Tree Azin Safety

Tree Azin is the treatment of choice for trees affected by Emerald Ash Borer. Questions have been asked about its safety … here is the answer (and no, not written by the manufacturers or anyone associated with them).

The compound in question is marketed as TreeAzin and is a derivative of Neem Tree Seed Oil. The toxicity data available is patchy, but quite well summarised in this document from Health Canada – start reading at page 11:–9–2012–16-eng.pdf
What strikes me is that while all the lay conversation about TreeAzin makes much of the fact that it is a “natural” compound, by which they mean derived from something that occurs in nature rather than being entirely cooked up in a laboratory, to most people natural = safe which is a totally false assumption. Cobra venom is entirely natural, fly agaric fungi are entirely natural but you wouldn’t want to get too close to them! Saccharin is a laboratory concoction that people imbibe in huge quantities, seemingly with little harm.
In this case (quote) “The main insecticidal activity of NeemAzal Technical is attributed to azadirachtins, a family of steroid-like tetranortriterpenoids (limonoids). Most toxicity studies that have been done were performed in mammals as the main fear is to know the possible effects on humans. The studies done were patchy at best but indicated liver and thyroid changes in rats that are indicative of enzyme induction at high doses – certainly well above levels to which operators and the general public would be exposed.” 
I believe it very unlikely that there is a human toxicity risk at all if this stuff is applied correctly.
But the question raised in the article is one of the ecotoxicity – specifically to other insects and to birds. This aspect of toxicity is always less thoroughly explored simply because the regulatory requirements for ecotoxicity studies are less stringent than for human exposure.
(Quote) While exposure to soil-dwelling organisms and terrestrial plants is expected to be minimal, birds and mammals that feed on fruits, seeds or other parts of treated trees or that are attracted by the target pest infesting the tree could be exposed to NeemAzal Technical. Similarly, honeybees and other pollinators could be exposed to NeemAzal Technical when they consume the nectar and the pollen of treated trees.
There is a potential problem here, but if the compound is applied after the blooming season it will be minimised.  (Quote) While adult foraging bees could be exposed directly to residues in pollen and nectar of treated trees, the exposure pathway for the brood and the queen is more complicated. Because these bees remain in the hive, they can only be exposed to contaminated pollen and nectar through the worker bees. Exposure could also be affected by the proximity of the treated trees to the hive, the availability of alternative sources of food, the stability of the active ingredient, and the timing of treatment in relation to bloom. The translocation pattern between tree species may also vary and be influenced by environmental/climatic conditions. A screening survey of open literature confirms the greater sensitivity of insect larval stages and the potential effects of neem extracts on honeybees. Because a potential risk to pollinators was identified, precautionary and advisory label statements are required on the label and application to hardwood species is restricted to the post- bloom period.
Seemingly less of a problem than insects as there seems to be low avian toxicity. (Quote) In acute oral and dietary studies conducted with the bobwhite quail, azadirachtin had no treatment-related effects on mortality or clinical signs of toxicity and no treatment-related abnormalities were observed upon necropsy. Similarly, in a reproduction study with the bobwhite quail, azadirachtin had no treatment-related effects on the parental generation, reproduction parameters and hatched chicks. Note that in those studies the test species will have received known doses of the substance, probably admixed with food. The studies will not have looked at exposure in the wild.
To the above, I would add that no studies appear to have been done on the potential for exposure of birds to insects carrying the active compound. For example, Woodpeckers taking insects from below the bark of a treated tree will be exposed to higher levels of the substance than will birds that do not feed in trees. Small songbirds such as the many Warbler species and Vireos etc take small insects such as caterpillars from leaves and twigs and those insects could be exposed to the compound by means of their feeding on leaf materials. The greatest insect harvesting by birds happens during the nesting period as even seed eating species feed insects to their young in order to help them grow – thus there is at least a slight theoretical risk of nestling exposure and they would be expected to be more susceptible to harm than adults. We simply do not have the data to make this assessment but the above is the likely scenario.
* and so:

Like all chemicals (natural or synthetic) there is a degree of risk at some dosage level. However, in this case, I am of the opinion that handled properly and applied appropriately the risk is likely to be minimal but not completly non-existent. 

Richard Gregson PhD MPhil CBiol FRSB

Genuinely Independent Information & Comment from Baie-D'Urfé