Iron Phosphate Slug Bait - How Dangerous is it in the Garden?
by Bill Meyer
    A few years ago a new type of slug bait began appearing on the market. Instead of the tried and true metaldehyde baits that had been in use for quite some time, this new bait used iron phosphate. This new product has made significant inroads into the market, riding on claims of being "natural" and safe to use around pets and wildlife. A quick check of the EPA's info on iron phosphate seems on the surface to back up these claims of safety, but is that the whole story? 
    Much of the claims about the safety of this product are based on the fact that iron phosphate occurs widely in nature. It is also used in vitamin supplements. It is a safe compound that is not easily digested so does not easily release iron into the system if ingested. The EPA seems to just give these products a pass without insisting on further testing because of this, but I began to wonder what would happen if a dog or even a child might ingest a large amount of this product. Like the metaldehyde baits, it is in a bait form that is attractive to pets and maybe even to small children.
    Like metaldehyde baits, these iron phosphate baits are mostly a food-based pellet that smells strongly like cereal to attract the slugs from a distance. Unlike the metaldehyde baits, the iron phosphate baits do not appear to contain Bitrex to prevent unintentional ingestion by pets and children. Bitrex is an extremely bitter-tasting substance that most mammals will not eat. The EPA recently mandated that metaldehyde bait products sold in the U.S. increase their Bitrex amount tenfold to reduce the risk of accidental poisonings. Iron Phosphate baits like the popular Sluggo do not list Bitrex as an ingredient, and are not required or presumed to have it.
    The marketing campaign by the companies that sell iron phosphate slug baits is full of statements like "doesn't harm pets and wildlife" and "no danger to dogs, cats, and birds" and "not harmful to beneficial animals, such as earthworms and frogs". These exact statements are found in a brochure directly from Neudorff, the manufacturer of these baits. Retailers seize on these claims and sell the product with enthusiastic claims like "safe and non-toxic" and "safe around children and pets". They also target the organic-lifestyle crowd with claims of being "all-natural" and "completely organic". The label on the product lists only iron phosphate as the active ingredient, and "inert ingredients". The dubious organization NCAP (Northwest Coalition for Alternatives to Pesticides) says the following "According to a phone call to NCAP from the company that manufactures iron phosphate slug bait, there is only one “inert” (unidentified) ingredient in these baits, wheat gluten.

    My first thoughts on seeing the marketing for this product were to wonder if it was indeed as safe as its proponents were claiming. A quick look at data from the EPA was oddly inconclusive, as they say "no testing required" in several key areas because of iron phosphate's common presence in the environment and low solubility. Essentially iron phosphate will pass through the digestive system largely if not completely unchanged, making it pretty harmless in truth. A bait made up of iron phosphate and (if NCAP can be believed) wheat gluten would in fact be as safe as it is advertised to be. It would also not kill slugs or snails, and would rot much quicker than it seems to do.
    The first signs that it is not all that safe have begun to appear. Dog poisonings are being reported and two recent studies concluded that normal usage kills earthworms. The Ohio State study says the EPA reports "5 domestic animal deaths, 8 major domestic animal incidents and 106 moderate and minor domestic animal incidents from the use of iron phosphate slug and snail baits" as of 2008. Since iron phosphate itself is a pretty harmless substance, something just wasn't adding up. When I found the Ohio State study I found out what it was that was missing from not only the advertising but from the label itself.
    Iron phosphate is non-toxic to both humans and dogs, as well as other pets and wildlife. Studies also show that it is equally non-toxic to slugs and snails, because it does not release its load of poisonous elemental iron very easily. If this is the case, why do other studies show that it is a very effective product that rivals the metaldehyde baits? How can these baits made of nothing but iron phosphate and wheat gluten be as effective as they are shown to be when other studies show that snails can live indefinitely on a diet of iron phosphate?

    Enter a man-made chemical called EDTA, a chelating agent that causes the iron phosphate to release its elemental iron easily in the digestive systems of not only slugs and snails but of pretty much anything that eats it. EDTA or the similar EDDS are the only reason these baits are effective, yet interestingly the label only reads Active Ingredient: Iron Phosphate - 1%, Inert Ingredients - 99%. No mention is made of the presence of another chemical that can turn harmless iron phosphate into a deadly poison. Apparently EDTA was slipped through the cracks in our regulatory system as an "inert" ingredient, and inert ingredients do not have to be listed on the label. Since iron phosphate is harmless, and EDTA is the ingredient that makes it effective, not to mention dangerous,  something is really wrong here.

    Missing from most of the literature about iron phosphate slug baits is their mode of action - the "how" of what they do. Some trying to write about them even say that the mode of action is not well understood. Once you know that EDTA is present in the bait, the mode of action becomes clear pretty quickly - iron poisoning. In Australia, these baits are labeled as containing EDTA. An article about them contains the following mode of action description:

"Iron chelates can be incorporated into bait, which is palatable to the mollusc and it appears that at an appropriate location in the mollusc's gut the iron is released as Fe3+, and is toxic causing death if the concentration is sufficiently high. A number of chelates are efficacious, particularly those belonging to the group of compounds referred to as complexones, but to date the iron EDTA complex formed by the reaction of ferric EDTA with hydroxide ions is the most effective on the basis of the total iron concentration. A number of iron complexones have been shown to be effective."

    A review of these products by the Swiss organic certification organization (FiBL) discovered the EDTA content and stated that these products were likely no safer than the metaldehyde baits, that EDTA itself was significantly more poisonous than metaldehyde, and even said they weren't even sure that it wasn't the EDTA alone that was killing slugs and snails. When I started posting the link to that study and warning people about these baits, the report was quickly removed from the website that hosted it. It is referenced in the Ohio State study, though. A graphic comparing the toxicity of EDTA and metaldehyde was also taken down.
    The actual effect on slugs and snails does seem to be iron poisoning from what I can find. The referenced pet poisonings also seem to be the result of iron poisoning, from iron freed up from the iron phosphate by EDTA.

Iron Poisoning

    The following is a fair description about the effects of iron poisoning in humans from the Linus Pauling Institute:

"Accidental overdose of iron-containing products is the single largest cause of poisoning fatalities in children under six years of age. Although the oral lethal dose of elemental iron is approximately 200-250 mg/kg of body weight, considerably less has been fatal. Symptoms of acute toxicity may occur with iron doses of 20-60 mg/kg of body weight. Iron overdose is an emergency situation because the severity of iron toxicity is related to the amount of elemental iron absorbed. Acute iron poisoning produces symptoms in four stages: 1) Within 1-6 hours of ingestion, symptoms may include nausea, vomiting, abdominal pain, tarry stools, lethargy, weak and rapid pulse, low blood pressure, fever, difficulty breathing, and coma; 2) If not immediately fatal, symptoms may subside for about 24 hours; 3) Symptoms may return 12 to 48 hours after iron ingestion and may include serious signs of failure in the following organ systems: cardiovascular, kidney, liver, hematologic (blood), and central nervous systems; and 4) Long-term damage to the central nervous system, liver (cirrhosis), and stomach may develop two to six weeks after ingestion"
    The above child poisonings are not from the slug baits, but the potential is clearly there. If we look at a 2.5 lb. container of Sluggo, it contains roughly .148 oz of elemental iron. An LD50 number is the number at which half (50%) of the affected life form will die. The above LD50 numbers indicate that a 45lb child would be at LD50 if he/she ate the entire 2.5lb container of Sluggo, if all the iron was absorbed in their system. I don't know what percentage would be absorbed, because testing of these iron EDTA products doesn't seem to have been done. A child that size eating that much iron phosphate slug bait in one sitting seems pretty unlikely. On the other hand the above relates "symptoms of acute toxicity" at only 10% the LD50 amount, or only 4oz of Sluggo for a 45lb child - an amount that could be eaten in one sitting.
    There is no doubt therefore that elemental iron can safely be described as toxic to humans in high enough amounts, and that elemental iron is released by EDTA from iron phosphate. Excess iron is not easily removed from the human body, but the situation is worse for dogs, which are the main problem with metaldehyde-based slug baits. The iron LD50 for dogs is about the same as it is for people, but they have no mechanism for getting excess iron out of their systems. That means that each time they ingest iron it adds to the amount already in their body, building higher and higher until symptoms appear and can lead to death. So, for a 45lb dog, eating 2.5 lbs of Sluggo will be lethal half the time, again if all the iron is absorbed. That is bad enough, but the real danger there is if the dog eats a little every few days, slowly building up the iron in its system. Before the appearance of iron phosphate slug baits, iron poisoning in dogs was rare, resulting mainly from their getting into iron supplements designed for humans. Now with these baits becoming commonly available and advertised everywhere as safe around pets, we can expect to see a dramatic rise in iron poisoning in dogs, and it seems we are beginning to see that.
    Just like the metaldehyde baits, the iron phosphate baits seem perfectly designed as a mechanism for getting children and especially dogs to ingest dangerous amounts of a compound that is toxic in amounts it is possible to eat. I was unable to find clear information on how much iron is absorbed into the system by eating iron phosphate/EDTA either in dogs or humans, but there is no doubt that some is and that it results in iron poisoning.
    Iron phosphate slug baits are fairly new in the garden and their danger is not yet fully researched or understood. A recent article (June 2009) in the Australian Veterinary Journal about the treatment of five dogs that had eaten iron EDTA slug baits and were poisoned by them concludes that it "requires further study and minimum toxic doses need to be established". I agree and call for responsible testing of the toxicity of these products, and for appropriate warnings to be required on the labels and in all advertising.

Another "safe" new product hits the market

    As if the iron phosphate baits weren't enough, the apparently mis-named Safer Brand company has trotted out its "improved" iron chelate slug bait that it calls Dr. T's Nature Products Slug and Snail Killer. This product features 6% (as opposed to 1%) active ingredient, this time Sodium Ferric EDTA. It's ads for the product make such claims as "Safe for use around children, pets, wildlife and edible crops" and the bizarre "It will not harm beneficial insects. In addition, since iron is naturally found in soil, it will not persist in the environment like a synthetic formula." Iron may be naturally found in the soil, but EDTA certainly isn't. It isn't "natural" either by any stretch of a copy writer's imagination. I have no idea what "synthetic formula" they might be referring to - apparently not the synthetic formula called sodium ferric EDTA.
    Interested in what the National Organic Standards Board thought of this product? Well it received a resounding unanimous "No" vote from them for multiple reasons. The link is below.

The Bottom Line 

    The dangers of metaldehyde slug baits are well understood and fairly well documented. No one anywhere puts forth the idea that they are safe for people or animals to eat. The dangers of eating iron phosphate EDTA slug baits on the other hand are not even mentioned, certainly not by those who are trying to sell or promote those products. Virtually no research has been done on the consequences of a child or dog consuming the product, and the first dog poisoning cases, including deaths, have been confirmed. It's toxicity to pets and humans, especially children, seems to be on a par with the metaldehyde baits, as the reported dog poisonings makes clear. 
    Although it is highly irresponsible, many sources of gardening information continue to tout iron phosphate baits as completely safe for children, pets, and wildlife despite having no real proof that such claims are true and can point to no studies that show that. The Swiss FiBL study said that EDTA is more poisonous than metaldehyde and that they didn't think the iron phosphate slug bait products would be much safer than metaldehyde baits. As poisoning reports come in, it appears they are right. If Ohio State University and Australia's Veterinary Journal are to be believed, dogs are being poisoned by these baits, and the potential is there for children to be as well. Why does all U.S. advertising of these products hide the fact that EDTA is in these products and that iron poisoning is what kills slugs and that it is a hazard to any mammal that eats them? I don't know, but that does seem to be what is going on. 
    If you have these products or are planning to use them, I strongly recommend that you treat them the same way as you would the metaldehyde baits, and consider them equally dangerous until we know more about them. Be extremely careful to keep children and pets out of the containers. Use only sparingly as directed, don't put big bands or piles anywhere, and clean up spills. Do not allow children or pets to play unsupervised in treated areas, and watch for neighbor's dogs or kids when the product is down. There is nothing wrong with these products - they work very well as a slug and snail bait. The problem is the deceptive advertising that hides the true nature of these products, and disarms the caution users should have with a dangerous poison.
    It is ultimately our responsibility to keep kids, pets, and wildlife safe from poisoning when we use or store poisons. Both metaldehyde and iron phosphate baits are pretty safe if used properly, but they are both dangerous poisons if consumed in enough quantity. Remember too that the iron phosphate baits as far as I know do not contain Bitrex so they are much easier to eat in large quantities, and that iron builds up in the system so eating smaller amounts over time will increase the amount of poison until symptoms appear.

Dog Poisonings:

Earthworm Poisonings:
Swiss Investigation for Organic Certification:
(Suddenly taken down after I started posting! Link left here in case it reappears)

Sluggo Label and Advertising:
NY Department of Environmental Conservation Statement:

Australian Article with Mode of Action for Iron Chelate products:

Dr. T's Nature Products Slug and Snail Killer:

National Organic Standards Board review of above product:

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