> 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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