The United States Food and Drug Administration has studied sodium benzoate extensively and found that it is safe when consumed in amounts found in normal diets. It would take approximately 90 times the amount of sodium benzoate found in a typical diet before any problems might occur.
Benzoates and Benzenes
Sodium benzoate is sometimes used as a preservative in soft drinks, along with ascorbic acid (vitamin C). With excessive heat exposure, the two additives may interact to form benzene, which is known to cause cancer. Low levels of benzene were detected in a variety of soft drinks in 2005, however all levels were far below five parts per billion, which was considered safe for humans.
Benzoid Acid. United States Food and Drug Administration. Accessed August 3, 2009. http://www.accessdata.fda.gov/scri pts/fcn/fcnDetailNavigation.cfm?rpt=scogsListing&id=36
Chemical Food Preservatives: Bonzoate and Sorbate. New York State Agricultural Experiment Station. Accessed August 3, 2009. http://www.nysaes.cornell.edu/nec fe/pubs/pdf/Venture/venture2_chemical.html