Arsenic

Figure 1. Arsenic, atomic number of 33 and atomic weight of 74.9216.

Figure 2. Arsenic crystal.

Arsenic (As) is the 33^rd element on the periodic table, and is found naturally in trace amounts on Earth. It is most often found combined with other elements, but is also found in its pure form. Historically, it was the poison of choice until its detection became easy. It is still used today as a poison for rats and pests, in a strictly controlled manner.

Arsenic also forms a semiconductor when combined with gallium, used for integrated circuits in supercomputers and other forms of technology.

Some properties of arsenic include:

Atomic weight	74.9216
Density (at 0oC)	5.776 g/cm3
Boiling point*	887 K
Melting point (at 28 atm)	1090 K

*Note: The boiling point is actually lower than the melting point because arsenic change phases directly from a solid to a gas under normal atmospheric pressure. It requires pressures of 28 atm in order to phase change from a solid to a liquid, hence the higher temperature.

Emissions of arsenic

Arsenic is emitted from various energy related sources. It can be emitted from external combustion boilers, copper and zinc smelting, copper mining, uranium mining, and lead smelting. It may also arise from waste incineration and glass manufacturing.

Emissions of arsenic from these sources is caused by the trace amount of arsenic in the fuels they use and the materials they process. The actual amount of arsenic emitted varies quite considerably, for instance the emissions of arsenic contained in coal may vary up to 4 orders of magnitude.

Toxicity

Arsenic is relatively safe in its organic form (bound to carbon), however it is extremely toxic in its inorganic form. Organic arsenic is often found in seafood and at safe levels. Inorganic arsenic is found in groundwater in high amounts in some countries around the world, or in the air as pollution. People may be exposed to arsenic through contaminated water. This can be a problem if water with arsenic is drank, used for food preparation, or raising crops. Smoking tobacco and some industrial processes also expose people to arsenic.

Drinking water contaminated with arsenic can lead to chronic arsenic poisoning, with skin lesions and skin cancer being the most common effects.

Effects

Acute effects (short term) include vomiting, abdominal pain, and diarrhea. Numbness of extremities may occur shortly after, and even possibly death.

Long-term effects can often be observed on the skin, typically after 5 or more years of exposure, including skin pigmentation, lesions, and hard spots on the palms and feet, all of which may be precursors for skin cancer. Lung and bladder cancer may also be attributed to chronic arsenic exposure. Other effects include neurotoxicity, development problems, diabetes, and cardiovascular disease.

The World Health Organization's guideline for maximum dose is 10 μg/liter, yet some nations experience doses over 5 times that amount. It is still difficult to gauge how big of a problem arsenic is however, since it is hard to isolate its effects compared to other external factors. Even so, it is still of major concern around the world.

Visit the EPA for more information about arsenic.

Video

The video below is from the University of Nottingham's periodic videos project. They have created a complete suite of short videos on every element on the periodic table of elements.