An “EAR” on Environmental Surveillance and Monitoring: A Case Study on the Use of Exposure–Activity Ratios (EARs) to Prioritize Sites, Chemicals, and Bioactivities of Concern in Great Lakes Waters

Current
environmental monitoring approaches focus primarily on
chemical occurrence. However, based on concentration alone, it can
be difficult to identify which compounds may be of toxicological concern
and should be prioritized for further monitoring, in-depth testing,
or management. This can be problematic because toxicological characterization
is lacking for many emerging contaminants. New sources of high-throughput
screening (HTS) data, such as the ToxCast database, which contains
information for over 9000 compounds screened through up to 1100 bioassays,
are now available. Integrated analysis of chemical occurrence data
with HTS data offers new opportunities to prioritize chemicals, sites,
or biological effects for further investigation based on concentrations
detected in the environment linked to relative potencies in pathway-based
bioassays. As a case study, chemical occurrence data from a 2012 study
in the Great Lakes Basin along with the ToxCast effects database were
used to calculate exposure–activity ratios (EARs) as a prioritization
tool. Technical considerations of data processing and use of the ToxCast
database are presented and discussed. EAR prioritization identified
multiple sites, biological pathways, and chemicals that warrant further
investigation. Prioritized bioactivities from the EAR analysis were
linked to discrete adverse outcome pathways to identify potential
adverse outcomes and biomarkers for use in subsequent monitoring efforts.