Keynote papers Cell bioassays for detection of aryl hydrocarbon (AhR) and estrogen receptor (ER) mediated activity in environmental samples J.P. Giesy a, * , K. Hilscherova a , P.D. Jones a , K. Kannan a , M. Machala b a Department of Zoology, National Food Safety and Toxicology Center, Institute for Environmental Toxicology, Michigan State University, East Lansing, MI 48824, USA b Veterinary Research Institute, Hudcova 70, 621 32 Brno, Czech Republic Abstract In vitro cell bioassays are useful techniques for the determination of receptor-mediated activities in environmental samples containing complex mixtures of contaminants. The cell bioassays determine contamination by pollutants that act through specific modes of action. This article presents strategies for the evaluation of aryl hydrocarbon receptor (hereafter referred as dioxin-like) or estrogen receptor mediated activities of potential endocrine disrupting compounds in complex environmental mixtures. Extracts from various types of environmental or food matrices can be tested by this technique to evaluate their 2,3,7,8-tetrachlorodibenzo- p-dioxin equivalents or estrogenic equivalents and to identify contaminated samples that need further investigation using resource- intensive instrumental analyses. Fractionation of sample extracts exhibiting significant activities, and subsequent reanalysis with the bioassays can identify important classes of contaminants that are responsible for the observed activity. Effect-directed chemical analysis is performed only for the active fractions to determine the responsible compounds. Potency-balance estimates of all major compounds contributing to the observed effects can be calculated to determine if all of the activity has been identified, and to assess the potential for interactions such as synergism or antagonism among contaminants present in the complex mixtures. The bioassay approach is an efficient (fast and cost effective) screening system to identify the samples of interest and to provide basic information for further analysis and risk evaluation. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: In vitro cell bioassays; Dioxin-like activity; Estrogen receptor-mediated activity; Complex mixtures; Fractionation; Toxic equivalents; Endocrine disruptors 1. Introduction There is increasing concern over the potential adverse effects of xenobiotics present in the environment and foodstuffs on human and wildlife populations. Two groups of toxicants of current interest are dioxin-like and (anti) estrogenic chemicals. Many of these ubiqui- tous compounds are hydrophobic, lipophilic and resis- tant to biological and chemical degradation. These properties impart persistency and propensity to bioac- cumulate and biomagnify to concentrations that can cause deleterious effects on cells and tissues. In the en- vironment, chemicals occur as complex mixtures in- cluding different congeners and isomers of both natural and anthropogenic origin. The concentrations and toxic potencies of compounds present in complex mixtures can range over several orders of magnitude. In addition, interactions among different classes of compounds (e.g., estrogenic vs. anti-estrogenic) can modulate the toxic potential. This complicates hazard evaluation and risk assessment of complex mixtures of xenobiotics. Fur- thermore, toxic effects of some contaminants, even those, which are analytically determined, are not well characterized. There are many potentially significant classes of contaminants that are not studied in detail, primarily due to a lack of suitable instrumental tech- niques or analytical standards. In other words, chemical analysis has been used to identify and quantify only those chemicals for which analytical techniques and standards are available. Instrumental analyses do not account for interactions among the chemicals in com- plex mixtures and provide little information on their biological effects. Chemical analyses can also be costly * Corresponding author. E-mail address: jgiesy@aol.com (J.P. Giesy). 0025-326X/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0025-326X(02)00097-8 www.elsevier.com/locate/marpolbul Marine Pollution Bulletin 45 (2002) 3–16