Thimerosal is a preservative that is added to vaccines (has been since the 1930s) that is almost half (49.6% by weight) mercury. Preservatives are added to vaccines to prevent bacteria and fungi from growing. These vaccines include antivenins, skin test antigens, ophthalmic and nasal products. Thimerosal preserved vaccines have been given to children as well as adults.

The FDA department CBER (Center for Biologics Evaluation and Research) found that in more than 30 vaccines Americans are given the EPA established limit for mercury intake in the first 6 months of live was exceeded by up to 30-50 times. Mercury causes such concern because it is the second most toxic element on earth and has been known to cause learning disabilities, autism, Alzheimer