What microbiological contaminant is most resistant to chlorine disinfection?

What microbiological contaminant is most resistant to chlorine disinfection?

• A. Fecal coliform
• B. Giardia
• C. Viruses
• D. Cryptosporidium

Answer: (D)

Chlorine disinfection is most challenged by organisms with tough, protective structures. Cryptosporidium produces oocysts with a durable outer shell that limits chlorine’s ability to penetrate and inactivate the organism, so they survive standard chlorination doses. This makes Cryptosporidium more resistant than other common contaminants like Giardia, fecal bacteria, or most viruses, which are typically inactivated more readily by chlorine under ordinary conditions. Because of this high resistance, water treatment relies on additional barriers—such as filtration and possibly UV or ozone—to effectively reduce Cryptosporidium risk.

Chlorine disinfection is most challenged by organisms with tough, protective structures. Cryptosporidium produces oocysts with a durable outer shell that limits chlorine’s ability to penetrate and inactivate the organism, so they survive standard chlorination doses. This makes Cryptosporidium more resistant than other common contaminants like Giardia, fecal bacteria, or most viruses, which are typically inactivated more readily by chlorine under ordinary conditions. Because of this high resistance, water treatment relies on additional barriers—such as filtration and possibly UV or ozone—to effectively reduce Cryptosporidium risk.