Sluggo: not "completely nontoxic"

Dog-loving gardeners face a dilemma when it comes to slug control. Prior to 1995, the only commercially available slug baits contained metaldehyde, a chemical highly toxic to mammals. A few licks can cause seizures in an average-sized dog; a tablespoonful or two can be lethal.

In 1995, a new class of slug baits entered the US market, with the active ingredient listed as iron phosphate. This is a naturally-occurring compound found in soils, and has been used in nutritional supplements. These baits were marketed as “completely nontoxic”, and were embraced with fervor by organic gardeners and animal lovers.

But as the new products have gained in popularity, veterinarians have seen more and more dogs poisoned by these products. The ASPCA Poison Control Center has documented hundreds of cases. No deaths have been documented; affected dogs typically exhibit vomiting, diarrhea and lethargy. At minimum, it is clear that vomiting and diarrhea do not spell “completely nontoxic” to any reasonable person.

Sluggo is the best-known of the iron phosphate baits sold in the US. It is manufactured by a German company, Neudorff. Similar products, including Ecosense, Escar-Go and Worry-Free, are all licensed by Neudorff.

Product labels list iron phosphate as the only active ingredient, at one percent. The remaining 99 percent consists of “inert ingredients”, which the Environmental Protection Agency does not require to be listed on the label. The patent application for these products clearly indicates that the unlisted ingredients include a chelating agent, usually EDTA.

The first scientist to publish information on this problem was Clive Edwards, a researcher at Ohio State University. He found that earthworms exposed to iron phosphate alone suffered no ill effect, but those exposed to Sluggo exhibited reduced feeding and increased mortality. He cited the patent and other supporting documents. His paper can be found online at http://www.biosci.ohio-state.edu/~soilecol/Full%20articles/2008/Crop%20Protection%2028.pdf

Now, additional evidence is more widely available. An April 2010 presentation by a Neudorff representative to the National Organic Standards Board discusses and defends the presence of EDTA in Sluggo. The paper can be found online at http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5085124

EDTA functions to release elemental iron from the iron phosphate and make it available for bioabsorption—thus the toxicity to slugs and mammals alike. Toxicologists* agree that knowing that these products contain EDTA greatly influences our thinking about their potential toxicity.

Hosta expert Bill Meyer’s online paper, “Iron Phosphate Slug Bait - How Dangerous is it in the Garden?” ( http://www.hostalibrary.org/ firstlook/RRIronPhosphate.htm ) contains a clear and comprehensive explanation of the issues related to slug bait toxicity, and multiple informative links.

Meyer explains that while metaldehyde baits pose a greater acute poisoning risk, the iron phosphate slug baits pose more risk of cumulative poisoning, as “each ingestion slowly raises the iron level in the body. Additionally there is a significant amount of organ damage that can occur in non-fatal poisonings.” Meyer suggests that due to the widespread belief among pet owners and veterinarians alike that these products are nontoxic, poisonings may be underreported. He adds, “Both the metaldehyde baits and the iron phosphate baits are being reported in poisoning incidents, and only time will tell which is posing the more serious risk to our dogs.” (email communication).

Sluggo remains a comparatively safe garden chemical when used and stored appropriately. Very small quantities are effective for most applications. Younger animals and those with smaller body size will be more vulnerable, particularly with access to the container. Additional concerns about iron phosphate products concern the harm to earthworms, which as all organic gardeners know, are essential to healthy soils.

For people disinclined to take risks with their pooches and the environment, it may be time to take another look at a variety of less convenient methods of slug dispatchment. These include hand-picking and beer. Check the internet and organic gardening books for details.

*Thanks to the following professionals for their generous help in preparing this article: Fred Berman, DVM, PhD, Oregon Health and Science University; Karen Bischoff, DVM, Cornell University School of Veterinary Medicine; Clive Edwards, PhD, Ohio State University; Bill Meyer, Education Director, American Hosta Society; Robert Poppenga, DVM, PhD, UC Davis School of Veterinary Medicine; Tina Wismer, DVM, ASPCA Poison Control Center.