Why is Sodium Thiosulfate added to Fecal Coliform samples?

Sodium thiosulfate is used in the analysis of fecal coliform samples specifically to neutralize residual chlorine present in the samples. Chlorine is commonly used as a disinfectant in wastewater treatment processes, but it can be toxic to microorganisms, including fecal coliform bacteria. If chlorine remains in the sample when it is being tested, it can kill or inhibit the growth of these bacteria, leading to inaccurate test results.

By adding sodium thiosulfate, chlorine is effectively neutralized, allowing for a more accurate assessment of the fecal coliform population in the sample. This ensures that the test results truly reflect the microbial content without the interference of residual chemicals that could skew the data. Other options do not pertain to the role of sodium thiosulfate in this context, making the use of this compound essential for reliable fecal coliform testing results.