" Also curious, how many other toxins, like some of the growth regulators, also have the characteristic to bioaccumulate and are we missing their effects in the larger context."

Bioaccumulation is something the regulators have looked at very carefully ever since the DDT days.  What the regulators are concerned about is bioaccumulation up the food chain.  That is daphnia, just to pick an example, might bioaccumulate some low level pesticide in the environment and fail to degrade it to non toxic metabolites.  It might well do no harm at all to the daphnia due to the low concentration.  Then some small fish eats the daphnia and bioaccumulates more and some larger fish eats the small fish and accumulates enough to harm the large fish.  Or harm the human or birds that eat the large fish.  In this case insects are the target that fipronil is supposed to kill.  So, if the stuff bioaccumulates in insects, but does not get passed up the food chain I have not seen regulatory concerns.  After all, most insecticides must bioaccumulate in the target insects to make them work.  For example insect growth regulators only work because they bioaccumulate.  In general you do not want any insecticide to be easy for insects to biodegrade.  If they are easy to biodegrade it is too easy for a mutant or two to happen that speeds up degradation and renders the insect resistant.  What you want is a product that does not bioaccumulate in non target species, particularly as you move up the food chain.

I have no first hand knowledge at all about fipronil and how it behaves in the environment, nor how it is degraded by non target organisms.  But, the fact it got registered tells me those kinds of studies had to have been done.  You simply do not get a registration without doing them unless it is a natural product.

There are a bunch of internet citations that show bad bee toxicity going clear back to the early 1990s, including links to CCD.  For example:
"Fipronil is one of the main chemical causes blamed for the spread of colony collapse disorder among bees. It has been found by the Minutes-Association for Technical Coordination Fund in France that even at very low nonlethal doses for bees, the pesticide still impairs their ability to locate their hive, resulting in large numbers of forager bees lost with every pollen-finding expedition.[22] A synergistic toxic effect of fipronil with the fungal pathogen Nosema ceranae was recently reported[23]. The functional basis for this toxic effect is now understood: the synergy between fipronil and the pathogenic fungus induces changes in male physiology leading to infertility[24] A 2013 report by the European Food Safety Authority identified fipronil as “a high acute risk to honeybees when used as a seed treatment for maize and on July 16, 2013 the EU voted to ban the use of fipronil on corn and sunflowers within the EU. The ban took effect at the end of 2013.”[25][26]"
quote from:  https://newdrugapprovals.org/tag/fipronil/

Dick

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