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Radioactive sand causes mutations in human DNA
  

Radiation has been known to cause cancer and damage to human cells, but it has been less clear to what extent it affects human DNA. Now, researchers have observed that high levels of naturally occurring radiation significantly increase the number of mutations in human DNA.


Radioactive black sand in Kerala, southern India. Thousands of traditional fishing families have lived here for generations, exposed to the highest levels of natural radiation in the world.

The study was carried out among residents of Kerala, a densely populated area at the southern tip of India, where thousands of traditional fishing families have lived for generations. The residents are exposed to a naturally occurring radiation dose ten times higher than the worldwide average.

The glistening black sand on the beaches contains radioactive materials such as thorium and monazite. Kerala has the world's highest level of natural radioactivity in a densely populated area, according to the researchers. The radioactive strip measures an area of ten kilometers by one kilometer.

"Our family study encompasses several generations per family, and therefore we saw what was really happening with the new mutations," says Peter Forster, a molecular geneticist at the McDonald Institute, University of Cambridge, U.K.

Forster and his team studied 988 individuals of 248 families that have been exposed to high and low levels of natural radiation throughout their lives, including five families with four generations. Residents from nearby low-radiation islands served as a control population.


High-radiation and low-radiation localities sampled in this study. Radioactive areas are identifiable by the presence of black monazite sand, rather than the white nonradioactive sand elsewhere.

For two years, Lucy Forster, of the University of Münster, Germany, and others on the team collected DNA samples in Kerala and analyzed them in the lab.

The researchers looked at the DNA from mitochondria, the tiny energy producers of human cells that live outside the nucleus and have their own DNA. Mitochondrial DNA is inherited only from the mother and can be used to determine whether a mutation is passed on from the mother to her descendents.

The scientists identified 22 mutations in the mitochondrial DNA sequences of families living in the high-radiation area. By comparison, a control population living on white sand nearby only had one mutation.

Interestingly, these mutations were located at positions the researchers refer to as "evolutionary hot spots," which mutate much faster than other positions during evolution, according to the findings published in Proceedings of the National Academy of Sciences.

The research doesn't necessarily suggest a link between the 22 mutations and disease. "We intentionally analyzed a non-coding region of the DNA where mutations have no effect on health or on any other visible features," says Forster.

The new findings may have implications for current radiation standards. "It might be worth considering whether to lower the allowed limits for radiation workers of reproductive age," says Forster. The maximum allowed for workers exposed to radiation (in research or in nuclear facilities) is 50 times higher than normal.

Previous studies indicate that there is no conclusive evidence that people living in places with natural radioactivity are at a higher risk for cancer and other health-related problems.

There are similar natural radiation areas in southern China, Iran and Brazil, but the Kerala coast in southern India is believed to be the only high-radioactivity region with a high population density.

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Forster, L. et al. Natural radioactivity and human mitochondrial DNA mutations. Proc Natl Acad Sci USA. Published online October 07, 2002.
 

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