Health-Based Screening Levels for Evaluating Water-Quality Data

Health-Based Screening Levels (HBSLs) are non-enforceable water-quality benchmarks that can be used to (1) supplement U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) and Human Health Benchmarks for Pesticides (HHBPs), (2) determine whether contaminants found in surface-water or groundwater sources of drinking water may indicate a potential human-health concern, and (3) help prioritize monitoring efforts. HBSLs were developed by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project for contaminants without USEPA MCLs or HHBPs.

HBSLs were updated in May 2018 in order to:

  • Update toxicity information and benchmarks, when possible, for the 808 contaminants included in the online searchable HBSL database, including 31 new contaminants added since the last HBSL update in 2014.
  • Update all HBSLs to be consistent with new USEPA methods and exposure assumptions.
  • Replace HBSLs for 4 contaminants that have new USEPA Chronic Noncancer or Carcinogenic HHBPs.

The searchable table below contains 808 contaminants, of which 174 have HBSLs, 79 have MCLs, 140 have HHBPs, and 415 have no available benchmark. MCLs and HHBPs are provided for user convenience; for more information about them, and to obtain current values, please visit the USEPA websites. Learn more about HBSLs and guidance on their use.

Glossary, Metadata, Documentation, and Revision History

  • Download Glossary and Metadata: Excel (.xlsx) file with an explanation of all acronyms used in the table and related metadata.
  • Download Documentation for HBSLs: Excel (.xlsx) file with the detailed supporting toxicity information used to calculate HBSLs and related metadata.
  • Download History of HBSL Revisions: Excel (.xlsx) file with a table of those compounds with HBSLs that have changed since March 21, 2006, when HBSLs first became available online. The table includes the most recent date that an HBSL value was revised, the type of revision, and the reason for the revision.

HBSL Values Current as of May 31, 2018

click a column heading to sort by that column USEPA Benchmarks USGS Benchmarks
Chemical Name CAS Registry Number ® a USGS Parameter Code(s) Chemical Class MCL (µg/L) b more info Chronic Noncancer HHBP (µg/L) c,d more info Carcinogenic HHBP (µg/L) c,d more info Noncancer HBSL (µg/L) d,e more info Cancer HBSL (10-6 to 10-4) (µg/L) d,e more info Benchmark Remarks more info

USEPA Maximum Contaminant Levels (MCLs) are legally enforceable drinking-water standards. Users should verify MCL values here or here.

USEPA Chronic Noncancer Human Health Benchmarks for Pesticides (HHBPs) are non-enforceable advisory values protective of chronic noncancer effects. HHBPs listed on this website were current as of August 2013, but were updated in January 2017; this website will be updated to reflect those changes. Users should obtain current HHBP values here.

USEPA Carcinogenic Human Health Benchmarks for Pesticides (HHBPs) are non-enforceable advisory values protective of cancer effects. The HHBP range represents a one-in-one million (10-6) to one-in-ten thousand (10-4) cancer risk range. HHBPs listed on this website were current as of August 2013, but were updated in January 2017; this website will be updated to reflect those changes. Users should obtain current HHBP values here.

USGS Noncancer Health-Based Screening Levels (HBSLs) are non-enforceable benchmarks protective of chronic noncancer effects. HBSLs are current as of June 30, 2014.

USGS Cancer Health-Based Screening Levels (HBSLs) are non-enforceable benchmarks protective of cancer effects. The HBSL range represents a one-in-one million (10-6) to one-in-ten thousand (10-4) cancer risk range. HBSLs are current as of June 30, 2014.

Benchmark Remarks provide additional information about some MCLs, HHBPs, and HBSLs.

a This study contains Chemical Abstract Service (CAS) Registry Numbers ®, which is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CAS Registry Numbers through CAS Client Services ℠.
b USEPA Maximum Contaminant Levels (MCLs) were current as of April 2018. Users should verify USEPA MCL values here or here.
c USEPA Human Health Benchmarks for Pesticides (HHBPs) were current as of January 17, 2017. Users should verify HHBP values here.
d See HBSL Methods & Guidance for guidance on the use of multiple benchmarks for a single compound.
e See HBSL Methods & Guidance for equations used to calculate USGS noncancer and cancer Health-Based Screening Level (HBSL) values.