TABLE 2 Calculated Exposure Limits for Mercury, Using Various Agency Guidelines for Exposure to Methylmercury, in Infants ≤ 6 Months of Age by Percentile Body Weight


Percentile Body Weight






65 μg

89 μg

106 μg


194 μg

266 μg

319 μg


259 μg

354 μg

425 μg


305 μg

417 μg

501 μg

• Calculate Exposure Limit = dose/kg body weight/week × average weight x 26 weeks × 0.932 (mercury molecular weight/methylmercury molecular weight); e.g., EPA calculated exposure limit = 0.7 μg/kg body weight/week × 26 weeks × (2.36kg + 5.25 kg)/2 × 0.932 = 65 μg.

• Assumes average of 5th, 50th, and 95th percentile weight for females at birth (2.36 kg, 3.23 kg, 3.81 kg) and 6 months (5.25 kg, 7.21 kg, 8.73 kg) = 3.81 kg, 5.22 kg, 6.27 kg. Females were selected because their smaller body weight makes them more susceptible than males.

• Recommended limits on methylmercury exposure: EPA: 0.1 μg/kg body weight/day; ATSDR: 0.3 μg/kg body weight/day; FDA: 0.4 μg/kg body weight/day; WHO: 3.3 μg/kg body weight/week. For calculations, daily limits multiplied by 7 to obtain weekly limits.

NOTE: Data were bolded by the IOM, not by the original authors of the table. EPA: Environmental Protection Agency; ATSDR: Agency for Toxic Substances and Disease Registry; FDA: Food and Drug Administration; WHO: World Health Organization.

SOURCE: Ball et al., 2001. Reprinted with permission from Pediatrics 107:1150, Table 1, Copyright 2001.

as a preservative by March 2000. With the FDA approval of a second thimerosal-free version of DTaP vaccine in March 2001, all formulations of vaccines on the U.S. recommended childhood immunization schedule for children 6 years of age or younger became available free of thimerosal used as a preservative. Based on information from vaccine manufacturers provided to the FDA, the lots of vaccine manufactured before this time that contained thimerosal as a preservative and had been released to the market had expiration dates in 2002 (FDA, 2004e). Based on these changes, the maximum amount of mercury from vaccines on the recommended childhood immunization schedule that an infant (less than 6 months of age) can now be exposed to is <3 μg,6 down from 187.5 μg in 1999 (FDA, 2001; 2004e). (See Appendix C for thimerosal content in currently licensed vaccines.)


3 μg is the maximum amount that could have been received by an infant in the first 6 months of life if they received trace-containing formulations (e.g., Engerix B hepatitis B vaccine, Tripedia DTaP vaccine) as opposed to those that contain no thimerosal (e.g., Recombivax HB hepatitis B vaccine pediatric formulation, Infanrix DTaP, Daptacel DTaP) (FDA, 2004d).

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