The Natural Presence of Lanthanum
Lanthanum (La) is a soft, silvery-white rare earth metal that is the 28th most abundant element in the Earth's crust, making it more common than lead. It does not exist as a free metal in nature but is found in various minerals, such as monazite and bastnäsite, which are often rich in phosphates. Through the natural process of mineral weathering and decomposition, trace amounts of lanthanum are released into the soil and water.
Plants can absorb elements from the soil and water they use for growth. As a result, minute quantities of lanthanum can be taken up by plants and become part of the human and animal food chains. Research has identified that some vegetables and other food crops naturally contain these trace levels, which are generally considered insignificant from a health perspective for the average consumer. The concentration can be influenced by the regional geology and soil composition where the food is grown.
Specific Food Sources Containing Trace Lanthanum
Research from databases like FooDB indicates the presence of trace lanthanum in a variety of common food items.
Vegetables and Herbs
- Broccoli: A widely consumed vegetable that can contain very small amounts of lanthanum.
- Carrots: This root vegetable has been reported to contain low levels of the element.
- Dill: This aromatic herb is another food item where trace concentrations of lanthanum have been detected.
- Garlic: Known for its potent flavor and medicinal properties, garlic can also contain minute traces of this rare earth element.
- Leafy Greens (e.g., Lettuce, Bok Choy, Cabbage): Various studies have shown that edible leafy plants can accumulate lanthanum from soil, with levels dependent on growing conditions.
Other Food Items
- Almonds: Nuts can also contain trace minerals absorbed from the soil, and almonds are one such example where lanthanum has been noted.
- Soybeans: Studies have investigated the uptake of lanthanum in soybeans, an important global crop, confirming its presence.
- Cereals, Meats, and Eggs: A Chinese study analyzing lanthanum in major food categories confirmed its presence across different food groups, including cereals, fresh aquatic products, fresh meats, and eggs.
Dietary Intake and Human Health Considerations
The amount of lanthanum absorbed from food by the human body is very low. The gastrointestinal tract poorly absorbs lanthanum, and the element is not believed to have any known biological function in humans. For the general population, the mean dietary intake is extremely small—estimates suggest it is less than 5% of the estimated acceptable daily intake. This low absorption rate means that the trace amounts found in food do not pose a significant health risk. However, it's worth noting that high, non-dietary exposure, such as through industrial inhalation, can be harmful.
Medical vs. Dietary Lanthanum: An Important Distinction
While the amounts in food are minuscule and poorly absorbed, it is important to distinguish this from the medical use of lanthanum carbonate. This drug, sold under brand names like Fosrenol®, is specifically prescribed to patients with end-stage renal disease to manage hyperphosphatemia (high phosphate levels in the blood).
Comparison of Dietary and Medical Lanthanum
| Feature | Dietary Lanthanum | Medical Lanthanum (as Lanthanum Carbonate) |
|---|---|---|
| Source | Naturally occurring trace amounts in various plant and animal foods. | Prescription medication administered in high doses. |
| Dose | Minute, measured in micrograms ($\mu$g), absorbed inefficiently from food. | High, therapeutic doses of up to 3000 mg per day to bind phosphate. |
| Purpose | Naturally present with no known human biological function. | Binds excess phosphate in the gut for patients with kidney failure. |
| Health Impact | Not considered a health risk at natural intake levels due to poor absorption. | May cause side effects like gastrointestinal upset, but carefully monitored by doctors. |
| Excretion | Very little is absorbed and what is passes through the digestive tract. | The primary mechanism is binding and excretion via feces. |
This table highlights the significant difference between a naturally occurring trace element and a pharmaceutical compound used for a specific medical condition. Medical doses are thousands of times higher than dietary intake. For more on the clinical use, an article on the medical applications of lanthanum is available from ScienceDirect.
The Role of Soil and Fertilizer
The concentration of lanthanum in food is a function of the soil in which it was grown. As a component of rare earth element (REE) fertilizers, primarily used in countries like China, lanthanum has been intentionally introduced into agricultural systems to enhance crop yield. This has led to higher, though still safe, levels in crops from these regions compared to those from areas without REE fertilizer use. However, environmental and food chain effects are areas of ongoing research. Scientists continue to monitor how these practices affect the uptake of lanthanum and other rare earth elements in edible plants.
Conclusion
While many foods, especially vegetables, nuts, and cereals, naturally contain very small, trace amounts of lanthanum, this does not pose a health concern for the average person. The human body absorbs this element poorly, and it serves no known biological purpose. The levels encountered through a normal diet are negligible compared to the high, medically-prescribed doses used to treat specific conditions. Therefore, while it is true that some foods contain lanthanum, the intake is minimal, and its presence is largely a byproduct of the element's natural abundance in the Earth's soil.
