Monday, 18 January 2010

Black Sand

This is the tourist season in Brazil, with millions flocking to the beaches. Every stretch of sand is covered with gaily patterned parasols, but especially the town of Guarapari just along the coast. Formerly a fishing village it is now famous far and wide for it's tourist infrastructure and it's golden, and black, sands.

The black sands derive from monazitic rock, which has a high Thorium content, which means in turn, that it is radioactive. Guarapari has actually the 2nd highest background level of radiation in the world, with Ramsar in Iran (ironically) having the highest. The dose varies, but averages at 5.5 mGy/year, compared to a world average of 0.4. The third place incidentally is occupied by parts of Kerala, with 3.8 mGy/year, again in areas of black monazite sand.

I should say that studies of Kerala and in Iran have failed to find any detrimental genetic effects of living near these sands. Indeed there have been studies in Taiwan and Eastern Europe where people were accidentally exposed to low, but long term, doses of man made radiation, that appear to show a protective effect against cancer, by bucking up the immune system and antioxidant defences - the radiation hormesis model. This is highly controversial, to say the least, as it depends completely on who you compare the exposees too, you need an identical group in terms of age, social level, smoking habits etc.

In the past, Guarapari was widely believed to be beneficial for rheumatism and arthritus, though this has not yet been scientifically proved. But who knows, maybe the original tourists to "the city of health" were right after all!

Nobody seems to have done the obvious study of looking at radioactive effects on sand living animals, such as ........

Crab of the day
The ghost crab, Ocypode quadrata

The Ghost, or Sand, crabs are found on many continents, living in burrows in the beach. Their name drives either from their pale translucent appearance ( or their extremely rapid movements, especially when about to be photographed.
They dart back into their holes, which are about an inch wide and up to 4ft deep, at the first sign of danger. Despite this seemingly nervous behaviour, they are astonishingly tolerant of disturbance, living on, or in, beaches that are noisy with tourists all day, only to emerge at night or in the dawn to feed on the refuse. In fact, human presence may be to their advantage, driving away predators and competitors.

A few minutes with a shovel and a BBQ would present an adequate, if crunchy, meal. The local crab eating fox (Cerdocyon thous) dispenses with both, although it should be said that he eats many more small mammals than crabs.


sann2282 said...

I see that it's the same phenomenon seen in Kovalam too. My father voiced the same opinion: that the sands are derived from Monazites and hence has its own, er, problems. Unfortunately, the government insists that there ain't any.

On the brighter side, it is quite heartening to know that this may have some health benefits too!

sann2282 said...

Oops, should be ilmenite!

Anonymous said...

Funny the role! The crab was so fast!!!. . .

Mynah Bird said...

Excellent post!

It would be interesting, as you rightly point out, to find out whether the radiation has any detrimental effects on the ghost crab, but then, it makes me wonder whether it would be the best model as a lot of athropods show a high degree of tolerance. But I am sure there are other aquatic/semi aquatic ogranisms one could work on.

Look forward to the next editions