Sunday, December 26, 2010

Is DEET Toxic to Anacondas?

The following is a news article from the Telegraph. This is one story I am more than a bit skeptical about. DEET is N,N-Diethyl-m-toluamide and Google searches in Scholar do not return articles that link this molecule with toxicity in reptiles. If anybody knows about this please let me know. I have no doubt DEET is toxic to snakes at some level. However, it is difficult for me to believe that it is killing anacondas in the concentrations that the snakes would be exposed to from being near tourists. It seems to me an other cause of the snake mortality will be found once it is investigated. JCM The story that follows is unedited.

World's biggest snake threatened by backpackers
The lure of seeing the anaconda in its natural habitat is bringing thousands of British backpackers to a small corner of the Amazon that has become one of the continent's biggest eco-tourism destinations.
By Michael Howie, La Paz 4:47PM GMT 21 Dec 2010

But for the anacondas that live in the swamps surrounding the Yacuma River in northern Bolivia, this invasion of gap year travellers and other hardy tourists is proving disastrous.

Biologists say the entire population of anacondas in one of the jewels of the Amazon basin will be wiped out within three years because of the deadly effect on the snakes of the insect repellant used by most backpackers to help protect against malaria.

The number of tourists going on tours of the pampas that snake there way through jungle and grasslands 250 miles north of La Paz has exploded from a few hundred to nearly 12,000 a year in the past decade.

Travellers are enticed by the promise of getting up close and personal with the world's largest snake - sometimes picking them up and hlding them - as well as swimming with river dolphins, catching pirhanas, and spotting monkeys, sloths and an array of other flora and fauna.

But sightings of the snake are becoming increasingly elusive and as many as 30 of the awe-inspiring creatures, which can measure up to 30ft in length and are known to strangle and devour prey as diverse as caiman crocodiles and cows, are being found dead every year, according to local guides.

Roberto Justiniano, a tour guide and biologist working closely with other scientists to assess the impact of the unrestrained tourism boom, revealed that the growing quantity of toxins being washed into the waterways from travellers is proving too much for the anacondas.

"The high-strength insect repellant that tourists use to protect themselves from mosquitos is absolutely fatal to the anacondas.

"They are amphibians and breath through their skin. The insect repellant, along with some types of sun cream, is extremely toxic. It is getting washed into the pampas and left in the swamps where tourists are hunting for the snakes.

"We are finding between 25 and 30 dead anacondas which have been poisoned. It is terrible."

Amphibians, such as snakes and frogs, are highly susceptible to the chemicals contained in many types of insect repellant, in particular those that contain DEET. This is partly because they breathe and absorb water through their skin, providing an easier way for contaminants to enter the animal's body. Environmentalists recommend using safer insect repellants based on natural oils, but many tourists complains these are less effective.

Zoologists estimate that only around 200 anacondas remain in the Yacuma River swamps, a sharp fall from the population of nearly 1,000 a few years ago.

"A few years years ago you had a 90 per cent chance of seeing anacondas - maybe three or four together. Now you are very lucky if you see one."

He added: "A study has been carried out by other biologists which shows the ecosystem will collapse in three years if things continue as they are."

The fear is that insects, fish and smaller amphibians would be wiped out within the river basin, resulting in the collapse of the entire food chain.

Mr Justiniano, who has guided tours of the pampas for four years, blames uncaring tour agencies and the carefree attitude of travellers who come to experience this once untouched natural wilderness.

"People come to be entertained by the natural world, to touch and play with the animals. This is wrong, we have to have more respect," he said.

He is now striving to set up an association of tour agencies to protect the wildlife. A proposed code of conduct would encourage tourists to use only eco-friendly insect repellant and set a cap on visitor numbers.

"During the 1990s only a few hundred people came here. Now we have had 35,000 in total over the last three years, many of them from Britain. The tourism at this moment is completely unsustainable for this beautiful environment," he said.

Anacondas, which are native only to the Amazon basin, are already in increasing danger from loss of habitat due to deforestation.

Mr Justiniano says the snakes continue to thrive in more remote parts of Amazonian Bolivia where tourism has not yet penetrated, but fears that could change as the growing number of travellers encourages tour operators to sell packages further afield.

His fears about anacondas and the rest of the wildlife in the pampas are backed by Conservation International Bolivia, which says tourism is having a "major negative effect" on the ecosystem which the snakes rely on.

Candido Pastor Saavedra, the body's director of programmes, told The Sunday Telegraph that while the invasion of tourists provided an economic boon to relatively poor communities, the anacondas were paying heavily. Water used for washing and showers was returned to the waterways, he said, carrying insect repellant and other chemicals with it.

"In the pampas of the Yacuma, the quantity of tourists has increased so much that there is a negative effect. This is a result of practices such as the manipulation of animals like the anacondas, discharging service water into the river or dumping waste.

"These bad practices must be corrected or we will end up killing the goose that lays the golden egg," he said.

Most backpackers are oblivious to the devastating impact their presence is having for the anacondas.

Roberta Spence, 23, from London, who quit her accounting job to go travelling, was among a group of English backpackers about to go looking for the snake.

"I didn't know they were getting harder to find," she said, as she prepared to head out with her guide. "I really want to touch one. It's very exciting. It's a shame if they are dying out. No-one at the agency told us about this."

Nicola Smith, 22, from Bristol, added: "They advertise the trips as a chance to find anacondas, which was the main reason I wanted to come. But I haven't met anyone who's actually found one yet. It's sad to think they are suffering because of us.

"But I'm not sure I would stop using insect repellant. I don't want to get malaria."


  1. I work for the DEET Education Program. I spotted the same story YOU did and we are looking into it. I rather doubt this is true, but our toxicologists will have more information than I do. Reach me at or 800-7898-3300. Soon as I have an answer, I'll let you know.

  2. Here's what the toxicologist said:

    Certainly, John C. Murphy’s point of view in the blog linked below referring to the article in The Telegraph is one with which I would agree:

    “…I have no doubt DEET is toxic to snakes at some level. However, it is difficult for me to believe that it is killing anacondas in the concentrations that it would be exposed to from being used by tourists. It seems to me an other [sic] cause of the snake mortality will be found once it is investigated. JCM”

    Interestingly, Roberto Justiniano, an Amazon basin (Yacuma River in northern Bolivia) tour guide and biologist states that “The high-strength insect repellant that tourists use to protect themselves from mosquitoes is absolutely fatal to the anacondas.” also is quoted in the The Telegraph article as saying, “They [anacondas] are amphibians and breathe through their skin.” In fact, anacondas are reptiles and breathe only through their lungs.

    Clearly, Mr. Justiniano is providing his opinion; however, he offers no data to support his contention that DEET is highly toxic to anacondas and as John C. Murphy points out in his blog, Google searches in Scholar (as well as comprehensive literature searches conducted by us) do not find articles that link DEET with toxicity in reptiles. A recently published study in an amphibian (which presumably would be more sensitive than reptiles because during early lifestages amphibians do “breathe water” with gills and their skin would be expected to be more permeable to an organic compound like DEET than skin of reptiles) using a standardized procedure called the Frog Embryo Teratogenesis Assay – Xenopus (Xenopus laevis), Harada et al. (2008) reported no effects at the highest concentration tested, 10 mg/L. To give this concentration perspective to levels of DEET reported in the environment, 10 mg/L is at least 1,000-fold greater than the DEET concentrations reported for surface waters in numerous published studies. Therefore, unless the Yacuma River is extremely polluted by insect repellents, it is not plausible that insect repellents, including DEET, are responsible for the high mortality among anacondas reported anecdotally for this region of Bolivia.

    Reference: Harada A, Komori K, Nakada N, Kitamura K, Suzuki Y. 2008. Biological effects of PPCPs on aquatic lives and evaluation of river waters affected by different wastewater treatment levels. Water Sci Technol 58: 1541-1546.

  3. I took the time to write them a comment when i first came across that article. It was done on their website, so I do not have a copy of it. Here is the response I got, and my response to the response:

    That article was so full of inaccuracies, it should be retracted and rewritten. Its no wonder that it was not attributed to an author, as no one would want to take credit for putting in print something that wasnt fact checked at a grade school level. Fundamental biological errors are blatant, but how does that fair for the validity of the subject matter? Is DEET really a concern to snakes?

    Pass this link along, to whomever penned that "article" :

    I still find no substantiated claims that ANYTHING in your news clipping is correct. Maybe the tour guides name. Maybe.

    - Rob

    Subject: Telegraph Reference: 678135
    Date: Wed, 29 Dec 2010 10:19:37 +0000

    29 December 2010

    Dear Mr -,

    Thank you for taking the time and trouble to write to the Telegraph and please accept my apologies for the delay in responding to you.

    Your comments concerning how a snake breathes has been forwarded on to our editorial team for their reference and future knowledge when writing on the subject in the future.

    We value your readership and appreciate your comments.

    Yours sincerely

    Andy King

    Editorial Information Executive

  4. As a reptile ecotoxicologist, Id like to point out that we are finding that so-called "new generation" insecticides can be VERY toxic to reptiles while having little toxicity to birds and mammals (e.g. pyrethroids). This is in large part due to newer insecticides being designed so that they are not toxic to organisms with high metabolism (i.e. birds and mammals). However, snakes and amphibians having lower metabolism are often more susceptible.

    A good example:

    Brooks et al. 1998. The oral and dermal toxicity of selected chemicals to brown tree snakes (Boiga irregularis). Wildlife Research 25: 427-435.

    I realize DEET is not, in reality, an insecticide, Im just pointing out that some chemicals that are considered "safe" can be quite toxic to organisms other than birds, mammals, and fish (who receive a majority of the ecotoxicology research).

    That said, Im skeptical as well. It is unlikely that DEET is killing off anacondas at environmentally relevant concentrations, however we need more data on reptiles to confirm this. A study on xenopus tadpoles doesnt really put my mind at rest (as xenopus are somewhat notorious for being more tolerant than other amphibian species). Also interspecies variability is huge in all taxa. I have found rotenone LD50s that range form 113 to 5000 ppm for various bird species. I was also unable to find that published study (Harada et al. 2008) given only the first authors last name and year.

    At low concentrations DEET (along with other anthropogenic PPCPs) could be causing endocrine disrupting effects, but I dont think it would be causing a short term mass die off.

  5. "Amphibians, such as snakes and frogs..."

    Snakes aren't amphibians; they're reptiles.