The Sun declined to publish my response (below) to Dr Looi Hoong Wah's earlier letter .

In the interests of reasoned exchanges, I hope this response to Dr Looi's latest letter sees the light of day.

In this letter, Dr Looi's cites the Argonne National Lab's fact sheet on thorium to argue that only a miniscule portion of thorium-232 which is ingested via food or water is absorbed into the bloodstream, of which only 4% gets deposited in the liver where it is retained with a biological half-life of 700 days.

He neglects to mention that thorium-232 is much more readily absorbed into the human body via an inhalation route, and furthermore that 70% of the amount entering the bloodstream gets deposited in bone where it is retained with a biological half-life of about 22 years, all that while irradiating the much more radio-sensitive blood-forming tissues there with highly mutagenic alpha-particles (20 times more damaging to cellular genetic material than beta or gamma radiation).

Could this be the reason for the cluster of childhood leukemias observed among the children of Bukit Merah? (Recall also the inverse square law - the intensity of radiation from a radioactive particle a meter away from a human body increases a trillion-fold when that same particle sits at micron level distances on the body's cells and tissues).

Dr Looi considers that inhalation exposures to thorium-containing dusts is solely an occupational problem which is not relevant to the greater Kuantan-Kemaman community.

Let's recall that the ARE rare earths refinery at Bukit Merah, like LAMP, had no long-term waste management plan.

Ad hoc arrangements, including the aborted Papan dump-site, eventually led to a situation of indiscriminate, clandestine dumping of radioactive thorium-cake wastes at Lahat, Menglembu, Pengkalan, Jelapang, Buntong, Simpang Pulai among other locations: http://www.merdekareview.com/bm/news_v2.php?n=11823

The Kuantan-Kemaman community similarly faces the prospect of unknown numbers of dump-sites at unknown locations scattered in and around the cities, if Lynas does not come up with an acceptable plan for long-term waste disposal.

Allow me also to bring to Dr Looi's attention a 1993-1994 study of male miners at the Bayun Obo Rare-Earth and Iron Mine in Inner Mongolia which was reported in the Journal of Radiological Protection in 2005.

In that study, highly dust-exposed miners had 5.15 times the age-adjusted lung cancer rate as compared to the rate among Chinese males in the general population. The less-exposed mining staff had 2.30 times the general population rate. Both groups had similar smoking rates (78 percent, vs. 67 percent for the general adult male population).

On this basis, the authors concluded that the excess lung cancer risk among the less-exposed was largely due to above-average smoking, and the further difference between the two miner groups was due to high exposure to airborne crystalline silica particulates (mainly) and to thorium-containing dusts and its radioactive daughter nuclides such as thoron gas.

These conclusions are highly debatable, and it is precisely in this situation of uncertainty and lack of consensus that the Kuantan-Kemaman community shouldn't end up as tikus makmal (lab rats) in a natural experiment for Lynas.

Finally, it should also be noted that the ores that the Chinese miners were exposed to contained 400 ppm of thorium. The rare earth oxide concentrates that will be arriving shortly at Kuantan port will have 1,600 ppm of thorium.

The US Public Health Service (1990) reports that the natural background level in North American soil is typically ~ 6 ppm of thorium.

Chan Chee Khoon, ScD (Epidemiology) works at the Center for Population Health, Dept Social & Preventive Medicine. Faculty of Medicine, University of Malaya.