In the investigation of interaction between organic pollutants and active chlorine in water, hydroxycinnamic acids were found to afford various chlorinated styrene and chlorinated quinone derivatives. Phenolic amino acids tyrosine gave chlorinated benzyl acetonitrile derivatives. Furthermore, it was discovered that, in general, free amino acids afford nitrile derivatives even in a very high dilution. To evaluate the possible effects of these products to human and ecological systems, antimicrobial, molluscicidal activities and acute toxicities to mice were investigated. In each case, mild activity was observed with most of the compounds. This means that chlorine used in water and sewage treatment is partly fixed by binding with these organic compounds to form possibly toxic compounds.