Pyrethroids are highly neurotoxic and have been linked to cancer, endocrine disruption, suppression of the immune system, and various reproductive effects(Beyond Pesticides, November 16, 2011) On November 9, 2011, the U.S. Environmental Protection Agency (EPA) issued its cumulative risk assessment for the pyrethroid class of insecticides, concluding that these pesticides “do not pose risk concerns for children or adults,” ignoring a wealth of independent data that links this class of chemicals to certain cancers, respiratory and reproductive problems, and the onset of insect resistance. The agency went as far to state that its cumulative assessment supports consideration of registering additional new uses of these pesticides, potentially opening the flood gates for manufacturers to bombard the market with more pyrethroid pesticides, endangering the health of the public.EPA issued the final pyrethins/pyrethroid cumulative risk assessment in the Federal Register and is requesting comment until January 9, 2011, including information that may be used to further refine the assessment. Pyrethroids are a widely used class of insecticides used for mosquito control and various insects in residential and agricultural settings. However pyrethroids are highly neurotoxic and have been linked to cancer, endocrine disruption, suppression of the immune system, and various reproductive effects. This class of chemicals includes permethrin, bifenthrin, resmethrin, cyfluthrin and scores of others. Read Beyond Pesticides’ factsheet “Syntethic Pyrethroids.” Once the agency completes and approves the pyrethroid chemical assessment, it is likely that new uses of these pesticides will be added. The agency claims that more pyrethroid registrations may help combat recent pervasive pest problems, such as stink bugs and bed bugs, even though this class of chemicals is already known to be ineffective against these pests due to growing resistance issues compounded with continued pesticide use. However, serious issues such as the carcinogenic and endocrine disrupting potential of several pyrethroids were not mentioned in the risk assessment even though a recent study published in Environmental Health Perspectives finds that low-dose, short-term exposure to esfenvalerate, a synthetic pyrethroid pesticide, delays the onset of puberty in at doses two times lower than EPA’s stated no observable effect level.
Most troubling is the agency’s decision to reduce the Food Quality Protection Act (FQPA) protective safety factor from 10X (an additional margin of safety of 10 times) to 1X for children and adults over six years, and to 3X for children under six years of age. The FQPA safety factor is intended to protect vulnerable infants and children to account for their special susceptibility to pesticides taking into account the potential for pre- and post-natal toxicity. Given that children are especially sensitive to the effects of synthetic pyrethroids like permethrin, this reduction in the special safety factor is egregious. Studies have found that certain pyrethoids like permethrin are almost five times more toxic to the young compared to adults. Additionally, studies have shown that permethrin may inhibit neonatal brain development. In this new cumulative risk assessment, the agency even states, “Based on pharmacokinetic data, there is evidence that indicates an increase in sensitivity to pyrethroids of the young compared to adults,” which is attributed to the difference in the ability of the adults and juveniles to metabolize pyrethroids. EPA’s modeling data also predict a 3-fold increase of pyrethroid concentrations in juvenile brains compared to adults. Similarly, researchers at Emory University and the Centers for Disease Control and Prevention (CDC) in a published study conclude that residential pesticide use represents the most important risk factor for children’s exposure to pyrethroid insecticides. Despite all this, EPA chooses to forgo this evidence and green light more uses of pyrethroid chemicals which will inevitably impact more vulnerable children.
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 break down, and are often formulated with synergists, increasing potency, and compromising the human body’s ability to detoxify the pesticide.
As a consequence of their widespread use, many pests such as bed bugs are now becoming resistant to pyrethroids. A recent study shows that modern bed bugs have developed the ability to defend themselves against pyrethroid pesticides, with a required dosage of as much as 1,000 times the amount that should normally be lethal, due in part to the widespread use of such treatment methods. Due to the ability of these organisms to develop resistance to chemical agents, exposing these bugs to more pesticides would lead to higher rates of resistance among insect populations, a point that EPA does not acknowledge.
EPA is mandated to complete cumulative risk assessments for chemicals that have the same mechanism of toxicity. In 2009, EPA conceded that pyrethroid chemicals did in fact have a common mechanism of toxicity. In this risk assessment, not all pyrethroids were evaluated and various routes of exposures, such as dermal and inhalation exposures, were not adequately examined, with the agency stating that these exposures “generally do not significantly contribute to the overall risk picture,” even though numerous pyrethroid formulations of ‘apply to skin’ mosquito repellent and indoor bug sprays are widely available. In an EPA National Exposure Research Laboratory study, several synthetic pyrethroids and their degradates were found in indoor dust collected from homes and childcare centers in North Carolina and Ohio, meaning that children inhale contaminated dust particles daily while these exposures go unevaluated. Given that asthma is the most common long-term childhood illness today, persistent residues of pyrethroids in house dust and air need to be taken very seriously.
Exposure to synthetic pyrethroids has been reported to lead to headaches, dizziness, nausea, irritation, and skin sensations. There are also serious chronic health concerns related to synthetic pyrethroids. EPA classifies permethrin and cypermethrin as possible human carcinogens, based on evidence of lung tumors in lab animals exposed to these chemicals. EPA also lists permethrin as a suspected endocrine disruptor. Synthetic pyrethroids have also been linked to respiratory problems such as hypersensitization, and may be triggers for asthma attacks. Material Safety Data Sheets, issued by the Occupational Safety and Health Administration (OSHA), for pyrethroid products often warn, “Persons with history of asthma, emphysema, and other respiratory tract disorders may experience symptoms at low exposures.” Although synthetic pyrethroids are often seen as safe alternatives to organophosphate insecticides, they are persistent and are making their way into human bodies at alarming rates. CDC ‘s Fourth National Report on Human Exposure to Environmental Chemicals reports that widely used pyrethroids are found in greater than 50% of the subjects tested.
In addition to human health effects which this cumulative risk assessment addresses, pyrethroids are also persistent in the environment and adversely impact non-target organisms. A 2008 survey found pyrethroid contamination in 100 percent of urban streams sampled in California. Researchers also find pyrethroid residues in California streams, although at relatively low concentrations (10-20 parts per trillion) in river and creek sediments that are toxic to bottom dwelling fish. Other studies find pyrethroids present in effluent from sewage treatment plants at concentrations just high enough to be toxic to sensitive aquatic organisms.
At the same time, there are clear established methods for managing homes and schools that prevent infestation of unwanted insects without the use of synthetic chemicals, including exclusion techniques, sanitation and maintenance practices, as well as mechanical and least toxic controls (which include boric acid and diatomaceous earth). Based on the host of health effects linked to this chemical class, an increase in synthetic pyrethroid use is hazardous and unnecessary.