How poisonous are pesticides and weed killers?

Today's guest blogger is Alexis Gross, PharmD Candidate, and Poison Information Provider at The Poison Control Center at the Children's Hospital of Philadelphia.

Pesticides and weed killers are popular this time of year to maintain lawns and landscaping. But how safe are children and pets being around these chemicals?

Thousands of exposures are reported to U.S. poison centers every year. Fortunately, the majority of cases have mild to no symptoms. However, major effects or even death can occur. These cases usually involve deliberate, large ingestions. Inadvertent or exploratory ingestions by children generally only cause mild irritation of the exposed tissue in areas such as the gastrointestinal tract, skin, eyes, or respiratory tract.

The two major classes of herbicides in the U.S. are glyphosates and chlorophenoxy compounds. Glyphosate is a broad-spectrum systemic herbicide, and is the most widely used herbicide in the US. It is available under a variety of trade names, including Roundup. Glyphosate is related to the amino acid glycine and kills plants by interfering with the synthesis of other amino acids. The addition of other chemicals to glyphosate mixtures (such as diquat and surfactants) are responsible for much of the reported toxicity. Exposure is common because of the popularity of these products, but severe toxicity is rare.

Ingestion of products containing glyphosate can cause gastrointestinal effects (nausea, vomiting, diarrhea, and abdominal pain), oral pain, and slight sedation. Skin exposure can cause it to become red and irritated along with "goose bumps". These products are not expected to produce significant adverse effects when users follow the recommended instructions.These products generally say that, "Pets such as cats and dogs should remain out of the treatment area until it is thoroughly dry. Once the application area has dried, your pets may reenter the area. Although they may eat a small amount of grass, they will not be able to eat enough of the product to cause a health hazard."

Chlorophenoxy compounds (also known as 2,4-D compounds) are other chemicals commonly found in weed killers. Several hundred commercial products contain these compounds in various forms, concentrations, and combinations. They are often mixed into commercial fertilizers to restrict the growth of broadleaf weeds. Chlorophenoxy compounds have been shown to cause skin irritation with skin contact; airway irritation with inhalation; and nausea, vomiting, and increased acid levels with large ingestions.

We are still learning about the long term effects of chronic exposure to humans, including possible increased risks with certain cancers and effects on the endocrine system. There are also concerns about the effects on the ecologic system from residential and industrial applications. For those who prefer non-chemical options for weed control: manually pulling out weeds by the roots to prevent regrowth, mulching, and possibly by applying acetic acid like vinegar to unwanted plants may be considered.

Overall, pesticides and weed killers intended for residential use are considered safe when used appropriately. It is important to read all instructions on the product's labeling and allow the product to completely dry before permitting children or pets to enter the lawn. As with all chemicals, be sure to store in the original container and out of reach from children. The Poison Control Center at Children's is a trustworthy and easily accessible resource to take advantage of if an inadvertent exposure occurs, as well as to ask any questions.

Check out the Agency for Toxic Substances and Disease Registry publication titled "How to Reduce your Exposure to Chemicals at Home, Work, and Play" for more information on how to reduce your exposure to chemicals used in gardening and in other areas of the home.

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