To blur the environment or your mental ray material, you can add the mia_envblur to your shading network as follows:

1. Apply the mia_material or any other reflective mental ray shader to the object that you wish to blur. The mia_envblur shader should be used in conjunction with the reflective mental ray shaders.
2. Add an HDR image or the mia_physicalsun/ mia_physicalsky shader to your environment.
3. To add the mia_envblur to your scene, in the mia_materialSG node, map the mia_envblur shader to the Environment Shader attribute under the Custom Shaders section under mental ray.
4. Tweak the settings in the mia_envblur Attribute Editor to obtain the desired look.