Filter for filtering mutagens from an engine oil

A filter for filtering mutagens from an engine oil, which filter comprises a body, an inlet for oil passing into the body, an outlet for oil passing out of the body, and a filter material in the body for filtering the oil as the oil passes through the body, and the filter material being such that it comprises activated carbon for removing the mutagens and a retainer material for retaining the activated carbon in place, the activated carbon is activated particulate carbon, the activated carbon is separate from and not integrally formed with the retainer material, the activated carbon has substantially its entire surface available for contact with the oil, the retainer material is an absorbent material, and the retainer material is in the form of a plurality of radially extending adjacent layers or pieces with the activated carbon between the layers or pieces wherein the activated carbon extends radially to a depth defined by the layers or pieces.