In order to conduct any form of comparison of the FDA’s assumed mercury vapor dose(1 to 5 μgs per 7 to 10 fillings) to the EPA RfC or ATSDR MRL (0.3 μg/m3 and 0.2 μg/m3,respectively) it is necessary to convert both the exposure estimate and the reference exposure levelto the same units. To do this, both must be converted to absorbed, weight-standardized doses inunits of μgs/kg body weight/day.
If we assume, arguendo, that ten amalgam fillings deliver a daily dose of mercury of5 μgs/day as an absorbed dose (per the FDA Final Rule), then one filling delivers an absorbeddose of 0.5 μgs/day. When standardized to body weight, as is routine for toxicological referenceexposure levels and exposure assessments, this daily dose represents differing doses for differentage groups with differing average body weights. Using data on body weights of different agegroups provided by the EPA (2008), the weight-standardized doses associated with that 0.5 μg/daydose are:
|
Age group |
Body Weight |
|
Number of fillings |
Number of fillings |
|
3 – 6 |
18.6 kg |
0.027 μg/kg bw/day |
2 | 2 |
|
6 – 11 |
31.8 kg |
0.016 μg/kg bw/day |
3 | 2 |
|
Teens |
56.4 kg |
0.009 μg/kg bw/day |
5 | 4 |
|
Adults |
71.8 |
0.007 μg/kg bw/day |
7 | 5 |
Assuming FDA is correct in its estimate of dose associated with ten amalgam fillings, this table clearly demonstrates the following conclusions:
- weight-standardized dose increases as body weight (and age) decreases
- the weight-standardized dose to young children (aged 3-6 years) is almost four times greater than the weight-standardized dose to adults, due entirely to the difference in bodyweights between these age groups
- young children who have two or more amalgam fillings exceed the weight standardized absorbed dose associated with the EPA RfC and ATSDR MRL
- Adults with seven or more amalgam-filled teeth will exceed the RfC and with five ormore amalgam fillings will exceed the MRL
- All age groups will exceed the doses associated with U.S. regulatory reference air concentrations with less than the average of seven to ten fillings assumed by the FDA to be ‘safe.
We have no doubt that FDA has the resources and expertise to properly assess the risksassociated with dental amalgam. Sadly, FDA’s clear priority is to defend at all costs the continueduse of mercury in dentistry — even at the expense of the public health. It is not surprising,therefore, that FDA declined to validly and defensibly compare its estimate of the average ortypical mercury vapor exposure to the very reference exposure levels it represents to be safe forthe general population.
