Historically, sulfur emissions have come from coal-fired power plants. In the years since the Clean Air Act helped fossil fuel pollutants get their act together—along with the closures of many facilities—sulfur emissions have decreased significantly from this sector. However, a study reveals we have a new source to worry about: agriculture.
Published in Nature Geosciences on Monday, the paper highlights the changing landscape of sulfur emissions. With less sulfur in the atmosphere, farmers must now apply more sulfur—used as both a fertilizer and pesticide depending on the crop—to their fields.
Pesticides and fertilizer are bad news as it is, but sulfur comes with it own set of dangers. It’s highly reactive and can become other pollutants, such as sulfur dioxide or sulfuric acid aka acid rain. It’s harmful to human health if someone breathes in sulfur dioxide and detrimental to ecosystems if it winds up there. The new study, which has analyzed long-term trends of atmospheric sulfur deposition, raises the alarm on the shifting sources of sulfur.
“While atmospheric sulfur deposition has declined as a result of the Clean Air Act and amendments, sulfur inputs to agricultural systems are at levels that are four to 10 times greater than the 1973 peak of sulfur deposition in acid rain,” author Eve-Lyn Hinckley, the director of the Arikaree Environmental Lab at the University of Colorado, said in an email. “This paper is a call to action, both to research the consequences of agricultural sulfur use for environmental and human health and to work collaboratively with farmers and other land managers to optimize sulfur use.”
The authors looked at these emission data from 1980 to the present day. They used national and state databases, as well as peer-reviewed literature on the topic. Through this assessment, the team discovered that sulfur pollution is becoming an increasing threat to our water systems. According to the paper, sulfur inputs for major crops average around 3.5 pounds (1.6 kilograms) per acre a year. However, if you take a closer look only at the crops that require more regular use of sulfur as a fungicide, fertilizer, or soil pH controller, the number is closer to 35 pounds (16 kilograms) per acre a year. At the peak of the sulfur disposition in acid rain in 1973, as Hinckley mentioned, we saw 17.6 pounds (8 kilograms) per acre a year.
“As a result of the Clean Air Act and amendments, atmospheric sulfur deposition is currently down to pre-Industrial levels in many parts of the U.S.,” Hinckley said. “We compared the deposition numbers to the inputs of sulfur used in a variety of crops and found that the amounts of sulfur used are much higher than atmospheric deposition today and even when deposition was at its highest from fossil fuel emissions.”
Runoff is a huge source of risk for all chemicals applied to crops, including sulfur. The most concerning finding, perhaps, is that models show sulfate—another sulfur product typically tied to acid rain—is increasing in streams near agricultural areas, as well as areas recovering from previous acid rain damage. So while we may be breathing less of this junk today than we used to, it’s still making its way into the fish we eat, the soil we need to grow our food, and the riverine environment. Climate change is also playing a roll in increasing heavy downpours that can lead to more runoff, meaning the future could become even more sulfuric.
This is bad. We knew the agriculture sector is a major polluter. Several politicians have had plans to fix that, but none have been put into action yet. Democratic presidential candidate Joe Biden has a plan for rural America, which includes lowering its carbon footprint, but there are not many specifics for everything else that’s wrong with how the sector currently runs.
As the authors make clear, creating effective solutions can’t come from the top down. Policymakers need to work with farmers and other stakeholders to come up with a solution that works. The goal isn’t to ban sulfur. It’s to take action to limit its harm and use widely.