- 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.
Australian Article with Mode of Action for Iron
Chelate products:
http://www.regional.org.au/au/asa/2001/6/c/young.htm
Dr. T's Nature Products Slug and Snail
Killer:
http://www.saferbrand.com/store/sister-products/flower-garden/insect-control/DT125
National Organic Standards Board review of
above product:
http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5066636
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