Step 1: Review each statement.
- Statement 1 is true, as hydrogen peroxide is indeed a chemical threat agent when in high concentrations.
- Statement 2 is false, as hydrogen peroxide is actually used in disinfection, including water treatment.
- Statement 3 is correct, as hydrogen peroxide is often used to assess oxidative stress in biological systems.
- Statement 4 is correct as well; hydrogen peroxide plays a role in inflammatory processes.
Final Answer:
\[
\boxed{2}
\]