Compounds in the database
Data for 435 unregulated compounds analyzed by the USGS's National Water-Quality Assessment (NAWQA) Program are in the Health-Based Screening Level (HBSL) database:
- 157 Pesticides
- 81 Pesticide degradation products
- 66 Volatile organic compounds (VOCs)
- 60 Semi-volatile organic compounds (SVOCs) such as phenols, amines, and polynuclear aromatic hydrocarbons (PAHs)
- 31 Emerging contaminants such as manufacturing additives, personal care & domestic use products, and plant- or animal-derived biochemicals
- 11 Major ions
- 15 Trace elements
- 7 Nutrients
- 7 Polychlorinated biphenyl (PCB) compounds
Chemical classes in the HBSL database were assigned on a chemical-by-chemical basis. Chemical classes were designated using USGS analytical schedules, USGS reports, other government agency websites and databases, and the primary literature. When available, HBSL values and information about how each HBSL value was calculated can be obtained from the HBSL database.
USEPA toxicity information in the database
The HBSL database contains U.S. Environmental Protection Agency (USEPA) cancer classifications and toxicity values (oral Reference Dose (RfD) and oral Slope Factor (SF) values). Data are collected from three USEPA offices and four data sources. See "What hierarchy of toxicity information is used to calculate HBSLs?" and "How are HBSLs calculated?" for more information about USEPA cancer classifications and toxicity values.
Database maintenance and updates
The Health-Based Screening Level (HBSL) database is maintained by the USGS. The four U.S. Environmental Protection Agency (USEPA) data sources are reviewed periodically for any updates to cancer classifications or toxicity values. Any updated information is entered into the database and evaluated to determine whether the updates affect HBSL calculations. All new database entries or revisions are subjected to a quality-control process.
Database quality-control procedures
of data quality-control procedures were performed for data in the
Health-Based Screening Level (HBSL) database: (1) verification of
toxicity information collected from U.S. Environmental Protection
Agency (USEPA) data sources and (2) verification of HBSL values and the
methodology and information used to calculate them. These two
procedures are described below.
(1) Toxicity information collected from USEPA data sources was
entered into the HBSL database. After data entry, each record was
manually re-checked against its original USEPA data source. Any
incorrect values were corrected in the database with the correction
date noted. The process was then repeated to ensure that the
corrections made were accurate (see figure). This quality-control
procedure is followed each time updates are made to the database
in order to minimize
data entry errors.
(2) Using toxicity information collected from USEPA data sources,
HBSL values were independently calculated by two individuals from the USGS.
The independently calculated HBSL values were
compared with each other and discrepancies were iterated and resolved
before the values were entered into the database. The quality control process includes consulting with USEPA OW in a variety of cases when the computation of an HBSL is not straightforward (see Exceptions to how HBSLs are calculated). This procedure is followed
each time updates to toxicity information result in an update to an