Arsenic Exposure And its Effect on Health

Arsenic is known as a poison and human carcinogen. Arsenic trioxide (As2O3), a water-soluble powder that produces a colorless, tasteless, and odorless solution, was a favorite homicidal agent during the Middle Ages and its use continues today, although not to the same extent. There is much debate on Napoleon's death, whether he was poisoned by arsenic-tainted wine during his exile on the island of St. Helena.



Arsenic is the 20'th most abundant element in the earth's crust, and is present in the natural environment. The current problem of arsenic is devastating in history as the cause of the largest mass poisoning ever. In Bangladesh and India, millions of people are affected by high levels of arsenic in drinking water. Millions of wells have been installed since the 1970''s with the aim of providing clean water, free of microbial pathogens. However, the rock containing naturally high levels of arsenic releases of arsenic in water, arsenic in water higher than concentration several hundred micrograms per liter (µg/L) or even milligrams per liter (mg/L) in some wells. Ingestion of such high levels of arsenic in drinking water over several years can lead to a variety of adverse health effects including cancers of the skin, bladder, and lung as well as possible neurological and cardiovascular effects.



The magnitude of the arsenic problem and the seriousness of the adverse health outcomes resulting from exposure to arsenic make arsenic the single most important environmental contaminant. As a consequence, regulations on arsenic have become more stringent. Arsenic is also abundant in seafood at concentrations as high as several hundred micrograms per gram (µg/g). Arsenobetaine is the major arsenic species in most seafood (crustaceans). It is excreted into urine without metabolism, and is essentially non-toxic.

Arsenic-induced hyperkeratosis of the hands

More than 20 arsenic compounds (species) are present in the natural environment and biological systems. The following Table lists some of the common arsenic species. Although the trivalent arsenic species, such as inorganic arsenite (AsIII), monomethylarsonous acid (MMAIII), and dimethylarsinous acid (DMAIII) are highly toxic (8-13), arsenobetaine (AsB), the predominant arsenic species present in most crustaceans, is essentially non-toxic.

History Of Arsenic: Toxic Element

Arsenic has been found in Nature since Antiquity. Aristotle makes reference to sandarach (arsenic trisulfide) in the 4th century B.C. In the 1st century A.D., Pliny stated that sandarach is found in gold and silver mines and arsenic (arsenic trioxide) is composed of the same matter as sandarach. By the 11th century three species of arsenic were known, the white, yellow and red - since then recognized as arsenic trioxide, arsenic trisulfide (orpiment) and arsenic disulfide (realgar), respectively. (reference)

The Picture below you can see is Eye Disease caused by Arsenic

Albertus Magnus is reputed in the 13th century to be the discoverer of metallic arsenic. However, his documentation is considered vague. It was not until 1649 that J. Schroder clearly reported the preparation of metallic arsenic by reducing arsenic trioxide with charcoal. Thirty-four years later, N. Lemery also observed that metallic arsenic was produced by heating arsenic trioxide with soap and potash. By the 18th century the properties of metallic arsenic were sufficiently known to classify it as semimetal.

Safe Water Technology for Arsenic Removal

Arsenic removal efficiency is excellent (typically > 95%), for both arsenate
and arsenate, but arsenic capacity varies significantly, and is controlled primarily by pH and influent arsenic concentration and speciation. Arsenate removal capacity is best in the narrow range from pH 5.5 to 6.0, where the alumina surfaces are protonated, but acid anions are not yet concentrated enough to compete with arsenic for sorption sites (Trussell et al., 1980; Rosenblum and Clifford, 1984; Clifford, 1999). Typically, activated alumina has a point of zero charge (PZC), below which the surface is positively charged, and above which the surface bears a negative charge, at pH 8.2. Arsenic removal capacity drops sharply as the PZC is approached, and above pH 8.5, is reduced to only 2-5% of
capacity at optimal pH (Clifford, 1999). For neutral and basic waters, therefore,pH adjustment may be necessary for effective arsenic removal.

Fine (28-48 mesh) particles of activated alumina are typically used for
arsenic removal, with an Empty Bed Contact Time of five to eight minutes
(Rubel and Woosely, 1979). When operated in the optimal pH range, activated
alumina beds have much longer run times than ion exchange resins. The number
of bed volumes that can be treated at optimal pH before arsenate breaks through
is mainly controlled by the influent arsenic concentration.

Frank and Clifford reported an arsenate capacity (at pH 6) of about 1.6 g/L of
activated alumina, consistent with an earlier reported capacity of 4 mg/g,
assuming a bulk density of 0.5 kg/L (Gupta and Chen, 1978). Fox reported a
somewhat lower capacity of 1 mg/g, but this is likely due to the elevated pH (7.4-
8.0) of the influent water (Fox, 1989).
The sorption sites on the activated alumina surface are also attractive to a
number of anions other than arsenate: Clifford reports the selectivity sequence of
activated alumina in the pH range of 5.5 to 8.5 as (Clifford, 1999):

OH-> H2AsO4-> Si(OH)3O-> HSeO3-> F-> SO42-> CrO42->> HCO3->Cl-> NO3-> Br->I

Trussell and others reported a similar selectivity sequence, but included
phosphate as the second most preferred anion, after hydroxyl, and placed fluoride
above arsenate in the sequence (Trussell et al., 1980). Because of activated
alumina’s strong selectivity for arsenate, competing anions pose less of a
problem than with ion exchange resins. Sulfate, and to a lesser extent, chloride,have been shown to reduce capacity, but the competition effect is not as dramatic as with ion exchange resins (Rosenblum and Clifford, 1984). Phosphate and
fluoride are also sorbed onto activated alumina, producing improvements in
drinking water quality, but at the same time reducing arsenic removal potential.
Activated alumina can be regenerated by flushing with a solution of 4%
sodium hydroxide, which displaces arsenic from the alumina surface, followed
by flushing with acid, to re-establish a positive charge on the grain surfaces.