Water-Quality Benchmarks for Contaminants

A water-quality benchmark is defined here as a threshold value against which measured concentrations can be compared to help assess the potential effects of contaminants on water quality. Benchmarks typically apply to a specific contaminant(s) in a specific sampling medium for a specific beneficial use:

• Contaminant: contaminant classes for which benchmarks are available include pesticides, volatile organic compounds (VOC), pharmaceuticals, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), metals, and nutrients;

• Sampling medium: drinking water, ambient surface water, bed sediment, whole fish, or edible fish tissue; and

• Beneficial use: the use that the benchmark is designed to protect, for example, drinking water, recreation, aquatic life, or wildlife.

“Benchmark” is a generic term, and can include any of the following:  

• Standard or regulation: threshold values that are legally enforceable by agencies of the U.S. Government or Canada. Within the U.S., the National Primary Drinking Water Regulations (NPDWR) include standards and treatment techniques that apply to public water systems as part of the Safe Drinking Water Act (SDWA).

• Guideline: threshold values that have no regulatory status but are issued in an advisory capacity.

• Criteria: within the U.S., criteria are part of the definition of a water-quality standard in Sec 303(c) of the Clean Water Act (CWA). Also, 304(a) criteria are published values that reflect scientific knowledge on the effects of priority pollutants on health and welfare, including effects on aquatic life, plants, wildlife, shorelines, beaches, esthetics and recreation; the concentration and dispersal of pollutants or their byproducts; and the effects on biological community diversity, productivity, and stability (Section 304(a) of CWA).

This web page focuses on national-scale benchmarks established for freshwater systems in the United States or Canada. However, a few types of benchmarks from the States or the general scientific literature also are included, for particular sampling media and beneficial uses that have few or no national guidelines. Examples of these include whole-fish benchmarks for protection of wildlife, or human health benchmarks for pharmaceuticals.

Use of Benchmarks in Interpreting Water-Quality Data

Contaminant benchmarks can be used in screening-level assessments, in which site-specific estimates of contaminant exposure (concentrations or concentration statistics) determined from measurements of contaminants in various sampling media are compared to water-quality benchmarks. This approach has been used for many years by the USGS National Water Quality Program (such as in USGS Circular 1291, Pesticides in the Nation’s Stream and Ground Water 1992-2001), and it is similar in concept to U.S. Environmental Protection Agency (USEPA) screening-level assessments for pesticides, which USEPA uses in early stages of ecological risk assessments to evaluate the potential impact of pesticides to non-target organisms. Screening-level assessments are not a substitute for either risk assessments, which include many more factors (such as additional avenues of exposure), or site-specific studies of effects. Rather, comparisons of measured or estimated concentrations with water-quality benchmarks provide an initial perspective on the potential for adverse effects, as well as a framework for prioritizing additional investigations that may be warranted. Concentrations that exceed a benchmark do not necessarily indicate that adverse effects are occurring—they indicate that adverse effects might occur and that sites where benchmarks are exceeded may warrant further investigation. (See Characteristics and Limitations of Screening-Level Assessments section.) In general, effective use of benchmarks in water-quality assessment requires an understanding of how the benchmarks were derived and information about the specific hydrologic system being studied. Users are encouraged to consult the online sources for background information on the technical basis for the benchmarks being used, and any underlying assumptions, to better interpret what it means if a measured concentration exceeds a benchmark.

Benchmark Types and Sources

Click on the links below or scroll down the page to see specific benchmarks listed, with links to more information.

I. WATER COLUMN
   A. DRINKING WATER
       1. USEPA Drinking Water Regulations and Health Advisories
       2. USEPA Human Health Benchmarks for Pesticides
       3. USGS Health-Based Screening Levels
       4. USEPA Regional Screening Levels for Chemical Contaminants at Superfund Sites
       5. Canadian Guidelines for Drinking Water Quality
       6. Minnesota Department of Health Pharmaceutical Water Screening Values

   B. AMBIENT SURFACE WATER
       1. USEPA Ambient Water-Quality Criteria for the Protection of Human Health
       2. USEPA Recreational Water-Quality Criteria
       3. USEPA Ambient Water-Quality Criteria for the Protection of Aquatic Organisms
       4. USEPA (Office of Pesticide Programs) Aquatic Life Benchmarks
       5. Canadian Water Quality Guidelines for the Protection of Aquatic Life
       6. State numeric water quality criteria for Nitrogen and Phosphorus
       7. Aquatic life water quality criteria for selected pesticides 
       8. Pesticide Toxicity Index (2014 update): an additive model for pesticide mixtures

II. BED SEDIMENT
   A. WHOLE BED SEDIMENT
        1. USEPA Equilibrium Partitioning Sediment Benchmarks
        2. Canadian Interim Sediment Quality Guidelines
        3. Consensus-Based Sediment Quality Guidelines
        4. Chronic Toxicity Thresholds for Fipronil and Pyrethroid Pesticides in Sediment
        5. Freshwater Sediment Benchmarks for Currently Used Pesticides

III. FISH AND SHELLFISH TISSUE
   A. EDIBLE FISH AND SHELLFISH TISSUE
       1. USEPA Tolerances
       2. FDA Action Levels
       3. USEPA Recommended Screening Values
       4. USEPA database of U.S. State, Territory, and Tribal fish consumption advisories

   B. WHOLE FISH
       1. Canadian Tissue Residue Guidelines for the Protection of Wildlife Consumers of Aquatic Biota
       2. New York Fish Flesh Criteria for Piscivorous Wildlife
       3. Pesticide Whole-Fish Benchmark Ranges for Protection of Fish-Eating Wildlife, Compiled by the
           USGS National Water-Quality Assessment Program

Characteristics and Limitations of Screening-Level Assessments 

Screening-level assessments are a first step toward addressing the question of whether contaminants are present at concentrations that may affect human health, aquatic life or wildlife. They provide a perspective on where effects are most likely to occur and what contaminants may be responsible. Screening-level assessments are primarily intended to identify and prioritize needs for further investigation and have the following characteristics and limitations:

• The benchmarks used in a screening-level assessment are selected to correspond to both the sampling medium (drinking water, ambient surface water, bed sediment, whole fish, or edible fish tissue) and the beneficial uses of the hydrologic system being studied (human health, aquatic life, or wildlife). More than one type of benchmark may be appropriate for some samples and some hydrologic systems (such as surface water from a stream that is used for drinking water and that also supports aquatic life).
   
• Many water-quality benchmarks selected for the screening-level assessment are estimates of no-effect levels, such that concentrations below the benchmarks are expected to have a low likelihood of adverse effects and concentrations above a benchmark have a greater likelihood of adverse effects, which generally increases with concentration. One exception is for sediment benchmarks, which sometimes come in pairs for a given contaminant; if so, typically the lower value defines concentrations below which adverse effects are not expected and the upper value defines concentrations above which adverse effects are likely.
   
• The presence of contaminants in environmental samples at concentrations that exceed benchmarks does not indicate that adverse effects are certain to occur. Conversely, concentrations that are below benchmarks do not guarantee that adverse effects will not occur but indicate that they are expected to be negligible—subject to the limitations of both benchmarks (e.g., underlying assumptions) and concentration measurements (e.g., analytical detection limits), and the assumption that effects of the contaminant are not unduly affected by environmental conditions or the presence of co-occurring contaminants.
   
• The potential for adverse effects of contaminants on humans, aquatic life, and fish-eating wildlife can only be partially addressed because monitoring studies typically analyze for a small fraction of all the contaminants that may be present in the environment. In addition, some contaminants do not have benchmarks available.
   
• Most water-quality benchmarks are based on toxicity tests of individual chemicals, whereas contaminants usually occur as mixtures. Comparisons to single-compound benchmarks may tend to underestimate the potential for adverse effects.
   
• Water-quality benchmarks for different contaminants and media are not always comparable because they have been derived by a number of different approaches, using a variety of types of toxicity values and test species.
   
• For some benchmarks, there is substantial uncertainty in underlying estimates of no-effect levels, depending on the methods used to derive them and the quantity and types of toxicity information on which they are based.
   
• Estimates of contaminant exposure derived from either measured or estimated concentrations are also uncertain—particularly for short-term exposure of aquatic organisms to pesticides in lotic systems (rivers and streams), which tends to be underestimated by periodic discrete sampling procedures.

Benchmark Types and Sources:

I. WATER COLUMN

A. DRINKING WATER

1. USEPA Drinking Water Regulations and Health Advisories

Contaminant Types: Microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals, radionuclides

Sampling Medium: Drinking water

Resource Protected: Human health

Sources: National Primary Drinking Water Regulations (List of Contaminants and their MCLs), Drinking Water Standards and Advisory Tables (List of Contaminants and their MCLs, Health Advisories (HAs) and Cancer Risk Concentrations) (March 2018)

2. USEPA Human Health Benchmarks for Pesticides

Contaminant Types: Pesticides

Sampling Medium: Drinking water

Resource Protected: Human health

Sources: Human Health Benchmarks for Pesticides (available for food-use pesticides without drinking water regulations or health advisories) (2017), Supporting document: Human Health Benchmarks for Pesticides: Updated 2017 Technical Document  (January 2017)

3. USGS Health-Based Screening Levels

Contaminant Types: Pesticides, hormones, pharmaceuticals, other emerging contaminants, volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), organochlorine compounds, trace elements, major ions, nutrients, radionuclides

Sampling Medium: Drinking water

Resource Protected: Human health

Sources: Health-Based Screening Levels for Evaluating Water-Quality Data (May 2018), Supporting document: Development and Application of Health-Based Screening Levels for Use in Water-Quality Assessments (2007), Updated 2018 Technical Information (May 2018)

4. USEPA Regional Screening Levels for Chemical Contaminants at Superfund Sites

Contaminant Types: Pesticides, PAHs, PCBs, other organic chemicals, inorganic chemicals

Sampling Medium: Drinking water (also available for soil and air)

Resource Protected: Human health

Sources: Regional Screening Levels (RSLs) (May 2018), RSLs Tables (May 2018), RSLs User Guide

5. Canadian Guidelines for Drinking Water Quality

Contaminant Types: Microorganisms, pesticides, other organic chemicals, inorganic chemicals, physical parameters, radionuclides

Sampling Medium: Drinking water 

Resource Protected: Human health

Sources: Canadian Drinking Water Guidelines (August 2018), Guidelines for Canadian Drinking Water Quality, Summary Table (February 2017)

6. Minnesota Department of Health Pharmaceutical Water Screening Values

Contaminant Types: Pharmaceuticals

Sampling Medium: Drinking water 

Resource Protected: Human health

Sources: Rapid Assessments for Pharmaceuticals Project, Pharmaceutical Water Screening Values Report, Download the table of screening values: Pharmaceutical Water Screening Table (July 2018)

B. AMBIENT SURFACE WATER

1. USEPA Ambient Water-Quality Criteria for the Protection of Human Health

Contaminant Types: USEPA priority pollutants (organic and inorganic chemicals)

Sampling Medium: Ambient surface water 

Resource Protected: Human health

Sources: National Recommended Water Quality Criteria

2. USEPA Recreational Water-Quality Criteria

Contaminant Types: Microorganisms/pathogens

Sampling Medium: Ambient surface water 

Resource Protected: Human health/ recreation

Sources: 2012 Recreational Water Quality Criteria; Recreational Water Quality Criteria document, Office of Water 820-F-12-058 (2012); Draft Human Health Recreational Ambient Water Quality Criteria and/or Swimming Advisories for Microcystins and Cylindrospermopsin (2016)

3. USEPA Ambient Water-Quality Criteria for the Protection of Aquatic Organisms

Contaminant Types: USEPA priority pollutants (organic and inorganic chemicals)

Sampling Medium: Ambient surface water 

Resource Protected: Aquatic life

Sources: National Recommended Water Quality Criteria

4. USEPA (Office of Pesticide Programs) Aquatic Life Benchmarks

Contaminant Types: Pesticides, pesticide degradates

Sampling Medium: Ambient surface water 

Resource Protected: Aquatic life

Sources: Office of Pesticide Programs' Aquatic Life Benchmarks (October 2018)

5. Canadian Water Quality Guidelines for the Protection of Aquatic Life

Contaminant Types: Pesticides, PAHs, VOCs, other organic chemicals, metals, other inorganic chemicals

Sampling Medium: Ambient surface water 

Resource Protected: Aquatic life

Sources: Canadian Environmental Quality Guidelines; Canadian Environmental Quality Guidelines, Summary Table (online searchable database and access to downloadable Excel file)

6. State numeric water quality criteria for Nitrogen and Phosphorus

Contaminant Types: Nutrients

Sampling Medium: Ambient surface water 

Resource Protected: Multiple, including aquatic life, public health, navigation (impacts from eutrophication)

Sources: Numeric Nutrient Water Quality Criteria; State Progress Toward Developing Numeric Nutrient Water Quality Criteria for Nitrogen and Phosphorus (May 2018)

7. Aquatic life water quality criteria for selected pesticides (derived via the UC Davis method) (2012)

Contaminant Types: Organophosphate insecticides, pyrethroid insecticides, diuron

Sampling Medium: Ambient surface water 

Resource Protected: Aquatic life

Sources: Aquatic Life Water Quality Criteria for Selected Pesticides: Tjeerdema, R.S., ed., 2012, Reviews of Environmental Contamination and Toxicology

8. Pesticide Toxicity Index (2014 update): an additive model for pesticide mixtures

Contaminant Types: Pesticides

Sampling Medium: Ambient surface water 

Resource Protected: Aquatic life

Sources: Pesticide Toxicity Index: A Tool for Assessing Potential Toxicity of Pesticide Mixtures to Freshwater Aquatic Organisms, Nowell, L.H., et al., 2014, Science of the Total Environment, v. 476-477, p. 144-157.

II. BED SEDIMENT

A. WHOLE BED SEDIMENT

1. USEPA Equilibrium Partitioning Sediment Benchmarks

Contaminant Types: Organochlorine pesticides, PAHs, other nonionic organic chemicals, metals

Sampling Medium: Bed sediment 

Resource Protected: Benthic organisms

Sources: Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Procedures for the Determination of the Freely Dissolved Interstitial Water Concentrations of Nonionic Organics (2012): EPA/600/R-02/012:

Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms:

     Compendium of Tier 2 Values for Nonionic Organics. See Table C-1. (March 2008) EPA/600/R-02/016
     Dieldrin (2003) EPA/600/R-02/0010,
     Endrin (2003) EPA/600/R-02/009,
     PAH Mixtures (November 2003) EPA/600/R-02/013,
     Metal Mixtures (Cadmium, Copper, Lead, Nickel, Silver, and Zinc) (2005) EPA/600/R-02/011

2. Canadian Interim Sediment Quality Guidelines

Contaminant Types: Organochlorine pesticides, PAHs, PCBs, metals

Sampling Medium: Bed sediment 

Resource Protected: Aquatic Life

Sources: Canadian Environmental Quality Guidelines (includes introductory text, fact sheets for individual contaminants, and the 1999 protocol for derivation of Canadian sediment-quality guidelines for the protection of aquatic life); Canadian Environmental Quality Guidelines, Summary Table (online searchable database and access to downloadable Excel file)

3. Consensus-Based Sediment Quality Guidelines

Contaminant Types: Organochlorine pesticides, PAHs, PCBs, metals

Sampling Medium: Bed sediment 

Resource Protected: Aquatic Life

Sources: Development and Evaluation of Consensus-Based Sediment Quality Guidelines for Freshwater Ecosystems. MacDonald, D.D. et al., 2000, Archives of Environmental Contamination and Toxicology, v. 39, p. 20-31; Prediction of Sediment Toxicity Using Consensus-Based Freshwater Sediment Quality Guidelines, Ingersoll, C.G. et al., 2001, Archives of Environmental Contamination and Toxicology, v. 41, p. 8-21. 

4. Chronic Toxicity Thresholds for Fipronil and Pyrethroid Pesticides in Sediment

Contaminant Types: Fipronil and pyrethroid insecticides

Sampling Medium: Bed sediment 

Resource Protected: Aquatic Life

Sources: Contaminants in Stream Sediments from Seven U.S. Metropolitan Areas: Data Summary of a National Pilot Study, Moran, P.W., et al., 2012, USGS SIR 2011-5092. See Table 13 for pesticide benchmark values and p. 19 of the text for the derivation. Available for pyrethroid and fipronil compounds 

5. Freshwater Sediment Benchmarks for Currently Used Pesticides

Contaminant Types: Pesticides

Sampling Medium: Bed sediment 

Resource Protected: Aquatic Life

Sources: Development and application of freshwater sediment-toxicity benchmarks for currently used pesticides, Nowell, L.H., et al., 2016, Science of the Total Environment, v. 550, p. 835-850.

III. FISH AND SHELLFISH TISSUE

A. EDIBLE FISH AND SHELLFISH TISSUE

1. USEPA Tolerances

Contaminant Types: Pesticides

Sampling Medium: Edible fish and shellfish 

Resource Protected: Human health

Sources: Regulation of pesticide residues on Food (Information about EPA tolerances); Code of Federal Regulations, go to current year, Title 40, Chapter I, Part 180, Subpart C

2. FDA Action Levels

Contaminant Types: Pesticides

Sampling Medium: Edible fish and shellfish 

Resource Protected: Human health

Sources: Compliance Policy Guide, Sec. 575.100, Pesticide Residues in Food and Feed - Enforcement Criteria

3. USEPA Recommended Screening Values

Contaminant Types: Pesticides, PAHs, PCBs, dioxins & furans, metals

Sampling Medium: Edible fish and shellfish 

Resource Protected: Human health

Sources: EPA Guidance for Developing Fish Advisories (national and regional guidance); 

Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories:

• Vol. 1, 3rd ed., Fish Sampling and Analysis (November 2000) EPA 823-B-00-007. See especially Ch. 5, Table 5-3 (Dose-response variables and recommended screening values for target analytes - Recreational fishers) and Table 5-4 (Dose-response variables and recommended screening values for target analytes - Subsistence fishers); 
   
• Vol. 2, 3rd ed., Risk Assessment and Fish Consumption Limits (November 2000) EPA 823-B-00-008. See especially Ch. 4, risk-based consumption tables by contaminant.

4. USEPA database of U.S. State, Territory, and Tribal fish consumption advisories

Contaminant Types: Mercury, PCBs, chlordane, dioxins, DDT, other bioaccumulative contaminants

Sampling Medium: Edible fish and shellfish 

Resource Protected: Human health

Sources: National Listing of Fish Advisories Database (2011 data); Search for Advisories Where You Live

B. WHOLE FISH

1. Canadian Tissue Residue Guidelines for the Protection of Wildlife Consumers of Aquatic Biota

Contaminant Types: DDT, methylmercury, PCBs, dioxins & furans, toxaphene

Sampling Medium: Whole fish 

Resource Protected: Fish-eating wildlife

Sources: Canadian Environmental Quality Guidelines (includes introductory text, fact sheets for individual contaminants, and the 1999 protocol for derivation of Canadian tissue residue guidelines for the protection of wildlife that consume aquatic biota); Canadian Environmental Quality Guidelines, Summary Table (online searchable database and access to downloadable Excel file)

2. New York Fish Flesh Criteria for Piscivorous Wildlife

Contaminant Types: PCBs, organochlorine pesticides, other chlorinated organic compounds

Sampling Medium: Whole fish 

Resource Protected: Fish-eating wildlife

Sources: Niagara River Biota Contamination Project: Fish Flesh Criteria for Piscivorous Wildlife, Newell, A.J. et al., 1987; reprinted February 2000. New York State Department of Environmental Conservation Technical Report 87-3

3. Pesticide Whole-Fish Benchmark Ranges for Protection of Fish-Eating Wildlife, Compiled by the USGS National Water-Quality Assessment Program

Contaminant Types: Organochlorine pesticides

Sampling Medium: Whole fish 

Resource Protected: Fish-eating wildlife

Sources: Pesticides in the Nation’s Streams and Ground Water, 1992–2001, Gilliom et. al. (2007), U.S. Geological Survey Circular 1291. See Appendix 3, Table B (benchmarks list); Derivation (see page 109)

Last updated: March 1, 2019