*Toxicity of metallic species-Lead(Pb). .Introduction *Industrial uses *Pollution Sources. *Speciation of Lead. *Environmental levels & Ecological effects. *Transport & Metabolism. *Biochemical effects and toxicology. * Treatment and control measures

1. TOXICITY OF
METALLIC
SPECIES:LEAD(Pb)
Dr. Vikas A. Thakur
Deptt. Of Chemistry
K.B.P.College, Vashi( Empowered Autonomous)

2. Introduction
 Lead :
 Atomic number :82
 Atomic weight :207.2
 Density : 11.34gm/cm3
 Colour: Metallic grey.
 M.P :. :600.61
 B.P.2022K

3. Images of Galena

4. INTRODUCTION
 Lead is one of the seven metals of antiquity.(Gold, Silver, Copper, Tin,
Lead,iron and mercury)
 It was perhaps discovered by accidental dropping of galena(pbs) into a
campfire.
 The average lead content of igneous rock is about 15ppm.
 Hence it is categorized as a rare element.
 Fortunately, it is concentrated as sulphide deposits in many parts of the world.
 Which is easily mined and smelted.
 In Nature, lead occurs mainly as a galena(Pbs), though it also exists as a
carbonate and chloride ores.

6. INTRODUCTION
 Ancient peoples used lead for ornaments, dishes, trays and core for bronze
status.
 As a sinkers for fishing nets etc.
 Greek and Romans use lead extensively for sweetening the bitter taste of the
wine, food cooked in bronze pots, storing Olive oil.etc.
 Incidentally, it is believed that one of the main reason for the fall of Roman
empire was endemic lead poisoning due to over exposure to Pb.
 Sweetening of wine with lead salts caused an endemic disease called as ‘’lead
colic.’’

7. INDUSTRIAL USES
❖ Lead is used in
▪ Building construction.
▪ Preparation of various alloys with Cu, Sn and Sb.
▪ As a accumulator plates in storage batteries.
▪ Paints, pigments and varnishes.
▪ For cable coatings.
▪ For making lead pipes, containers for corrosive liquids and lead chambers.
▪ Ammunition.
▪ White lead, red lead and litharge are used in pigments and paints.
▪ Lead arsenate is used as a pesticide.
▪ Lead borate is used in Plastic Industries.

8. INDUSTRIAL USES
 Lead is used for preparing alloys like Solder, Pewter(3-9 tin + 1 Pb + Sb + Cu)
For making utensils, woods metal(Alloy Bi-50%, Pb-25%, Sn-12.5%, Cd-12.5%)
 Rose metal(Bi-50%, Pb-25%, Sn-25%, ).
 Lipowitz alloy(Cd-38%, Sn-4%,Bi-15%, Pb-8%).
 Newton Metal(Bi-8%, Pb-8%, Sn-3%).
 These fusible alloys are used for making soft solders, electric fuses, safety plugs for
automatic water sprinklers etc.
 Organic forms of lead e,g. Tetra alkyl leads are used as antiknocking additives to
gasoline in internal combustion engines alongwith dichloro ethane or dibromo ethane as
a Scavenger etc.

9. POLLUTION SOURCES
 Tetra alkyl lead accounts for 20% of lead used by mankind accounts for the main
environmental lead pollution problem.
 Street dusts and roadside soils on busy streets may contain Pb in the range of 1000 to 4000
mg.Kg-1.
 Natural weathering process.
 Main source of pollution are mining and smelting of lead ores.
 Emission from automobile exhaust.
 Effluent from storage battery industries.
 Use of glazed earthen wares-containers.
 Lead pipes and lead pigments.
 Hair dyes
 Eye paints.

10. POLLUTION SOURCES
 Canned foods.
 Sea foods.
 Painted toys.
 Wicks in decorative candles.
 Coloured pages in magazines.
 Putty on the window fames.
 Pewter ware et.c.

11. Speciation of Lead
❖ The term Speciation means identification of inorganic, organometallic or organic species
of an element in the environment.
❖ Chemical Speciation is an important aspect of environmental analysis.
➢ The present role of organo-lead compounds in the environment on living system have caused
great concern.
➢ These originate from leaded gasoline and petrol used all over the world.
➢ The organo-lead compounds are more toxic than inorganic lead.
➢ Commercially, Tetra Alkyl Lead(TAL) compounds are important.
➢ Tetra Methyl Lead(TML), Tri Methyl Ethyl Lead(TMEL), Di Methyl Di Ethyl
Lead(DMDEL), Methyl Tri Ethyl Lead(MTEL) and Tetra Ethyl Lead(TEL).
➢ Most organic Pb enters the atmosphere during manufacture, transfer of leaded gasoline and
use in vehicles.

12. Speciation of Lead
 These are also indication of natural methylation of inorganic lead in the environment.
❖ The ionic alkyl Pb compounds are considered as highly toxic to mammals.
❖ TAL compounds in the environment decompose to form highly soluble ionic alkyl Pb.
❖ The degradation appear to follow the path was
❖ PbR4 → PbR3+ → PbR2
2+ → PbR3+ → Pb2+
❖ Where R is the alkyl group.
❖ In order to understand their pathways and toxicity, it is important to use analytical
methods which can be distinguish between inorganic Pb and different forms of organic
Pb.

13. ENVIRONMENTAL LEVELS AND ECOLOGICAL
EFFECTS
 Lead levels of urban dwellers are as high as 200mg.
 Due to continuous use of leaded gasoline, the blood-lead levels of pollution in a major
cities vary between 2 to 35μg/l.
 World Health Organization(WHO)suggests tolerance of 7 μg/kg body weight per day
for adults.
 The degree of inorganic lead poisoning can be indicated by determining lead content in
blood, hair and urine.
 Leafy vegetables, potatoes and beans are likely to absorb more lead than fruiting crops
like tomatoes, beets etc.
 It is beter not to grow carrots, turnips, beet root and sprouts near highways where
contamination by vehicular exhaust is more.

14. ENVIRONMENTAL LEVELS AND ECOLOGICAL
EFFECTS
 The movement of lead into vegetables grown in soil can be controlled from lead by adding
large amount of compost .
 Maintaining soil PH near 6 to 7.
 Human activities have seriously disturb the natural cycle of lead.
 Urgent action is needed to prevent continuity and commulative poisoning of the environment
with lead.
 Improved plant control in smelting operations and improving the automobile engine design
are suggested.
 So that lead free gasoline can be used and at the same time emission of the other pollutants
like CO in the exhaust should be controlled by using suitable catalytic control devices.
 Immediate attention is imperative for controlling Pb pollution because normal levels in
humans are so close to the lowest prescribed safety levels.

15. TRANSPORT AND METABOLISM OF LEAD
 A striking aspect of lead in the body is its very rapid transport to bone and storage there.
 Lead tends to undergo bio-accumulation in bone throughout life and about 90% of the
body burden of lead is in bones after long-term exposure.
 The half-life of lead in human bones is estimated to be around 20Years.
 Some workers exposed to lead in an industries have as much as 500mg of lead in their
bones.
 Out of the soft tissues, the liver and kidney tend to have some elevated lead levels.
 About 90% of blood lead is associated with Red Blood Cells(RBC)
 Measurement of concentration of lead in the blood is standard test for recent or ongoing
exposure to lead.
 This test is used routinely to monitor industrial exposure to lead in screening children.

16. Biochemical effects, Toxicology and Toxicity
➢ Lead poisoning is called Plumbism or Saturnism.
 It has proved to be more dangerous to the children than the adults..
 The reasons to Justify this observations are.
❑ 1.Once the lead enters the human body it tends to concentrate in the bones.
❑ It remains in the bones in a relatively inert form causing no ill effects.
❑ But, When body feels shortage of an essential element like calcium or phosphorous, the
blood leaches out these minerals from the bones .
❑ And supplied it to the relevant organ.
❑ In this process lead to becomes mobile and enters the blood stream.
❑ It is then Concentrates in the tissue where it elicits toxic effects.

18. Images of Plumbism

22.  Since the metabolic rates are higher in children than it adults, the
chances of lead being leached out of the bones are higher in children
than adults.
 2.Due to the higher metabolic rates in children, the ratio between the
quanties of lead consumed through food to the body weight is more in
case of infants.
 3.The opportunities for oral intake of significant amount of lead from
non-food sources e,g. from lead bearing dust soil, painted walls, toys
and plasters is considerably higher in small children.
 The habit of oral exploration, sucking fingers, mouthing and chewing
objects is a natural activity amongst the toddlers.
 Children below the age of five eat flecks of lead contining paints from
the walls of deteriorating buildings.
 This behaviour is termed Picca

23. Toxic Effects
❖ 1.Lead is considered as a general protoplasmatic poison, which is cumulative, slow acting
and subtle.
❖ Although Pb exerts much of its activity through sulphhydryl inhibition, it also interacts with
carboxyl and phosphoryl groups.
❖ Pb causes an inhibition of enzyme activity.
❖ 2.The dearest manifestation of inhibitory effect of Pb is disturbance in the biosynthesis
scheme.
❖ The decrease in heme biosynthesis, causes decrease in life span of red cells and then
decreases in their numbers. This leads to anaemia.
❖ 3.One of the most insidious effects of inorganic lead is its ability to replace carbon in bones
and accumulate there as a reservoir for long term release.
❖ This lead is subsequently remobilized along with phosphate from the bones and exert toxic
effects when transported to soft tissues.

24. ❖ 4.Air-borne lead of small particle size is readily absorbed through the lungs.
❖ On an average only about 10% of inorganic lead that is ingested is absorbed and is
distributed in the various tissues-liver, bones, kidneys and brain.
❖ 5. Chronic exposure to lead causes weight loss, constipation(brain pile) and loss of
teeth.
❖ If exposure of Pb is high for women, it can cause sterility and if pregnant may result
in miscarriage or still birth.
❖ 6.Pb does not permit utilization of O2 and glucose for life sustaining energy
production.
❖ 7. There might be leaching of Pb from bones into blood with Ca.
❖ 8.Organic lead, as tetra ethyl lead and tetra methyl lead is even more acutely
poisonous( 10 to 100 times) than inorganic lead.
❖ Tetra ethyl Lead(TEL) is non-polar and lopophilic and hence is less soluble in water
than inorganic lead.
❖ TEL is absorbed by inhalation of the volatile compound or by dermal entry into the
body.
❖ Brain is target organ for tetra ethyl Lead

25. Treatment of Lead Poisoning
❑ Treatment of lead poisoning consists in supportive measures and chelation therapy.
❖ (1) Treatment is carried out with chemotherapeutic reagents.
❖ Two agents are administered in the body by injection- BAL(British Anti Lewisite) and
Ethylene Diammine Tetra Acetic Acid(EDTA).
❖ This reduces tissue level of Pb to normal and then D-Penicillammine can be administered
orally as follow up therapy.
❖ (2) Lead poisoning can be cured by treatment with chelating agents, which strongly binds
Pb2+.
❖ Thus Calcium chelate in solution is fed into the victim of lead poisoning.
❖ Pb2+ displaces Ca2+ from the chelate and the resulting Pb2+ chelate is rapidly excreted in
the urine.
❖ (3) Treatment in acute poisoning by Pb compounds cannot be treated with any chelating
agents. Sedative, anticonvulsant and fluid and electrolytic therapy may be required.

26. Control Measures on Lead Poisoning
❖ (1). Control measures have to be instituted at every stage of lead processing : mining,
Extraction and manufacture of commodities.
❖ The lead smelting and refining plants are located in isolated regions.
❖ (2).The most commonly used technique to reduce air borned emissions is the electronic
Precipitator.
❖ (3). The lead content of natural water system is removed by adding lime or dolomite.
❖ Lead gets precipitated as insoluble hydroxide or carbonate.
❖ Old Pb water pipes has to be changed
❖ (4).More environmentally friendly materials are replacing lead-based commodities.
❖ The use of titanium dioxide in place of lead pigments in paints has brought down cases of
pica.
❖ (5). Unleaded petrol is gradually replacing the conventional leaded gasoline.

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