A naturally occurring chemical element, the symbol of arsenic is As, while its atomic number is 33. Arsenic is found in a variety of minerals, more often than not combined with different metals and sulfur. However, sometimes pure form of arsenic is also present in the form of crystals. Precisely speaking, arsenic is a type of metalloid. While it comprises a variety of allotropes, only the grey form of this chemical element that has a metallic look has many important uses in industry.
Arsenic is mainly used in lead alloys, such as ammunition and batteries meant for cars. In electronic gadgets, arsenic serves as a general n-type dopantin semiconductor. While doped silicon is most widely used semiconductor in electronic devices, the next most commonly used semiconductor is optoelectronic compound called gallium arsenide. Arsenic as well as various compounds of this chemical element, particularly its trioxide, is also widely used in pesticide, insecticide and herbicide production. They are also treated with wooden products to keep them safe from pest infestation. However, these applications of arsenic compounds are on the downside these days as both arsenic and its compounds are poisonous.
A number of bacteria species possess the aptitude to utilize arsenic compounds in the form of respiratory metabolites. In fact, trace amounts of this chemical element are vital in diets of chicken, rats, goats, hamsters and possibly in some other species also. However, the role of arsenic or its compound in human metabolism is yet to be ascertained.
When larger than required amounts of this chemical element or its compounds are found inside multicellular organisms it often results in arsenic poisoning. Moreover, arsenic often contaminates the groundwater and this problem has been affecting numerous people across the globe. In fact, arsenic is a carcinogenic element and has been categorized as group-A carcinogen.
In certain places of the world, arsenic concentration may be higher than that in others places. While natural conditions may also contribute to the presence of higher concentration of arsenic in some places, mostly it is due to human activities like rampant use of pesticides or mining.
Arsenic is often present in combination with other chemical elements in different forms of chemical compounds. Arsenic, in its organic form, contains carbon. However, inorganic arsenic does not contain carbon. Arsenic is not soluble in water. In fact, compared to organic arsenic compounds containing carbon, inorganic compounds of this chemical element are more detrimental for our health. The chances of inorganic arsenic compounds reacting with the cells in our body are more. Such arsenic compounds have the ability to dislodge specific elements from the body’s cells and also change the functioning of these cells.
It is known that cells make use of phosphate to generate energy and also to send signals to other cells for communication. However, arsenate, a particular type of arsenic, possesses the aptitude to imitate phosphate and also replace it from the cells. When this happens, the cells lose their ability to send signals to other cells and also generate energy.
The ability of arsenic to alter the components of a cell may, however, be helpful in treating cancer. Findings of a number of studies have revealed that arsenic possesses the ability to cut back a disease and also aid in thinning the blood. These days some cancers are treated using arsenic-based chemotherapy, for instance arsenic trioxide is one such arsenic compound.
Sources of exposure
A naturally occurring chemical element found on the earth’s crust, arsenic is widely distributed across the environment. It is present in land, water and air. In its inorganic form, arsenic is very toxic and, hence, detrimental for human health.
People often come in contact with high concentration of inorganic arsenic either by drinking water contaminated by this chemical element or using arsenic contaminated water for cooking food, irrigating crops, using inorganic arsenic in industrial processes or consuming contaminated food or smoking tobacco containing this chemical element.
Being exposed to inorganic arsenic for a prolonged period of time by consuming contaminated food and water can often result in chronic cases of arsenic poisoning. Such people are likely to suffer from skin cancer and skin lesions – the two most common traits of arsenic poisoning.
Drinking-water and food
Groundwater contaminated by inorganic arsenic is the utmost threat to the health of public. In several countries like India, Bangladesh, China, Argentina, Chile, the United States of America and Mexico inorganic arsenic is found in high concentrations in the groundwater. People in these countries as well as elsewhere are exposed to inorganic arsenic when they drink use such contaminated water or use it for cooking foods and irrigating crops. This often leads to arsenic poisoning, the main symptoms of which are skin cancer and skin lesions.
Dietary sources of arsenic poisoning may include shellfish, fish, dairy and poultry products as well as cereals. However, the damaged caused by these foods is comparatively less than that of arsenic contaminated groundwater, because these foods contain lesser levels of this chemical element and its inorganic compounds. Though seafood also contains arsenic, it is the lesser harmful organic form of the chemical element and, hence, consuming them is less harmful.
Arsenic alloys have a number of industrial uses. They are also used in the processing of pigments, paper, glass, textiles, wood preservatives, metal adhesives and even in ammunition. Hide tanning process also makes use of this chemical element. To some extent, arsenic is also used in pharmaceuticals, pesticides and feed additives.
Here is some bad news for people who smoke tobacco. Smokers can also be exposed to inorganic arsenic as the tobacco plants have the natural ability to draw arsenic from the soil, especially where the groundwater is contaminated by this chemical element. In fact, earlier the chances of smokers being exposed to higher levels of inorganic arsenic was more because those days farmers used to treat tobacco plants with pesticides containing lead arsenate.
Scientific studies have confirmed that inorganic arsenic is a carcinogen, which is found in the groundwater in many parts of the world. People who drink water contaminated by inorganic arsenic or cook food with it are exposed to this toxic substance easily. Aside from inorganic arsenic, this chemical element is also present in organic form. While inorganic arsenic compounds like those that are found in groundwater are extremely toxic, organic arsenic compounds like those present in seafood are comparatively less detrimental to our health.
Exposure to arsenic and its compounds often lead to a condition known as arsenic poisoning, whose initial symptoms include diarrhea, vomiting and pain in the abdominal region. Subsequently, a person suffering from arsenic poisoning may experience muscle cramps, tingling and numbness of the extremities and in extreme cases it can eventually result in death.
When an individual is exposed to inorganic arsenic for a prolonged period of time, by means of drinking water contaminated by this chemical element or its compounds or cooking foods with it, the initial symptoms of arsenic poisoning they develop include skin lesions, changes in pigmentation of the skin as well as formation of hard patches on the soles of feet and palms – a condition known as hyperkeratosis. All these skin-related symptoms occur when an individual is exposed to inorganic arsenic for a minimum period of five years. If not treated timely, these conditions may lead to skin cancer.
Aside from developing skin cancer, being exposed to arsenic for a prolonged period of time may lead to other forms of cancer – cancers of the lungs and bladder. The IARC or International Agency for Research on Cancer has classified arsenic and the various compounds of this chemical element as a carcinogenic substance for humans. In addition, the IARC has clarified that drinking water containing arsenic or its compounds is also carcinogenic for humans.
Drinking water containing inorganic arsenic and ingestion of foods contaminated by this chemical element for a long period of time may lead to other adverse effects such as diabetes, cardiovascular diseases and pulmonary diseases. For instance, myocardial infarction (also known as heart attack) induced by exposure to arsenic may often result in death. In fact, this is one noteworthy cause for several deaths. Many people in China who have been exposed to arsenic have developed a condition known as “blackfoot disease” – a severe ailment related to the blood vessels that may result in gangrene. Interestingly, this disease has not been found in people in other regions of the world. Hence, it is believed that aside from exposure to arsenic, malnutrition may also responsible for the development of “blackfoot disease”.
In addition, in many instances arsenic poisoning also affects pregnancy adversely and is a reason for infant mortality in many areas. It also has a negative effect on children’s health. Moreover, it has been found that exposure to arsenic in utero as well as during early childhood may result in death of young adults owing to lung disease, various forms of cancer, kidney failure and heart attacks. Findings of several studies have shown that exposure to inorganic arsenic for a prolonged period also has a negative effect on intelligence, cognitive development and memory.
While arsenic, especially inorganic arsenic, has been classified as carcinogenic for humans, this chemical element has multiple uses in various fields ranging from agriculture to military.
Primarily, arsenic is used for wood preservation. Since this chemical element is toxic, it is very effectual in eliminating pests, bacteria and fungi – ideal for treatment of wood. Earlier, arsenic was extensively used for this purpose in industry. However, it was later banned by many countries. Over the years even the use of arsenic in consumer products has been banned by many countries owing to its extreme toxicity.
One very important use of this chemical element is its utility in the form of a doping agent in solid state devices, for instance transistors. Briefly speaking, doping involves a process wherein any impurity, for instance arsenic, is included in a semiconductor to enhance the device’s conductivity.
In its inorganic state, arsenic is employed in producing wood treated under pressure. Chromated copper arsenate is used in wood preservation. In this case, the chemical is injected into the cells of the wood. Wood produced by pressure treatment is mainly used for residential, industrial and commercial applications such as highway noise barriers, decking, playground equipment, landscaping, utility posts, signposts and even retaining walls. Compared to other types of wood, pressure-treated wood using chromate copper arsenate offers us one significant benefit – it not only resists insect attacks, but also does not rot. Hence, it is not surprising that places where the risks of insect attacks are more use pressure-treated wood with higher concentration of chromate copper arsenate. In fact, the life span of any wood can be enhanced greatly by pressure-treating it, especially with chromate copper arsenate.
As in the case of wood, arsenic also has a major role in the leather tanning industry where it is used to preserve leather from fungus and decay. This toxic chemical element is extensively used for eliminating weed. It is sprayed over fields infested with weeds from small aircraft to obliterate all such infestation. In addition, arsenic is widely used in the form of insecticides since this chemical element is highly effectual in obliterating termite infestation. However, in recent times the popularity and use of organic pesticides have increased manifold resulting in a decline in use of insecticides containing arsenic.
Arsenic has a number of other industrial uses. It is often employed for hardening lead and also in the form of an anti-friction chemical addition to ball bearings. This chemical element also has a purpose in the production of optical materials made from germanium-arsenide-selenide. Earlier, indium-gallium-arsenide was employed in short-wave infrared equipment.
The toxic properties of arsenic compounds, they had a number of medical applications. In the 18th and 19th century they were used in many pharmaceutical products. Much before penicillin was discovered; physicians used arsenic compounds mainly for treating syphilis. Discovered in 1786, another arsenic compound called Fowler’s solution – a solution containing 1% potassium arsenite, was recommended for treating a variety of diseases. A number of other arsenic solutions were also employed as medicines. Some of these were arsenic trichloride (also known as de Valagin’s solution) and arsenic trioxide (also known as Donovan’s solution). Even in modern times, arsenic is used for treating specific diseases such as a number of cancer forms, but their use is still controversial.
Aside from their industrial and medical uses, arsenic compounds are also employed in the manufacture of special variety of glass. In addition, they are also used for preserving wood. In recent times, they are also used in the manufacture of sold state semiconductor gallium arsenade, which can alter electric current into laser light. Similarly, for the microchip industry, arsine gas (chemical formula AsH3) is now an essential dopant gas. However, it is mandatory for the manufacturers to follow stringent parameters when using this gas as it is a very toxic substance.
Several arsenic compounds were employed in the form of medicines back in the 18th, 19th, and 20th centuries; while another arsenic compound called copper acetoarsenite was employed in the form of a green pigment, which was known by several different names.