Pesticides are designed to be lethal, and many are hazardous to plants, animals and soil organisms that are not target pests.
When these chemicals are applied to agricultural fields, a significant percentage is released into the environment by drifting offsite, runoff into surface water and leaching into groundwater. For a high-level overview of what is known about the environmental effects of pesticides, see our Environmental Toxicity resource page.
In previous versions of the Pesticide Info database, users were able to search Ecotoxicity by Chemical, Species and Effect. However because this functionality searched downloaded, static data from the Environmental Protection Agency (EPA), our information was out-of-date as soon as the agency updated information. We now provide detailed guidance for users to search the EPA site directly.
How to search the ECOTOX database
EPA’s ECOTOX database provides toxicity data showing the impact of individual chemicals on aquatic life, terrestrial plants and wildlife. For a literature review, one can search by Chemical, Species, Effects and more. Because the site is complex, we have developed the step-by-step guidelines below:
Step 1: Go to EPA’s ECOTOX site
Step 2: Select Explore (from top menu bar) _Alternatively you can Select Chemicals or Effects
Step 3: Select the Species button – then select one or more species
Step 4: Select Explore Data (upper Right corner)
Step 5: Exploring the data
- Make selections in Left column.
- You can only select one chemical name in the second box from the top (e.g. chlorpyrifos)
- You can select “Chemical Group” in the first box from the top, though only a few of these groups are pesticides (e.g. neonicotinoids; DDT and metabolites)
- Enter publication date range (bottom row on Left column)
- Select View All Applied (very bottom of Left column) to see your search criteria. Make sure to close this window (at the bottom) to proceed.
- Select Records (above summary table and to the right of Terrestrial and Aquatic check boxes) instead of the default “Group Summary” to see a link to the abstracts (far right column).
Aquatic toxicity and the ECOTOX database
The ECOTOX database contains over 170,000 records related to aquatic ecotoxicity, representing a compilation of individual studies conducted on the acute and chronic toxicity of selected pesticides to a variety of aquatic organisms. These data are drawn from a variety of sources, with peer-reviewed journal articles being the primary source.
This dataset within the ECOTOX data only includes single-ingredient toxicity tests. In some cases, a single ingredient might be a pesticide product with both active and inert ingredients. Not included in the dataset are in vitro toxicity tests or tests on pesticide mixtures containing more than one active ingredient.
This dataset is the largest aquatic ecotoxicity dataset that we know of. Other datasets on ecotoxicity are maintained by the U.S. Geological survey (approximately 10,000 records) and the U.S. EPA Office of Pesticide Programs (OPP) (approximately 10,000 records). There is some overlap between these datasets.
How Are Ecotoxicity Tests Conducted?
Acute toxicity of a pesticide is determined by exposing an organism to a measured dose of pesticide for a specified length of time (the study time), and noting the dose that causes a measurable effect (usually death or some other endpoint that can easily be measured) in a predetermined fraction of the organisms (usually 25% or 50%) within the specified study time.
This dose is expressed in one of several ways.
The LD50 (LD25) is the Lethal Dose of the pesticide in milligram (mg), microgram (ug), or nanogram (ng) of pesticide per kilogram (kg) of body weight that is lethal to 50% (25%) of the test organisms within the stated study time. Units used are: ppm (mg/kg), ppb (ug/kg), and ppt (ng/kg). For bees, the dose is given in microgram per bee (see conversion factors between one unit and another in table below).
The LC50 (LC25), or Lethal Concentration, is defined as the amount of pesticide present per liter of aqueous solution that is lethal to 50% (25%) of the test organisms within the stated study time. Units used are mg or ug of pesticide per liter of solution. Units used are: ppm (mg/L) and ppb (ug/L).
The EC50 is the Effective Concentration of the pesticide in mg/L or ug/L that produces a specific measurable effect in 50% of the test organisms within the stated study time. Similarly, the EC25 is the effective concentration that produces a specific measurable effect in 25% of the test organisms within the stated study time.
The NOEL (NOEC) is the “No Observed Effect Level (Concentration),” or the level below which no adverse effects are observed. Note that this level depends strongly on the sensitivity of the techniques used to measure the effects.
The LOEL (LOEC) is the “Lowest Observed Effect Level,” or the lowest level (Concentration) at which adverse effects are observed. Note that this level also depends strongly on the sensitivity of the techniques used to measure the effects.
The MATC is the “Maximum Acceptable Toxicant Concentration” and is a hypothetical threshold concentration that is the geometric mean between the NOEC and LOEC concentration.
For aquatic organisms (fish, zooplankton, and phytoplankton), tests are carried out using either static (S) or flow-through (F) methods. In the static method, the pesticide and test organisms are added to the test solution and kept there for the remainder of the study time. In the flow-through method, a freshly prepared, pesticide-spiked test solution flows through the test chamber continuously for the duration of the test. The flow-through method provides a higher continuous dose of the pesticide; however, the static method does not remove waste products and may accumulate toxic pesticide breakdown products and metabolites. Neither method exactly mimics a natural system.
How Are LC50 Numbers Used?
Lethal Concentration values are generally used as comparison values to actual concentrations found in the environment. If the environmental value exceeds the laboratory value known to cause harm, it is generally agreed that adverse effects are likely to occur to organisms in the environment.
The limitations of this assumption are:
- The species used in laboratory tests are frequently not the same as those found in the environment; and
- Conditions in the environment, particularly the aquatic environment, may either accentuate or attenuate the effects of the pesticide. Factors that may contribute to such differences are: pH, temperature, alkalinity, salinity, dissolved oxygen, and the presence of suspended sediment, dissolved minerals, and/or other pesticides.
Resources
Environmental Toxicity Resource page
Assessment of acute insect toxicity loading