Who has the PRIMARY authority to decide if additional risk treatments are required to mitigate...

The risk owner is the person who has the authority and accountability to make decisions about the risk, including whether to accept, avoid, transfer, or mitigate it. The risk owner is also responsible for implementing and monitoring the risk treatment plan and reporting on the risk status. The risk owner is usually the business process owner or the information owner of the asset affected by the risk. (From CISM Review Manual 15th Edition)