Posts Tagged: ozone
Strawberry fields forever
Methyl iodide – yes, that volatile chemical that could find use as a soil fumigant – has been in the news lately, and mostly in a negative light. In April, California’s Department of Pesticide Regulation made a preliminary decision to approve the use of methyl iodide as a fumigant under strict conditions, and soon after received more than 50,000 public comments.
Methyl iodide, it turns out, is not only toxic, like all fumigants, it “can cause cancer, brain damage and miscarriages.” Its potential use in California’s strawberry fields in place of its ozone-depleting and toxic cousin, methyl bromide, is what shot the compound into news orbit.
Why phase out methyl bromide as a soil fumigant? Answer: Ozone loss up in the stratosphere, leading to more ultraviolet light penetrating the Earth’s atmosphere, leading, in turn, to increases in skin cancer. When methyl bromide is released in the lower atmosphere, a fraction gets transported into the stratosphere where it undergoes a series of chemical reactions leading to stratospheric ozone depletion.
Cousin methyl iodide, on the other hand, is photolyzed quickly in the lower atmosphere, leaving none of it to escape into the stratosphere.
While public opinion currently leans heavily against the use of methyl iodide as a soil fumigant replacement, James Sims, a professor emeritus of plant pathology at UC Riverside, supports its use. For one thing, it delivers results similar to methyl bromide, he says, and, second, it can be used safely. He explains that it is not applied directly to plants; it is injected into the soil two weeks before any plants are planted.
Methyl iodide is a liquid boiling at 42.5 degrees C or 108.5 degrees F. Sims says it is therefore safer for workers to handle than a gas like methyl bromide. Moreover, it can be applied using the same equipment with few or no modifications, and it is effective in reducing pest, weed and plant disease problems. Other alternatives — solarization, anaerobic soil disinfestations, crop rotation, steaming, etc. — are not effective, Sims says.
Critics are not convinced of methyl iodide’s relative safety and growers, meanwhile, continue to insist that their fields need a fumigant that poses no harm to our precious ozone layer.
How then might the controversy play out? We will have to wait and see – for several weeks at least. After processing the public comments received, state officials plan to weigh in on the “controversial effort to register the fumigant methyl iodide.”
Valley ozone story takes off
Research by UC Davis scientists that revealed a substantial amount of San Joaquin Valley ozone is generated by animal feed is getting wide coverage in the news media. Google News reported 126 articles on the subject.
Many newspapers ran the Associated Press version of the story, written by Fresno-based Tracie Cone. She reported that the study — funded by the U.S. Department of Agriculture, California Air Resources Board and the San Joaquin Valley Air Pollution Control District — was initially intended to measure the impact of animal manure, urine and flatulence on ozone levels.
However, the researchers discovered that millions of tons of fermenting cattle feed bears greater responsibility.
Mark Grossi of the Fresno Bee noted in his story that the study was published last month in the journal Environmental Science & Technology. This week's flurry of interest was generated by an April 21 news feed from the American Chemical Society press office. ACS publishes the journal.
In his story, Grossi wrote that the cattle feed explains only half of the Valley's ozone problem. The other half, Nitrogen oxide, or NOx, comes from vehicles. San Joaquin Valley Air Pollution Control District believes NOx is more important to control, the Bee article said.Meanwhile, Capital Press reported yesterday that the U.S. Environmental Protection Agency has rescinded its long-standing exemptions for agriculture under emission-control rules.
"Air quality in the San Joaquin Valley is consistently among the worst in the nation," said Deborah Jordan, director of the Air Division for the EPA's Pacific Southwest region, in a statement. "New and modified facilities will now be subject to the most stringent requirements, which will contribute to the health of our communities."/span>/span>
A dairy cow eats its rations.
Animal feed generates lots of valley ozone
Scientists have been puzzled by the fact that the San Joaquin Valley often suffers high ozone levels even though the mostly rural, agricultural domain has fewer cars and trucks than big cities. Research by UC Davis scientists is now showing that some of the ozone in the valley is being generated by fermented animal feed, according to a story posted yesterday on the website Science News.
While ozone provides a protective barrier for the earth in the stratosphere, it is an unwelcome molecule to have around where people are breathing. Ozone (O3) is a powerful oxidizing agent, far stronger than O2. It can harm lung function and irritate the respiratory system.
The UC Davis team, led by environmental engineer Cody Howard, tested seven types of animal feed in a one-meter-square tented chamber, according to writer Janet Raloff, author of the Science News story. They added a mix of gases that matched the valley’s air and simulated sunlight with lamps. The result was lots of ozone.
Corn silage generated about 125 parts per billion ozone, alfalfa silage a little less, and mixed oat-wheat silage 210 ppb, Raloff reported. These emissions pale in comparison to cars. However, because the San Joaquin Valley has so much silage to feed its animal agriculture industry, the feed appears to be the single biggest contributor to the region’s ozone problem, the story said.
Cars and light-duty trucks in the valley can generate 13 metric tons of ozone per day, while feed for the valley’s 10 million head of dairy cattle can produce 24.5 million tons of ozone per day.
Corn silage livestock feed.