- Metaldehyde Slug Bait - How Dangerous is it in
by Bill Meyer
- First, the facts: Metaldehyde is a poison that is
highly toxic if inhaled and moderately toxic if ingested. It is not a
carcinogen. It is metabolized and does not build up in the body. Poisoning
symptoms will appear in 1 - 3 hours, and include severe abdominal pain,
nausea, vomiting, diarrhea, fever, convulsions, and coma. It is toxic to
all mammals and birds, but not to aquatic life. Breakdown in the
environment is rapid. Metaldehyde is in regular use in farming, with about
48,000 pounds of active ingredient used per year in the US. It is mainly
used on seed crops, lemons, artichokes, oranges, strawberries and grapes.
Easily the most common poison baits used to control
slugs are the ones containing metaldehyde. These are typically bran
pellets, often dyed blue, which contain 4% or less of the chemical.
Metaldehyde is poisonous to mammals, so does pose a threat to pets if used
in the garden. If pets ingest enough of it, it can be fatal.
The average amount necessary to be fatal for a dog is
somewhat variable, with the lowest being 100mg/kg, or 100 milligrams per
kilogram of dog weight. This would roughly be a tablespoon of bait for the
average dog. For cats, twice the amount per kilogram of body weight. As
cats are smaller, this would be less than a teaspoon of bait. These
amounts are not so large to be impossible for dogs and cats to ingest, so
the possibility of poisoning is real in the home garden if they are used.
Children could be poisoned as well, but a lethal dose has not been
established, as no child deaths were ever reported from metaldehyde slug
To get a look at how often child poisoning happens I checked with
the EPA and found that there were 1,892 incidents reported of children
being taken to poison centers because of concern they had ingested metaldehyde
slug bait during the years
1993 - 2004 in the US. Of these, 3 exhibited moderate symptoms that had no
long term effects, 29 had minor symptoms that cleared quickly, and the
remainder did not show any symptoms. None of the incidents were
Pet poisoning statistics are not kept in the US,
but they are in Great Britain, where perhaps even more metaldehyde baits
are used per person. In a 2000 study, 10 dogs were found to have been
fatally poisoned by metaldehyde. These were classified as follows:
4 were due to abuse, such as leaving piles of it to kill pest animals or
5 were due to misuse, such as getting into stored baits or spillages in
1 was due to proper use, although it was not included whether it was
agricultural or garden use.
No cases of cat poisoning were recorded, but it is expected they would be
significantly less than dog poisonings.
- There are often anecdotal
reports of pet poisonings which tend to be confusing. Usually in these
cases, veterinarians treat dogs for symptoms, but do not know for certain
what caused them. These situations are often referred to as
"probable" or "possible poisonings". Because these are
so difficult to pin down, no numbers on these are included here. Pets can
be poisoned by many things in the home and garden, including bad pet food,
and often neither the owner or the attending veterinarian knows for
certain what the problem was. I was unable to find any reports of bird
poisonings in garden use, but it remains a possibility that birds could be
poisoned. Secondary poisoning by animals eating poisoned slugs, snails, or
even mice has been disproven in studies and is apparently just a myth.
Because of concern over poisoning from what could be an
attractive bait, makers of slug baits containing metaldehyde were required
to include denatonium benzoate, commonly known as Bitrex, the most
bitter-tasting substance in the world. The amount of Bitrex was upped from
30ppm to 300ppm in late 2003, a tenfold increase, to help further reduce
the number of poisonings.
From the above information it can be seen that
poisoning of children does occur, but no serious life-threatening
poisonings were reported. Increasing the amount of Bitrex seems likely to
prevent many of the mild poisonings that have occurred in the recent
past. Cats in general do not have excessive interest in the bait products,
so are not considered to be very much at risk. Dogs are likely to remain
at risk because of their interest in eating almost anything edible, but
the most danger to them lies in improper use and storage rather than
from areas in the garden where it has been properly applied.
- Whenever the choice is
made to use toxic chemicals in the garden, we need to understand the
dangers they present and be careful to act in the best interests of those
who might be harmed by our actions. Whether a toxic chemical is
"organic" or synthetic is largely irrelevant when it comes to
assessing how dangerous it is. Safety information is often very easy to
find on synthetic chemicals, but actual information can be much more difficult for
"organic" products, which often are not tested to any real
extent. To find safety information on the internet,
just type (chemical name) + safety into a search engine.
- Genuine U.S. safety
information is available in the form of EPA documents and MSDS papers from
OSHA. Other good sources are university sites, and other government safety
organizations. Be wary of misleading information from various
manufacturers and "activist" groups.
Recent Discovery about how Metaldehyde Works: