j. Šedlbauer e-mail: [email protected] tel.: 48-535-3375
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
J. Šedlbauer
e-mail: [email protected]
tel.: 48-535-3375
Materials for Environmental Chemistry:
www.fp.tul.cz/kch/sedlbauer (link to the subject)
Contacts and materials
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
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
Syllabi 2/2 + literature
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)
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
Why to care about chemicals in the environment?
Sources of environmentally important chemicals
Hydrocarbons (aromatic, polyaromatic): oilHalogenated hydrocarbons:
C1 – C3 - coolant media, solvents, aenestetics
Aromatic – combustion, tarBiphenyls – isolation liquidsVarious structures – pesticides
Oxygen compounds: Cresols and chlorophenols – combustion, disinfectionAcetone, aldehydes – smog Humic acids – soil complexesPhtalates – increase plasticity of polymersDioxines – combustion
Nitrogen compounds: amines, amides, pyridines – dyesSulfur compounds: thiols, benzenesulfonates – detergentsPhosphorus compounds: organophosphates – pesticidesHeavy 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 non-reactivity, 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 = Z f
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:
332211
332211
332211321
ZVZVZVf
fZVfZVfZV
CVCVCVmmmM
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 Pa-1
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).