> Although some CCD deadouts had fairly high levels of legal mitacides 
> testing showed that most the boxes were at levels below the known LD 50. 
> The symptoms of mitacide death were not seen.

An interesting statement, inasmuch as the exposure time in the hive, being 
the bees' home is not limited as it is in measured LD50 tests, any amount 
approaching the known LD50 would mean the hive would kill half the bees in a 
comparatively short time, and virtually all the bees shortly thereafter.

The point is that any contamination approaching the LD50 of any contaminant 
can be expected to prohibit brood rearing long before being achieved, so in 
order to allow for any bee life in  the hive, the contamination would have 
to occur quickly before the collapse event under observation, and not be a 
gradual build-up.

We often talk about LD50, possibly without contemplating the limitations and 
true meaning of the concept.

That got me wondering, and I see Wikipedia has summarized my thoughts better 
than I could ever do.  See
http://en.wikipedia.org/wiki/Median_lethal_dose

--- quote ---

In toxicology, the median lethal dose, LD50 (abbreviation for "Lethal Dose, 
50%"), LC50 (Lethal Concentration, 50%) or LCt50 (Lethal Concentration & 
Time) of a toxic substance or radiation is the dose required to kill half 
the members of a tested population after a specified test duration. LD50 
figures are frequently used as a general indicator of a substance's acute 
toxicity. The test was created by J.W. Trevan in 1927.[1] It is being phased 
out in some jurisdictions in favor of tests such as the Fixed Dose 
Procedure;[2] however the concept, and calculation of the median lethal dose 
for comparison purposes, is still widely used.

As a measure of toxicity, LD50 is somewhat unreliable and results may vary 
greatly between testing facilities due to factors such as the genetic 
characteristics of the sample population, animal species tested, 
environmental factors and mode of administration.[3] Another weakness is 
that it measures acute toxicity only (as opposed to chronic toxicity at 
lower doses), and does not take into account toxic effects that do not 
result in death but are nonetheless serious (e.g. brain damage). There can 
be wide variability between species as well; what is relatively safe for 
rats may very well be extremely toxic for humans, and vice versa. In other 
words, a relatively high LD50 does not necessarily mean a substance is 
harmless, but a very low one is always a cause for concern.

--- end quote ---



 

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