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You are here: NPIC Home Page Pesticides and the Environment Groundwater Ubiquity Score (GUS)

Groundwater Ubiquity Score (GUS)

In the environment, a number of things can influence a pesticide’s potential to move toward and contaminate groundwater. This includes characteristics of both the soil and the pesticide, as well as water movement in soil, and soil surface disturbances (crop agriculture, insect or animal activity, landscaping, etc.).

Characteristics that determine soil sensitivity include: sorption (driven by clay and organic matter content), permeability, and water table features. For example:

• Soils that have slow permeability, high clay and/or organic matter, and a low water table may be less sensitive.
• Soils that have fast permeability, low clay and/or organic matter, and a high water table may be more sensitive.

Physical and chemical properties of the pesticide can also influence its potential for movement through soil. Some of these factors include pesticide persistence (half-life) in different settings, solubility in water, sorption potential (Koc), and its ability to become a vapor (vapor pressure), among other things.

• Pesticides that have a short half-life, low water solubility, and high sorption potential may have less potential to move through soil.
• Pesticides that have a long half-life, high water solubility, and low sorption potential may have greater potential to move through soil.

The GUS or Groundwater Ubiquity Score is an experimentally calculated value that relates pesticide half-life and Koc (from laboratory data). The GUS may be used to rank pesticides for their potential to move toward groundwater. GUS = log10 (half-life) x [4 - log10 (Koc)].

(Citation: Gustafson, D.I. 1989. Groundwater ubiquity score: A simple method for assessing pesticide leachability. Environmental Toxicology and Chemistry 8:339-357)

GUS Value	Potential for movement toward groundwater
Below 0	Extremely Low
0 – 1.8	Low
1.8 – 2.8	Moderate
Above 2.8	High

Source: Goss, Don, and R. Don Wauchope. "The SCS/ARS/CES pesticide properties database: II Using it with soils data in a screening procedure." Pesticides in the next decade: The challenges ahead (1990): 8-9.

For more information, check the “Environmental Hazards” section of the pesticide label, or call NPIC at 1-800- 858-7378.

Related Topics:

What are pests?

What are pesticides?

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NPIC provides objective, science-based information about pesticides and pesticide-related topics to enable people to make informed decisions. NPIC is a cooperative agreement between Oregon State University and the U.S. Environmental Protection Agency (cooperative agreement #X8-83560101). The information in this publication does not in any way replace or supersede the restrictions, precautions, directions, or other information on the pesticide label or any other regulatory requirements, nor does it necessarily reflect the position of the U.S. EPA.