This course is designed to provide an overview of the principles of ecotoxicology and the process by which chemicals cause adverse effects to living organisms and their habitats. Special emphasis is placed on ecotoxicity assessments of organic compounds that directly apply to GHS and REACH/CLP regulations. The course will provide essential principles of aquatic and environmental chemistry, fate and transport of organic chemicals in the aquatic environment. The use of specific QSAR models for estimating ecotox data will also be presented. This is then followed by presentation of the criteria for aquatic hazard assessment, classification and communication. The skills developed in the course will allow participants to better understand and/or participate in the interpretation of ecotoxicological data for hazard determination, assessments and communication under the GHS and REACH/CLP regulations. Course format is lecture and group discussion and individual exercises.