Mold grows in areas with high temperature, high relative humidity, and low air circulation. Isolate moldy record materials in a cool, dry location, with plenty of air circulation so they will not contaminate nearby items; do not return the records to their original location until the conditions causing the mold growth are addressed.
Once record materials are removed to a less hospitable environment, the mold will become loose and powdery as the substrate dries and the mold turns dormant. It may then be gently brushed off the record materials. Because the mold is merely dormant, if it remains on the record materials or is distributed throughout the space and onto other objects, it will grow whenever environmental conditions are favorable again. Mold should, therefore, be removed either outdoors or into a vacuum cleaner equipped with a HEPA filter -- regular vacuum cleaners will merely exhaust and recirculate mold back into the room.
Ideally, the faster record materials are dried the better. However, some record materials may distort physically if dried too quickly. Contact a preservation professional for advice on how to handle moldy record materials of high value. For a referral see: American Institute for Conservation's (AIC) Guidelines for Selecting a Conservator
Many people are sensitive to mold and some mold species are toxic. Moldy items should, therefore, be handled with extreme care. Do not proceed with any treatment once any negative health effects are observed, no matter how minor they appear.