About HBSLs

What are the benefits of using HBSLs?

  • The use of Health-Based Screening Levels (HBSLs) more than doubles the number of human-health benchmarks available for unregulated compounds measured by the National Water-Quality Assessment (NAWQA) Program. Of the 435 unregulated compounds in the HBSL database, 95 had human-health benchmarks before HBSL calculations and 221 have benchmarks after HBSL calculations. Benchmarks are not available for about half of the unregulated compounds in the database because of a lack of toxicity values.
  • The most recent U.S. Environmental Protection Agency (USEPA) toxicity information is used to calculate HBSLs, therefore, HBSLs provide a mechanism for the timely incorporation of updated toxicity information in the interpretation of water-quality data.
  • HBSLs can be used as planning tools to help prioritize contaminants that may merit further study or monitoring and to provide an early indication of contaminant concentrations of potential human-health concern in water resources.
  • Because HBSLs supplement existing USEPA drinking-water standards and guidelines, they provide a basis for a more comprehensive evaluation of contaminant-occurrence data in a human-health context than by using USEPA benchmarks alone.