A leak from a poly bottle containing radiological liquid is considered:

A leak from a poly bottle containing radiological liquid is classified as contamination because it refers to the unwelcome presence of radioactive material in an area or on surfaces due to a release of radiologically active substances. When a radiological liquid leaks, it can spread particles or droplets that can adhere to surfaces, equipment, or even personnel, creating a contamination scenario. This is critical in radiological safety as contamination can result in exposure to radiation and complicates the decontamination efforts.

In this context, contamination involves discrete radiological substances being present where they should not be, leading to potential health hazards and breaches of safety protocols. Proper containment and handling procedures are essential to prevent such leaks and minimize contamination risks.

The other options refer to different concepts. Radiation pertains to energy emitted in the form of particles or electromagnetic waves, which is not the focus here. Fixed contamination implies that radioactive material is securely attached to a surface and is not easily removed, distinct from a liquid leak. Background refers to the natural ambient radiation levels universally present, which doesn't relate to the incident of a leak. Understanding these distinctions is key for managing radiological safety in the workplace.