Michigan Tech researchers have developed a singlet oxygen model to calculate how particular
chemicals break down in surface water.
In addition to providing vitamin D, helping flowers grow and creating the perfect
excuse to head to the beach, sunlight also helps break down chemicals in streams,
lakes and rivers.
What is Singlet Oxygen?
- Singlet oxygen is a dissolved oxygen at an excited state with high kinetic energy
that causes it to be quite reactive with organic compounds.
- This reactivity makes singlet oxygen responsible for photodegradation — how materials
are altered by exposure to light. For example, ink will fade in sunlight and plastic
becomes brittle and thin.
- Singlet oxygen can be used as a disinfectant against viruses and bacteria at water
- The term singlet oxygen refers to the total number of electron spins. Singlet oxygen
is also known as dioxidene.
While swimming pools use blue tiles to mimic the color of the Caribbean, most surface
water is yellow or brown. For example, Tahquamenon Falls, a popular Upper Peninsula
destination, is known for the caramel color of its chutes. That color comes from leaf
and bark debris that make tannins — polyphenols, or naturally occurring organic compounds
in plants. It’s this debris that absorbs sunlight and creates the singlet oxygen that
This reactive species of oxygen causes what’s called photochemical transformation,
a process in which light and oxidizing materials produce chemical reactions. But how
long does it take for a particular chemical to break down under this sunny and vegetative
Understanding how many hours or days it takes a particular contaminant to break down
halfway helps environmental engineers and scientists protect our waterways. Knowing
a particular chemical’s half-life helps resource managers estimate whether or not
that chemical is building up in the environment.
Daisuke Minakata, associate professor of civil, environmental and geospatial engineering at Michigan Technological University, developed a comprehensive reactive activity model that shows how singlet oxygen’s
reaction mechanisms perform against a diverse group of contaminants and computes their
half-life in a natural aquatic environment.
“We tested 100 different organic, structurally diverse compounds,” Minakata said.
“If we know the reactivity between singlet oxygen and contaminants, we can say how
long it will take to degrade one specific structure of a contaminant down to half
Minakata’s collaborators are graduate students Benjamin Barrios, Benjamin Mohrhardt
and Paul Doskey, professor in the College of Forest Resources and Environmental Science.
Their research is published in the journal Environmental Science and Technology.
A Superior Mind
The researchers used the Superior supercomputer, housed in the Great Lakes Research Center, to calculate chemical reactivity energies.
Sunshine Oxidizes and Degrades Toxic Chemicals
The rate of indirect-sunlight-initiated chemical oxidation is unique to the body of
water; each lake, river or stream has its own distinct mix of organic matter. And
because the process does not occur in the dark, the amount of sunlight a water body
receives also affects reactions. For example, singlet oxygen plays a partial role
in degrading the toxins in harmful algal blooms and in breaking down the excess nitrogen
and phosphorus produced by agricultural runoff.
The reactive oxygen species also has benefits beyond our favorite lakes and rivers.
“Singlet oxygen can be used for disinfection of pathogens,” Minakata said. “It can
oxidize chemicals in drinking water or wastewater treatments. There are many ways
to use this strong chemical oxidant for many purposes in our lives.”
Moving Beyond Reactions Toward Byproducts
With the half-life calculations established by Minakata’s model, the research team
plans to further study the byproducts produced by singlet oxygen/chemical reactions
— with an eye toward predicting whether the byproducts themselves will be toxic. By
understanding the stages of degradation, Minakata and his team can develop an expanded
model to predict the formation of sun-worn byproducts and how the interactions start
Grants and Funding
National Science Foundation award CHE-1808052
Ultimately, a full understanding of the half-lives of the many chemicals that infiltrate
our water sources is a step toward ensuring clean water for human use.
the singlet oxygen model. Image Credit: Daisuke Minakata
Michigan Technological University is a public research university, home to more than
7,000 students from 54 countries. Founded in 1885, the University offers more than
120 undergraduate and graduate degree programs in science and technology, engineering,
forestry, business and economics, health professions, humanities, mathematics, and
social sciences. Our campus in Michigan’s Upper Peninsula overlooks the Keweenaw Waterway
and is just a few miles from Lake Superior.