CAREER POINT UNIVERISTY
MAJOR ASSIGNEMNT CHEMISTRY
Anugyaa Shrivastava K12986
Ashish Kumar Jha K12593
Sanjay Singh Chaudhary K12336
TOXIC CHEMICALS IN THE
Of the numerous chemicals present in the atmosphere, only
some are toxic. The toxic chemicals are released mostly from
chemical activities. They get into human food chain and once
they get in there, they often lead to fatal consequences. An
effort will be made here to study the mode of action of these
chemical in chemical toxicology.
The list of these chemicals is very long and even now,
one is not sure whether a particular chemical is toxic or not,
since non-toxicity has not been adequately established. Any
division of these basis can be misleading. Many of these
listed as environmental hazards are often essential
ingredients for animal growth, viz. Al, Ba, B, Co, Cu, Cr, etc.
Sonwatz drew a concentration line, to show the
1. Essential in trace level for sustenance of life process,
2. Toxic in higher levels, causing adverse effects, and
3. Deficient in lower levels causing metabolic disorder.
Thus, even well-known toxic elements as Pb, Cu, Cd are
required in trace quantities for animal growth. The well-
known inert Al, causes brain disorder.
Toxic chemicals can be classified according to their
environmental effect. The US Environmental protective
agency has listed 24 extremely hazardous chemicals found in
the atmosphere. Acetonitrile, As, Asbestos, Benzene, Be, Ca,
Chlorinated solvents are some of them.
TOXIC ELEMENTS IN WATER
Toxic Elements in Waste Water and Normal Water
Elements Sources Effect
Arsenic Byproducts of
Boron Coal, detergent
Toxic to some
Beryllium Coal, nuclear
power and space
Copper Metal plating,
Toxic to animals +
algae at moderate
Floride Natural geological
Bone damage at
about 5 ms/1
Lead Industry, mining
coal and gasoline
Anemia, wild life
plating and water
activities + coal
Highly toxic in all
Molybdenum Natural resources
+ Industrial waste
Possibly toxic to
Selenium Natural sources Toxic at higher
Zinc Industrial waste
Toxic to plants at
*K. Schwartz, Chemical Toxicology of metals (Elsevier, 1977)
cited in G.S. Fell, Metals in Environment Chem, Britain, 1980.
PESTICIDES IN WATER
Drainage of agricultural land does leave a large number of
pesticides belonging primarily to two major groups.
Chlorinated hydrocarbons and the more biodegradable
IMPACT OF TOXIC CHEMICALS ON
Toxic chemicals attack the active sites of enzymes, and thus
inhibit enzymes functioning. Divalent Cd2+
effective enzyme inhibitors, they have affinities for
containing liquid SCH3 and SH, which are part of the enzyme
These enzymes known as metalloenzymes contains
metals in their structures and thus inhibit the functioning of
the enzyme. One metal ion is replaced by another metal of
similar size. Thus, Zn2+
in some metalloenzymes is replaced by
leading to Cd2+
The biochemical effects of some typical toxic substances
are discussed below.
BIOCHEMICAL EFFECTS OF ARSENIC
This metal commonly occurs in all herbicides, fungicides and
insecticides. Triopositive As3+
is most toxic, and it attacks SH
groups of an enzyme thereby inhibiting enzyme action.
This adversely affect the generation of cellular energy in the
citric and cycle, which is based on the inactivation of
pyruvate dehydrogenase by complexation with As(III)
preventing the generation of ATP.
P and As have a chemical similarities, therefore, As
interferes with some of the biochemical ATP (adenosine
triphosphate). An important step in ATP regeneration is the
enzymatic synthesis of AQ single compound
High concentration of As (III) compounds coagulates
proteins and attaches s bonds maintainingthe secondary and
tertiary structures of proteins.
The general antidotes for As poisoning are devices
having----SH groups are capable of bounding to As (III).
In nature Cd occurs in association with Zn minerals.
Growing plants require Zn and they up and concentrate Cd.
BIOCHEMICAL EFFECTS OF LEAD
Lead is relatively abundantin nature and the major source of
lead is in the combustion gases of petrol and gasoline. Lead is
added primarily as lead tetraethyl and tetramethyl. Pb(C2H5)4,
Pb(CH3)4 along with scavengers 1,2 dichloro methane CH2
Pb(CH3)4 and 1,2 dichloro ethane, Pb(C2H5)4. This causes an
enrichment in street dust amongst other things.
The major biochemical effect of lead is interference with
heme synthesis which leads to haematological damage. Pb
inhibits several key enzymes. An important phase of heme
synthesis is conversion of delta aminolevunic acid to
The overall effect is the disruption of the synthesis of
haemoglobin and allied respiratory pigments like
cytochromes, which require heme.
Pb also does not permit utilization of O2 and glucose. The Ag
interference can be detected at lead levels in the blood of
about 0.3 ppm. At higher level of Pb in the blood, symptoms
of anemia appear due to haemoglobin deficiency Pb level
(0.5-0.8) ppm are dysfunction of kidney and finally, brain
Due to chemical analogy of Pb2+
, bones act as
respositories of Pb in the body.
Lead poisoning can be cured by treatment with chelating
agent which binds Pb2+
1. Chlor-alkali plants must stop using Hg electrodes, and
switch-over to new technology.
2. All mercurial pesticides banned or restricted to a limited
BIOCHEMICAL EFFECTS OF CARBON
The global atmosphere contains about 530 million tonnes of
CO with an average residence of 36 to 100 days.
It attacks haemoglobin and forms carboxy haemoglobin
O2Hb + CO COHb + O2 (Hb = haemoglobin)
The initial effect of CO poisoning is loss of awareness and
BIOCHEMICAL EFFECTS OF PESTICIDES
The biochemistry of pesticides is of considering significance,
and constitue the major mechanism by which pesticides in
the environment are degraded and detoxified.
Amongst the pesticides, the biological action of DDT on
the environment has been most extensively studied. DDT is
fairly stable persists in the environment while the
organophosphate and carbomates degrade quite rapidly in
the environment. The latter reacts with O2 H2O, undergoing
decomposition in a few days in the environment producing
compounds which are non-toxic.
The mechanism of action of these insecticides is that
they inhibit the vital enzyme, acetylcholine sterase as per the
Acetylcholine neurotransmitter which triggers nerve
cells insecticide the nerve cells called synapse contains the
enzyme chloniesterarte, which decomposes acetylcholine
and prevents the nerve cells from firing in steps (1) and (2).
In the first step, the enzyme acts upon acetylcholine
preventing it from acetyl enzyme and one of the products,
chlorine. In the next, the actual enzyme is decomposed by
H2O to form CH3COOH regenerating the enzyme.
An organophosphateinsecticidecan mimic acetylcholine
and induce the formation of a phosphonyl enzyme, the rate
of the reaction is determined by the rate of displacement of
X group from P by the enzyme. In step(2), breakdown of this
intermediate is much slower than that of that actual enzyme
in A (2).
DDT IN FOOD CHAIN
As mentioned above, DDT is a persistent chemical. Once
introduced into the environment, it keeps circulating for
It is interesting to note the manner in which DDT
accumulates in the food chains. Plankton in river/sea water
contains about 0.04 ppm DDT. The clams that consume
planktonconcentrate it ten times, i.e., they contain about 0.4
ppm DDT. From clams, to fish which feed on this clams, to
fish eating birds, the DDT level builds up from 0.4 to 2.1 and
up to 75.5 ppm.
DDT which was first introducing during World War II, is
widely used in agriculture. It was later banned because of its
long-term effects on health. DDT does not act on human
system in the same way as on insects. The potential long-
term effects of DDT being stored in the human body
compelled the environmental protection agency to ban DDT
particularly in areas where it is still endemic.
It is a well-known fact that birds having higher levels of
DDT is threatened with extinction, as the eggshells become
too thin and fragile due to interferences with hormones
which control calcium deposition.
METHYL ISOCYNATE (MIC)
Methyl isocynate CH3NCO (MIC) is the raw material for the
production of carbomate pesticide. MIC is a volatile liquid
(bpt 43-45°C), extremely hygroscopic and is, therefore,
stored in moisture-free refrigenration tanks.
It is synthesized by its reaction of phosgene with
primary amine. The intermediate product is decomposed by
heating with time.
CH3NH3Cl + CoCl2 CH3NHCOCl + 2HCl
2CH3NHCOCl + CaO CH3NCO + CaCl2 + Ca(OH)2
MIC is always associated with unreacted phosgene,
CoCl2 to the event of 2%. The threshold limiting value of MIC
is 0.02 ppm and for CoCl2 is 0.1 ppm. It can be fatal for most
A.K. De, Environment Chemistry, Wiley Eastern Limited.
B.L. Valle and D.D. Ulmen, Biochemical Effects of Lead,
Cadmium and Mercury.
R. White Stevens, Pesticides in Environment,Marcel Dekkar
Inc. New York (1971).
J. Weber, ”The pesticides scoreboard”. Environ. Sc. Tech.
C.A. Edwords, Pesticides in Environment, 2nd
ed., CRC Press,