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

Abstract

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.

Figure 1.

A) Number of detected chemicals within each analytical method at each watershed reported in the chemical occurrence dataset. The value within each column represents the total number of samples from a watershed. B) Number of detected chemicals with available data in each ToxCast assay platform. See SI Figure S2 for more detailed information on chemical coverage across assay platforms. ACEA = ACEA Biosciences; APR = Apredica; ATG = Attagene; BSK = BioSeek; CT = CeeTox; CLD = CellzDirect; NCCT = National Center for Computational Toxicology; NZF = NHEERL zebrafish; NVS = NovaScreen; OT = Odyssey Thera; TZF = Tanguay Lab zebrafish; Tox21 = Tox21 Initiative

Figure 2.

A) Cumulative EAR_mixture (i.e., sum of EAR_mixture values across all assays) values within each watershed. The value within each row represents the total number of samples from a watershed. For graphical purposes, sites with EAR_mixture equal to 0 (three samples; all from St. Louis River) were removed. B) Cumulative EAR_mixture values for each site within the St. Louis River watershed. The value within each row represents the total number of samples from a site. For graphical purposes, sites with EAR_mixture equal to 0 or with only one sample are not shown. Site information is available from the original data source.

Figure 3.

A) Mean EAR_mixture values within each assay category as defined by the ‘intended_target_family’ annotation field (see SI Table S2). The number in each row is the number of assays in a category. B) Mean EAR_mixture values within the ‘nuclear receptor’ assay category as defined by the ‘intended_target_gene_symbol’ annotation field (see SI Table S2). The number in each row is the number of assays in a category. C) Mean EAR_mixture values for individual assays under the ‘ESR’ category.

Figure 4.

Comparison of exposure-activity ratios (EARs) generated from 16 estrogen receptor (ER) related assays in the ToxCast database and in 17α-ethinylestradiol equivalents (EEQs; ng/L, in red) derived from in vitro screening with T47D-Kbluc cell line (mean±SEM; n=3). Samples are grouped by collection date and ordered (left to right) from upstream to downstream along the wastewater gradient. For graphical purposes, a site with no EAR calculated was assigned a value of 0.001, and EEQs below detection threshold were assigned a value of 0. Site information is available from the original data source.