Increasing thallium levels damage plant DNA.

Oct 09, 2008

Radic S, P Cvjetko, K Glavas, V Roje, B Pevalek-Kozlina and M Pavlica. 2008. Oxidative stress and DNA damage in broad bean (Vicia faba L.) seedlings induced by thallium. Environmental Toxicology and Chemistry online August 21.

Synopsis by Carys L. Mitchelmore

Researchers report for the first time that an obscure, but increasingly common, highly toxic metal called thallium accumulates in plants and elevates harmful oxygen radicals that damage the plants' DNA. Humans are exposed to the metal by eating contaminated food crops. Small amounts can make people sick. Levels of the naturally-ocurring thallium are increasing as a result of its release from iron and zinc refineries.

The metal thallium accumulates in bean plants, where it increases harmful oxygen radicals (a process called oxidative stress) that break DNA strands. This study is one of the first to identify exactly how this highly toxic metal harms plants. It is important to understand because many crops accumulate the metal, which can affect plant growth and be passed on to human consumers.

Thallium is a natural metal that is not required by plants and animals. It is known to be quite toxic but how it affects organisms was not fully known.

Concentrations in the environment are increasing because of human activities. More than 1,500 tons of thallium per year are released from smelting plants as a byproduct of iron and zinc refining. Also, agricultural soils receive thallium from sewage sludge and from potassium fertilizers. Human exposure occurs mainly through eating plants grown in thallium-contaminated soils. Very low levels (8 mg/kg) can be lethal to people. In this study, bean plants were exposed to thallium concentrations (some environmentally relevant) using short-term water exposures. The extent of oxidative stress and resulting DNA damage were evaluated using a variety of laboratory biomarkers.