"This book uses Caenorhabditis elegans as model animal to introduce the toxicity induction of toxicants at environmentally relevant concentrations under different conditions. It also discusses the systematic introduction of different molecular signaling pathways, as well as G protein coupled receptors and ion channels, in regulating the toxicity of toxicants at environmentally relevant concentrations. The intestinal, neuronal, and germline molecular networks required for the regulation of toxicity of toxicants at environmentally relevant concentrations is further introduced and discussed. This book aims at providing a systematic understanding of the knowledge system on toxicology at environmentally relevant concentrations in Caenorhabditis elegans. "