Aerial Spray Against Mosquitos Might Have Hidden Risks

As the cases of Zika and West Nile Virus continue to rise in Dallas County (20 Zika cases and ten West Nile as of today) more pesticides will be sprayed from trucks in more neighborhoods, insect repellent will be applied to ourselves and our children more thoroughly, and aerial spraying will be considered by cities across the county. 

All of these products have been approved by the Environmental Protection Agency, recommended by the Centers for Disease Control and Prevention, and encouraged by our local Health and Human Services division. 

Though there is debate on how effective methods like aerial spraying are in preventing disease outbreaks, these are the recommended strategies by the CDC and EPA, who say the methods are safe, the most effective with the least risk. 

However, these products may be much more dangerous than we know. Once you take a dive into the deep, dark world of EPA risk assessments, many questions are left unanswered. 

As it turns out, chemical companies are able to get their products approved by the EPA without what many researchers would agree is adequate evidence that shows their products are safe — and the EPA has been turning a blind eye to this for decades.

Typically toxicologists test the negative effects of chemicals in isolation through a range of experiments that determine a standard “benchmark,” says Dr. Arch Carson, Associate Professor and Program Director of the Occupational and Environmental Medicine Residency at University of Texas Health Science Center in Houston.

The EPA, too, does this. The agency generally only assesses the toxicity of pesticides by testing each individual ingredient, which does not take into account the fact that in real life, most pesticides are made up of a combination of chemicals. 

This presents a problem. Essentially, it means the EPA does not know how the interactions between chemicals in a product affect its toxicity, unless those interactions have been studied previously or it is brought to their attention by the chemical company. Yet, they are still approving the product. 

Furthermore, the EPA only requires chemical companies to provide risk assessment studies for the active ingredients in their products (though the EPA can request further experimentation if they deem it necessary). However, the EPA does not require testing of “inert” ingredients which, in the pesticide world, simply means any ingredient that is not the “active ingredient,” but is still an active chemical and may have hazardous properties, says Dr. Nathan Donley, a scientist with the Center for Biological Diversity.

In nature, when chemicals come into contact with each other, they either interact in such a way as to change their toxicity — “synergy” — or they don’t interact at all — “additivity.”  The EPA's practice of only testing active ingredients in isolation assumes additivity, Donley says. 

For example, Off!, one of the most common insect repellent companies, has a product called FamilyCare Insect Repellent I (Smooth & Dry). The product is 15 percent DEET, its only active ingredient. The other 85 percent of it is made up of inert ingredients.

Duet, the aerial spray used by the county to combat mosquitoes carrying West Nile Virus, contains three active ingredients: Prallethrin and Sumithrin, both synthetic pyrethroids, which are chemical derived from chrysanthemum flowers; and Piperonyl Butoxide (PBO), a known synergist and a chemical in many household products. 

"A lot of us have said for a long time that we should be testing the formulations, not just the active ingredient because the formulation could be really different," says Jennifer Sass, senior scientist with the Natural Resources Defense Council. "Its persistence in the environment, its toxicity, etc. ... all of those things could be really different." 

Both the products mentioned above have been "conditionally registered" by the EPA since 2005. Conditional registration means that the EPA approved the product, but there remain questions about its safety.

"What it means is that there are studies the EPA has required (of the company), but those studies are currently ongoing and instead of waiting for those studies to come in to ensure that the product is safe, the EPA has decided to grant a conditional registration," says Donley. "Then after the fact, if their studies demonstrate their product may not be safe, it could be pulled." 

Synthetic pyrethroids, commonly used in insecticides, have been thought to be some of the least toxic chemicals out there. However, research has shown synthetic pyrethroids may be more dangerous in the long run than originally thought. 

"Synthetic pyrethroids ... have been linked to endocrine disruption and neurodevelopmental disorders such as autism-like behavior," Sass wrote in an email. "Their metabolites have been found in the urine of the general population. Environmental health scientists are becoming increasingly concerned about the pyrethroids, including Sumithrin and Prallethrin, both in the Duet product."

On the other hand, Carson says that the screening process for chemicals that could be endocrine disruptors is actually pretty strong. 

"PBO was originally thought to be a possible disruptor, but the screening tests knock it out of that category and into a lower-concern category," Carson says. "Some individual pyrethroid chemicals do have endocrine-disrupting characteristics, but most of the ones that have been tested are thousands of times less of an issue than some of the other things we know very much about. We're pretty good at preventing endocrine-disruptors from entering our environment at this stage." 

Still, the issue of the inert ingredients may muddle these sureties. There are many reasons the EPA does not test such synergistic qualities of products, but the primary reason is, in brief, that it is too time-consuming.

For one, the testing is complicated: Different ingredients at different concentrations can interact in very different ways. Plus, there are so many different species of animals, plants and other living organisms that the number of studies the EPA would have to do to really accurately study how safe a product is, is beyond their resources.

“It’s a tough problem to work out because it increases the amount of work that has to be done exponentially when you start looking at interactions between chemical substances,” says Carson. 
“Recently with capabilities of computers and other information-processing systems, we have been able to do more in the way of looking at the toxicity and interactions of mixtures,” Carson says. “Government agencies as well as private ones are engaging the issue of testing mixtures and chemical interactions that may occur in the environment. We’re getting much better at that, but we’re still not at a point where we can say we’ve done what needs to be done. So, I would say that the EPA is doing everything they can in that regard, they're not dragging their feet at all, but they're somewhat limited by their congressional mandate and their budget.”

Other experts would disagree. For some of the most common and controversial pesticides out there that are used in agriculture, on residential lawns, and in playgrounds and parks, the synergistic quality of the chemicals is actually the defining factor to justify the product’s patent.

In a systemic review of patents for pesticide products containing two or more active ingredients recently approved by the EPA for four major agrochemical companies (Bayer, Dow, Monsanto and Syngenta), a report by the Center for Biological Diversity found that 69 percent of 140 products reviewed had “at least one patent application that claimed or demonstrated synergy between the active ingredients in the product” and that 72 percent of those products contained some of the most highly used pesticides in the United States.

Though it cannot be said for certain that the patent data on synergy identified in this report was not used in the EPA’s registration decisions, it is likely that it was not, given the EPA does not generally do mixture analyses for its ecological risk assessment, the report states.

“In order to really know for sure the risks associated with this product, you would need to do a rigorous analysis of the mixtures in the products and how they affect different species of animals and without that you're making assumptions based on how the individual ingredients work," says Donley, who is also the author of the report. “Those assumptions may be correct, but they also may not. It’s just one of those uncertainties that is constantly in the background with a lot of these (EPA) product registrations.”

The report shows that pesticide companies are collecting more information about the synergistic effects of their products that they are not sharing with the EPA. In other words, an EPA-approved chemical may by itself be considered “safe,” — or rather, not cause unreasonable adverse effects on humans and the environment — but combined with another chemical, the EPA really has no idea the true impact.

“With the report, what we were trying to find was a way that the EPA could gain some of this information without requiring a lot of studies, so patent applications seem like a really good place because chemical companies are already doing this now,” says Donley.

The EPA has been aware of the issue of testing mixture toxicology for decades, says Carson. Sass learned of this problem 15 years ago, when she was just starting her career.

“(The study) found an important loophole because the company is really playing both ends of the stick,” says Sass. “It is really making the point that this is not just environmental groups wondering whether all of these ingredients are making the product more toxic, but that it’s the company often claiming that it’s the basis of the patent.”

However, the issue first came into the public eye last November when the EPA petitioned the Ninth US Circuit Court of Appeals to revoke its approval of a major weed-killing product, Enlist Duo, made by Dow AgroScience, Dow’s agriculture subsidiary.

The EPA discovered that Enlist Duo had synergistic qualities that made it toxic to non-target plants that the studies provided by Dow had not shown, after finding the product's patent in the U.S. Patent and Trademark Office Database. This information was not presented to the EPA because currently there is no protocol on how the EPA assesses mixture toxicity to plants and animals other than humans.

“It’s a very complicated issue,” said Donley. “I think the real problem is that the EPA is allowing all of these mixtures to occur without having the data. If you can’t get the data, why are you approving these in the first place?”

The EPA did not provide comments in response to the Observer’s questions. 
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