Kale chips linked to thallium exposure in a California family
What it found
A mother and her three young children had high levels of thallium in their urine, which fell after they stopped eating a brand of kale chips.
The kale chips themselves contained thallium at 1.98 and 2.15 mg/kg.
What they found
Studies in people
Urine thallium levels
The mother's urine thallium peaked at 5.6 µg/g creatinine (adult reference ≤0.4). Her children's levels peaked at 10.5 µg/g creatinine (child reference ≤0.8). The father, who did not eat kale chips, had levels within the adult reference range.
Symptoms and recovery
The mother had numbness and tingling, loose stools, hair loss, and fatigue. After the family stopped eating the kale chips, her stomach symptoms resolved and her nerve tests improved. Some symptoms in the twins persisted, but they continued to meet developmental milestones.
Other findings
Kale chip thallium content
The kale chips the family ate contained thallium at 1.98 mg/kg and 2.15 mg/kg when tested with ICP-MS. A handheld X-ray device did not detect thallium above its limit of 5 mg/kg.
Thallium in brassicas
Kale and other brassica vegetables can take up thallium from soil into their leaves, up to 80 times the level in the soil. Dehydration during manufacturing can further concentrate thallium in products like kale chips.
Gaps in knowledge
There is no reference dose for thallium in food, and the U.S. EPA withdrew its previous reference dose in 2009 due to lack of confidence in the key animal study. Human data on low-dose, long-term exposure are scarce, especially for children.
What the authors conclude
“Our investigation of a cluster of elevated spot urine levels and reported associated symptoms among a family showed commercially available kale chip consumption as a potential source.”
Also in their conclusions
- They conclude that the family's elevated urine thallium levels and symptoms were likely caused by eating contaminated commercial kale chips.
- They advise that improved understanding of thallium toxicology could guide a national oral reference dose and food standards.
- They state that enhanced monitoring is key to understanding the scale of thallium in the food supply.
How it was done
Thallium is a metal that can be toxic, but it is not regulated in food and little is known about low-dose or long-term exposure, especially in children. The authors wanted to share what they learned from investigating this family's exposure.
They investigated a family of five in California after a mother and three children were found to have elevated urine thallium. They surveyed the household, tested environmental samples and the kale chips the family ate, and monitored the family's urine thallium and symptoms for about a year after the family stopped eating the chips.
What it can’t tell you
- This is a single case report, so it cannot prove that the kale chips caused the family's symptoms or that thallium at these levels causes health effects in other people.
- The authors could not definitively determine if the thallium levels were associated with the symptoms experienced.
Who paid
- Conflicts
- The authors declare no conflicts of interest.
- Authors work at
- University of California San Francisco, USA
The paper
- Title
- Thallium Exposure Secondary to Commercial Kale Chip Consumption: California Case Highlights Opportunities for Improved Surveillance and Toxicological Understanding
- Type
- Case report
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Choudhury A, Fowles J, Bartlett R, et al (2025). Thallium Exposure Secondary to Commercial Kale Chip Consumption: California Case Highlights Opportunities for Improved Surveillance and Toxicological Understanding. International journal of environmental research and public health. doi:10.3390/ijerph22081235Free full textPubMed 40869821DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error