J. Šedlbauer

e-mail: josef.sedlbauer@tul.cz

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).