Which of the following is not a property of biological agents used in an attack?

The property that distinguishes biological agents from other options is their immediate detectability. Biological agents typically do not produce immediate symptoms or detectable effects, making it challenging to identify their presence quickly after an attack. Unlike some chemical agents that can be rapidly identified through changes in the environment or immediate physiological reactions, biological agents often require specialized testing and may take time to show effects.

On the other hand, biological agents tend to be low-cost, have high availability due to their natural occurrence, and can often be produced relatively easily. This combination makes them particularly concerning in the context of terrorism and asymmetric warfare. Thus, the property of immediate detectability does not align with the characteristics associated with biological agents.