Herbicides

Herbicides: How Toxic Are They? 1

Written by:
Fred Fishel, Jason Ferrell, Greg MacDonald, and Brent Sellers2

An herbicide is any agent used to bring about plant death. Although everything from salt to soap has been used for this purpose, herbicides are primarily synthetic chemicals manufactured for use in the agriculture, industrial, and ornamental and turf industries. For many years, these products have been seen as toxins that poison plants and are equally harmful to the applicator. To compound this issue, organically produced food is becoming more popular because it is pesticide-free and is seen as being healthier. These factors have led to a prevalence of an opinion that pesticides are bad for the environment and harmful to humans.

Although there have been pesticides that were toxic and dangerous to handle, most of these products are no longer used and have been replaced by newer chemistry. Pesticides now must go through rigorous testing by the U.S. Environmental Protection Agency (EPA) before they can be sold. This has led to many herbicides that possess little or no mammalian toxicity and are less harmful than many everyday household products (Table 1).

Surprisingly, household chemicals that many of us store under the kitchen sink pose more risk to the handler than herbicides.

A common way to document toxicity is by oral LD50 values. LD50 is the amount of chemical required to provide a “lethal dose” to 50% of the test population. LD50 is measured in mg of chemical administered per kg of body weight. Therefore, an oral LD50 of 500 means that 500 mg of chemical was needed to obtain lethality in a 1 kg subject (rabbit). The lower the LD50 value, the less chemical that is required to reach lethality. A chemical with an LD50 of 10 mg/kg is more acutely toxic than one with an LD50 of 100 mg/kg.

Table 1 demonstrates that herbicides often have higher LD50 values than many commonly used or consumed products. Why is this? Why are chemicals that are so effective on plant species not equally harmful to humans? The reason is two-fold. First, herbicides target highly specific biological or biochemical processes within plants, such as photosynthesis and production of branch-chain amino acids. However, mammals (humans included) do not photosynthesize or produce branch-chain amino acids. Therefore, herbicides that target photosynthesis or branch-chain amino acid production have no place to bind in our bodies and have a very little impact. Secondly, since these herbicides do not bind in our bodies, they are often excreted in urine within 24 hours of the dose. This flushing of the herbicide does not allow concentrations to build up to toxic levels within the body. This in no way means that it is safe to intentionally ingest herbicides, but the fact is that our bodies are well equipped to safely dispose of accidental exposure to many common herbicides.

Table 1.

Comparison of oral LD50 values for my commonly used herbicides and various household products.

Herbicides:

  • Bifenthrin-70
  • Imidicloprid-450
  • Surge-470
  • Triplet-500
  • Trimec 1000-1030
  • Escalade-1750
  • Quinclorac-2610
  • T Zone-3129
  • Roundup-4900
  • Prodiamine-5000
  • Dimension-5000

Household Products:

  • Cascade-2
  • Clorox-4
  • Dawn-7
  • Nicotine-9
  • Antifreeze-20
  • Caffeine-192
  • Toilet Bowl Cleaner-240
  • Tylenol-338
  • Household Ammonia-350
  • Ibuprophin-636
  • Windex-1000
  • Oven Cleaner-1720
  • Salt-3000
  • Tide-4000
  • Washer Fluid-5000

Footnotes

1. This document includes parts of PI-133, one of a series of the Pesticide Information Office, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date: September 2006. Revised: February 2013. Visit the EDIS website at http://edis.ifas.ufl.edu.
2. Fred Fishel, professor, Agronomy Department, and director, Pesticide Information Office; Jason Ferrell, associate professor, Agronomy Department; Greg MacDonald, professor, Agronomy Department; Brent Sellers, associate professor, Agronomy Department, Range Cattle Research and Education Center, Ona, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
Use herbicides safely. Read and follow directions on the manufacturer’s label.