Darolles, C, D Broggio, A Feugier, S Frelon, I Dublineau, M De Medro and F Petitot. 2009. Different genotoxic profiles between depleted and enriched uranium. Toxicology Letters. http://dx.doi.org/10.1016/j.toxlet.2009.11.00
Radiation is not uranium's only health concern, say researchers who report the less radioactive form of the metal can also damage DNA, but in a different way that could also lead to cancer.
Meticulous research identifies for the first time how two main types of uranium – enriched and depleted – damage a cell's DNA by different methods. The manner – either by radiation or by its chemical properties as a metal – depends upon whether the uranium is processed or depleted.
This study shows that both types of uranium may carry a health risk because they both affect DNA in ways that can lead to cancer.
Why does it matter? Regulatory agencies determine safe uranium exposure based on the metal's radioactive effects. Currently, safe exposure levels for workers and military personnel are based on enriched uranium – which is the more radioactive form and is considered to have a higher cancer risk than depleted uranium. Uranium exposure has been shown to affect bone, kidney, liver, brain, lung, intestine and the reproductive system.
Yet, many people are exposed at work or through military activities to the less radioactive, depleted form. They may not be adequately protected based on current methods that evaluate uranium's health risks.
As a naturally-occurring element, most people are exposed to low levels of uranium through food, air and water. Additional exposure to uranium occurs when it is mined and altered for civilian or military purposes. Workers who process uranium into nuclear fuel for energy or weapons face additional exposure to enriched uranium. Depleted uranium – a by-product of the enriching process – is used in military armor and in armor-piercing ammunition. Soldiers on a battlefield or civilians who live near these areas can be exposed to this form.
Studying uranium's effects is challenging because it can damage DNA in two distinct ways. The similarities make it difficult to tease apart which form and which method is responsible for the harm.
The French scientists who conducted this study started by exposing mouse cell cultures to enriched and depleted uranium. They applied different toxicity tests to distinguish which uranium caused which kinds of DNA damage.
They found the enriched uranium caused breaks in the chromosomes that make up the DNA. Called clastogenic damage, the effects were related to the amount of radiation the enriched uranium released.
In addition, the radiation-related effects were more pronounced, suggesting that the chromosome breaks were caused by the radiation and not by the chemical effects of uranium. The chemical effects of uranium did not seem to contribute to the DNA damage seen with enriched uranium, at least in the context of this study.
However, the depleted uranium had a different type of effect. It altered the number of chromosomes in the cell. These effects are due to improper migration of chromosomes when cells divide. This type of damage – called aneugenic damage – was not related to the amount of radiation the cells received and was likely caused by the metal properties of uranium.
The methods used in this study clearly provide a new way to assess the different types of genetic harm caused by uranium. The findings will help ferret out whether the genetic damage caused by the depleted uranium also carries a high risk of causing cancer, which is something those who work with or are around the metal want to know. Further study is warranted to truly assess human health risks.
Synopsis by Paul Eubig, DVM
Mar 16, 2010