Page 108 - Materials Chemistry, Second Edition

L1644_C03.fm Page 83 Tuesday, October 21, 2003 3:11 PM

3.3.5 ECO-TOXICITY
Eco-toxic substances are those toxic to organisms in a manner that affects the
functioning and structure of the ecosystem in which the organism lives and, as result,
affects the health of the ecosystems. They are characterized by their persistence (low
degradability) in the environment and their ability to bioaccumulate in organisms.
Substances such as toxic heavy metals (Cd, Pb, Hg), persistent organic compounds
(dioxins and furans, PCDD/Fs, polycyclic aromatic hydrocarbons, PCBs, etc.), and
organic substances (PVC, etc.) that are emitted into the environment can accumulate
in organisms and cause different types of damage. The target system is not one
organism as in human toxicity, but a variety of organisms (fauna and flora, entire
ecosystems). This makes the assessment even more complex.
In contrast to other environmental impact categories in the LCIA, the impacts
of these types of substances are not based in one individual mechanism but in a
large number, such as genotoxicity, inhibition of specific enzymes, etc.

3.3.6 PHOTO-OXIDANT FORMATION

Human activities can increase air concentrations of photo-oxidant substances that
can affect the health of living organisms and human beings. These substances can
arise via photochemical oxidation of volatile organic compounds (VOCs) and carbon
monoxide (CO) emitted by human activities in the troposphere.
The photo-oxidants include a large number of unstable substances formed when
VOCs react with different oxygen compounds and oxides of nitrogen (NO ). The
x
most important oxygen compounds are hydroxyl radicals, OH·. Among the most
important photo-oxidants are ozone and peroxyacetyl nitrate (PAN). The transfor-
mation of VOCs and CO to ozone requires, apart from the reactive forms of oxygen,
sunlight and NO , which have a catalytic effect. The potential contribution to pho-
x
tochemical ozone formation is described by its maximum incremental reactivity
(MIR) in the American literature and by its photochemical ozone creation potential
(PCP) in Europe.

3.3.7 ACIDIFICATION
Combustion processes contribute greatly to the air emission of contaminants as NO x
and SO . In contact with water these oxides are converted to acids (nitric acid, HNO )
2
3
and sulfuric acid (H SO ). Once deposited (by dry and wet deposition), these chem-
2
4
icals may lead to exceeding the acid buffer capacity of the soil and water, generating
degradation of terrestrial and aquatic ecosystems. The presence of NH (emitted
3
primarily from agricultural soil) increases the potential uptake of SO in drops of
2
water in clouds and rains by the formation of (NH ) SO , and thus affects the forest
4 2
4
in which SO is deposited.
2
The principal effect of acidification of the environment is the loss of health
especially among conifers in many forests. The acidification of lakes can lead to
dead fish. On the other hand, metals, surface coatings and mineral building materials
exposed to air conditions are attacked by the air and acid rain, leading to patrimonial
and economic loss of historic monuments.
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