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Davis, California

Wednesday, June 19, 2024

Are discarded LEDs a danger in landfills?

Light Emitting Diodes, more commonly known as LEDs, are touted as the energy efficient alternative to conventional incandescent and fluorescent light bulbs. LEDs are used in nearly every electronic device from computer monitors to remote-control cars. However, a new study co-published by researchers from UC Davis and UC Irvine shows that the LED lights used in many electronic devices can contain harmful substances that affect human health.

Julie Shoenung, a professor in the department of chemical engineering and materials science at Davis, as well as one of the head authors of the study, was part of an interdisciplinary team that analyzed the chemical makeup of nine different kinds of LEDs. All of the LEDs studied were 5-millimeter5mm diodes that serve as indicator lights – green for on, orange for standby, etc.

In order to measure the toxicity levels in these LEDs, the researchers performed a test called a Toxicity Characteristic Leaching Procedure (TCLP). TCLP is a method for simulating how chemicals leach into the ground in a landfill.

“The [TCLP] is a standard protocol established by the U.S. Environmental Protection Agency that requires taking an object that you are interested in and crushing or pulverizing it down to some defined particle range,” said Shoenung. “We then expose the substance to certain acids under certain pH conditions and measure how much of the [pulverized LED chemicals] leaches out into the acid.”

The researchers found that there was slight variation in toxicity among the tested LEDs depending on color. Most of these differences were statistically insignificant. However, red LEDs turned out to be the only LED that contained lead. The LEDs were also found to contain small amounts of other heavy metals.

“LEDs that are semi-conductor based use a lot of different rare earth and other elements such as arsenic, indium and gallium,” Shoenung said.

When combined in electronics, these elements form Indium Gallium Arsenide (InGaAs), the dust of which can be an irritant to human skin, eyes and lungs. InGaAs is the foundation material for LEDs, lasers and infrared detectors, and is also used in solar panels.

InGaAs is used in electronics because it has a crystalline structure similar to that of diamonds.

“[InGaAs] is a solid, stable chemical. It is very difficult to break down,” said Shoenung.

According to the study however, InGaAs can break down into other substances under certain conditions, and is not as stable as once thought.

The study, published in December in the Journal of Environmental Science and Technology, also focused on resource depletion, specifically the depletion of gold and silver. Gold and silver are used in very small amounts in LEDs, but the shear quantity of LEDs is making a dent in supplies of these precious metals.

“We keep making all these things that use other things like gold and silver, and the amount of those things in the world is finite,” said Shoenung. “Rather than mining out of the earth, we can mine [for these materials] out of landfills.”

Shoenung explained that since the article came out, the research team has received notifications from a few companies about new, commercially available lighting systems that can provide focused, task and indicator lighting that does not rely on InGaAs.

These research findings do not apply to all LEDs. The study only included 5mm 5-millimeter diode LEDs, not the LEDs commonly used in home lighting.

HUDSON LOFCHIE can be reached at science@theaggie.org.


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