Hi All - I'm chiming in here because I have been wondering about using Frontline for my chix fleas (4 layers), that have spread throughout the garden and are now into the house. Its making the chix unhappy, and me as well, so in addition to treating the garden and house (we don't have other pets), I'm also going to go to the source and take care of the chix with Frontline.
But first, I felt like I had to do some research. I'm a scientist, so this might get a little technical, but you can jump to the end if you want. As mentioned before, there is low mammal toxicity from Fipronil (see fact sheet at: http://npic.orst.edu/factsheets/fiptech.pdf ). So, some calculations to ask the question: What if I ATE the entire dose of fipronil I was giving to my chickens every month, how much would that be, and how would it compare to "allowable" doses.
1 drop per chicken per month
1 drop = 0.05 mL (this is the standard conversion)
density of Frontline plus = 1 g/mL - i.e. that of water
Frontline Plus is 9.8% by weight Fipronil.
1 drop per chicken per month x 4 chickens = 4 drops per mongh
4 drops per month x 0.05 mL per drop = 0.2 mL frontline plus per month
0.2 mL frontline plus per month x 1 g/mL = 0.2 g frontline plus per month
0.2 g frontline plus per month x 9.8% fipronil by weight in frontline plus = 0.0196 ~ 0.02 g fipronil per month = 20 mg fipronil per month.
Per the factsheet linked above, the chronic reference dose (RfD) for fipronil is 0.0002 mg/kg/day for humans - this is 100 x less than the NOAEL (No Observable Adverse Affects Level) for rats.
I weigh ~100 kg and one month = 30 days, so:
0.0002 mg/kg/day x 100 kg x 30 days/month = 0.6 mg per month as the chronic reference dose for me.
So, IF I WERE TO EAT all of the fipronil I was dropping on chickens I would be eating ~ 20 mg fipronil per month. The chronic reference dose is 0.6 mg per month for me, so IF I WERE TO EAT all of the fipronil, I would be eating about (20/0.6 33 times the reference dose. While higher than the reference dose, this is still about 1/3 of the NOAEL.
Based on this, I wouldn't feel comfortable eating all of the Frontline, and DO NOT suggest anyone drink the stuff, but since I'm not eating the whole chicken (and therefore not all of the fipronil) do I feel comfortable eating the eggs?
So, lets assume (though this doesn't seem to be the case as noted below) that when I put the fipronil on a chicken, it evenly distributes throughout the entire chicken, even into the egg she is just about to lay:
1 chicken = 4.5 lbs which is around 2 kg
1 egg ~ 60 g ( http://wiki.answers.com/Q/What_is_the_average_mass_of_a_chicken_egg )
To calculate the concentration of Fipronil in the chicken:
1 drop = 0.005 g fipronil
0.005g fipronil divided by the mass of the chicken (2 kg) = 2.5 x 10^-6 g fipronil per gram chicken =2.5 ppm by mass fipronil for my chicken.
So, using my assumption that the egg has the same concentration of fipronil as the chicken, a 60-g egg has 60 g x 2.5 x 10^-6 = 0.15 mg fipronil
My chicken lays ~ 20 eggs/month so that's 20 eggs/month x 0.15 mg fipronil/egg = 3 mg fipronil per month if I eat every single egg my chicken lays.
This is still 5 times the reference dose of 0.6 mg/month for me, but this is assuming that 1) the fipronil partitions evenly into all parts of the chicken and 2) the fipronil concentration is the same all month (it isn't because it goes away via loss of poop, skin, feathers, etc). If I use all of the same assumptions, but assume that fipronil goes down throughout the month (either linearly to concentration of 0 at 30 days or exponentially using the whole-blood half-life given in the linked fact sheet ~7 days, calculations not shown, but I can share with the interested), my total fipronil consumption will be either 1.5 mg/month or 1.2 mg/month, meaning just 2 or 3 times the reference dose, which, remember is 100 times LESS than the NOAEL.
Using the exponential model, if I withhold eggs for 2 days, I'm down to 0.82 mg/month and after 5 days withdrawal, I am at 0.6 mg/month, which is the reference dose.
So, assuming that I EAT ALL OF THE EGGS for a chicken for a month and THE CONCENTRATION OF FIPRONIL IN THE EGGS IS THE SAME AS THE ENTIRE CHICKEN - I am just about at the reference dose, especially if I withdraw the eggs for a few days.
Getting more realistic, the concentration in the eggs is likely not the same as the whole chicken. If the concentration in the eggs was 1/2 of the entire chicken, then assuming you ate all of the eggs (in the exponential model) you'd be right at 0.6 mg/month, my reference dose. If it is 1/10th of the entire chicken, you'd be about 5x below the reference dose (0.012 mg/month).
I could find no data on the partitioning of fipronil into eggs from the chicken, but if what the manufacturer says about the fact that fipronil stays mostly in the skin (a fact backed up by: http://npic.orst.edu/factsheets/fiptech.pdf ) then the 1/10th partitioning into an egg seems extremely conservative (i.e., I'd guess it was lower)
My conclusion: even if I were to eat all of my chicken's eggs in a month, I would be well below the reference dose. By the way, the chronic reference dose is the the United States Environmental Protection Agency's maximum acceptable oral dose of a toxic substance under chronic exposure ( http://en.wikipedia.org/wiki/Reference_dose )
In future work - maybe I'll measure the amount of Fipronil in my chickens' eggs....
Hope this was helpful. It puts my own mind at ease. Lots of people made other excellent points (about alternatives etc.)