Holly Hommerding, DVM
Associate Veterinarian, Clinical Toxicology

Summer brings with it copious amounts of sunshine and warm weather, and with it, follows the aching need to break our cabin fever and explore the great outdoors.  As gardening and yard work efforts increase, so do the inadvertent exposures of our pets to the various tools of the trade that help to ensure vibrant roses, blossoming buds, trailing ivy, and the greenest of grasses.  Fertilizer and herbicide exposures may range from the unwitnessed and potentially small ingestion with Frank the Yorkie, to a hold nothing back, near whole bag ingestion in Lexi the Lab.  This brief summary aims to ease the care and concern of such risks and adventures in our patients and pets.

Fertilizers

Nearly all fertilizer products are labeled with a distinct and relatively unique N-P-K, or nitrogen, phosphorus, and potassium (potash) ratio, which can be found on most organic and non-organic products.  Most ready-to-use fertilizer products intended for the average consumer are not highly toxic but pose a risk for irritant effects such as dermal irritation, vomiting, diarrhea, and inappetence.  Exposure to industrial, concentrated, or undiluted products pose a more significant risk for poisoning, although such events are uncommon in companion animals. There is also limited concern with most fertilizer products once they have dried or been watered in. In general, gastrointestinal effects occur within 10 hours of ingestion and can often be managed supportively with anti-emetics (so long as foreign body obstruction (FBO) is not a concern), gastroprotectants, digestive diets, and fluid therapy as needed. The following information details some of the more common and concerning ingredients found in fertilizer products.

• Bone Meal: This is comprised of defatted, dried and flash frozen animal bones that have been ground to a powder and are then re-purposed as a mineral supplement with high concentrations of calcium or phosphrous. Small ingestions may lead to vomiting and diarrhea but large ingestions may lead to a FBO as the product congeals in the GIT. Early emesis (within 60 minutes) is imperative to reduce risk of obstruction and need for surgery.  Supportive care with digestive diets, fluid support, anti-emetics (only if obstruction is of low concern), and rarely, surgical removal of FBO may be considered.
• Blood Meal: This is comprised of dried, ground, flash frozen blood and is repurposed as a source of nitrogen and phosphorus in fertilizer products. It may alternatively be used as deer or rabbit repellent.  Ingestion may lead to vomiting, fetid diarrhea, and pancreatitis.  Supportive care, as noted above, is recommended.
• Iron: Fertilizers containing iron may pose a risk for iron poisoning, although this is dependent on the nature of exposure and dose (e.g., eating straight from the bag, post spreading, etc.) and the nature of the iron in the product (iron vs iron salt or derivative). Iron toxicosis initially mimics the irritant effects of general fertilizer ingestion with vomiting and diarrhea.  Advanced cases or large ingestions may suffer from more severe signs of hematemesis, melena, lethargy, tachycardia, acidosis, and effects on the liver and kidneys.  Calculating the amount of elemental iron to which the patient was exposed is the best way to assess the risk of poisoning. When such values cannot be obtained, serum iron concentrations drawn 4-6 hours post ingestion may be warranted to determine the concern for intoxication and aid in dictating the need for chelation. In general, dosages grater than 20 mg/kg of elemental iron are concerning and require therapy.  Supportive measures with anti-emetics (so long as FBO is of low risk), fluid therapy, gastroprotectant medications, and milk of magnesia may all be considered in treating these patients.
• Nitrates: Although urea has largely replaced ammonium nitrate in most residential use fertilizers, nitrate fertilizers are still commonly found on farms, ranches, and commercial properties. Nitrates are water soluble so may also contaminate natural and contained water sources. Intoxication is largely the result of the in vivo conversion of nitrate to the more toxic nitrite. Nitrites result in vasodilation following conversion to nitric oxide and cause methemoglobinemia by oxidizing hemoglobin’s ferrous iron (Fe²⁺) to ferric iron (Fe³⁺). Ruminants are most at susceptible to nitrate poisoning although, in large enough doses, horses, rabbits, dogs, cats, and other monogastrics can suffer intoxication too.
• Urea: Urea is commonly used as a nitrogen source in many residential-use fertilizers. Monogastric animals such as dogs and cats tend to tolerate ingestions well, with gastrointestinal signs predominating. Large ingestions may result in methemoglobinemia (see Nitrates). As with nitrates, ruminants may suffer more deleterious effects at much lower doses than monogastrics. Care is supportive.
• Insecticides: Some fertilizers may be manufactured with insecticide and/or fungicide ingredients, and are commonly used in rose and flower care products. Imidacloprid and tebuconazole are among the more commonly used ingredients in these products.  Ingestion may lead to mild irritation with vomiting and/or diarrhea. Care is typically supportive.

Herbicides

Used for the control of unwanted plant species and weeds, residential-use herbicides tend to carry a relatively wide margin of safety in our companion animals.  I most cases, gastrointestinal signs predominate following accidental ingestion. Vomiting, diarrhea, inappetence, and abdominal discomfort may be managed symptomatically and supportively.  The following products may commonly be found in consumer available herbicide products:

• Glyphosate: This is an amino acid inhibitor that affects metabolic pathways specific to plants (skikemic pathway). These pathways that are not present in mammals. Ingestions typically result in gastrointestinal irritation with vomiting and diarrhea predominating.
• Chlorophenoxy Herbicides (e.g. Mecoprop, 2,4-D): These act at multiple sites in a plant to disrupt protein synthesis thus altering growth. Specifically used to control broadleaf weeds, these herbicides as available in commercial form will typically lead to vomiting, diarrhea, and abdominal discomfort.  Exposure to large amounts or concentrate/industrial formulas may rarely lead to myotonia, ataxia, and tremors.
• Benzoic Acid Herbicides (e.g. Dicamba): This is a plant growth regulator with an unknown site of action within the plant. Exposures to consumer available products typically result in irritation and gastrointestinal distress at most.  Exposure to large amounts or concentrate/industrial formulas may rarely lead to myotonia, ataxia, and tremors.
• Pyridine (dithiopyr, triclopyr), Dinitroaniline (trifluralin, nitralin, benefin, etc), and Benzamizole (isoxaben) herbicides may also be found in various products and typically lead to GIT irritation and distress. These are generally recognized as low toxicity herbicides.  In uncommon exposures, one human poisoning case report following intentional ingestion of triclopyr resulted in hypotension, metabolic acidosis, coma, and cardiovascular impairment.  Rare cases of human poisoning via ingestion of dinitroaniline herbicides have lead to vomiting, CNS depression, and aspiration pneumonitis.