Texas Commission on Environmental Quality (TCEQ). Class C Water License Exam

Which microorganism in water is known for its resistance to chlorine?

1. E. coli

2. Giardia

3. Cryptosporidium

4. Salmonella

The correct answer is: Cryptosporidium

Cryptosporidium is renowned for its remarkable resistance to chlorine, which makes it a significant concern in water treatment processes. This microorganism, a protozoan parasite, forms oocysts that are highly resilient, surviving in chlorinated environments where many other pathogens might be effectively neutralized. Traditional chlorine disinfection methods, though effective for a wide range of bacteria and viruses, often fall short against Cryptosporidium. As a result, alternative methods such as filtration or UV disinfection may be required to effectively remove or inactivate this organism in drinking water supplies. In contrast, other microorganisms listed typically do not exhibit the same level of chlorine resistance. For example, E. coli and Salmonella, both bacteria, can be efficiently controlled and neutralized through adequate chlorination. Giardia, while more resistant than some other pathogens, does not possess the same level of chlorine tolerance that Cryptosporidium does, making it less of a concern in this specific context. Understanding the unique characteristics of these microorganisms is essential for effective water treatment and ensuring public health safety.