Which compound is regulated by the MRDL at 4.0 mg/l due to public health concerns?

The compound regulated by the Maximum Residual Disinfectant Level (MRDL) at 4.0 mg/l due to public health concerns is chlorine. Chlorine is widely used in water treatment as a disinfectant to kill pathogens and ensure safe drinking water. However, excessive levels of chlorine can pose health risks, including potential formation of harmful disinfection byproducts and respiratory problems. The MRDL is set to maintain chlorine levels in drinking water at a point that is effective for disinfection while minimizing any adverse health effects on consumers. This regulation reflects the need to balance effective water treatment with the safety of the public, ensuring that water remains free of harmful microorganisms without creating undue health risks from the disinfectant itself.