Contamination of water sources with sewage is commonly assessed by detecting which of the following biological indicators?

Consumption of drinking water contaminated with high levels of which one of the following substances is most commonly associated with the occurrence of methemoglobinemia (Blue Baby Syndrome) in infants?

With reference to sources and characteristics of radioactive pollution, consider the following statements: I. Certain radioactive substances may remain hazardous for very long durations, depending on their half-life. II. Radioactive particulate matter released into the atmosphere can be transported to higher altitudes through atmospheric circulation. III. Security screening devices using X-rays at airports are classified as major contributors to environmental radioactive contamination. Which of the statements given above is/are incorrect?