Toxicity of metallic species, Aresenic.pdf

Toxicity of Metallic Species
Arsenic(As)
Dr. Vikas Anant Thakur
Department of Chemistry
K.B.P.College Vashi( Empowered Autonomous)

Introduction
 Arsenic:
 Symbol : As
 Atomic Number : 33
 Atomic Weight : 74.921
 Density : 5.723 g/cm3

Introduction
❑ Arsenic is a metalloid which is widely distributed in the biosphere.
➢ It was used in medicine and as a poison in ancient times.
➢ It is another Chalcopile element and it accumulates in sulphide deposits.
➢ It is distributed in earth’s crust at an abundance level of about 2 ppm.
➢ It exists in nature mostly as sulphide ore.
➢ Copper aceto arsenite is another feed additive.
➢ Arsenic is found in concentration of about 1% in Pb-Zn concentrates used in
smelters and because of its volatility.(Sublimation point of As in 650 0C).
➢ It can be spread into atmosphere as a pollutant.

Introduction
❖ The greatest source of pollution from Arsenic is its use in agricultural chemicals
such as weed killers, fungicides, insecticides and rat poisons.
❖ Arsenous oxide which is known as white arsenic, is produced a by product in
smelting of copper, lead and gold ores.
❖ Arsenic occurs in the air wherever coal is burnt, particularly near smelters and
refineries.
❖ Sea water contains 2 to 5 ppb of As and in public water supplies, its concentration
may be higher.
❖ In normal soils, 1 to 40 ppm of As may be present.
❖ But in areas where continuous arsenical sprays used, high levels can be observed.

Industrial Uses and Pollution Sources
 Elemental Arsenic is used in the
 manufacture of glass, particularly infra-red transmitting glass.
 In the manufacture of electrical semi-conductors and photo conductors .
 Iin the manufacture of linoleum and oil cloth.
 As2S3 is used as depilatory for hides. It is highly refractory material.
 It is also used in pigments and in light filters as thin sheets.
 Hemiselenide of Arsenic is used in glass manufacture.
 As2O3 is a byproduct in smelting operation.
 As2O3 is used in rodenticides, insecticides, herbicides and as a mordant in textile industry.
 Lead Arsenate, Sodium Arsenate and Calcium arsenate were used as pesticides.

Industrial Uses and Pollution Sources
 Mono Sodium arsenate and dimethyl Arsenic Acid are specifically used as weed killers.
 Chromated Copper Arsenate(CCA) and Flurochrome arsenate Phenyol(FCAP) are used as
wood preservative.
 Elemental Arsenic is incorporated in some copper and lead-based alloys to enhance their
hardness and thermal resistance.
❖ Arsenic released from natural agencies such as weathering processes on a global scale is
estimated to about 8 x 104 metric tonnes per year.
❖ While manmade activities account Arsenic for about 24 x 104 metric tonnes per year.
❖ Environmental arsenic pollution occurs mainly from its release into air from smelting of As
containing ores, burning of coal and use of arsenic compounds in various applications such
as fungicides, insecticides, herbicides, pesticides and preservatives.

 Arsine (AsH3), which is a byproduct of many industrial processes involving
arsenic, is the most poisonous of all arsenicals.
 It is toxic even at dilutions of 1:20,000.
 Cases of chronic arsine poisoning were reported in workers involved on ore
smelting and metal refining, etching, soldring, galvanizing and lead plating
operations.
 Arsine may be liberated by the action of fungi in sewage plants.
 Accidental Arsine poisoning was reported in Petroleum Industry.

Speciation of Arsenic
❖ The term Speciation means identification of inorganic, organometallic or organic
species of an element if in the environment.
❖ Chemical Speciation is an important aspect of environmental analysis.
❖ Sodium borohydride(NaBH4) reduction is usually used for total arsenic content using
AAS.
❖ NaBH4 is also used for reduction of alkyl and aryl arsenic compounds.
❖ As(III) is reduced to AsH3 above pH 4 while As(IV) is reduced at pH 1.5.
❖ Methyl arsenic compounds are found in several water bodies in substantial %. But
these are small % of total As in sea water.
❖ Arsenic speciation in air samples is carried out using a glass wool filter to trap the
particulates followed by silvered glass beads to trap volatile arsines.

❖ Ambient air appear to contain As. Mostly as the inorganic species, some
(CH3)3As in vapour form and some methyl arsenic compounds as particulate.
❖ Speciation of As in water, urine and biological samples has been conducted
by I- reduction instead of NaBH4 reduction.
❖ As(V) compounds are converted to iodides in the presence of I- which are
then allowed to react with diethyl ammonium, diethyl dithio carbonate to
form the As- complexes of diethyl dithio carbonates.
❖ [As(C2H5)2 NCS2]3
❖ [CH3- As(C2H5)2 N-CS2]
❖ [(CH3 )2- As(C2H5)2 N-CS2]
❖ These complexes are then separated by Ge with an electron capture detector.
❖ The detection limits are 73 ng/l for inorganic As, 40 ng/l for methyl arsenic
compounds and 15 ng/l for dimethyl arsenic compounds.

Environmental levels and Ecological Effects
 Most human foods like vegetables, fruits, dairy products and meats contain less than 0.5ppm and
it rarely exceed 1 ppm of Arsenic.
 On the other hand, foods of marine origin are much richer in Arsenic.
 Mussels, Oysters and bony fish contain As upto 120 ppm, 3 to 10 ppm and 2 to 8 ppm
respectively.
 The total amount of As in normal adult human body was estimated at 1.5 to 20 mg or 0.2 to 0.3
ppm.
 Analysis of As in human hair and blood gives an indication of As poisoning and it can be done
by Neutron activation analysis.
 Normal cows milk contains 0.03 to 0.06 ppm of As.
 Subsequent methylation of arsenic takes place by some soil microbes such as bacteria and fungi
leading to release of dimethyl and trimethyl arsine.

Biochemical Effects, Toxicology and Toxicity
 Arsenic is a general protoplasmatic poison and it affects all the systems in the body.
 It is a cumulating poison.
 The major biochemical effects of Arsenic are
❖ 1. Complexation with coenzymes.
❖ 2. Uncoupling of phosphorylation and
❖ 3. Coagulation of proteins.
▪ Trivalent arsenicals react with Sulphhydryl (-SH) groups in cells and thus inhibit the
sulphhydryl containing enzyme systems essential to cellular metabolism.
▪ SH O- S
▪ Enzyme + As --- O EnZyme S As –O

 The pyruvate oxidase( or pyruvate dehydrogenase) system gets inactivated by
complexation with As(III).
 Thus the generation of adenosine Triphosphate(ATP) which is an important energy
source is inhibited.
 The enzymes generating cellular energy in the citric acid cycle are also adversely
affected.
❖ Arsenic uncouples phosphorylation.
❖ Arsenic also interferes with some biochemical processes involving phosphorous due to
the similarity in their chemical properties.
❖ This is particularly noticed in the biochemical generation of ATP.
❖ A vital step in the generation of ATP is the enzymatic synthesis of 1,3-
diphosphoglycerate from glyceraldehyde 3-phosphate.
❖ Arsenic(III) interferes in this reaction by producing 1-arseno, 3-phosphoglycerate
instead of 1,3-diphospha glycerate.
❖ The former compound undergo spontaneous hydrolysis forming 3-phosphoglycerate
and arsenate.
❖ Thus, instead of phosphorylation, arsenolysis takes place.

 Arsine(AsH3) combines with haemoglobin and is oxidized to a hemolytic compound
that does not appear to act by sulphhydryl inhibition.
❖ Low chronic doses of arsenic ingested tend to accumulate in lipid rich tissues.
❖ High Arsenic levels in man are usually found in hair, nails and skin.
❖ When Arsenic is inhaled, it is deposited in lungs and is retained in the lung tissues for
a long time.
➢ Soluble arsenicals are absorbed from all mucous membrane.
➢ Arsenic containing ointments or lipid soluble Vesicants are absorbed through the skin.
➢ Non-allergic contact dermatis and conjunctivitis are frequently suffered by workers
exposed to arsenic containing dusts.
➢ Continued inhalation of arsenic dusts may cause perforation of the nasal septum, as is
the case with Chromium and other metallic dusts.

❖ Chronic ingestion of inorganic arsenic causes peripheral arterio sclerosis,
commonly known as black foot disease.
❖ It may also cause peripheral neuritis resulting in motor and sensory paralysis of the
nerve extremities.
❖ Arsenic is toxic to liver and it produces fatty infiltration and causes central necrosis
and cirrhosis.
❖ Arsenic poisoning also affects bone marrow and cellular elements of blood.
❖ Symptoms include sensory changes, muscle sensitivity, prickling and tingling
sensations(Paresthesia) and muscle weakness.
❖ Liver injury is a common symptom of chronic arsenic poisoning.
❖ Studies of victims of chronic Arsenic poisoning from contaminated drinking water
in Taiwan and Chile have exhibited blueness of the skin in extremities. This
condition is called as acrocyanosis which is result of peripheral vascular disease.
❖ In extreme case, this may progress to gangrene and in lower extremities, a
condition is called black foot disease.
❖ Arsenicals are carcinogenic to lungs in humans. They also lead to skin cancer.

Treatment for Arsenic poisoning
❖ Acute Arsenic poisoning is usually diagnosed by gastro-intestinal symptoms such
as intense pain, projectile vomiting, diarrhea etc.
❖ Followed by shock, hypoxic convulsions and coma.
❖ Sometimes headache, vertigo, loss of memory followed by stupar and coma may
occur without any gastrointestinal symptoms.
❖ Acute Arsenic poisoning is treated with the antidote, Dimercaprol(British Anti-
Lewsite, BAL).
❖ Restriction of fluid and electrolyte balance is mandatory.

Control measures for Arsenic
❖ 1. Arsenic should be banned in pesticides, paints and pigments.
❖ 2. Arsenic is avoided with lead for making better bullet shots.
❖ 3. Waste water containg As is treated properly and then discharged into the
environment.
❖ 4. Electrostatic precipitation used to control the release of As polluted in the air.
❖ 5.Electrodialysis to remove Arsenic from water.

 Q. The sources and toxic effects of Arsenic.
❖ Arsenic Sources:
➢ 1.Weathering of rocks, forest fire, volcanic erruptions etc.
➢ 2.Arsenicals used in pesticides, fungicides and wood preservatives.
➢ 3. As is combined with Pb and used in industries.
➢ 4.As is used in textile industry, Calico painting, paints and pigments.
➢ 5.As is used in making opal glass and in bullet shots.
❖ Health Hazards.:
➢ 1. General weakness, fatigue.
➢ 2.Respiratory distress.
➢ 3.Cardiac damage.
➢ 4. Gastro-intestinal problems.
➢ 5.Nervous system disorder.
➢ 6.Skin infection.
➢ 7.Lung and skin cancer.

Toxicity of metallic species, Aresenic.pdf

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