Aluminum - Toxicology of Metals - page 332

4 DIETARY, ENVIRONMENTAL, AND
OCCUPATIONAL EXPOSURE

The primary normal source of aluminum for the
human is food. Daily aluminum intake averages
5-10 mg. The aluminum content of food is highly
variable. The average aluminum content of spices and
herbs ranged from less than 0.005 mg/100 g for salt to
200 mg/100 g for thyme. Although the quantities of
spices and herbs used in foods is generally very small,
a diet high in spicy foods may be high in aluminum
(e.g., a teaspoon of cayenne powder could contribute
about 4 mg of aluminum). Baking powder containing
aluminum additives was extremely high in alumi-
num, providing more than 2 g of aluminum per 100 g.
The most commonly used foods that may contain
substantial amounts of aluminum-containing food
additives except baking powder are processed cheese,
cake mixes, frozen dough, pancake mixes, and pickled
vegetables (Saiyed and Yokel, 2005). Concentrations of
aluminum in tea leaves and tea powder can be quite
high, up to 140 mg/100 g. Based on these values, a cup
of tea could contain 1 mg of aluminum (Pennington,
1987). Tea and aluminum utensils were estimated to
increase aluminum in the diet by approximately 4 and
2 mg per day, respectively (Jorhem and Haegglund,
1992).
Beverages from aluminum cans contained generally
higher levels of aluminum than beverages from glass
bottles. Noncola and cola soft drinks averaged 900 and
660

FIGURE 1

Metal Inert Gas (MIG) welding of aluminum.

5 METABOLISM

5.1 Absorption
There have been several studies in animals and
humans dosed with 27 Al using atomic absorption
spectroscopic analysis and dosed with 26 Al using
accelerator mass spectrometric analysis to estimate
the percentage of aluminum absorbed from drinking
water. The results suggest 0.3% is orally absorbed

(Priest et al ., 1998; Stauber et al ., 1999; Yokel et al ., 2001).
On the basis of daily aluminum dietary consumption
and urinary aluminum excretion, the oral bioavail-
ability of aluminum from the diet has been estimated
to be 0.1-0.3% (Ganrot, 1986; Priest, 1993; Nieboer
et al ., 1995). Bioavailability of 26 Al that was incorpo-
rated into two FDA-approved food additives, acidic
and basic sodium aluminum phosphate, which were
then incorporated into a biscuit and a processed cheese,
respectively, was

∼

g/L from glass
bottles, respectively, whereas beer in cans or bottles
averaged about 160

µ g/L from cans and 150 and 240 µ

g/L. The highest concentration
in a noncola soft drink can was 10,000

µ

µ g/L (Duggan

et al ., 1992).
The contribution of aluminum from drinking water
is about 100 g/day (Yokel and McNamara, 2001).

Air aluminum concentrations vary between 20 and
500 ng/m 3 in rural settings and 1000 and 6000 ng/m 3
in urban settings. Humans exposed to ambient alumi-
num concentrations of 2000 ng/m 3 and particle size
<5

µ 0.05%

from the cheese (Yokel et al ., 2005). Several studies
demonstrated increased aluminum absorption when
taken with citrate. Aluminum hydroxide is still used as
an antacid and a phosphate binder. The recommended
dose can deliver up to 1.6 g of aluminum per day. Thus,
the absorption from this dose may exceed 1 mg/day
(Yokel and McNamara, 2001). The site of aluminum
absorption is the upper intestine. The mechanisms of
gastrointestinal aluminum absorption have been sug-
gested to include passive (diffusion) and active (car-
rier- and vesicular-mediated) transport across intestinal
cells and paracellular diffusion between these cells.
There is evidence for an energy-dependent compo-
nent of uptake. Aluminum absorption is enhanced by
processes that mediate calcium uptake. Citrate may
enhance aluminum absorption through the paracellu-
lar pathway by increasing permeability between cells

∼ 0.02% from the biscuit and ∼

m and who have a normal ventilatory volume of
20 m 3 /day would inhale 40

µ

µ g aluminum/day (WHO/

IPCS, 1997).
Occupational exposure to aluminum particles
reached 100 mg/m 3 during production of stamped
aluminum powder in the 1950s (Mitchell et al ., 1961).
However, in the 1990s reported levels were 5-21 mg/m 3
during production of aluminum powder and 1-4 mg/
m 3 during production of aluminum paste (Letzel et al .,
1996). Aluminum welding (Figure 1) produced levels
of 0.2-5 mg/m 3 (Sjögren et al ., 1988). Powder produc-
tion and aluminum welding are generally associated
with the highest occupational aluminum exposure.