Investigation Spotlight: Thallium and Kale Chips
Problem
In 2022, CDPH was alerted about a family who had elevated levels of thallium in their urine laboratory tests (above the national 95th percentile). The family members, including children, were also experiencing gastrointestinal and neurologic symptoms. Exposure to high amounts of thallium may cause several harmful health effects, including nervous system effects.
Thallium was used historically in rodenticides, which were banned in the U.S. in 1975. Although the use of thallium in products has largely stopped in the U.S., thallium is a naturally occurring trace metal in the Earth’s crust. Exposure to thallium can occur as a result of the uptake of thallium in food crops that may be a result of mining operations that stir up geologic thallium deposits, releases from coal burning plants, and other industrial processes.
Investigation
To identify the source of the family’s thallium exposure, CDPH surveyed the family about their diet and activities, and worked with the U.S. Environmental Protection Agency to conduct on-site environmental testing. The environmental testing did not show anything unusual, but the dietary survey indicated the family consumed large amounts of a consumer brand of organic kale chips. Two separate samples of this brand of kale chips revealed elevated amounts of thallium.
CDPH identified the kale chips as the likely source of the family’s thallium exposure, and the family was encouraged to stop eating the kale chips.
Outcomes and Impact
Per CDPH’s recommendation, the family stopped eating the kale chips. After doing so, the family’s urine thallium levels decreased and some of their symptoms improved.
CDPH turned its investigation over to the U.S. Food and Drug Administration, which at the time agreed to investigate the source of thallium in the kale chips. Additionally, CDPH petitioned the National Toxicology Program (NTP) to request a thorough toxicology study of thallium. Due to the lack of data on thallium from the NTP, state and federal food regulatory agencies do not know what an acceptable food standard or safety threshold should be for thallium.
The investigation findings were presented at the CDC 2023 Epidemic Intelligence Service Conference (Elevated Spot Urine Thallium Levels Within a Family Associated with Kale Chip Consumption).
In August 2025, an article on the investigation was published. The article highlights the need for research on the toxicity of thallium and improved surveillance of the food supply to understand the extent to which people are exposed to thallium. Thallium is not well studied and is not regulated in food. Little is known about the health effects of low-dose or chronic exposures on children and other sensitive populations.
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