With this proceedings of the fourth symposium on complex mixtures, we continue to revise and extend our knowledge of genetic methods for the evaluation of chemical mixtures in the environment. The early chapters of this volume are devoted to new bioassay techniques that are directly applicable to the monitoring of environments contaminated with genotoxic chemicals. Microbiological methods have been further refined to meet the special needs of atmospheric monitoring so that very small samples may now be efficiently tested. New in situ methods utilizing green plants actually avoid many of the usual difficulties of sample collection and preparation and offer special advantages in monitoring wastewater, sludges, and hazardous wastes. Insects also are being employed very effectively in the evaluation of gaseous air pollutants in controlled laboratory investigations. Increased emphasis has been placed on a comprehensive assessment of the potential of complex mixtures t9 cause various kinds of genetic damage. New assays for chromosome structural and numerical aberrations in mammalian cells in vitro have been developed and are being applied in laboratory studies. Efforts to link tests for gene mutation and cell transformation in vitro with assays for tumorigenesis in vivo are contributing to the validation of the short-term testing approach. Studies comparing in vitro and in vivo data on a coal conversion by-product, on polycyclic aromatic hydrocarbons, and on mineral fibers are reported in separate papers. Later chapters are devoted to investigations on the fractionation and biological evaluation of specific chemical components within complex mixtures.

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Keynote Address.- Keynote Address.- Session 1: New Developments and Techniques.- Use of the Microscreen Assay for Airborne Particulate Organic Matter.- Development of an InSitu Test System for Detection of Mutagens in the Workplace.- Perturbations of Enzymic Initiation of Excision Repair Due to Guanine Modification in DNA.- Plant Genetic Assays to Evaluate Complex Environmental Mixtures.- Studies with Gaseous Mutagens in DrosophilaMelanogaster.- Anaphase Aberrations: An InVitro Test for Assessing the Genotoxicity of Individual Chemicals and Complex Mixtures.- Anaphase Aberrations: An InVivo Measure of Genotoxicity.- Measurement of Chemically Induced Mitotic Nondisjunction Using a Monochromosomal Human/Mouse Hybrid Cell Line.- Toxicologic Responses to a Complex Coal Conversion By-Product: Mammalian Cell Mutagenicity and Dermal Carcinogenicity.- Increased Virus Transformation by Formaldehyde of Hamster Embryo Cells Pretreated with Benzo(a)pyrene.- Enhancement of Anchorage-Independent Survival of Retrovirus-Infected Fischer Rat Embryo Cells for Determining the Carcinogenic Potential of Chemical and Physical Agents.- Correlation Between InVivo Tumorigenesis and InVitro Cytotoxicity in CHO and V79 Cells After Exposure to Mineral Fibers.- Quality Assurance and Good Laboratory Practice Regulations for Short-Term Bioassays of Complex Mixtures.- Generation and Characterization of Complex Gas and Particle Mixtures for Inhalation Toxicologic Studies.- Session 2: Integrated Assessment.- Nitro Compounds in Environmental Mixtures and Foods.- The Effect of Atmospheric Transformation Upon the Bacterial Mutagenicity of Airborne Organics: The EPA Experience.- Mutagenicity Studies of New Jersey Ambient Air Particulate Extracts.- Interurban Variations in the Mutagenic Activity of the Ambient Aerosol and Their Relations to Fuel Use Patterns.- Mutagenicity Analyses of Industrial Effluents: Results and Considerations for Integration into Water Pollution Control Programs.- Isolation of Mutagenic Compounds from Sludges and Wastewaters.- Session 3: Risk Assessment.- Application of Short-Term Tests in Monitoring Occupational Exposure to Complex Mixtures.- An Integrated Approach to Human Monitoring.- Human Cytogenetic Monitoring: Occupational Exposure to Ethylene Oxide.- Direct Mutagen Risk Assessment: The Development of Methods to Measure Immunologic and Genetic Responses to Mutagens.- Risk Assessment of Complex Mixtures.- Comparative Potency of Complex Mixtures: Use of Short-Term Genetic Bioassays in Cancer Risk Assessment.