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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:

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) (binding affinity), and its ability to become a vapor (vapor pressure), among other things.

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 ValuePotential for movement toward groundwater
Below 0Extremely Low
0 – 1.8Low
1.8 – 2.8Moderate
Above 2.8High

Source: Goss, Don; Wauchope, R.D. "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.

If you have questions about this, or any pesticide-related topic, please call NPIC at 1-800-858-7378 (8:00am - 12:00pm PST), or email at npic@ace.orst.edu.

Last updated January 19, 2021

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