A website selling Himalayan Salt advertises:
As a trace mineral, arsenic is a necessary part of healthy blood. Small amounts of arsenic are essential to life.
Is this claim true?
It is currently not known if arsenic is essential for humans, but it might be required for the metabolism of the amino acid methionine:
Even arsenic, the poison of choice for many fictional murderers, is now close to qualifying as a micronutrient in animals. It seems that arsenic has a role in the metabolism of the amino acid methionine and in gene silencing (Uthus, 2003). Other work suggests that it has a positive interaction with the more important micronutrient selenium (Zeng et al, 2005).
In fact, if arsenic is essential for humans, its recommended daily intake would be little different from selenium, which is so important that evolution incorporated it into the rare amino acid selenocysteine—the crucial component of the antioxidizing selenoproteins that help to repair other proteins from oxidative damage. The recommended dose of selenium is 40 μg per day, whereas extrapolations from mammalian studies suggest that humans might need between 12.5 μg and 25 μg of arsenic. This is, to some extent, academic; a normal diet will contain 12–50 μg of arsenic in most parts of the world, but it shows that arsenic—the famous poison—and selenium—one of the most widely studied elements in the dietary context—could well have almost identical levels of nutritional necessity and toxicity.
Dairy products can contribute as much as 31 percent of arsenic in the diet; meat, poultry, fish, grains and cereal products collectively contribute approximately 56 percent (Mahaffey et al., 1975).
So, arsenic is present in common foods in sufficient amounts.
According to this source, Himalayan salt contains <0.02 ppm (<0.02 μg/g or 0.1 μg/5 g) arsenic, which is an insignificant amount if the estimated requirement is 12.5-25 μg/day.