Chemistry Reference
In-Depth Information
the extremities; decreased touch, pain and temperature sensation; and mus-
cular tenderness. Chronic consumption of high amounts of inorganic arsenic
in drinking water results in hyperkeratosis of the hands and feet, symmetrical
pigmentation, conjunctivitis, tracheitis, acrocyanosis and polyneuritis and
skin cancer.
The FNB (Food and Nutrition Board: Institute of Medicine, 2001)
set no dietary reference intakes (DRI) for arsenic. Animal data would
suggest that intakes of 12-25 mg/d may be beneficial (Nielsen, 2006).
Recent surveys indicate that arsenic intakes from food are less than this;
the median intakes of adult men and women in the United States are
approximately 2.0-2.9 and 1.7-2.1 mg/d, respectively (Food and Nutrition
Board: Institute of Medicine, 2001). Earlier surveys indicated higher mean
intakes of arsenic ranging from 23 to 72 mg/d (Food and Nutrition Board:
Institute of Medicine, 2001).
The mean arsenic concentration in healthy adult human tissues was
reported to be highly variable and between 40 and 90 mg/kg dry weight (Anke
et al., 1997). Human milk was found to contain 0.2-6 mg arsenic/l, with no
differences between colostrum and mature milk (Anke et al., 1997). Normal
bovine milk was found to contain 15-60 mg arsenic/l (Anke et al., 1997).
Increasing dietary arsenic did not increase the arsenic concentration in bovine
milk. Reported arsenic concentrations in milk indicate that dairy products
can contribute a substantial portion of the total daily dietary intake of
arsenic.
10.18.
Nickel
Nickel is not generally regarded as an essential nutrient for higher animals
and humans, apparently because of the lack of a clearly defined specific
biochemical function (Committee on Minerals and Toxic Substances in
Diets and Water for Animals, 2005; Nielsen, 2006). However, nickel has
been identified as an essential component of seven different enzymes involved
in hydrolysis and redox reactions in some lower forms of life (plants and some
bacteria). Interestingly, in microbes, the substrates or metabolites of the
enzymatic reactions are dissolved gases of hydrogen, carbon monoxide,
carbon dioxide, methane, oxygen and ammonia. Additionally, nickel depri-
vation studies show that it has beneficial actions in higher animals (Nielsen,
2006). Nickel deprivation detrimentally affects reproductive function and
bone strength. Nickel deprivation also has been shown to increase sensitivity
to salt, increase triacylglycerol levels in serum and liver and reduce the activity
of enzymes that degrade glucose. Nickel might have a function that is asso-
ciated with vitamin B
12
, because lack of this vitamin inhibits the response to
