Prometryn (belongs to the chemical class of sulfur-substituted triazine or thiomethyl herbicides or thio-S(symmetrical)-triazines.
Prometryn is commercially available from 1964 (in the United States first), 6 years after the first commercial use of first chloro-S-triazines (atrazin, simazin), 8 years after the first experimental use of atrazin, and 12 years after the discovery of herbicidal properties of S-triazines.
It is synthesized by successive N-alkylations of cyanuric acid with the addition of thiomethyl group by mercaptan.
Triazines, and concordantly prometryn, were the most applied herbicides throughout the world in the second half of the twentieth century for their presumably low toxicity and relatively low environmental persistency. Prometryn was among 350 most used food pesticides in United States (Environmental Protection Agency (EPA) List A). However, significant evidence was gathered that S-triazines are groundwater contaminants with diverse toxic properties (genotoxic, endocrine disrupting, and immunotoxic). This resulted in the restricted use of atrazine and chloro-S-triazines and finally led to their complete ban in many countries. It was believed that methylthio-S-triazines (prometryn) were less toxic but some countries also banned prometryn together with other triazine herbicides . In 2006, there were at least 11 big manufacturers registered in China, 7 in the USA, 2 in Taiwan and India, and at least 1 big manufacturer in Switzerland, Israel, Italy, and Canada. Even though banned in European countries, large areas of Asia, Africa, Australia and Pacific region, Canada, China, India, and United States are still treated with this herbicide. Large quantities are still being produced; for example, in 2010 one single manufacturer in China produced 20 000 tons of prometryn.