Health-Based Screening Levels (HBSL)

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.


row(s) 1 - 10 of 808Next
HBSL values current as of May 31, 2018USEPA BenchmarksUSGS Benchmarks
row(s) 1 - 10 of 808Next

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 ServicesSM.
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.