Tikus Makmal in a Natural Experiment?

By Chan Chee Khoon, ScD (Epidemiology)

On June 7, 2011, in a live interview with CNN, Arnie Gundersen, a licensed nuclear power engineer with 39 years experience in managing and coordinating projects at 70 nuclear power plants in the US, noted that with the prevailing wind patterns after the Fukushima disaster’s radioactive discharges, air filter monitors in Seattle detected about half the level of “hot” (radioactive) suspended fine particulates as were detected in the air over Tokyo, 7700 km away.

Gundersen didn’t clarify what the baseline level of airborne radioactive particulates in Seattle was, pre-Fukushima, but if the measured levels in April 2011 were indeed largely blown over from Fukushima, it’s very sobering considering that Kuantan and Kemaman are within a 28 km radius of the Lynas rare earths refinery being built at Gebeng, which will be handling rare earth concentrates ground and milled into a fine powder for acid extraction at the plant.

The ARE experience from Bukit Merah in the 1980s tells us that beyond the dust-generating cracking, grinding and milling operations, powdery thorium cake waste was also spilling onto roads during transportation, during packing and unpacking, loading and unloading, and children were frequently playing in the vicinity of exposed mounds of the waste. Indeed, the thorium waste was reportedly offered to local farmers as fertiliser.

It is for these reasons that the issue of radioactive dusts and internal emitters – from inhalation and ingestion, or absorption through the skin – becomes crucial. It matters a lot whether the source of radiation is a solid lump of radioactive material (intensity of external irradiation rapidly falls off with the square of distance), or whether it exists as a pile of fine radioactive particulates which are respirable when airborne and mobile.

The Lynas Radiological Impact Assessment submitted by Nuklear Malaysia (dated June 2010) does attempt to estimate the risks from inhaled emitters for LAMP employees (average volume of air intake, presumed level of dust concentrates and associated radioactivity internalised by the employee) (p.56) but it then proceeds to compare the (internalised) absorbed radiation energy – averaged over the whole body – with existing threshold levels of ‘safe’ exposure.

This is precisely what was contentious in CERRIE’s deliberations (www.cerrie.org), and within radiobiology and radiation carcinogenesis circles – by way of analogy, averaging the absorbed radiation energy over the whole body is equivalent to saying that a burning cigarette butt on your palm doesn’t hurt because the heat is negligible when averaged over your whole body.

But cancer biologists and educated laypeople know that cancer can emerge from a single cell that has sustained the requisite mutations which allow it to multiply uncontrollably, i.e. it is a highly discontinuous phenomenon and averaging radioactive exposures over the whole body is not meaningful for a discrete event in radiation carcinogenesis which involves intense, localised radiation doses delivered to cells surrounding the radioactive particle.

Aside from cancer biology, radiation risk can also be approached from an epidemiological perspective. One of the very few empirical attempts at this was a 1993-1994 study of male miners at a combined iron ore-rare earth minerals mine in China which was reported in the Journal of Radiological Protection in 2005 (attached). 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%, vs. 67% 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 radon 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 1600 ppm of thorium. The US Public Health Service (1990) reports that the natural background level in soil is typically ~ 6 ppm of thorium.

Chan Chee Khoon, ScD (Epidemiology)
Professor & Consultant
Center for Population Health
Dept Social & Preventive Medicine
Faculty of Medicine
University of Malaya
50603 Kuala Lumpur, Malaysia

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