Transcript Snímek 1

Contacts and materials
J. Šedlbauer
e-mail: [email protected]
tel.: 48-535-3375
Materials for Environmental Chemistry:
www.fp.tul.cz/kch/sedlbauer (link to the subject)
Syllabi 1/2
1. Transport of chemicals and their distribution in the
environment: parameters of the „environmental
compartments“ model, thermodynamic description and
data sources
2. Wet and dry atmospheric deposition, chemical equilibrium
of rain droplets with acid-forming oxides, gas solubility
3. Solubility of solids and liquids in water, solubility of
reactive gases - CO2 and carbonate formation
4. Transport of contaminants in soils and sediments
5. Model of bioaccumulation in food chains
Syllabi 2/2 + literature
6. Distribution of chemicals in the environment including
advection and degradation processes
7. Kinetic model of wastewater treatment
8. Non-equilibrium transport of chemicals in the environment
- diffusion
9. Summary: data, models and estimation methods for
calculating the distribution of chemicals in the environment
MACKAY D. Multimedia Environmental Models, CRC Press, 2001.
MANAHAN S.E. Environmental chemistry, Lewis Publishers. , 2003.
THIBODEAUX L.J. Environmental Chemodynamics, 2. Ed., J. Wiley. , 1995.
web pages
Exam
Seminar project
Written exam – mostly calculations, a few theoretical
quizzes (study materials can be used)
Why to care about chemicals in the environment?
Environmental chemistry provides tools necessary to evaluate
the fate of chemicals in the environment in both qualitative
and quantitative way.
Robert Boyle (1627-1691): „The task of chemistry is to study the essence of chemical
compounds regardless of their utility“
About 100 000 chemicals are used industrially (European
Chemical Bureau), at least 30 000 are transported in the
environment, over 2000 chemicals on the EPA Priority
Pollutant List
Chemicals such as polychlorinated biphenyls dioxins, freons,
some polyaromatic hydrocarbons… are purely human
products
Many chemicals (pharmaceuticals, pesticides) are directly
designed to affect living organisms
Sources of environmentally important chemicals
Hydrocarbons (aromatic, polyaromatic): oil
Halogenated hydrocarbons:
C1 – C3 - coolant media, solvents, aenestetics
Aromatic – combustion, tar
Biphenyls – isolation liquids
Various structures – pesticides
Oxygen compounds:
Cresols and chlorophenols – combustion, disinfection
Acetone, aldehydes – smog
Humic acids – soil complexes
Phtalates – increase plasticity of polymers
Dioxines – combustion
Nitrogen compounds: amines, amides, pyridines – dyes
Sulfur compounds:
thiols, benzenesulfonates – detergents
Phosphorus compounds: organophosphates – pesticides
Heavy metals: Hg, Pb, Cu, Sn, Cr etc.
„Laws“ of waste production
THE NATURAL LAWS OF HAZARDOUS WASTE (Thibodeaux)
__________________________________________________________
1. I AM, THEREFORE I POLLUTE; undeniably, the production of some
waste by beings and machines is not preventable.
2. RECYCLE, REUSE AND MINIMIZATION are only partial solutions to
waste production.
3. CONVERT REMAINING WASTE to earthen-like materials that are
environmentally compatible.
4. SMALL WASTE LEAKS ARE UNAVOIDABLE and acceptable.
5. NATURE SETS the standard for the earthen like forms and acceptable
leak quantities.
________________________________________________
What decides about the distribution of chemicals - criteria
Before setting regulation priorities, it is necessary to know
the potential of chemicals to affect the environment – 4
criteria:
Persistence (chemical reactivity and kinetic factors, P)
Bioaccumulation potential (mobility from water or air to
living tissues, BCF)
Toxicity (biochemical factors, T)
Potential of long-range transport (LRT)
In addition, it is always necessary to estimate the amount,
which we are dealing with. Environmental impact of a
contaminant is a combination of all these factors.
What decides about the distribution of chemicals - examples
Physico-chemical properties of chemicals can be very
different (vapor pressure, solubility in water, reactivity…),
which results in their very different distribution in the
environment (e.g. freons quickly escape to the
atmosphere and retain there for decades due to their nonreactivity, PCBs are primarily adsorbed on soil and
sediment particles, the lifetime of alkenes in the
atmosphere is only hours…)
The most risky chemicals are non-reactive (i.e. long half-life
of degradation), with high vapor pressure (distribution to
atmosphere and an easy transport), hydrophobic
(tendency to accumulate in fat tissues).
What do we actually mean by distribution of chemicals?
Distribution of chemicals among environmental
compartments
(Environmental Partitioning)
Environmental compartments are chemically and physically
homogeneous media, which are separated from other
media by a phase boundary (or boundaries). Due to
complexity of environmental phases, their definition
always depends on the applied level of approximation.
Compartments: Most commonly considered are atmosphere,
water, soil, sediments. Additional: snow and ice, aerosols,
suspended colloids in water. Distribution to biota is
sometimes evaluated a posteriori, because the most
substantial transport occurs among abiotic compartments.
Four-compartment model
Eight-compartment model
Routes of transport
Model of distribution of chemicals among compartments
The simple model of distribution is based on Nernst’s Law,
which defines distribution coefficient between two
systems with a phase boundary:
Kij = (Ci / Cj )eq
Ci , Cj are concentrations of a given compound in the two
phases (environmental compartments)
This relation is approximate and distribution coefficients
depend on temperature – usually available only at 25°C
and temperature dependence must be estimated.
Useful physico-chemical quantities
Water solubility CS (mol m-3)
Vapor pressure pS (Pa)
Henry’s law constant H (Pa m3 mol-1) H = pS / CS
Distribution coefficient octanol – water KOW
Distribution coefficient organic carbon – water KOC
(l/kg = mg/kgorg uhlík_v_půdě / mg/lvoda)
Partition coefficient soil – water KP = fOC KOC (fOC is the fraction
of organic carbon in soil)
Distribution coefficient biota – water Kb (closely related to KOW
and BCF)
Data: basic thermodynamic data are available e.g. at
webbook.nist.gov/chemistry
Specific data sources will be mentioned later
Fugacity model (Mackay)
When all phases (compartments) are in equilibrium, fugacity
of a compound is the same in each phase – this follows
from thermodynamic intensive equilibrium criterion.
For concentration in each phase:
C=Zf
f – fugacity of a compound (Pa)
Z – fugacity capacity (mol m-3 Pa-1)
It holds:
Kij = (Ci / Cj ) = (f Zi / f Zj ) = (Zi / Zj )
Fugacity capacity - Z
Scheme of the equilibrium Environmental Compartments Model
Example of Level I fugacity model application
Estimate the distribution of selected contaminants (naphthalene,
anthracene, pyrene, phenol) among air, water and soil. Consider
the relative proportions of these compartments as 11000:22:1 and
the soil density as 2000 kg/m3
mass ballance:
M  m 1  m 2  m 3  V1C 1  V 2 C 2  V 3 C 3
 V1 Z 1 f  V 2 Z 2 f  V 3 Z 3 f
 f V1 Z 1  V 2 Z 2  V 3 Z 3 
Example Level I - data
Other needed data:
Kp= 25,8 (exp. KOC for naphthalene from Bahnick and Doucette, 1988)
Basic parameters of environmental compartments
Area and volume are not universal – locality dependent!
Example Level I – calculation and comparison
CS = C / M = 0,242 mol m-3; H = pS / CS = 43,01 Pa m3 mol-1
Z1=4,034·10-4 mol m-3 Pa-1; Z2=0,02325 mol m-3 Pa-1; Z3=1,200 mol m-3 Pa1
Assume e.g. M=100 mol: f=16,97 Pa; C1= 6,845·10-3 mol m-3;
C2=0,3945 mol m-3; C3=20,36 mol m-3
m1= 75 mol; m2= 4.5 mol; m3= 20.5 mol
Higher level fugacity models
Level II
Assumes equilibria among compartments (the same as
Level I), includes advection – degradation of a
contaminant by chemical reactions (usually modeled by
1st order kinetics with half-life as a parameter) and the
rate of income/outcome of a chemical between the
considered systems and its surrounding environment (i.e.
the sources and LRT are considered).
Level III
Does not require thermodynamic equilibrium among
compartments, transport through the phase boundaries is
controlled by diffusion (diffusion coefficients in all phases
are required as parameters).