Since my name keeps coming up with respect to this issue -- the study
presented in Canada was a very detail oriented, intensive set of trials, carefully
orchestrated, and expensive set of trials. No one questioned issues such as
did the investigators set out to thoroughly investigate the issue, have a
good statistically based sampling design, or the reputation of the lab, etc.
But, as I remember, this study was done because beekeepers were concerned
about bee losses in the area and use of imidacloprid. Many of the soil samples
showed detectable residue levels, with only a trace in a few nectar/pollen
samples. The conclusion was that imidacloprid was not reaching the bees, or
at least not in toxic doses, therefore there was no evidence for bee losses
relative to use of imidacloprid.
My concerns with this study were:
1) Sample size - the study used many subplots. It was easy to get large
soil samples, but even after laborious removal of pollen and nectar from bees,
the resultant sample size was very small.
Small enough that issues of representativeness and detection limits needed
to be addressed/reported,
2) Routes of exposure - the assumption seemed to be, the major route of
entry must be from soils through plants to nectar and pollen, then to bees.
That's not necessarily true -- dust borne materials such as would occur with
contaminated soils tend to re-entrain on windy days, deposit on plant surfaces,
bees, etc. And, as we've shown in several publications, particulates are
adsorbed onto the bodies of bees, and the amount on the bees varies by particle
size and electrostatic charge on the bee.
This route of entry was not considered, yet our data says that in cases like
this, it may be the principal route of exposure,
3) Bees were collected, but at the time of the presentation, no bees had
been analyzed and there did not seem to be any intention to do so.
Until body burdens of the target insect are examined, the question of
exposure remains unanswered.
4) GLP extends to the field, its not just an internal lab issue. The
responsibility for this rests with the primary investigators, not necessarily the
lab. Field blanks and field spikes should be part of a well designed study to
determine whether anything is lost or gained during handling, transport,
storage, and processing. There are too many places along this path where
materials of interest could be lost (tissue degradation, chemical breakdown,
sublimation) or gained (contamination).
Everyone involved was trying to do a good job. Elaborate steps were taken
to get uncontaminated samples - plastic gloves, etc. Someone sat in a cooler
to remove the pollen pellets, obtain nectar from bees. Samples were sent to
a GLP lab. All well and good. But, the aforementioned issues were not
addressed, at least not at the time of the presentation Allen references.
Jerry
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