We're all familiar with arsenic as a poison, but did you know that an organic kind of arsenic exists that's not toxic?
According to some Oregon researchers, that organic version of the chemical could be the key in how we make sure that our drinking water supplies don't contain the inorganic toxic kind of arsenic.
Arsenic in drinking water happens all over the world, even in the U.S. Water with over 10 micrograms of arsenic is unsafe to drink and brings with it the risk of cancer. But removing arsenic is tricky, particularly if that water comes from an underground well.
There are, however, natural processes that occur that convert toxic arsenic into a non-toxic organic form. And the Oregon research team thinks we need to focus more on that process.
"Traditionally the presence of the organic form in groundwater has been ignored," says University of Oregon geologist Qusheng Jin. "The focus has always been on inorganic forms, arsenate and arsenite."
Arsenic continually cycles through different forms based on its environment. Natural events, such as rain and drought, affect it, as do human activities, including pumping and irrigation. And organic arsenic is everywhere in the Earth's crust. Containing carbon, the purest form of the chemical is as a metal.
After collecting water samples from underground wells, the Oregon research team studied one specific stage of arsenic known as demthylarsinate (DMA), which appears in water in a slushy state. More often than not, that same well water also contains inorganic arsenite and arsenate. With the help of native bacteria, though, DMA can convert that toxic inorganic arsenic into gas that's released into the soil.
To test this, the team did three experiments where the water had dissolved DMA and inorganic arsenic in it. By adding ethanol to the water, though, DMA concentrations increased, resulting in more inorganic arsenic being converted to gas.
This means that the presence of organic arsenic in water could be vital in keeping concentrations of inorganic arsenic down. And adding methane to existing systems that keep arsenic levels in water down could be the key to safely and inexpensively keep drinking water clean.
But researchers stress that we need more studies focused on organic arsenic.
"I am concerned about the impact of this cycling process in aquifers," says Jin. "If this process is as important as we believe it is, it will impact the transport and fate of arsenic in groundwater.
