revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 225
2. HEALTH EFFECTS
Estimating mercury exposure from dental amalgams is also difficult because of high variability in the
number of amalgam fillings per individual and the differences in chewing, eating, and breathing habits.
Dental amalgams, however, would be the most significant source of mercury exposure in the absence of
fish consumption or proximity to a waste site or incinerator. A report from the Committee to Coordinate
Environmental Health and Related Programs (CCEHRP) of the Department of Health and Human Services
determined a level of from 1 to 5 µg Hg/day from dental amalgam for people with 7–10 fillings (DHHS
1993). The World Health Organization reported a consensus average estimate of 10 µg amalgam Hg/day
(range: 3–17 µg/day) (WHO 1991). Weiner and Nylander (1995) estimated the average uptake of mercury
from amalgam fillings in Swedish subjects to be within the range of 4–19 µg/day. Skare and Engqvist
(1994) estimated that the systemic uptake of mercury from amalgams in middle-aged Swedish individuals
with a moderate amalgam load (30 surfaces) was, on the average, 12 µg/day, an amount said to be
equivalent to a daily occupational air mercury exposure concentration of 2 µg/m 3 . Other researchers have
estimated the average daily absorption of Hg from amalgam at 1–27 µg/day, with levels for some
individuals being as high as 100 µg/day (Björkman et al. 1997; Lorscheider et al. 1995).
Richardson et al. (1995) estimated total mercury exposure for Canadian populations of different ages to be
3.3 µg/day in toddlers (3–4 years old), 5.6 µg/day in children (5–11 years old), 6.7 µg/day in teens
(12–19 years old), 9.4 µg/day in adults (20–59 years old), and 6.8 µg/day in seniors (aged 60+). Of this
exposure, amalgam was estimated to contribute 50% to the total Hg in adults and 32–42% for other age
groups. Estimates based on 2 independent models of exposure from amalgam alone were 0.8–1.4 µg/day
in toddlers), 1.1–1.7 µg/day in children, 1.9–2.5 µg/day in teens; 3.4–3.7 µg/day in adults, and
2.1–2.8 µg/day in seniors (Richardson 1995).
Higher levels of mercury exposure can occur in individuals who chew gum or show bruxism, a rhythmic or
spasmodic grinding of the teeth other than chewing and typically occurring during sleep (Barregard et al.
1995; Enestrom and Hultman 1995). Richardson (1995) reported a transient 5.3-fold increase in levels of
mercury upon stimulation by chewing, eating, or tooth brushing. Sallsten et al. (1996) also reported over a
5-fold increase in plasma and urinary mercury levels (27 and 6.5 nmol/mmol creatinine versus 4.9 and
1.2 nmol/mmol creatinine, respectively) in a sample of 18 people who regularly chewed nicotine chewing
gum (median values of 10 sticks per day for 27 months), compared to a control group.
Berdouses et al. (1995) studied mercury release from dental amalgams using an artificial mouth under
controlled conditions of brushing and chewing and found that although the release of mercury during initial