Chlorine dioxide has gained popularity because it:

• A. reacts with ammonia faster, Giardia
• B. produces fewer disinfection byproducts, all pathogens
• C. reacts with ammonia faster, all pathogens
• D. produces fewer disinfection byproducts, Cryptosporidium

Answer: (D)

Chlorine dioxide is often chosen because it can inactivate many microbes while forming fewer disinfection byproducts than chlorine. Its different chemistry oxidizes microbial components without producing as many halogenated byproducts like trihalomethanes and haloacetic acids, which helps meet DBP limits while still controlling pathogens. It is also more effective than chlorine against Cryptosporidium, a protozoan that is notoriously resistant to chlorination, and it handles Giardia reasonably well. The other statements don’t fit: it doesn’t react with ammonia faster for disinfection, and claiming it works against all pathogens is not accurate since no single disinfectant covers every microbe perfectly.