Which of the following is typically associated with trihalomethanes?

Trihalomethanes (THMs) are chemical compounds that can form when chlorine, used as a disinfectant in water treatment, reacts with natural organic matter present in the water. This typically happens when water contains organic substances, such as decomposed plant material, which when chlorinated, creates by-products like trihalomethanes.

The reason option B is the correct choice is that it highlights the presence of organics in the water that have undergone chlorination. When chlorine is added to water that contains these organic compounds, the reaction can lead to the formation of THMs, making it a direct association between the chlorination process and the organic matter present.

In contrast, high chlorine levels alone, stagnant water sources, and UV light treatment do not specifically relate to the production of THMs. High chlorine levels (as stated in option A) could suggest adequate disinfection, but without the presence of organic matter, THMs are unlikely to form. Stagnant water sources (option C) might contain some organics but are not necessary for THM formation; the critical factor is the chlorination of water already containing these organic materials. Finally, water treated with UV light (option D) is a method used to disinfect water without introducing chlorine