heavy metals chromium - air pollution
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HEAVYMETALS
INAIRPOLLUTION- CHROMIUM
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CONTENTS
APPEARANCE
DEFINITION
GENERAL PROPERTIES
SOURCES
NATURAL SOURCES OF CHROMIUM
HEALTH EFFECTS
ENVIRONMENTAL EFFECTS STANDARDS AND REGULATIONS
USES
APPLICATIONS
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APPEARANCE:
SILVERMETALLIC
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DEFINITION
Chromium is a hard steel-gray metal that is highly
resistant to oxidation, even at high temperatures.
It is the sixth most abundant element in the
earths crust, where it is combined with iron and
oxygen in the form of chromite ore.
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GENERALPROPERTIES
Name, symbol, numberChromium, Cr, 24
Atomic number 24
Atomic mass 51.996 g.mol-1
Density 7.19 g.cm-3at 20C
Melting point 1907 C
Boiling point 2672 C
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SOURCES
Chromium is a naturally occurring element found in rocks, animals,
plants, soil, and in volcanic dust and gases.
The most common forms are chromium(0), chromium(III), and
chromium(VI).
No taste or odor is associated with chromium compounds.
Chromium(III) occurs naturally in the environment and is an essential
nutrient.
Chromium(VI) and chromium(0) are generally produced by industrial
processes. The metal chromium, which is the chromium(0) form, is
used for making steel.
Chromium(VI) and chromium(III) are used for chrome plating, dyes
and pigments, leather tanning, and wood preserving.
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NATURALSOURCESOFCHROMIUM
It is a trace metal.
A trace metal is available in extremely small quantities, whichare present in animal and plant tissues.
Other trace metals include
Iron
Zinc
Copper
Nickel
CobaltVanadium
Arsenic
Molybdenum, and Selenium.
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SYMPTOMSOFCHROMIUMDEFICIENCY:
Anxiety,
Depression,
Irritability, Diabetes.
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FOODSOURCESOFCHROMIUMINCLUDE:
Whole grains,
Bread,
Brown rice,
Meat,
Mushrooms,
Green beans,
Brewers yeast, Beef, Beer, Chicken breast and
Fresh vegetables.
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CHROMIUM- CR
Chromium(III) is an essential nutrient for humans and
shortages may cause heart conditions, disruptions of
metabolisms and diabetes
But the uptake of too much chromium(III) can cause
health effects as well, for instance skin rashes
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CHROMIUM- CR
Chromium(VI) is harmful to human health, mainly forpeople who work in the steel and textile industry
People who smoke tobacco also have a higher chance
of exposure to chromium
Hexavalent ChromiumChromium (VI) is a species of
chromium that is forbidden to use in electrical &
electronic industry by RoHS Directive.
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HEALTH EFFECTS
When it is a compound in leather products, it can cause allergicreactions, such as skin rash
After breathing it in, chromium(VI) can cause nose irritations and
nosebleeds
Upset stomachs and ulcers
Respiratory problems
Weakened immune system
Kidney and liver damage
Alteration of genetic material
Lung cancer
Death
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ENVIRONMENTALEFFECTSOFCHROMIUM
Most of the chromium in air will eventually settle and end up
in waters or soils
Chromium in soils strongly attaches to soil particles and as aresult it will not move towards groundwater
In water chromium will absorb on sediment and become
immobile
Only a small part of the chromium that ends up in water will
eventually dissolve
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ENVIRONMENTALEFFECTSOFCHROMIUM
Chromium(III) is an essential element for organisms that
can disrupt the sugar metabolism and cause heart
conditions, when the daily dose is too low
Chromium(VI) is mainly toxic to organisms - it can alter
genetic materials and cause cancer
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ROUTESOFEXPOSUREFORCHROMIUM
The entry routes of chromium into the human body are
inhalation, ingestion, and dermal absorption.
Occupational exposure generally occurs throughinhalation and dermal contact, whereas the general
population is exposed most often by ingestion through
chromium content in soil, food, and water.
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ISATRISKOFEXPOSURETOCHROMIUM
Chromium is one of the most widely used industrial
metals.
Several million workers worldwide are estimated to be
exposed to chromium compounds in an array of industries
such as ,
1) pigment production,
2) chrome plating,
3) stainless steel welding, and
4) leather tanning.
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WORKEREXPOSURE
Workers in industries that use chromium are at increased
risk of chromiums adverse health effects.
Those workers at greatest risk are those involved instainless steel welding, chromate production, chrome
plating, and chrome pigment industries, where exposure
is primarily to Cr (VI) via inhalation of aerosols.
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STANDARDSANDREGULATIONSFORCHROMIUM
The Occupational Safety and Health Administration (OSHA)
has established an 8-hour time-weighted average (TWA)
exposure limit of 5 micrograms of Cr(VI) per cubic meter of air
(5 g/m).
OSHAs standard is based upon the best evidence currently
available that at the previous for Cr(VI), workers face a
significant risk to material impairment of their health.
The evidence in the record for this rulemaking indicates that
workers exposed to Cr(VI) are at an increased risk of
developing lung cancer.
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STANDARDSANDREGULATIONSFORCHROMIUM
The final rule also contains ancillary provisions for worker
protection such as ,
requirements for exposure determination,
preferred exposure control methods,
respiratory protection,
protective clothing and equipment,
hygiene areas and practices,
medical surveillance,
record keeping, and
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TOXICITYOFHEXAVALENTCHROMIUM
Severe and often deadly pathological changes are associated with
excessive intake of Cr(VI) compounds.
Cr(VI) exerts toxic effects on biological systems.
It has been found that occupational exposure to hexavalent
chromium compounds leads to a variety of clinical problems.
Inhalation and retention of materials containing Cr(VI) can cause
perforation of the asthma, bronchitis, inflammation of the larynx and
increased incidence of bronchogenic carcinoma.
Skin contact of Cr(VI) compounds can induce skin allergies.
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TOXICITYOFHEXAVALENTCHROMIUM
Hexavalent chromium compounds are irritating and
corrosive when allowed to come in contact with skin, the
digestive system or lungs. Chromium trioxide (CrO3) is a
common toxic hexavalent chromium compound.
In fact, chromic baths used to soak and clean laboratory
glassware are very toxic and are a safety risk to use incommon laboratory situations.
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USESOFCHROMIUM
Chromium is resistant to ordinary corrosive agents at room
temperature, which explains its uses as an electro-plated,
protective coating.
It is also used in ferrous and nonferrous alloys, in refractories,
and in chemicals.
Ferrous alloys, mainly stainless steels, account for most of the
consumption.
These steels have a wide range of mechanical properties as
well as being corrosion and oxidation resistant.
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USESOFCHROMIUM
Cast irons may contain from 0.5% to 30% of Cr, which
provides harden ability enability, toughness and corrosion
and wear resistance.
Chromium is also widely used in nonferrous alloys
(nickel, iron-nickel, cobalt, aluminum, titanium and
copper).
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OTHERUSES
Chromium(III) oxide is a metal polish known as green rouge.
Chromic acid is a powerful oxidizing agent and is a useful compound
for cleaning laboratory glassware of any trace of organic compounds.
Sodium dichromate is sometimes used because of its higher solubility
(50 g/L versus 200 g/L respectively). The use of dichromate cleaning
solutions is now phased out due to the high toxicity and
environmental concerns.
Potassium dichromate is a chemical reagent,used as a titrating agent.
It is also used as a mordant (i.e., a fixing agent) for dyes in fabric.
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APPLICATIONS
The largest amount is consumed to manufacturepigments for use in paints and inks.
Other applications include leather tanning, metal
corrosion inhibition, drilling muds, textile dyes, catalysts,
wood and water treatment.
Chromite is used in the refractory industry to make bricks,
mortar, and ramming and gunning mixes.
Chromite enhances their thermal shock and slag
resistance, volume stability, and strength.
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ENVIRONMENTALISSUES
As chromium compounds were used in dyes and paintsand the tanning of leather, these compounds are often
found in soil and groundwater at abandoned industrial
sites, now needing environmental cleanup and
remediation per the treatment of brownfield land.
Primer paint containing hexavalent chromium is still
widely used for aerospace and automobile refinishing
applications.
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