Many of the chemical substances are toxic. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Phenols chemically interact with many other substances. Helminths excrete into the intestine toxic substances after they feed. Aflatoxins are among the most carcinogenic substances known. The lake is contaminated with various toxic substances. Discharge of toxic substances has been sharply reduced. There are many ways to make relative comparisons between toxic substances. Real drugs were used in scenes showing the use of marijuana and other substances. Organisms use glucose as a precursor for the synthesis of several important substances. Benzoic acid is an important precursor for the industrial synthesis of many other organic substances. Ancient Egyptians were among the first to use minerals such as sulfur as cosmetic substances. IC methodology also established in analysis of impurities in drug substances and products. Psychedelics are a subcategory of psychotropics, which includes all psychoactive substances. The raw materials for many of these synthetic substances come from crude oil.