environmental toxicology: chemical aspects atmospheric ......environmental toxicology, master sc. in...

Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross

Environmental toxicology: chemical aspects

Atmospheric chemistry (2)

Atmospheric pollution




Gases:Natural and pollutants Liquids:

Natural and pollutants

Solids:Natural and pollutants




RELEVANT COMPONENTS OF ATMOSPHERIC CHEMISTRY

gaseous oxides

atmospheric methane

hydrocarbons (photochemical smog)

particulate matter (PM)

primary and secondary pollutants (e.g. H2SO4, NO2)

The characteristics of the atmosphere are determined by the balance of energy and

mass transfer processes.




Primary pollutants: emitted directly (e.g. SO2)

Secondary pollutants: formed by the atmospheric processes

acting upon primary pollutants or not pollutants (generally

from the tendency of atmosphere to oxidize primary

pollutants)




Particles ranging from aggregates of a few molecules to pieces of dust readily visible

to the naked eye are commonly found in the atmosphere

Some atmospheric particles, such as sea salts formed by the evaporation of water from

droplets of sea spray, are natural and even beneficial atmospheric constituents (e.g.

condensation nuclei serve as bodies for atmospheric water vapor to condense upon and

are essential for the formation of rain drops).

Colloidal-sized particles in the atmosphere are called aerosols:

dispersion aerosol: formed by grinding up bulk matter.

condensation aerosol: particles formed from chemical reactions involving gases.

Particles & colloids




Atmospheric trace

gases in dry air

near ground level




Trace gases

Carbon dioxide is the most abundant. It is a natural atmospheric constituent and it is

required for plant growth. The level of carbon dioxide in the atmosphere (actually at

about 400 ppm by volume) is increasing by about 2 ppm per year: associated with the

so-called greenhouse effect. https://www.co2.earth/

http://www.epa.gov/climatestudents/basics/today/greenhouse-effect.html

Increased levels of carbon monoxide represents a serious health threat because it

prevents blood from transporting oxygen to body tissues (carboxyhemoglobin).

Oxides of carbon, sulfur, and nitrogen are important constituents of the atmosphere

and are pollutants at higher levels.




Nitrogen oxides (collectively denoted as NOx) are both naturally occurring and

anthropogenic gases: associated with the so-called photochemical smog.

Sulfur-containing gases, in particular sulfur dioxide (SO2), are increasing atmospheric

components as by-products of the combustion of fuels: associated with acid rains.

Methane (CH4) is the most abundant hydrocarbon in the atmosphere. It is naturally

released from underground sources as natural gas and produced by the fermentation

of organic matter. Although quite unreactive, like other atmospheric hydrocarbons is

produced by several sources (mainly exhaust emissions): associated with the

photochemical smog. It is a greenhouse gas.




Inorganic gaseous pollutantsIn addition to solid pollutants (metal derivatives and particulates, see next Lecture), a

number of gaseous inorganic pollutants enter the atmosphere as the result of human

activities:Element Atmospheric inorganic form(s)

Oxygen O3

Carbon CO2, CO

Sulfur H2S, SO2, SO3, CS2, OCS

Nitrogen NH3, N2O, NO, NO2, N2O5

Halogens (X = Cl, F) X-, X2, HX

CO, SOx, NOx several hundred millions tons/year




Sulfur is mainly released into the atmosphere as either H2S or SO2, both toxic primary air

pollutants.

H2S is oxidized by HO· to SO2 (H2S + 3/2 O2 SO2 + H2O) in a three step process:

H2S + HO· HS· + H2O

HS· + O2 HO· + SO

SO + O2 SO2 + O

The primary source of anthropogenic sulfur dioxide is pyrite in coal:

4 FeS2 + 11 O2 2 Fe3O4 + 8 SO2

Essentially all sulfur is converted to SO2 (only 1-2% to SO3).

Sulfur dioxide (SO2)




Sulfur dioxide may react in the atmosphere in several ways:

photochemical reactions;

photochemical and chemical reactions in the presence of NOx and/or

hydrocarbons;

chemical processes in water droplets, particularly containing metal salts

and ammonia;

reactions on solid particles to form particulate matter and its reaction

products are thought to be responsible for some aerosol formation.



Atmospheric chemistry (2) *

much of the sulfur dioxide in the atmosphere is ultimately oxidized to sulfuric

acid and sulfate salts, particularly ammonium sulfate and ammonium

hydrogen sulfate.

The most important gas-phase reaction leading to the oxidation of SO2 is the

addition of HO· radical:

HO· + SO2 HOSO2·

HOSO2· radical can then react with another hydroxyl radical to form water

and SO3 or H2SO4 .




Sulfur dioxide dissolves in water droplets where it can react with oxygen:

SO2(aq) + H2O + 1/2O2(g) H2SO4(aq)

SO2(aq) can be also oxidized by other oxidants:

SO2(aq) + H2O2(aq) H2SO4(aq)

SO2(aq) + O3(aq) H2SO4(aq) + O2(g)

Eventually, sulfuric acid can react with atmospheric ammonia to form

ammonium bisulfate and/or sulfate.

Sulfuric acid and its ammonium salts are water soluble, so they are washed

out of the atmosphere with precipitations.




The sulfuric acid generated from anthropogenic sulfur dioxide emissions results in

precipitation with low pH values (<3.0 in extreme cases), and the phenomenon known as acid

rain may induce:

direct phytotoxicity to plants and destruction of forests;

respiratory problems to humans and other animals;

acidification of waters and subsequent toxic effects;

corrosion of exposed structures, electrical relays, equipment, ornamental materials, and

soil (e.g. limestone CaCO3);

formation of sulfuric mist (aerosol).

SO2 and acid rains




All current technologies involve the exposition of combustion gases to SO2

absorbent substance.




In addition to H2S, carbonyl sulfide (COS) and carbon disulfide (CS2) are important

gaseous components of the atmosphere → increasing source of atmospheric pollution.

Both COS and CS2 are oxidized in the atmosphere by reactions initiated by the hydroxyl

radical:

HO· + COS CO2 + HS·

HO· + CS2 COS + HS·

The HS· radicals can undergo further reactions to sulfur dioxide and, eventually, to sulfate

species.

Reduced sulfur gases




Carbonyl sulfide is so long-lived that significant amounts reach the

stratosphere where it can undergo photolysis:

COS + hn CO + S

S + O2 SO + O

SO + O2 SO2 + O

COS + O CO + SO

SO2 formed in this process is eventually oxidized to sulfuric acid and sulfate

aerosol, thus producing a stratospheric aerosol layer contributing to the

greenhouse effect.




The “modern” sulfur cycle

Differs quite dramatically from the original

one because of the large portion of

anthropogenic sulfur added to the

atmosphere (mainly in the form of sulfur

dioxide produced upon combustion of fossil

fuels).

Vulcanoes and biological decay of matter







Oxygen O3

Carbon CO2, CO








Carbon monoxide (CO)

Overall atmospheric concentration: 0.1 ppm, can reach 50-100 ppm in metropoles

From methane oxidation (1.6 ppm)

Anthropogenic emissions: 6% of CO

Decay of plant masses

Engines (increase air-fuel ratio > 16:1, CO → CO2)




Carbon monoxide (CO)Carbon monoxide causes problems in cases of locally high concentrations (metropolitan

areas) because of its toxicity.

20% vol of the CO released the to the atmosphere each year comes from natural sources

(degradation of chlorophyll, decay of plant matter).

Anthropogenic sources account for ca. 6% vol of CO emissions (mainly from incomplete

combustion of fossil fuels).

The remaining atmospheric CO comes from largely unknown sources (CO is an intermediate

in the oxidation of methane by hydroxyl radicals, and the methane content of the atmosphere

is about 10 times that of CO).




CO in the atmosphere reacts with hydroxyl radical:

CO + HO· CO2 + H·

Hydroperoxyl radical is subsequently formed:

O2 + H· HOO·

Hydroxyl radical is then regenerated:

HOO· + NO HO·+ NO2

HOO· + HOO· H2O2

H2O2 + hn 2 HO·




Carbon dioxide (CO2)




Carbon dioxide (CO2)

Very strong connection between life forms on Earth and the nature of Earth’s climate, which

determines its suitability for life.

The Gaia hypothesis by James Lovelock: the atmospheric O2/CO2 balance established and

sustained by living organisms determines and maintains Earth’s climate and other

environmental conditions.

When the first primitive life molecules were formed approximately 3.5 billion years ago, the

atmosphere was very different from its present state: chemically reducing and containing N2,

CH4, CO2, NH3, H2O, H2 but no O2.




The atmospheric O2/CO2 balance was supposed to be preserved by maintaining

atmospheric carbon dioxide at low levels through the action of photosynthetic

organisms.

Atmospheric carbon dioxide levels are determined by a long-term equilibrium

between CO2 in the air and CO2 dissolved in the oceans and surface water, releases

of CO2 from natural and anthropogenic sources, and losses by plant growth.

During the last 200 years human activities: increased levels of atmospheric CO2 due

to combustion of large quantities of fossil fuels, burning of biomass and vegetation,

vehicles exhausts.




Atmospheric CO2




CO2 and global warming

global warming: energy

balance of incoming solar

radiation.




The greenhouse effect




conversion nm → wavenumber (cm-1)




The greenhouse effect

https://www3.epa.gov/climatechange//kids/basics/today/greenhouse-effect.html




greenhouse gases

https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data




Global Warming Potentials (GWP)

depends upon:

ability to absorb energy (their "radiative efficiency")

how long they stay in the atmosphere (also known as their "lifetime")

it is a measure of how much energy the emissions of 1 ton of a gas will

absorb over a given period of time, relative to the emissions of 1 ton of

carbon dioxide (CO2).

The larger the GWP, the more that a given gas warms the Earth compared

to CO2 over that time period.

https://www.epa.gov/ghgemissions/understanding-global-warming-potentials




Global Warming Potentials (GWP) CO2, by definition, has a GWP of 1. CO2 remains in the climate system for a very long time: CO2

emissions cause increases in atmospheric concentrations of CO2 that will last thousands of years.

Methane (CH4) is estimated to have a GWP of 28–36 over 100 years. CH4 emitted today lasts

about a decade on average, which is much less time than CO2. But CH4 also absorbs much more

energy than CO2. The net effect of the shorter lifetime and higher energy absorption is reflected in

the GWP. The CH4 GWP also accounts for some indirect effects, such as the fact that CH4 is a

precursor to ozone, and ozone is itself a GHG.

Nitrous Oxide (N2O) has a GWP 265–298 times that of CO2 for a 100-year timescale. N2O

emitted today remains in the atmosphere for more than 100 years, on average.

Chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs),

perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are sometimes called high-GWP gases:

they trap substantially more heat than CO2.

https://www.epa.gov/ghgemissions/understanding-global-warming-potentials




Any substance absorbing re-emitted IR radiation would decrease the energy released

to space, leading to higher temperatures at Earth’s surface (greenhouse effect).

Water vapor, CH4 and CO2 are

very effective IR rays

absorbent: "greenhouse"

gases.

Increase of CO2 :

1-2 ppm/year

Doubled in this century: 1.5-

4.5°C increase




CO2 emissions: the carbon footprint

http://www.eea.europa.eu/

http://www3.epa.gov/carbon-footprint-calculator/







Oxygen O3

Carbon CO2, CO








Nitrogen oxides (NOx)





Involved in

- photochemical smog

- stratospheric ozone layer depletion

- acid rain




Three oxides of nitrogen are normally encountered in the atmosphere:

nitrous oxide (N2O), nitric oxide (NO), and nitrogen dioxide (NO2).

N2O: anesthetic known as “laughing gas,” is produced by microbiological

processes and is a component of the unpolluted atmosphere (ca. 0.3 ppm).

Relatively unreactive, does not seem to significantly influence the lower

atmosphere.

Concentration decreases rapidly with altitude in the stratosphere due to the

photochemical reaction

N2O + hn N2 + O





NO (colorless and odorless), NO2 (red-brown pungent): collectively

designated as NOx, these gases enter the atmosphere from natural sources

(lightning and biological processes) and from pollutant sources.

NO binds to hemoglobin, but concentration lower

Practically all anthropogenic NOx enter the atmosphere as a result of the

combustion of fossil fuels, mainly as NO generated from internal combustion

engines:

N2 + O2 2 NO (at very high temperature)

Rapidly converted to NO2 in the troposphere:

NO + ½ O2 NO2 / NO + O3 NO2 + O2





NO2 is a very reactive and significant species in the atmosphere

it absorbs light throughout the UV spectrum penetrating the troposphere:

NO2 + hn NO + O (l < 398 nm)

O + O2 O3

NO + O3 NO2 + O2

During daytime NO2 is rapidly converted back to NO

in the absence of photodissociation at night NO2 predominates over NO.

NO2 + hn NO2* (l > 430 nm)

In the stratosphere: HO· + NO2 HNO3 acid rain





Atmospheric chemical reactions of NO2

First observed in the troposphere in 1980, nitrate radical (NO3·) is now recognized as

an important atmospheric chemical species, especially at night.




nitrate radical (NO3·)

This species is mainly formed by the reaction

NO2 + O3 NO3· + O2

Levels of NO3· remain low during daylight (lifetime at sunlight: ca. 5 s) because of the

following two dissociation reactions:

NO3· + hn NO + O2 (l < 700 nm)

NO3· + hn NO2 + O (l < 580 nm)

It is likely that NO3· levels become high enough just before the sunset and strongly increase

at night.

[HO·] higher during daytime major oxidant

[NO3·] higher during the night major oxidant




NO3· exists in equilibrium with NO2:

NO2 + NO3· N2O5

N2O5 + H2O 2 HNO3 acid rain

HNO3 + HO· H2O + NO3· (in the stratosphere)

The chemistry of NOx in the troposphere is different from that in the

stratosphere: nitrogen chemistry at both levels is driven by the

photochemical dissociation of nitrogen dioxide, but the products formed

depend on other substances with which the photochemically excited NO2*

molecules can react.




Photochemical smog (=photochemically oxidizing atmosphere) formation is strictly

related conversion of nitrogen into many substances in the atmosphere through several

different reactions. Necessary requirements for the photochemical smog to be formed:

(i) nitrogen oxides (NOx),

(ii) hydrocarbons

react together due to:

(i) radiation (sunlight)

Hydrocarbons (originated from incomplete combustion of fossil fuels) react with NOx through

a sequence of reactions (all involving a free radical mechanism) to form oxidants (the final

product of photochemical smog).

NOx and the photochemical smog (troposphere)




https://energyeducation.ca/encyclopedia/Photochemical_smog




Photochemical smog




The final substances (aldehydes, peroxyalkylnitrates, peroxyacetylnitrates, etc.) are extremely

irritating to sensitive biological tissues and cause most of the health problems associated with

photochemical smog.

NOx and the photochemical smog



Atmospheric chemistry (2)*

NO and hydrocarbon radicals released

from exhausts gases;

NO converted to NO2:

NO + ½ O2 NO2

NO + O3 NO2 + O2

NO + RO2· NO2 + RO·

NO2 reacts with hydrocarbon free

radicals:

NO2 + RC(O)O2· RC(O)O2NO2




NO2 photodissociates:

NO2 + hn NO + O

Reactions of O:

O + H2O 2 HO·

O + O2 O3

Reactions of O3:

NO + O3 NO2 + O2

RH + O3 RO· + H2O




Formation of hydrocarbon radicals:

RH + HO· H2O + R·

R· + O2 RO2·

RO2· + NO NO2 + RO·

RO· + O2 RCHO + HO2·

RCHO + HO· RCO· + H2O

RCO· + O2 RC(O)O2·

Photochemical smog:

NO2 + RC(O)O2· RC(O)O2NO2







Oxygen O3

Carbon CO2, CO








Ozone (O3)

www.epa.gov




Stratospheric ozone (O3) layer (15-35 km) depletion




Ozone (O3)

Uses of ozone

For air purification at the crowded places like cinema halls and tunnel railways. Due to its strong

oxidizing power it also destroys the foul smell in slaughter houses.

In sterilizing drinking water by oxidizing all germs and bacteria.

For preservation of meat in cold storages.

For bleaching delicate fabrics such as silk, ivory, oils, starch and wax.

It helps to locate a double bond in any unsaturated organic compound by ozonolysis.




Ozone (O3)




Ozone layer depletion

Ozone (O3) forms a layer in the stratosphere (thinner on the equator, denser towards the

poles).

The amount of ozone above a point on Earth's surface is measured in Dobson Units (DU).

1 DU is 0.01 mm thickness slab at

standard temperature and pressure:

~260 DU near the tropics and higher

elsewhere, though there are large

seasonal fluctuations.




Ozone (O3)

www.theozonehole.com

absorbs very strongly in the region 220-

330 nm (filters UV-B radiation)

UV-A 320-440 nm less harmful

UV-C < 290 nm does not penetrate the

troposphere

Absorption converted to heat: increase

of T at 50 km

http://www.theozonehole.com/


O3 layer forms when UV radiation strikes the stratosphere

O2 + hn O + O (l < 242.4 nm)

O2 + O + O3

It provides a shield from the potentially harmful UV radiation from the sun (at wavelengths

between 240 and 320 nm) by absorbing such rays:

O3 + hn O + O2 (l < 325 nm) (ozone photodissociation)

It can then reform through the following reaction:

O2 + O O3



Ozone (O3)




It can also be destroyed by a series of reactions from which the net result is

O3 + O 2 O2

The concentration of ozone in the

stratosphere is a steady-state

concentration resulting from the

balance of ozone production and

destruction by the above processes.




Ozone (O3)

Although ozone is a desirable substance in the stratosphere, it is a major

environmental hazard at ground level (troposphere, smog):

it is formed naturally photochemically;

by-product of photochemical smog, the presence of nitrogen oxides (NOx) leads to

higher than normal background levels of ozone;

NO + ½ O2 NO2 / NO + O3 NO2 + O2

reacts with hydrocarbons to form peroxynitrates that damage eyes, nasal

passages, throat and lungs;

excessive levels are believed to be detrimental to plants through reactions with

chlorophyll.




Ozone (O3)

Number of days on

which ozone

concentrations

exceeded the

information

threshold during

the summer of 2014

http://www.eea.euro

pa.eu




Chlorofluorocarbons (CFCs)Chlorofluorocarbons (e.g. CCl2F2, commonly called Freons) are volatile

one- or two-carbon compounds containing Cl and F atoms bound to C.

widely used in recent decades in the fabrication of flexible and rigid foams

and as fluids for refrigeration and air conditioning, blowing agents.

Halons are related compounds containing bromine (e.g. CBrClF2) and are

used in fire extinguisher systems.

CFCs are notably stable (lifetime 60-420 y), nontoxic, volatile (not

removed in the troposphere, ultimately diffuse to the stratosphere) and

inert (unless they are exposed to the intense solar radiation).




In the stratosphere CFCs are exposed to the intense solar radiation that

cannot penetrate the ozone layer, and the CFCs become photochemically

active:

CCl2F2 + hn Cl· + CClF2·

Cl· + O3 ClO· + O2 (ozon destruction)

ClO· + ClO· ClOOCl (dimerization)

ClOOCl + hn ClOO· + Cl· / ClOO· Cl· + O2

2 Cl· + 2 O3 2 ClO· + 2 O2

This is a catalytic process (Cl·/ClO· is regenerated)!




Each Cl· can catalyze the destruction of about 100,000 ozone molecules

before being converted into inert molecules of HCl and ClONO2:

Cl· + CH4 CH3· + HCl

HO· + ClO· O2 + HCl

NO2 + ClO· ClONO2

Both HCl and ClONO2 are stable non-ozone destroying molecules and remain

in the air. Eventually, winds carry them into the troposphere.



Atmospheric chemistry (2)The most prominent instance of ozone layer destruction is the so-called “Antarctic

ozone hole”. This phenomenon is manifested by the appearance during the

Antarctic’s late winter and early spring of severely depleted stratospheric ozone (up

to 50%) over the polar region.

http://www.atm.ch.cam.ac.uk/cgi-bin/imagemap/toms_data

http://www.atm.ch.cam.ac.uk/cgi-bin/imagemap/toms_data




Why Antartica?

During the winter polar night, sunlight does not reach the south pole.

A strong circumpolar wind develops in the stratosphere (polar vortex)

sucking gaseous air components (including pollutants) and isolating the air

over the polar region.




Since there is no sunlight, the air within the polar vortex can get very cold and

special clouds form (Polar Stratospheric Clouds - PSCs):

- when temperature drops to -78°C, HNO3, H2SO4 and H2O condense to

form type I PSCs containing small particles (1 mm) that remain in the

stratosphere;

- as temperature drops to -85°C, H2O further condenses to form type II

PSCs which contain particles large enough (1 mm) to fall out of the

stratosphere, removing nitric acid and water from the stratosphere.




ClONO2 and HCl molecules in the air strike the type II cloud particles

attach to their surface where, although generally stable, they are

converted into Cl2, building up a reservoir of Cl2 and HOCl:

HCl + ClONO2 Cl2 + HNO3

ClONO2 + H2O HOCl + HNO3

During winter these compounds have no effect on ozone because of the

absence of UV radiation from the sun, required to convert these species

into reactive Cl· radicals.




When the sunlight returns to the lower stratosphere above Antartica in Spring,

ClONO2 and Cl2 undergo photodissociation:

Cl2 + hn 2 Cl·

HOCl + hn HO· + Cl·

Cl· radicals thus formed trigger the reactions causing

ozone depletion.

Cl· + O3 ClO· + O2

ClO· + ClO· ClOOCl (dimerization)

ClOOCl + hn ClOO· + Cl· / ClOO· Cl· + O2

2 Cl· + 2 O3 2 ClO· + 2 O2







Oxygen O3

Carbon CO2, CO








F2, HF and other volatile fluorides are produced in the manufacture of

aluminum

HF is a by-product in the conversion of fluorapatite (rock phosphate) to

phosphorous-based fertilizers. Highly corrosive (reacts even with glass),

irritating to the body tissues and the respiratory tract (brief exposure to HF

vapors at the part-per-thousand level may be fatal).

The acute toxicity of F2 is even higher than that of HF and causes fluorosis,

whose symptoms include mottled teeth and pathological bone conditions.

Gaseous halides




Cl2 does not occur as an air pollutant on a large scale but is widely used as a

manufacturing chemical in the plastics industry, for water treatment and as

bleach.

Quite toxic, very reactive and a powerful oxidizing agent, it dissolves in

atmospheric water droplets, yielding hydrochloric acid and hypochlorous acid.

HCl is released to the atmosphere mainly as a combustion product during

incineration of chlorinated plastics (PVC).

Some compounds (e.g. SiCl4, AlCl3) may hydrolize and release HCl.




Organic pollutants (natural or anthropogenic)

- hydrocarbons (both alkyl and aromatic)

- carbonyl compounds (aldehydes, ketones, carboxylates)

- alcohols

- ethers

- nitrogen-, sulfur-, halide-containing organics.

may have a strong effect upon atmospheric quality:

direct effects, such as cancer caused by exposure to vinyl chloride;

formation of secondary pollutants, especially photochemical smog.

Organic gaseous pollutants




Polychlorinated dibenzodioxins (PCDDs) are of considerable concern

because of their toxicity.

Numerous sources, including car engines, pesticides (by product of

organochloride pesticides production), steel and other metal production, and,

in particular, old municipal solid waste incinerators.

Formation in such incinerators results from the presence of chloro-

containing waste (such as PVC bottles) and of trace metals that can

catalyze reactions leading to their production.




DioxinesClasse di composti che raggruppa 75 dibenzo-para-diossine policlorurate (PCDD)

e 135 dibenzo-furani policlorurati

Prodotte da processi di combustione di sostanze organiche in presenza di cloro

(T> 300°C)

Anche da incendi boschivi ed eruzioni vulcaniche




One of the most relevant environmental pollutant chemical is 2,3,7,8-tetrachlorodibenzo-p-

dioxin (TCDD), often known simply as “dioxin”.

Organic gaseous pollutants: PCDDs

It has been released in a number of industrial accidents, the most massive of which exposed

several tens of thousands of people to a cloud of chemical emissions spread over a 3-square-

mile area at the La Roche manufacturing plant near Seveso in 1976.




Organic gaseous pollutants: PCDDs

Very low vapour pressure

High melting point (305°C )

Poorly water soluble

Chemically unreactive

Thermally stable up to 700°C

Poorly biodegradable

Stable, persistent environmental pollutant




DioxinesDiossina più tossica TCCD (valore 1 scala di tossicità in TEF = fattore di tossicità equivalente )

2,3,7,8-tetraclorodibenzo-p-diossina

Veleno di Seveso (1976)

Produzione di triclorofenolo

http://it.wikipedia.org/wiki/TCDD




Dioxines: TEFI fattori di tossicità equivalente (TEF) si basano sulla

considerazione che PCDD, PCDF e PCB diossina simili sono

composti strutturalmente simili che presentano il medesimo

meccanismo di azione (attivazione del recettore Ah) e producono

effetti tossici simili: proprio il legame tra le diossine e il recettore Ah

è il passo chiave per il successivo innescarsi degli effetti tossici.

I TEF vengono calcolati confrontando l’affinità di legame dei vari

composti organoclorurati con il recettore Ah, rispetto a quella della

2,3,7,8-TCDD (2,3,7,8- tetraclorodibenzodiossina), la più tossica,

considerando l’affinità di questa molecola come il valore unitario di

riferimento.

Per esprimere la concentrazione complessiva di PCDD/PCDF e

PCB diossina simili nelle diverse matrici si è introdotto il concetto di

tossicità equivalente (TEQ), che si ottiene sommando i prodotti tra i

valori TEF dei singoli congeneri e le rispettive concentrazioni,

espresse con l’unità di misura della matrice in cui vengono

ricercate.

http://www.arpa.piemonte.it/approfondimenti/temi-

ambientali/microinquinanti/Diossine%2C%20PCB%2C%20IPA%20-

%20guida%20alla%20lettura%20dei%20risultati%20analitici

http://www.arpa.piemonte.it/approfondimenti/temi-ambientali/microinquinanti/Diossine, PCB, IPA - guida alla lettura dei risultati analitici




In Europe, the catastrophic accident in the Italian

town of Seveso in1976 prompted the adoption of

legislation on the prevention and control of such

accidents. The so-called Seveso-Directive

(Directive 82/501/EEC) was later amended in

view of the lessons learned from later accidents

such as Bhopal, Toulouse or Enschede resulting

into Seveso-II (Directive 96/82/EC). In 2012

Seveso-III (Directive 2012/18/EU) was adopted

taking into account, amongst others, the changes

in the Union legislation on the classification of

chemicals and increased rights for citizens to

access information and justice. It replaces the

previous Seveso II directive.

The Directive now applies to more than 10 000

industrial establishments in the European Union

where dangerous substances are used or stored

in large quantities, mainly in the chemical,

petrochemical, logistics and metal refining sectors.

http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:31982L0501

http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:01996L0082-20120813

http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32012L0018

environmental toxicology: chemical aspects atmospheric ......environmental toxicology, master sc. in...

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