Randy

Re:  Pesticide Sample Analyses

I understand what you are trying to do, it's the how that's not so simple.

LD50 values are reported on a per bee basis.  If you analyze pollen or nectar, you get a measure of dose, although it is a measure of dose by ingestion, which is not the same as contact dose.  Still, some LD50s are based on feeding trials.

If, on the other hand, you are considering pesticide residue levels in dead bees, how are you converting residue values to exposures in order to compare to reported LD50s?  

You should ask the submitters whether the bee sample residue analysis value (and that of pollen) is being reported based on dry weight of sample, wet weight of sample, or something in between.   Nectar or honey is usually reported on a wet weight basis.

For all Superfund work that I did for EPA, all residue values were reported per dry weight of bee or pollen.  Analytical labs often just fracture the sample and analyze, disregarding the condition of the sample as received (wet, moist, dried) and report whatever the instrument detects - the reported values do NOT take into consideration the amount of water in the sample (weight/amount/condition of sample).  Also, the amount of pesticide measured as a residue value is NOT the amount of chemical per bee.

Don't consider moisture in the sample to be an issue? - consider this:  A live or freshly killed bee weighs about 0.1 gm.  Labs usually want at least 0.5 gm of sample - and I much prefer to see a 5.0 gm sample.  

The 0.5 gm sample  is the wet weight of about five bees - too small a number of bees to be representative of the colony of 10s of thousands of bees from which the bees are taken.
The 5 gm sample would be the wet weight of about 50 bees.   

However, whereas the wet weight of a bee is about 0.1 gm, the actual dry weight of a bee is only about 28 mg.  On a dry weight basis, that would be 17.9 bees per 0.5 gm; 178.6 per 5 gm.  

Let's say someone reports 5 ppb of a specific pesticide in dead bees.  Five ppb is a an amount of pesticide based on a gm of sample.  To estimate exposure per bee for comparison to reported LD50 values, what is your divisor - 10? 36? other?   As you well know, 5 ppb residue does not equal a 5 ppb dose per bee.

Finally, our published data from when I was doing a lot of Superfund work reports that in most cases one needs at least 25 bees before the amount measured in a bee sample can be considered to represent any realistic estimate of exposure to the colony as a whole (based on residues in forager bees).  And, our recent investigations have indicated that mites, nosema, etc. are a factor in bee kills, and that piles of dead bees may not always indicate a bee kill due to pesticides.  Have any of your respondents reported a suspected bee kill without evidence of exposure to a pesticide thought to be the cause?  Would they report anything at all to you?

My concern is making extrapolations without knowing the context.

Now, for some tips.

If any of you find what looks like a pesticide kill:

1) Get an independent person to take the samples - not you, or your family, or friends.  
2) Freeze the sample(s) as soon as possible and keep it frozen.
3) Ship to an analytical lab on a weekday, preferably not Monday, and never on a Friday - the samples will have a better chance of showing up at the lab in good shape, less chance of getting lost.
4) Keeping sample(s) frozen during shipping is best.  Blue Ice gel pacs may be ok at this time of year, but in heat of summer, dry ice is far better - if you can obtain it.  
    4a)Never ship on regular ice - it will melt and the melt water is likely to seep into the samples, contaminating them.
    4b) Dry ice sublimates, and the sublimation is faster in humid conditions.  The rule of thumb is 10 # of dry ice will last a full 24 hrs, maybe more.  Anything less and the dry ice may be gone before the samples are received, checked in, and put into freezers at the lab.
6) COUNT the number of bees in each sample of dead bees, record the number, and ask the lab to analyze all of the bees in each sample.  That way, when you get the residue analysis results, you can readily convert the reported value to the amount per bee.

NUMBER 6 is CRITICAL.  It is the easiest way of getting results that you can compare to LD50 values.  You can ask a lab to dry the samples before analysis (but if they use too high a temperature, some of the more volatile pesticides may be lost).  You can ask them to count out and dry a subsample of each bee sample, and then use value that to estimate the amount of water in the analyzed sample.  But, to save them work, and to save you from extra charges, just count the bees in each sample before sending.  Just don't contaminate the samples when you count.  We put down a sheet of aluminum foil or plastic wrap, pour out the sample onto the sheet, move bees around wearing an untalced latex or nitrile disposable glove, pour from sheet back into sample vessel.  Then, change gloves and sheet, do same for next sample.

A bit of work up front will provide far better results in the  end.

Jerry


 

 

 

  
 
 
  
 


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