The Green Drink Conundrum: Potential Thallium Exposure and Neurological Risks

Thallium elicits neurotoxic effects as it inhibits DNA and protein synthesis, binds sulfhydryl groups on proteins of neurons and mitochondria, impairs the production of ATP, and competes with potassium. Thallium accumulates in the tissues with high potassium content such as skeletal and cardiac muscle, and the central and peripheral nervous systems. 

Thallium toxicity may manifest as alopecia areata, fatigue, headaches, depression, sleeplessness, ataxia, neuropathy, vision disturbances, psychoses, gastric antacidity, loss of appetite and/or weight, cardiac arrhythmias, angina-like pain, hypertension and irregular pulse. Thallium is primarily excreted via the kidneys and secondarily in bile. It may be found in urine as long as two months after exposure. Urine levels are an appropriate measure of Tl exposure and possible body burden.

The greatest exposure to thallium is from food, although exposure from air and water may occur from industrial operations. Smokers have been shown to have twice as much Tl exposure than non-smokers. In 1972 Tl-containing rat poison was discontinued due to the risk to human health. Current irrigation practices permit the use of fracking wastewater for irrigation of crops such as vegetables and fruit.

 An Environmental Working Group report found that 95,000 acres of produce in California was irrigated with fracking wastewater brine. Analyses of surface stream water near a fracking site indicated significant Tl contamination. Spinacia and Brassica group vegetables, such as kale, cabbage, spinach and lettuce, efficiently assimilate Tl from soil. Alarmingly, this has made dark green leafy vegetables one of the most common sources of Tl exposure. Thallium has been detected in prenatal vitamins, and clinicians should be aware that the neurotoxic metal readily crosses the placenta to the developing fetus.

The human health issue appears to relate predominately to chronic low-dose exposure via air, water and food sources over time, as opposed to acute high-dose exposure. The more neurologically vulnerable populations such as pregnant women, infants and children are of greater concern and warrant more consideration. Particular caution is to be exercised in instances of large amounts of Spinacia and Brassica group vegetables, such as juicing, in the diet. 

The current culture strongly advocates dark green leafy vegetables as healthy due to their mineral and folate contents, yet the health risks of Tl exposure must be weighed against the benefits. Furthermore, in sensitive populations and those consuming large amounts of Spinacia and Brassica group vegetables, urine levels of Tl may be clinically relevant. Clinicians should be aware of the neurotoxic potential of Tl. Mitigating Tl exposure could benefit human health on the individual and greater community levels.