MAIN PARAMETERS DETERMINING
THE DANGER AND ENVIRONMENTAL
FATE OF CHEMICALS
ENVIRONMENTAL DISTRIBUTION
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The chemicals introduced into the environment for specific
purposes and in various manners.
will move from the entry point (phase environmental air,
water, soil) to their final destination, which is the
environmental sphere for which they have the greatest
affinity.
this segment can block or simply act as a reservoir so that
the chemicals can be transferred back to other sectors.
Undergo transformations included in each environmental
biota.
ENVIRONMENTAL DISTRIBUTION
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Pathways by which pollutants enter in the ecosystems
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Surface water
Contamination of the soil
Discharge into the atmosphere
ENVIRONMENTAL DISTRIBUTION
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Mode of release of pollutants in ecosystems
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Unintentional release in the course of human activitiesmining operations, shipwrecks, fires
 Dumping of waste-sewage, industrial effluents, discharges.
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Application of pesticides
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Natural action-ex. volcanic eruptions
ENVIRONMENTAL DISTRIBUTION
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The methods of contaminant dispersion in different
media
reflect the optimum conditions of distribution of the
pollutant and depend on its physical-chemical properties.
ENVIRONMENTAL DISTRIBUTION
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methods of contaminant dispersion in different media
if it is volatile can be released into the air and carried by the
wind;
if non-volatile with moderate or strong affinity for
adsorption by soil can be transported from the dust by wind
erosion;
if soluble in water and with low tendency to be adsorbed by
soil can be leached, infiltrate and percolate into groundwater;
can dissolve in runoff water and discharged into surface
waters;
ENVIRONMENTAL DISTRIBUTION
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The methods of contaminant dispersion in different
media
with strong affinity for soil and sediment
can be resuspended and poured with water during floods;
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if present in groundwater
may spill into surface water by discharge points where
present (wells, springs);
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if it is adsorbed in sediments
can be broken down into the water and interstitial pores
and become bioavailable;
ENVIRONMENTAL DISTRIBUTION
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Processes that can undergo a pollutant molecules
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Volatilization
transport: leaching, runoff, immobilization:
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Absorption occurs mainly in biota
 Adsorption occurs primarily on the surfaces of suspended
particulate matter, sediments and soil.
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The adsorbed molecules can still be degraded.
degradation:
Chemistry: hydrolysis, oxidation and reduction;
Physics: photolysis, dissociation and ionization;
Biological: biodegradation
ENVIRONMENTAL DISTRIBUTION
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Transport and “fate in soil”
* Leaching through the soil
* washout
* adsorption
* biodegradation
* accumulation
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Bioaccumulation in plants and animals and possible
metabolism
* volatilization
* phototransformation
ENVIRONMENTAL DISTRIBUTION
Transport and Fate in aquatic environments
biodegradation
photodegradation
Bioaccumulation in aquatic organisms
volatilization
Adsorption on suspended solids and sediments
ENVIRONMENTAL DISTRIBUTION
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Transport and Fate in the air
photodegradation
inhalation
absorption
precipitation
ENVIRONMENTAL DISTRIBUTION
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The physico-chemical properties of the pollutants and
the characteristics of the abiotic
–
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Ex. properties of molecules:
–
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determine how long and in what form a substance will or will
move to / from a given sector
mass, charge, solubility, Henry's law constant, vapor pressure,
partition coefficients
Ex. properties of the compartments:
–
pH, organic matter, soil texture, fine particulate matter,
temperature, etc..
ENVIRONMENTAL DISTRIBUTION
BREAKDOWN MECHANISMS
Mechanisms by which a substance
tends to move towards the environmental compartments
(air, water, soil, biomass, sediment) for which it has a
greater degree of affinity:
This affinity is determined
by the physical-chemical characteristics of the molecule
and the characteristics of the sector
ENVIRONMENTAL DISTRIBUTION
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MECHANISMS OF BREAKDOWN
Physico-chemical properties of the molecule:
molecular weight, density, melting point, boiling point,
solubility in water or other solvents (eg organic), vapor
pressure, partition coefficients
Features of the sector:
hydrophobicity (presence of groups with or without
charge), pH, temperature, physical state,
ENVIRONMENTAL DISTRIBUTION
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persistence:
understood as a residence is the residence time of a
pollutant in a given sector, whatever the way which it is
removed (degradation, mass transit, absorption).
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Resistance to degradation:
ability of a substance to remain unaltered in the
environment.
is represented by the half-life , which is generally related to
the various environmental compartments.
ENVIRONMENTAL DISTRIBUTION
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degradation
phenomenon that results in the elimination of a substance
by reaction
organic:
Biodegradation: aerobic and anaerobic organisms
Metabolism: higher organisms (production of metabolites)
abiotic:
photodegradation,
hydrolysis,
oxidation-reduction
ENVIRONMENTAL DISTRIBUTION
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The resistance to degradation depends on:
Similarity of the xenobiotic to a natural compound
Concentration (threshold needed for induction)
Possible toxic effect on microorganisms
poor bioavailability
Chemistry (polyaromatic rings with many Cl-are not
attachable)
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By environmental factors:
Physical: radiation, temperature, humidity
Chemicals: essential nutrients, pH, redox potential,
reactive species
Biological
ENVIRONMENTAL DISTRIBUTION
Biodegradation
Structural transformation of an organic compound
produced by reactions performed by microorganisms
Primary biodegradation or functional
other organic compounds (typically "smaller")
Total biodegradation or mineralization:
CO2, NH3, PO42-, H2O, SO42-
ENVIRONMENTAL DISTRIBUTION
Biodegradation
detoxification
Primary biodegradation is expected to lead directly
to less toxic compounds of the initial ones.
The primary biodegradation can lead
products more toxic, but less stable and more easily
degradable.
ENVIRONMENTAL DISTRIBUTION
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Biodegradation
substrate
with LOWER CONCENTRATION
can not induce the enzymes necessary for the
biodegradation
TOO CONCENTRATED
can be toxic to microorganisms
ENVIRONMENTAL DISTRIBUTION
Biodegradation
Very frequently biodegradation are carried out by
different microorganisms that operate togheter in
succession
microorganisms:
bacteria
mushrooms
protozoa
ENVIRONMENTAL DISTRIBUTION
Biodegradation
The greater biotransformations that occur in
biodegradations:
OXIDATION
REDUCTIONS
HYDROLYSIS
With these reactions
the xenobiotic is converted into compounds structurally
similar to the compounds usually metabolized by the
microorganism, which then degrades them in its normal
metabolic cycle.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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The first step in the risk analysis,
hazard identification of chemicals (hazard identification)
and their potential environmental fate.
becomes important to know
the physical, chemical, toxicological and bioaccumulation
of the substances in question
to assess the risk of their presence in the environment.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
PHYSICAL-CHEMICAL PARAMETERS
The physico-chemical parameters
only depend on the type of chemical
uniquely identify the substance.
parameters are obtainable by investigations in the
laboratory or from the literature.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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Temperature of Melting and Boiling
Knowing these two values,
can provide an idea of the physical state in which these
substances are found in nature.
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However, a substance can pass in the gaseous phase much
before the temperature reaches the boiling temperature
(volatility).

These two reference temperatures taken individually do not
have a lot of use from the environmental point of view;
they become, on the contrary, very useful for estimating
other properties.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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Solubility
is one of the most important factors that determine the
transport of pollutants in the subsurface.
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represents the ability of a substance to dissolve in water
is indicated by the ratio between the amount solute and the
volume of the solvent, in the environmental practice
represented by water.
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is a characteristic parameter of the substance
that changes with the conditions of temperature and
pressure and is generally expressed in mg / l in moles / l.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Solubility
Ionic and polar substances dissolve in water
Substances non-polar or weakly polar dissociate in water
in very low percentages.
Environmentally hazardous substances such as dioxins,
PCBs and some organochlorine pesticides, are weakly
dissolved in water.
These same substances are, however, dissolved in the most
important of the non-polar solvents and weakly polar or
lipid biotic.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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density
The density of a fluid ρ (g / cm ³), defined also in relation to that of
water which has a unit value,
is an important parameter since it determines the behavior of fluids in
the soil with respect to water.
compounds miscible
are transported in solution by water infiltration and tend to disperse
and go deep in the aquifer under the laws of hydrodynamic dispersion,
those immiscible lighter than water (LNAPL)
tend to float on the surface of the water,
heavier ones (DNAPL)
sweep water from the pores and deepen in the aquifer to reach a little
permeable horizon;
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
The immiscible organic fraction lighter than water forms a layer above the water
table.
The immiscible organic fraction heavier than water forms a layer below the
water table.
The direction of this layer depends on the compliance of the waterproof layer
and not by the direction of the water..
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Volatility
The volatility of a compound can be considered in relation
to the vapor pressure and to Henry constant
The vapor pressure (Pa) of a compound
represents the tendency of the same to evaporate
is expressed by the pressure exerted by the gas phase of a
substance when it is in equilibrium with the liquid phase.
higher is the vapor pressure greater is the tendency of the
compound to pass into the gas phase.
The boiling temperature is a parameter, related to the
vapor pressure,
indicates the tendency of the compound to pass in
gaseous environment.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Volatility
A volatile organic compound in the liquid state
in non-aqueous phase may cause plumes of steam
that may travel to the cell surface and into the
groundwater.
The relative percentage of vaporization
is controlled by the vapor pressure of the organic
compound,
which varies greatly with the compound and with the
temperature.
HAZARD CHEMICALS AND ENVIRONMENTAL FATE
volatility
volatility of the water
very important.
pair is the partial pressure of the
compound in the air at the
temperature T;
Cw is the concentration in the water
At a constant temperature, the amount of a given gas that dissolves
in a given type and volume of liquid is directly proportional to
the partial pressure of that gas in equilibrium with that liquid.
Henry's constant,
is given by the ratio between the partial pressure of a compound in
the gas phase and its solubility and can be expressed in atm · m³ /
mol.
HAZARD CHEMICALS AND ENVIRONMENTAL FATE
Ratio octanol / water (Kow = Poc =Pow)
One of the most used in the physical parameters characterizing
the hazard of chemicals
K OW
Conc.Octanol

Conc.Water
Measure the tendency of an organic compound to accumulate in
fatty tissues or to distribute itself between an aqueous phase and
an organic one; octanol (CH3-(CH2)7-OH) is in several ways
similar to the lipid content in the biotic compartment.
this parameter indicates the tendency of a chemical to be
distributed in the organic phase (fish, soil, etc. ..) or in the aqueous
phase.
measure the hydrophobicity of a substance
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Ratio octanol / water (Kow = Poc= Pow)
Low KOW values:
high solubility,
low coefficient of adsorption,
low bioconcentration factor in the life in the water.
K OW
Conc.Octanol

Conc.Water
This parameter is often used to express other parameters
adsorption, bioaccumulation and others.
for values ​of Kow below 1000 the compound does not
bioaccumulate.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
KOW values.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
KOC (Soil organic carbon-water partitioning coefficient)
KOC
 g adosrbed / g organic carbon in soil

chemical concentration in water (  g / ml )
Represents the tendency of a substance to be absorbed in
a solid phase, can be used for neutral compounds as long as
the content of organic matter in the soil is greater than a
minimal amount (2%).
the mobility of a substance in the soil
the distance traveled in a column of soil saturated with water
in a ratio to the distance traveled by the water.
High if it has a low tendency to be absorbed by the soil and
vice versa.
HAZARD CHEMICALS AND ENVIRONMENTAL FATE
KOC (Soil organic carbon-water partitioning coefficient)
It can be estimated using the octanol / water partition coefficient(KOW)
in this case the relation is the following:
The values ​of the constants a and b depend on the type of pollutant and
the type of soil used.
The mobility of a compound can be expressed in terms of this
parameter.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
KOC
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Classification of mobility in soil of substances through the
coefficient KOC
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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Partition Coefficient Kd
Considers the adsorption-desorption phenomena that Indicates the
tendency of compound to adhere to a solid matrice or go through
solution
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In case of linear behaviour and reversible, the
phenomena is indicated as Partition Coefficient, and is
given by the ratio between the concentration on solid CS
and the concentration on liquid phase CW (water).
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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Acid dissociation constant
The environmental impact of many chemicals
is usually assessed with reference to the undissociated
form.
A large amount of substances contain an acidic or basic
functional group,
that governs the physical, chemical, biological substance.
The proportions of the compounds species (neutral,
anionic, cationic) will depend on the pH value.
Do not consider this dissociation
could lead to a falsification of the results as
underestimation of the adsorption of the substance as
compared with the value of the undissociated form.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETERS OF BIOACCUMULATION
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In the risk assessment of chemicals on organisms
becomes important to estimate the amount of contaminated
bioaccumulated in the body.
bioaccumulation
the net accumulation of contaminant in the organism from all
sources including the water, the air and the solid phase.
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The solid phase, in turn, includes food, soil, sediments and
fine particles suspended in air or water.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETERS OF BIOACCUMULATION
In reference to the aquatic compartment.
The modeling of the process of bioaccumulation is very complex because it
takes into account several factors:
uptake is the phenomenon that indicates the movement of the contaminant
within the body and can affect the gills, the gut, the skin surface of the
lung, roots, leaves, etc..
biotransformation
the chemical in the body can be transformed.
elimination
excretion from the contaminated body. The processes of elimination vary
widely between plants, invertebrates, vertebrates, and depending on the
substance.
The biotransformation and excretion
are two processes that indicate a lowering of the concentration of the
contaminant in the body.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETER OF BIOACCUMULATION
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETER OF BIOACCUMULATION
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The simplest model to determine the bioaccumulation over
time uses an expression of the first order for the uptake (U)
from a single source in a single compartment
an expression for the first-order elimination (E) from that
behavior.
In this case the biotransformation is not counted directly, but
can be incorporated in the general term of elimination.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETER OF BIOACCUMULATION
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The time variation of the concentration of the contaminant in
the body is given by the following equation:
C1 is the concentration in the source, for example water;
C the concentration in the body, for example the fish;
kυ is the uptake rate;
kE is the elimination rate.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Where
– C1 is the concentration in the source, for example water;
C the concentration in the compartment, for example the fish;
KU is the rate of uptake;
kE is the rate of elimination.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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bioaccumulation
depends on the structure of the pollutant, the characteristics of
the organism and the environmental conditions.
Form of pollutant:
affect much on the bioavailability of the same.
For example the NH3 in water is more biologically available
than NH4+ ion.

The ionic form of the metal ions is more available and toxic.

For organic compounds greater is KOW , greater is the
concentration of the contaminant in the organism.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETER BIOACCUMULATION

Features of the organization:
type of diet, age, sex.
Environmental conditions:
temperature, and pH.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Bioconcentration
refers to the net accumulation of contaminants from source
water only.

Biomagnification
means that the contaminant concentration in the organism
increases progressively as it moves up a food chain, due to the
accumulation of food.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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
PARAMETER OF DEGRADATION
Hydrolysis and biodegradation
generally are considered the most important processes for
degradation of organic substances in aqueous environments
and soil.
while the photolysis
is important for chemicals in the vapor phase or in the gas
phase.
In water and soil
substances are not subject to the action of degradation of the
light.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETER OF DEGRADATION
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hydrolysis
The hydrolysis is a very important process of degradation.
Normally the process of hydrolysis is expressed by a function
of the first order:
Where C is the concentration of pollutant in water and k is the
coefficient of the first order of the hydrolysis
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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PARAMETER OF DEGRADATION
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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The biodegradation of a compound
occurs both in aerobic conditions (mainly) and anaerobic
conditions.
The behavior of a substance is deduced from the literature that
defines a compound:
degradable
persistent
recalcitrant.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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Biodegradation

A compound persistent
remains long in the environment, although sometimes
degrades
A compound recalcitrant
one that does not show signs of degradation.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Biodegradation
Subdivision of biological degradation processes in the soil and subsoil
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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CONTAMINANTS ENVIRONMENTAL FATE
For a detailed study of how dangerous a chemical distributed
in the environment should be considered at least 6 phases:

Air
Water
soil
suspended solids
Sediment
biological organisms.
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HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
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CONTAMINANTS ENVIRONMENTAL FATE
Some parameters that indicate the fate of a chemical
volatilization (air / water), adsorption (soil / water) and
bioconcentration (biota / water).

If a chemical is introduced into a system as complex and if one
assumes an equilibrium between all phases,
instead of introducing all the equations of equilibrium between
the phases and mass balances

you can use the concept of FUGACITY
to determine the distribution of the phase of the substance
concerned.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Fugacity
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
It expresses distribution of contaminants in terms of
fugacity instead of concentration
This facilitate the interpretation of dynamic processes in
which the substances are subjected.
Fugacity expresses the tendency of the substance to
escape from that phase, it is a potential quantity that
characterized the partition of mass in equilibrium
condition( like temperature characterizes the repartition
of thermal energy)
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Fugacity
As well as heat moves from the high temperature zones in
areas of low temperature,
the mass moves from areas of high to areas of low fugacity,
The factor that binds to the transience concentration is the
ability to Z.
C=fZ
Where C is the concentration, f is the fugacity capacity, Z,
defined for each substance at a fixed temperature.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE
Fugacity
Evaluation of the dissemination of environmental contaminants
When a chemical substance, such as DDT, is released into the environment
is dispersed in different environmental compartments (matrix or phases)
partially dissolved in water bodies,
in part present in the air,
in the soil,
sediments
in living matter (biota).
Then there is a constant exchange of substance between these
compartments.
In each of these matrices is possible to estimate the amount and
concentration of the substance,
once the release of the contaminant is complete and has passed a sufficient
time to establish a balance between the various stages.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
it seems absurd to find that Organochlorines and PAHs,
relatively non-volatile,
can migrate through the air for thousands of kilometers from
the release point
to contaminate relatively intact areas of the world such as the
Arctic.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
Have recently been in-depth knowledge on this long-distance
transport of air pollutants using the principles of physical
chemistry.
Through a process of global fractionation (or distillation)
pollutants migrate at different speeds deposited in various
geographical regions according to their physical properties.
At normal room temperatures, many persistent organic
pollutants have a volatility that often allow them to evaporate
rather slowly, from the temporary site on the surface of the
ground or on water bodies.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
given that the vapor pressure of any chemical substance
increases exponentially with temperature,
evaporation takes place rather in tropical or subtropical areas
why these geographic regions hardly represent the deposit of
pollutants.
By contrast, the cold temperatures of the air
favor the condensation and adsorption of gaseous compounds
on atmospheric particles suspended,
most of which are subsequently deposited on the earth's
surface.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
Arctic and Antarctic regions represent the pollutants well
relatively movable who have not deposited at lower latitude
because of their high volatility.
Unfortunately, these compounds are degraded more slowly
because of the freezing temperatures in these regions.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
Examples of pollutants that migrate to the polar regions
highly chlorinated benzenes, PAHs with three rings and PCBs, dioxins
and furans that have chlorine atoms.
Substances with even greater mobility : naphthalene and the less
chlorinated benzenes,
do not settle even to the freezing temperatures of the polar regions;
continue their migration more or less indefinitely
as long as they do not undergo a chemical destruction, usually through a
reaction with hydroxyl radicals initiated by the collision.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
The mobility of a chemical increases
with the increase of the vapor pressure of its condensed form
(measured on the basis of that of the super-cooled liquid)
with decreasing condensation temperature of the vapor state
form of gaseous pollutant.
Therefore, the substances which do not condense until the
temperature reaches -30 ° C, and even less,
accumulate in the polar regions where such temperatures are
commonly present.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
The substances with condensation temperatures below -50 ° C,
perpetually remain in the atmosphere,
given that, even at the level of the polar regions, will reach
such temperatures for a long period of time.
DDT occupies an intermediate position in these scales of
transport.
evaporates rather quickly
but its relatively high condensation temperature of about 13 °
C is to mean that much of it settles permanently at midlatitudes (especially in winter)
and only a small percentage migrates to the Arctic.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
Although we believe according to their behavior that PCBs
are deposited mainly in temperate areas
rather than migrate en masse to the Arctic,
their migration, however, is so high
that the animals in this polar region
appear to be heavily contaminated with these chemicals.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
The world record of PCB contamination, which is 90 ppm,
has been found in polar bears in Spitsbergen, Norway.
Even the breast milk of women living in the most northern
is more contaminated with PCBs than that of women living in temperate
zones.
This is partly due to their diet rich in fats that accumulate organochlorines.
HAZARD CHEMICALS AND
ENVIRONMENTAL FATE

Long-distance transport of air pollutants
On the basis of changes in atmospheric temperature
encountered during transport,
many molecules of pollutants furniture undergo several
successive cycles of evaporation and condensation,
with their gradual migration to colder climates.
HAZARD CHEMICALS AND ENVIRONMENTAL FATE

Long-distance transport of air pollutants
The grasshopper effect of a relatively movable pollutant with a pulse emission at time t0 near
the equator.
At subsequent time t1, a large part of the pollutants mass still stationed in tropical regions,
while at time t2 moves especially towards subtropical regions.
The fact that the migration or jump occurs from temperate regions and sub-polar to polar ones
(at time t6) depends on the mobility degree of pollutant molecule, which must be sufficiently
high.