ARSENIC

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Arsenic is a semi-metal element in the periodic table with number 33. It is widely distributed
in the Earth’s crust, and has a steel grey metal-like colour. However, arsenic is usually found
in the environment combined with other elements such as oxygen, chlorine, and sulphur.
Arsenic combined with these elements is called inorganic arsenic. Arsenic combined with
carbon and hydrogen is referred to as organic arsenic. Understanding the difference between
inorganic and organic arsenic is important because some of the organic forms are less harmful
than the inorganic forms. Most inorganic and organic arsenic compounds are white or
colourless powders that do not evaporate. They have no smell, and most have no special taste.
Inorganic arsenic occurs naturally in soil and in many kinds of rock, especially in minerals
and ores that contain copper or lead. Arsenic is present in more than 200 mineral species, the
most common of which is arsenopyrite. When these ores are heated in smelters, most of the
arsenic goes up the stack and enters the air as a fine dust. Smelters may collect this dust and
take out the arsenic as a compound called arsenic trioxide (As2O3). It enters drinking water
supplies from natural deposits in the earth or from agricultural and industrial practices.
WHO has set the arsenic standard for drinking water at .010 parts per million (10 parts per
billion) to protect consumers served by public water systems from the effects of long-term,
chronic exposure to arsenic.

Industrial applications 
About 90% of all arsenic produced is used as a preservative for wood to make it resistant to
rot and decay. The preservative is copper chromated arsenic (CCA) and the treated wood is
termed as “pressure-treated.” CCA wood still remains widespread in use in many countries. It
was heavily used during the latter half of the 20th century as an outdoor building material,
where there was a risk of rot, or insect infection in untreated wood. Although widespread bans
followed the publication of studies which showed low-level leaching from in-situ wood into
surrounding soil, the most serious risk is probably by the burning of CCA wood. In recent
years fatal animal poisonings have been seen, and serious human poisonings resulting from
the ingestion - directly or indirectly - of wood ash from CCA wood. The lethal human dose is
only approximately 20 grams of ash.
During the 18th, 19th, and 20th centuries, a number of arsenic compounds have been used as
medicines, including arsphenamine and arsenic trioxide. Arsphenamine as well as
Neosalvarsan was indicated for treatment of syphilis and trypanosomiasis. Arsenic trioxide
has been used in a variety of ways over the past 200 years, but most commonly in the
treatment of cancer. It was also used as Fowler's solution in psoriasis. In 2000 the Food and
Drug Administration approved Arsenic trioxide for the treatment of patients with acute
promyelocytic leukaemia.
Lead hydrogen arsenate has been used until recently as an insecticide on fruit trees causing
brain damage to the workers. A copper arsenate (Scheele's Green) has been used as a
colouring agent in sweets in the 19th century. In the last half century, monosodium methyl
arsenate (MSMA), a less toxic organic form of arsenic, has replaced lead arsenate's role in
agriculture.

Copper acetoarsenite was used as a green pigment known under many different names,
including 'Paris Green' and 'Emerald Green'. It caused numerous arsenic poisonings of artists.
Emerald Green was a pigment frequently used by Impressionist painters. Cezanne developed
severe diabetes, which is a symptom of chronic arsenic poisoning. Monet's blindness and Van
Gogh's neurological disorders could have been partially due to their use of Emerald Green.
Poisoning by other commonly used substances, including liquor and absinthe, lead pigments,
mercury-based Vermilion, and solvents such as turpentine, could also be a factor in these
cases.
Contamination of groundwater 
Arsenic contamination of groundwater has led to a massive epidemic of arsenic poisoning in
Bangladesh and neighbouring countries. It is estimated that approximately 57 million people
are drinking groundwater with arsenic concentrations elevated above the World Health
Organization's standard of 10 parts per billion. The arsenic in the groundwater is of natural
origin, and is released from the sediment into the groundwater due to the anoxic conditions of
the subsurface. This groundwater began to be used after NGOs implemented a drinking-water
program based on wells in the 1970ties and 1980ties. This program was designed to prevent
drinking of bacterially contaminated surface waters, but unfortunately the testing for arsenic
in the groundwater failed. Arsenicosis was reported in many other countries and districts in
South East Asia, such as Vietnam, Cambodia, Thailand, Tibet and China. These countries are
thought to have geological environments similarly conducive to generation of high-arsenic
groundwaters as in Bangladesh.
Potency 
The LD50 for pure arsenic is 763 mg/kg body weight (by ingestion) and 13 mg/kg (by
intraperitoneal injection). For a 70 kg human, this is about 53 grams. However, compounds
containing arsenic can be significantly more toxic.
Toxicity 
Arsenic and many of its compounds are extremely potent poisons. Arsenic disrupts ATP
production through several mechanisms. At the level of the citric acid cycle, arsenic inhibits
succinate dehydrogenase and by competing with phosphate it uncouples oxidative
phosphorylation, thus inhibiting energy-linked reduction of NAD+, mitochondrial respiration,
and ATP synthesis. Hydrogen peroxide production is also increased, which might form
reactive oxygen species and oxidative stress. These metabolic interferences lead to death from
multi-system organ failure probably from necrotic cell death, not apoptosis. A post mortem
reveals brick red coloured mucosa, due to severe haemorrhage.
Elemental arsenic and arsenic compounds are classified as "toxic" and "dangerous for the
environment" in the European Union under directive 67/548/EEC.
The IARC recognizes arsenic and arsenic compounds as group 1 carcinogens, and the EU lists
arsenic trioxide, arsenic pentoxide and arsenate salts as category 1 carcinogens. Arsenic is known to cause arsenicosis due to its manifestation in drinking water, “the most common species being arsenate [HAsO42- ; As(V)] and arsenite [H3AsO3 ; As(III)]”. The ability of arsenic to undergo redox conversion between As(III) and As(V) makes its availability in the environment possible. The study of chemolithoautotrophic As(III) oxidizers and the heterotrophic As(V) reducers can help the understanding of the oxidation and/or
reduction of arsenic.
Human exposure to arsenic can cause both short and long term health effects. Short or acute
effects can occur within hours or days of exposure. Long or chronic effects occur over many
years. Most cases of arsenic-induced toxicity in humans are due to exposure to inorganic
arsenic, and there is an extensive database on the human health effects of the common arsenic
oxides and oxyacids. Although there may be some differences in the potency of different
chemical forms (e.g., arsenites tend to be somewhat more toxic than arsenates), these
differences are usually minor. Exposures of humans near hazardous waste sites could involve
inhalation of arsenic dusts in air, ingestion of arsenic in water, food, or soil, or dermal contact
with contaminated soil or water. By the inhalation route, the most sensitive effect of inorganic
arsenic is an increased risk of lung cancer, although respiratory irritation, nausea, and skin
effects may also occur. There are only a few quantitative data on noncancer effects in humans
exposed to inorganic arsenic by the inhalation route. However, it appears that such effects are
unlikely below a concentration of about 0.1–1.0 mg As/m3. Animal data similarly identify
effects on the respiratory system as the primary noncancer effect of inhaled inorganic arsenic
compounds, although only a few studies are available. Only limited data on the effects of
inhaled organic arsenic compounds in humans or animals are available; these studies are
generally limited to high-dose, short-term exposures, which result in frank effects.
Relatively little information is available on effects due to direct dermal contact with inorganic
arsenicals, but several studies indicate the chief effect is local irritation and dermatitis, with
little risk of other adverse effects.
The database for the oral toxicity of inorganic arsenic is extensive, containing a large number
of studies of orally-exposed human populations. These studies have identified effects on
virtually every organ or tissue evaluated, although some end points appear to be more
sensitive than others. The available data from humans identify the skin as the most sensitive
noncancer end point of long-term oral arsenic exposure. Typical dermal effects include
hyperkeratinisation of the skin (especially on the palms and soles), formation of multiple
hyperkeratinised corns or warts, and hyperpigmentation of the skin with interspersed spots of
hypopigmentation. Oral exposure data from studies in humans indicate that these lesions
typically begin to manifest at exposure levels of about 0.002–0.02 mg As/kg/day. At these
exposure levels, peripheral vascular effects are also commonly noted, including cyanosis and
gangrene. Other reported cardiovascular effects of oral exposure to inorganic arsenic include
increased incidences of high blood pressure and circulatory problems. In addition to dermal
and cardiovascular effects, oral exposure to inorganic arsenic may result in effects on other
organ systems. Nausea, vomiting, and diarrhoea are very common symptoms in humans
following oral exposure to inorganic arsenicals, both after acute high-dose exposure and after
repeated exposure to lower doses; these effects are likely due to a direct irritation of the
gastrointestinal mucosa. Acute, high-dose exposure can lead to encephalopathy, with clinical signs such as confusion, hallucinations, impaired memory, and emotional lability, while longterm exposure to lower levels can lead to the development of peripheral neuropathy
characterized by a numbness in the hands and feet that may progress to a painful "pins and
needles" sensation. A recent study also reported decreases in intelligence scores of arsenicexposed children.
Data on the effects of oral exposure to inorganic arsenic on reproductive end points in humans
are not available. Animal data suggest that arsenic may cause changes to reproductive organs
of both sexes, including decreased organ weight and increased inflammation of reproductive
tissues, although these changes may be secondary effects. However, these changes do not
result in a significant impact on reproductive ability. Chronic exposure of humans to
inorganic arsenic in the drinking water has been associated with excess incidence of
miscarriages, stillbirths, preterm births, and infants with low birth weights, although doseresponse data are not presently available for these effects. Animal studies of oral inorganic
arsenic exposure have reported developmental effects, but generally only at concentrations
that also resulted in maternal toxicity.
Arsenic is a known human carcinogen by both the inhalation and oral exposure routes. By the
inhalation route, the primary tumour types are respiratory system cancers, although a few
reports have noted increased incidence of tumours at other sites, including the liver, skin, and
digestive tract. In humans exposed chronically by the oral route, skin tumours are the most
common type of cancer. In addition to skin cancer, there are a number of case reports and
epidemiological studies that indicate that ingestion of arsenic also increases the risk of
internal tumours (mainly of bladder and lung, and to a lesser extent, liver, kidney, and
prostate).
Non-cancer effects can include thickening and discoloration of the skin, stomach pain,
nausea, vomiting; diarrhoea; numbness in hands and feet; partial paralysis; and blindness.
Clinical symptoms 
Symptoms include violent stomach pains in the region of the bowels; tenderness and pressure;
retching; vomiting; sense of dryness and tightness in the throat; thirst; hoarseness and
difficulty of speech; the matter vomited, greenish or yellowish, sometimes streaked with
blood; diarrhoea; tenesmus; sometimes excoriation of the anus; urinary organs occasionally
affected with violent burning pains and suppression; convulsions and cramps; clammy sweats;
lividity of the extremities; countenance collapsed; eyes red and sparkling; delirium; death.
Some of these symptoms may be absent where the poisoning results from inhalation, as of
arseniuretted hydrogen.
Symptoms of arsenic poisoning start with mild headaches and can progress to lightheadedness
and usually, if untreated, will result in death.
Arsenicosis - chronic arsenic poisoning from drinking water
Chronic arsenic poisoning results from intake of drinking water with high levels of arsenic
over a long period. Effects include changes in skin colour, formation of hard patches on the
skin, skin cancer, lung cancer, cancer of the kidney and bladder, and can lead to gangrene. Non-carcinogenic chronic effects include liver injury—jaundice and cirrhosis;—peripheral
vascular disease involving blueness of the extremities; Raynaud's syndrome; blackfoot disease
(a type of gangrene); anemia, resulting from impaired haeme biosynthesis; and hyperkeratosis
of the skin.
Arsenic in seafood 
Concerns about the adverse effects of chronic arsenic exposure have focused on contaminated
drinking water and airborne workplace exposures; the risks of naturally occurring arsenic in
foods have received less attention. About 90% of the arsenic in US diets comes from seafood,
of which only a small proportion occurs in inorganic forms; the great majority consists of
complex organic compounds that generally have been regarded as non-toxic. However, recent
studies of seafood have documented formation of metabolites carcinogenic in some rodents.
Treatment and testing 
Chemical and synthetic methods are now used to treat arsenic poisoning. Dimercaprol and
Succimer are chelating agents which sequester the arsenic away from blood proteins and are
used in treating acute arsenic poisoning. The most important side-effect is hypertension. One
way to test for arsenic poisoning is by checking hair follicles. If arsenic is in the bloodstream,
it will enter hair and remain there for many years.
References 
 1.  Anonymous. Arsenic and arsenic compounds. 224 vol., 2001:1-501
 2.  U.S.DEPARTMENT OF HEALTH AND HUMAN SERVICESPublic Health
ServiceAgency for Toxic Substances and Disease Registry. Draft
Toxicological Profile For Arsenic.  2005.
 3.  Anonymous. Arsenic fact sheet.  2007.
 4.  Anonymous. Arsenic. www.wikipedia.org . 2007.
 5.  Anonymous. Some Drinking-water Disinfectants and Contaminants, including
Arsenic.  2004. IARC Monographs on the Evaluation of Carcinogenic
Risks to Humans.
 6.  Borak J, Hosgood HD. Seafood arsenic: implications for human risk assessment.
Regul Toxicol Pharmacol. 2007; 47:204-212  

SPDF PERIODIC TABLE

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The Quantum Mechanical Atom
Levels and Sublevels
Images displayed in all types of media depict atoms as dense spherical nuclei surrounded by
orbiting electrons. It’s a compelling image that’s easy to remember. However, this image leaves
out many important details, and so doesn’t help us to fully understand actual atomic structure.
For example, if a negative electron were simply in orbit around a positive nucleus, why
wouldn’t it be attracted to the positive charge and quickly spiral toward the center? There
must be something keeping an atom from collapsing in on itself.
In the early twentieth century, physicist Niels Bohr proposed an explanation. Bohr’s hypothesis
said that electrons must occupy discrete orbits around a nucleus based on the energy level of
those electrons. If an electron gains energy, it rises to a higher orbit; if it loses energy, it falls
to a lower orbit. Within each of the orbits were suborbits, which corresponded to smaller
variations in energy level. As part of his theory, Bohr proposed a systematic way for identifying
the energy levels and sublevels and their corresponding orbits and suborbits.
Let's take a look at the table of Levels and Sublevels, starting from the nucleus and working
outward: The levels (or shells) are numbered and the sublevels (or subshells) are indicated by
the letters s, p, d, or f.
Levels and Sublevels
1
1   s
2   s   p
3   s   p   d
4   s   p   d   f
5   s   p   d   f
6   s   p   d   f
7   s   p   d   f
You can see that the innermost zone, level 1, contains only one sublevel, s. Level 2 contains
sublevels s and p. Level 4 is the first level that can contain all four sublevels: s, p, d, and f.
Levels further outward from level 4 have the same sublevel configuration.
On any level, a single s sublevel exists by itself, containing two electrons. However, the other
three sublevels are actually composed of three or more sublevel orbitals. For example, on any
level, a p sublevel is actually made up of a group of three orbitals. Similarly, d sublevels are
made up of a group of five orbitals, and f sublevels are composed of a group of seven orbitals.
Each of these individual orbitals can contain a maximum of two electrons. Below is a summary
of sublevels and the maximum number of electrons that they can contain:2
Sublevel Sublevel Groups Total Electrons
In the simplest terms, this means that an s sublevel can contain as many as two electrons, a p
sublevel can contain as many as six electrons and so on as shown in the last column of the
table.
So the number of electrons in a given sublevel is expressed by writing the level number followed
by the sublevel’s letter, with the number of electrons in the sublevel written as a superscript.
For example:
3p2
(There are 2 electrons in the p sublevel of level 3.)
4d7
(There are 7 electrons in the d sublevel of level 4.)
With this information, we can discover the reason for the periodic nature of elements, the
“why” behind Mendeleyev’s periodic table.
Electron Configuration
To better understand electron configuration, let’s take a look at a specific element. Lithium,
element number 3 on the periodic table, is a member of group IA, the alkali metals. Its atomic
number, 3, is based on the three positive protons in its nucleus. These protons will, in turn,
attract and hold three electrons. The arrangement of these electrons about its nucleus is what
gives lithium its chemical properties. Let’s see how those electrons are distributed.
Start by looking at the table of Levels and Sublevels. Then check the table of Total Electrons to
see how many electrons each level can contain.
Level 1 contains a single s sublevel = 2 electrons
Lithium has three electrons, which leaves one electron unaccounted for. The table of Levels and
Sublevels shows us that we have used all of the available sublevels in level 1, so we move to the
next level and find that our final electron will be a single electron in level 2, sublevel s. The
electrons for lithium are recorded as 1s

. You can check the electron count by adding the
superscripts. The chemical nature of elements is due to the electrons in the outermost level, so
lithium’s highly reactive nature is a result of the s1 electron in its outermost level.
Sodium, element number 11, is also an alkali metal. It’s a member of the same group IA and has
similar properties. The number of electrons in the first two levels of an atom of sodium is as
follows:
Level 1 contains a single s sublevel = 2 electrons
Level 2 contains s and p sublevels = 2 + 6 = 8 electronsSo far, levels 1 and 2 have given us 10 electrons. But sodium has 11 electrons. The table of
Levels and Sublevels again shows us that we have used all of the available sublevels in levels 1
and 2, so we move to the next level and find that our last electron will be a single electron in
level 3, sublevel s. We can record all of the sublevels as before, and check our electron count
by adding superscripts:

Note that the last added electron is 3s
1
. From the outside, sodium looks just like lithium with a
single s
1
electron in its outermost level. Can you see why Mendeleyev put them in the same
column?
Repeating Electron Patterns
We’re beginning to see that the repeating properties of elements in the periodic table are due
to the repeating arrangement of electrons around the nucleus. Indeed, these and similar patterns appear throughout the periodic table. However, not all cases are as simple as those of
lithium, sodium, and other elements with low atomic numbers.
For all elements after calcium, number 20 on the periodic table, the nearness of energy
between sublevels blurs the order of electron selection. Scanning through the elements,
beginning with atomic number 21, scandium, we see s sublevels being filled before d sublevels
of the previous levels are filled. This is because the s sublevel of level 4, for example, is lower
in energy than the d sublevel of level 3. The nearness in energy between s and d sublevels
makes it important to read the Levels and Sublevels table in a special way. Reading straight
across levels as we did in the previous examples works only up to 3p. After that we need to
switch the fill order of d and s sublevels.