(Beyond Pesticides, September 22, 2008)
A study published in the September issue of Environmental Health Perspectives finds that low-dose, short-term exposure to esfenvalerate, a synthetic pyrethroid pesticide, delays the onset of puberty in rats at doses two times lower than U.S. EPA’s stated no observable effect level (NOEL) of 2.0 mg/kg/day. Synthetic pyrethroids are used for everything from lawn care and household insecticides, to mosquito control and agriculture. There are currently 348 pesticide products registered by the U.S. EPA.
The researchers conclude:
“Although the exact mechanism of action is unknown at this time, we observed the effects at dosage levels below the NOEL established through chronic dietary exposure studies in rats. The U.S. EPA (1998) http://www.epa.gov/fedrgstr/EPA-PEST/1998/April/Day-29/p11372.htm stated that ‘There is no evidence of additional sensitivity to young rats or rabbits following pre- or postnatal exposure to esfenvalerate.’ The present study shows that immature female rats exposed to 1.0 mg/kg/day are sensitive to this pesticide, as evidenced by their delay in the onset of puberty. Delayed pubertal onset in humans has been associated with low bone mass density (Ho and Kung 2005), and estrogen is necessary for bone mineral acquisition in both girls and boys (Yilmaz et al. 2005). Importantly, a lowered endogenous estrogen level in females is one factor associated with bone fragility (Hoffman and Bradshaw 2003).
“This could potentially affect current established exposure levels for humans, because the reference dose for [esfenvalerate] of 0.02 mg/kg/day is based directly on the rodent NOEL of 2.0 mg/kg/day.”
With the phase-out of most residential uses of the common organophosphate insecticides, chlorpyrifos and diazinon, home use of pyrethroids has increased. Pesticide products containing synthetic pyrethroids are often described by pest control operators and community mosquito management bureaus as “safe as chrysanthemum flowers.” While pyrethroids are a synthetic version of an extract from the chyrsanthemum plant, they are chemically engineered to be more toxic, take longer to breakdown, and are often formulated with synergists, increasing potency and compromising the human body’s ability to detoxify the pesticide. Pyrethroids may affect neurological development, disrupt hormones, induce cancer, and suppress the immune system. Researchers at Emory University and the Centers for Disease Control and Prevention (CDC) find that residential pesticide use represents the most important risk factor for children’s exposure to pyrethroid insecticides.
According to Ohio State University, esfenvalerate is one of over 75 commonly used pesticides that are highly or moderately toxic to bees. It has also been used on Christmas trees in North Carolina. Esfenvalerate has replaced fenvalerate, whose uses were voluntarily withdrawn from the market by varfious manufacturers, including The Scotts Company, from 2003 to 2008, although existing supplies can be sold off.
For more information, see Beyond Pesticides’ factsheet on synthetic pyrethroids.