on November 2 and 4. Both groups will continue their research. For now, though, construction soil and adding compost to existing soil both seem to be like promising concepts. At some point, the approaches might even work together, the scientists say.

“What I think is absolutely exciting from Sara’s give good results and our job is utilizing supplies that previously exist within the city,” Brabander says. Such recycling could help inner-city households enjoy safer, healthier foodstuff.

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