🚀 go-pugleaf

In article <877341053.9279@dejanews.com>,
Philip Ross  <pross@inhb.co.nz> wrote:
>Kym Horsell has suggested that plutonium is far more toxic than common
>highly toxic substances and has cited figures to bolster this point.
>
>There are some most significant misunderstandings in this which bear
>mentioning.

I doubt it. ;-) 
The material cited (Sax et al) has been around for a while...

>Hydrogen cyanide is often fatal at a dose of 50 milligrams. It is a highly
>volatile compound and is easily inhaled. A lethal dose of potassium
>cyanide is approx 250 milligrams. It is hydrolysed by stomach acid to
>generate hydrogen cyanide. It has been used as war gas, often in
>combination with phosgene (which is often fatal at a dose of 35
>milligrams) and sometimes in association with nerve gases.
>[Lots more  "explanations" of allegedly what LD50's in (e.g.) Sax don't 
take into account]

Firstly, a little caution. When someone representing the nuclear industry 
gets up and tries to downplay the dangerousness of a particular material, or
confuse -- perhaps to the minds of some _deliberately_ confuse -- danger 
with risk, etc, then they will be doing their industry (yet another in a 
long line of) dis-services. (*)

It would seem -- to some ;-) -- that (generally) advocates of an
industry saying "yes, this industry involves handling extremely
hazardous materials; and we take that danger and the resulting responsibilities
extremely seriously. The public can trust us" might meet with more
general acceptance than if they say "hey -- trust us. If you ignore
the main effects of the materials in question, they are less dangerous
than drinking coffee. And that's the kind of thing we keep in mind when
it comes to public health and doing business".

Additionally, if someone proposes to "explain" alleged "misunderstandings" 
related to what or what does not follow from a published LD figure, starting 
with but not restricted to phrases like "X is often fatal" and 
"a lethal [other conditions unspecified] dose of X is Y" they also are  
not likely to be particularly effective.

Overall, the argument -- as posted -- seems to be attempting to shift from 
the topic of "how dangerous is X" (aka "danger" and how likely something
is to kill once someone is exposed to it) to one of how "likely X is to kill 
you" (aka "risk", and related to how likely someone "normally" would be
to be exposed to a danger).

The distinction between risk and danger is only subtle if someone moves their 
hands rather quickly.

E.g. someone might say "tigers are quite dangerous animals", but
it sometimes is the case the argument will then shift ground
to something like "but tigers are not indigenous to LA". ;-)
I'm afraid this second type of claim doesn't make tigers any less "dangerous".
And we have to remind ourselves of (*), too. ;-)


There is quite a lot "wrong" with citing a specific LD50 (say), including
observed (say) 10-to-1 variations in the actual measurements  for test
species, and also the difficulty of extrapolating to humans, etc. 
I note, these things are generally not touched on. Presumably, because 
(as I indicated a few days back)  -- we are often hearing the
personal opinions of engineers, or even administrators on these newsgroups. ;-)


The classical saw that allegedly "some things are harder for a human
body to absorb than others" is not one of those things "wrong" with LD's.  
An LD takes such niceties into account -- since deaths are OBSERVED under the 
conditions specified in the test (i.e. at least dose, species, vector
and length of waiting time).

E.g. if some number, say 50%, of animals in a trial exposed to X are found to 
be DEAD and/or found to have tumours (in the case of tumorgenesis calculations)
at the end of the testing period, and that is statistically significant 
with respect to a control population, then you GOTTA figure some of the 
X actually WAS absorbed. No matter "how difficult" is may have been
allegedly been for the relevant GI tract or lung tissue to absorb and/or
retain X (although, of course, some materials have an extremely long
biological 1/2 life, as in the case of calcium-like radionuclides). 
Once the animals are dead and the experiment is over, it doesn't really 
matter how "hard" it may have been for ingestion to happen. It is 
"factored into" the relevant LD.


Getting back to the argument, above, stating that "lethal doses of X are Y" 
is, again, not particularly relevant to "disclaiming" a particular LD50  
value (say), since it seems willing to wave hands rather than stating 
EVEN APPROXIMATELY under what conditions such an observation is made, or 
what effects are observed with dose Y. (Let alone provide  any basis of 
comparison with any other substance).  

But we might PRESUME, given the context of the argument, that someone
might be trying an apples and oranges comparison of an LD at 1000 days with, 
say, an LD at a few hours.  Such things can develop into tried-and-true tactics.

After all -- if the MAIN effects of substance X (and those like it) is
effect Y, and Y takes some time to develop, the "best way" (according
to proponents of industries dealing with X)  to deal with measurements of 
the "dangerousness" of X, is simply to take all measurements before Y
can develop. E.g. if tumours take (say) 8 weeks to develop, then it's
"best" to stop the clock well before that time. Otherwise there is
some "danger" that tumours might show up in the experimental results,
thereby ruining the appropriate horizontal line. (This is, of course,
not news to any undergrad and most post-grads).


But, remember (*).  It certainly is true that radionuclides don't kill as 
_quickly_ as, say, your average toxin (leaving aside toxin vs toxicant). 
But -- we knew that to start with. 

Cancer isn't generally speedy.  From (say, a typical modern model)   of
a few (sometimes just one) initial damaged cells, it takes some time -- even 
at an enhanced reproduction rate (one of the results of said damage) -- before 
that becomes a significant growth that can withstand assaults from immune 
responses (sometimes also locally weakened, anyway) or other attacks, can 
migrate to other appropriate sites, etc.


So, comparing how lethal a substance is within 24 hrs (say) -- the
so-called "chemical toxicity of radionuclides" --  will trivially favour some 
arguments. But death over the 24 hr line has been known to happen -- and many
people don't ignore it. ;-)


For an LD50 -- i.e. 50% (usually interpolated on the basis of a number of 
independent trials at different doses)  of animals dead at (say) 1000 days 
after one (sometimes more) exposure to a given dose of X -- nerve gas etc are 
"good", but "many" radionuclides are generally somewhat "better" (i.e. 
exposure levels smaller), regardless of how difficult it may be to ingest any 
great quantity of the material.


For more detailed niceties on LD's and transuranics (obviously not
"limited" nor even _concentrating_ on their chemical properties), 
see (e.g.) Chapter 66 by Henru Me'tivier 
in "Handbook of Toxicity of Inorganic Compounds", Seiler, 
Sigel and Sigel (eds), Marcel Dekker Inc, NY, 1988.
(For additional material also see the article by Raabe & Goldman, 
"Radiation Research", 78:264 (1979)).


It cites the (I would have though "widely" accepted) LD50 for dog and monkey 
for inhaled Pu oxides as:
        period    LD50  239 Pu    LD50 238 Pu (MBq)
        30 days      21             5.5
        365          2.1            4.4
        1000         .85            1.7

Although the "Mega" Bq sounds like a massive unit, let's see what these
mean in terms of mass of materials (as LD's usually are determined).

We know that 1 milli Curie (mCi) of Pu239 == 16 mg of material,
and 1 mCi of Pu238 == .06 mg of material.
(Since Pu is a heavy metal we can pretty-much ignore the mass of the oxygen
component of any oxide, at least, for an order-of-magnitude calculation).
We also know that 1 mCi == 10 MBq.

Ergo the "large" sounding 1000 day LD50 of 1.7 MBq of Pu238 == 
0.01 mg == 10 \mu g of the "material". (It should be no surprise this is
in the ball-park of the previously-cited refs. ;-)
I.e. small amounts of Pu238 oxide has been observed to cause "termination"
via lung damage in exposed monkeys and dogs within 1000 days, and
those results when interpolated indicate 50% would die under the conditions
if initially exposed to 10 MICRO gram of the material. (The "interpolate"
part can also be criticised, as the associated linear and log-linear models 
"only" explain around 70% of the observed variation in experimental results ;-).


We note that the standard Sax figure (op cit) of 50 micro grams corresponds,
roughly then, to a 30 day LD50 in (some) mammals.
(Which all leads at least me to suspect that a previously and apparently
recently oft-cited on these newsgroups "mammal LD50", of at least ONE 
THOUSAND MILLIGRAMS PER KG BODYWEIGHT, must be an orange of a very very speedy 
death, indeed -- possibly related to acute affects from an oral dose ;-o).


Finally, I'll mention  another well-known public reference citing 
"health problems" for mammals inhaling hard-to-ingest Pu oxides:
===
ATSDR Public Health Statement, December 1990

PLUTONIUM
...
there is no information from studies in humans or animals to identify
the specific levels of exposures to plutonium in air, food, or water
that have resulted in harmful effects. However, it is generally
assumed that any amount of absorbed radiation, no matter how small,
may cause some damage. When expressed as the amount of radioactivity
deposited in the body per kilogram of body weight (kg bw) as a result
----------------------------------------------------------------------
of breathing in plutonium, studies in dogs report that 100,000 pCi
----------------------------------------------------------------------
plutonium/kg bw caused serious lung damage within a few months, 1,700
----------------------------------------------------------------------
pCi/kg bw caused harm to the immune system, and 1,400 pCi/kg bw caused
----------------------------------------------------------------------
bone cancer after 4 years. In each of these cases the dogs were
--------------------------
exposed to the plutonium in air for one day.
...
===


Let's ignore the initial hand-waving and just check the experimental 
observations (underlined).

It was observed that 10^5 pCi per kg over a 24 hr exposure period in dogs 
caused "severe lung damage" within several months. Again, 1 mCi of Pu239 
(i.e. the "not so dangerous" one) ==  16 mg. 
Hence 10^5 pCi /kg== 10^-4 mCi /kg== 0.0016 mg.  I.e. about 2 MICRO gram per 
kg. 

For the more dangerous Pu238 we'd be talking about .000006 mg -- i.e. 6 NANO 
grams/kg.

No matter how rare these materials are, no matter how "hard" is may be
to ingest them, these observations indicate they are DANGEROUS.

And hence the observed extremely low permissible levels in foodstuffs
(op cit).