Environmental Chemistry

Chapter 12:Environmental Chemistry and Pollution

of the Hydrosphere

Copyright © 2011 by DBS

Contents

• Nature and Types of Water Pollutants• Elemental Pollutants• Heavy meatls• Metalloids• Organically Bound Metals and Metalloids• Inorganic Species• Algal Nutrients and Eutrophication• Acidity, Alkalinity, and Salinity• Oxygen, Oxidants, and Reductants• Organic Pollutants• Pesticides in Water• Polychlorobiphenyls• Radionuclides in the Aquatic Environment

Nature and Types of Water Pollutants

Nature and Types of Water Pollutants

• Biological Agents – bacteria, protozoa and viruses cause waterborne diseases

• Chemical Agents – waterborne toxic chemicals

e.g. chemical threat to ground waters by:

- hydrofracturing

- industrial wastes (acid mine runoff)

- agricultural runoff

- Commercial wastes

- residential wastes

No. of synthetic chemicals produced

since WW2

Nature and Types of Water Pollutants

Nature and Types of Water Pollutants

• An enormous amount of material is published on this subject every year…

Elemental Pollutants

Elemental Pollutants

Trace element or trace substance is something found at a very low level

Ions Found in Natural Waters

Conc. Range

(mg L-1)

Cations Anions

0-100 Ca2+, Na+ Cl-, SO42

-, HCO3-

0-25 Mg2+, K+ NO3-

0-1 Fe2+, Mn2+, Zn2+ PO43-

0-0.1 Other metal ions NO2-

Reeve, 2002

Ariola et al, 2004

Elemental Pollutants

• Some are nutrients required for plant and animal life• Essential at low levels but toxic at high levels

• Some heavy metals are among the most harmful of elements• Have high affinity for sulfur and bind to sulfhydryl groups (SH) in

enzymes disrupting enzyme function• Metalloids are also toxic, e.g. As, Se, Sb• Inorganic chemicals also contaminate water with trace elements

Heavy Metals

Heavy Metals

• Five main heavy metals – Hg, Pb, Cd, Cr, As

• Widely distributed

• High toxicity

• Nondegradable, c.f. toxic organic compounds

Densities are high compared to others

Look at the periodic table, are all heavy metals toxic?

What is a Heavy Metal?

Heavy Metals

• Speciation and toxicity:– Free elements not very toxic (except Hg vapor)– Highly toxic as cations

Putnam, 1972

Mercury illuminated by incandescent and UV light

Heavy Metals

• Biochemical mode of action: inhibition of enzymes

Affinity for-SH (sulfhydryl groups)

• Occur in enzymes which control metabolic pathways

M2+ + 2 R-S-H → R-S-M-S-R + 2H+

Heavy Metals

Cadmium

• Pollutant cadmium from industrial discharges and mining wastes• Widely used in metal plating• Chemical similarity to zinc• Serious toxic effects• Replaces zinc in some enzymes

Heavy Metals

Lead

• From industrial and mining sources• Formerly used as a gasoline additive• Formerly used as a paint pigment and in paint primers• Adversely affects kidney, reproductive system, liver, brain,

central nervous system, blood• Body burdens have decreased with decreasing use

Lead Body Burden

Body burdens of lead in ancient people uncontaminated by industrial lead (left); typical Americans (middle); people with overt clinical lead poisoning (right). Each dot represents 40 µg of lead. Source: Patterson et al., 1991; adapted from NRC, 1980.

Heavy Metals

Mercury

• Emissions from coal burning are now major source

• Methylation by anoxic bacteria produces highly toxic mobile methylated mercury species, CH3Hg+ and (CH3)2Hg

• Uses of metallic mercury and in electrolytic generation of chlorine gas have been largely phased out

• Uses in batteries have diminished

• Organomercuries no longer widely used as fungicides

• Mercury is highly toxic

• Nervous system effects are especially prominent

• Tragic mercury poisoning in Minamata Bay Japan, 1953-1960

Fungicide (phenylmercury dimethyldithiocarbamate

Case StudyMinamata, 1953

• Minamata Bay, Japan (1953-1960)• Plastic manufacturer (Chisso Corp.), used mercury in the

production of acetaldehyde• Discharged methyl mercury into the bay• Main diet of locals was fish + shellfish

– 5-20 ppm (106 water)• Over 3,000 people suffered (730 deaths):

Minamata disease / Dancing Cat Disease

various deformities, damage to nervous system, retardation or death

• Developing embryos are especially vulnerable

WHO limit 0.5 mg kg-1

Minamata 50 mg kg-1

Heavy Metals

Arsenic• From mineral formations found associated with phosphorus

• By-product of copper, gold, and lead refining

• From fossil fuels, especially coal

• Formerly used in pesticides (Lead arsenate, Pb3(AsO4)2 , Sodium arsenite, Na3AsO3, Paris Green, Cu3(AsO3)2

• Bacteria methylate arsenic to produce species such as CH3AsO(OH)2 (methylarsinic acid)

• Acute and chronic toxicities

• May be carcinogenic

• Arsenic pollution from water wells drilled in Bangladesh

Organically Bound Metals and Metalloids

Organically Bound Metals and Metalloids

Two types of metal-organic interactions:

(i) Complexes between metal ions and complexing agents

• Reversible binding with species capable of independent existence

e.g. NTA chelate of metals (see Chapter 11)

Nitrilotriacetate

+ Mn+

Organically Bound Metals and Metalloids

(ii) Organometallics

• Direct metal C bonds, do not dissociate

e.g. alkyl groups (CH3, C2H5 etc.), carbonyl (CO) etc.

• Organometals that behave like organometallics, but do not have metal-carbon bonds

e.g. Titanium isopropylate

Organically Bound Metals and Metalloids

• Organotin compounds (stannanes):– More tin compounds in use than any other metal

– Have been common water pollutants because of use as industrial biocides

– Methylated species also found

Inorganic Species

Inorganic Species

• Elements (metals, metalloids and nonmetals)

• Some contribute to acidity, alkalinity and salinity

Inorganic Species

Cyanide, CN-

• Highly toxic as CN- or HCN (Ka = 6 x 10-10)

• CN- has a strong affinity for metal ions e.g. [Fe(CN)6]4-

• Byproduct of coke production

• Used to leach gold from gold ore (Cyanide Leaching Gold Recovery, CLGR)

• Occasionally people are killed by inhaling HCN

• Large fish kills from cyanide leached from minerals processing

New York Times, February 14, 2000

New York Times, February 14, 2000

‘…the worst disaster since Chernobyl’ (Cunningham, 2005)

Historical ExamplesTisza River, 01-30-00

• Baia gold mine (CLGR)

• Cyanide and heavy metal waste released Tisza – Danube – Black Sea

80% fish died + wildlife (MCL of 0.2 in USA)

• Romania had no international treaties with Hungary, decided it was not responsible for damages (Schaefer, 2000)

http://www.mineralresourcesforum.org/incidents/BaiaMare/index.htm

Inorganic Species

Ammonia, NH3

• Waste product of the metabolism of animals

• Water pollutant at higher levels

• Converts from NH4+ to more toxic NH3 above pH 9.26

• Presence often indicative of biodegraded organic matter

Inorganic Species

Hydrogen sulfide, H2S,

• From anaerobic decay of organosulfur compounds

• Characteristic rotten egg odor

• Highly toxic when inhaled

• Unpleasant water pollutant

• Tremendous affinity for heavy metals and precipitates their sulfides

Inorganic Species

Free carbon dioxide, CO2 in water

• Often in water from decay of organic matter

• Present in “sparkling” mineral water

• Acidic character can make water corrosive

• May be added to softened water (recarbonation)

Inorganic Species

Nitrite, NO2- rarely present at toxic levels

• Nitrite can destroy blood hemoglobin (hemoglobinemia)

• Nitrate, NO3-, can be tolerated at relatively high levels in water

• Infants, ruminant animals, convert NO3- to NO2

-, which is more toxic

Inorganic Species

Sulfite ion, SO32-

• Found in some industrial wastewaters

• Added to boiler feedwater as an O2 scavenger anticorrosive

• SO32- + O2 SO4

2-

Asbestos in water

• Some contamination from asbestos-based pipe

• Mineral taconite tailings can produce asbestos-like fibers in water

Algal Nutrients and Eutrophication

Algal Nutrients and Eutrophication

• Water eutrophication occurs when excess nutrients get into water

• Excessive algae and plant growth

• Vegetation chokes water and decays, consuming dissolved oxygen

• Excess nutrients are potassium, nitrate, and phosphate

• Phosphate usually limiting nutrient and is usually one controlled

• Nutrients are often from sewage effluent

• Application of green technology to limit eutrophication

• Nutrients in wastewater are good fertilizers for crops

• Treated sewage can be used to irrigate and fertilize crops

• Algae grown in sewage effluent has a significant potential for the production of biomass and oils that can be used for energy production

Algal Nutrients and Eutrophication

Acidity, Alkalinity, and Salinity

Acidity, Alkalinity, and Salinity

• Aquatic biota are sensitive to extremes of pH and changes in salinity

Acidity, Alkalinity, and Salinity

Acidity

• Pollutant acid mine water from bacterial action on pyrite, FeS2

2FeS2 + 2H2O + 7O2 4H+ + 4SO42- + 2Fe2+

• (Generates acidic H2SO4)

4Fe2+ + O2 + 4H+ 4Fe3+ + 2H2O

• The following chemical processes, which both generate acid

FeS2 + 14Fe3+ + 8H2O 15Fe2+ + 2SO42- + 16H+

Fe3+ + 3H2O Fe(OH)3(s) + 3H+

• Acid can also come from industrial pollution and acid rain

• Excess acid (low pH) can harm aquatic biota

• Excess acid can be corrosive in water systems

Acidity, Alkalinity, and Salinity

Pollutant Alkalinity

• Excess alkalinity and accompanying high pH generally are introduced from mineral strata aggravated by conditions created by humans

• Characteristic fringe of white solids around edge of bodies of water commonly indicates alkaline pollution

Pollutant Salinity

• Picked up in municipal systems, e.g. from water softeners and mineral spoil piles

• Picked up from irrigation water

• Harmful to plants

• May make water unsuitable for drinking water use

Oxygen, Oxidants and Reductants

Oxygen, Oxidants and Reductants

• Dissolved O2 present in water saturated with air at 25˚C only at levels around 8 mg/L

• Rapidly dissipated by biodegradation of organic matter, {CH2O}, by microbial action:

{CH2O} + O2 CO2 +H2O

• Oxygen consumed in biological oxidation of other species, such as ammonium ion:

NH4+

+ 2O2 2H+ + NO3- + H2O

• Depletion of O2 by chemical oxidation of reduced species:

4Fe2+ + O2 + 10H2O 4Fe(OH)3(s) + 8H+

2SO32-

+ O2 2SO42-

Oxygen, Oxidants and Reductants

• Degree to which solutes in water result in depletion of dissolved O2 by microbial action is expressed by biochemical oxygen demand, BOD

• Total organic carbon (TOC) can be measured chemically and usually is indicative of BOD

Oxygen, Oxidants and Reductants

Organic Pollutants

Organic Pollutants

• Sewage from domestic, commercial, food-processing and industrial sources

• Organics – oil, grease, solids are removed by sewage treatment

• Salts, heavy metals, and refractory (degradation resistant) organics are not

• Disposal of sewage sludge a problem due to left over heavy metals and refractory organics

Organic Pollutants

Organic Pollutants

• Offshore disposal at sea results in formation of sewage residue beds

• Warm sewage rises and is spread laterally before sedimenting out

Organic Pollutants

Soaps, Detergents, and Detergent Builders• Soaps – salts of fatty acids (e.g. sodium stearate)• Soap lowers water surface tension (makes it “wetter”)• Ionic carboxyl ‘head’ and hydrocarbon ‘tail’

• In presence of oils, fats and other insoluble OM – organic tail dissolves in OM, head remains in aquatic solution

• Soap emulsifies, or suspends OM in water

Organic Pollutants

Soaps, Detergents, and Detergent Builders• Primary disadvantage - soap forms precipitates with Ca2+ (water hardness)

2C17H35COO-Na+(aq) + Ca2+ (aq) Ca(C17H35COO)2(s) + 2Na+(aq)

• Formation of calcium precipitate with soap is good for the environment because it removes soap from solution leaving a biodegradable residue

• Not used to wash clothes!

Water-soluble soap Insoluble calcium precipitate (“bathtub ring”) not useful for cleaning

Organic Pollutants

Detergents• Synthetic detergents do not precipitate in hard water

• Large potential to contaminate water due to heavy use

• Detergents consist of a surfactant (surface-active-agent) plus builders and other additives

• Surfactants have an amphiphilic structure (acts to make water wetter) with an ionic “head” attracted to water and a hydrocarbon “tail” attracted to organics

• Early surfactants were of the alkyl benzene sulfonate (ABS) type

Organic Pollutants

Detergents

• ABS is very poorly biodegradable due to branched chain

• Severe problems with foam in wastewater treatment plants and receiving waters

• ABS replaced by biodegradable linear alkyl sulfonate, LAS

Organic Pollutants

• Detergent formulations contain a variety of builders and other auxiliary materials

• Builders bind hardness ions and make solutions basic

• Other ingredients may include:

Ion exchangers, alkalis (sodium carbonate), anticorrosive sodium silicates, amide foam stabilizers, soil-suspending carboxymethylcelluloss, bleaches, fabric softeners, enzymes, optical brighteners, fragrances, dyes, diluent sodium sulfate

Organic Pollutants

Biorefractory organics in Water

• A variety of hydrocarbons and halogenated hydrocarbons that resist biodegradation

• Include suspect carcinogens and are highly undesirable in water

e.g. aromatic or chloinated HCs, benzene, cmphor, chloroform, styrene etc.

• Methyl tert-butyl ether (MTBE) octane booster now removed from gasoline because of its detrimental effects on water quality

• Naturally occurring chlorinated and brominated compounds may be found in water

Pesticides in Water

Pesticides in Water

• Insecticides, molluscidies, namaticides, rodenticides, fungicides, bactericides, slimicides, hebicides, algicides etc.

Natural Product Insecticides

• Derived from plants

Pesticides in Water

DDT and Organochlorine Insecticides

• Historical interest (since banned), DDT especially important in early environmental movement, persistent, bioaccumulative water pollutants in the past

Pesticides in Water

DDT and Organochlorine Insecticides• Prepared by Zeidler in 1874, insecticidal

activity discovered by Müller in 1939• Hailed as miraculous during its use in WWII• Found to be effective against malaria (carried

by mosquitoes) and typhus (carried by lice)• Saved lives of millions of people• Its effectiveness led to overuse in agriculture

– resistance• Now banned in most countries for agricultural

use

DDT

2 planar rings

2 tetrahedral carbons

Para (1,4)

Ortho (1,3)

Meta (1,1)

para-dichlorodiphenyltrichloroethane

p, p’-isomer

DDT Analog(molecular shape)

1. Non-persistent 2. Doesn’t accumulate3. Forms water soluble compounds4. Toxic to insects, non-toxic to mammals – birds + mammals have

enzymatic detoxification pathway

Pesticides in Water

• Toxaphene:

Mixture of hundreds of similar substances (produced from chlorinated camphene- pine tree product) was widely used after DDT ban in 70s

• Toxaphene is extremely toxic to fish• Restrictions were placed in 1982

and a total ban in 1990

Spread of Toxaphene in N. America from SE cotton states

Pesticides in Water

Organophosphate Insecticides

• Biodegradable organophosphates were substituted for persistent organochlorine insecticides, but many are now phased out because of their toxicities

• Two relatively toxic organophosphates

Pesticides in Water

Organophosphate Insecticides

• Malathion, an organophosphate insecticide that is relatively non-toxic to humans because of their enzyme systems that can degrade it:

Pesticides in Water

Carbamates• Relatively non-toxic to humans and biodegradable

Pesticides in Water

Herbicides

• Because of their widespread use and the necessity of application over widespread land areas, herbicides are the pesticides of greatest concern

• Bipyridilium Compounds

• Two pyridine rings per molecule, destroy plant cells, toxic to humans

d

Pesticides in Water

Herbicides

• Herbicidal Heterocyclic Nitrogen Compounds:

• Triazines (3 heterocyclic rings) – inhibit photosynthesis

Widely used on corn Widely used on soy beans

Pesticides in Water

Herbicides

• Chlorophonoxy Herbicides

• 2,4,5-T produced contaminant TCDD as a byproduct (see bellow)

Pesticides in Water

Herbicides

• Substituted Amide Herbicides

• Nitroanaline Herbicides

Pesticides in Water

• Miscellaneous Herbicides

Pesticides in Water

Byproducts of Pesticide Manufacture

• Hexachlorobenzene, once widely used as a raw material in the manufacture of organochlorine pesticides has been a significant water pollutant and troublesome contaminant in hazardous waste sites

• 2,3,7,8-tetrachlorodibenzodioxin (TCDD) (“Dioxin”) is a pesticide manufacturing byproduct that has caused severe pollution problems in the past (Figure 12.9)

DioxinsAgent Orange

• Agent Orange – mix of 2,4-D and 2,4,5-T

Herbicide (defoliant) ~ 10 ppm TCDD dioxin

Used by U.S. military in its Herbicidal Warfare program during Vietnam War.

• Million of gallons used 1962 - 1971 to remove unwanted plant life otherwise provided cover for enemy forces during the Vietnam Conflict

• Veterans and to a greater extent the Vietnamese reported a variety of health problems due to exposure that continues to this day [graphic and disturbing images]

Movies: http://www.pulitzercenter.org/openitem.cfm?id=426

Dioxin IncidentsTimes Beach, Missouri

NYT 121682

Dioxin IncidentsTimes Beach, Missouri

Shown in History Channel Modern Marvels #20

1972-76dirt roads were sprayed with waste oil containing super concentrated dioxin from Agent Orange manufacture

1992 - Town was demolished

1997 - 265,000 tons of soil was incinerated on site

Now Route 66 State Park

Polychlorinated Biphenyls

PCBspolychlorinated biphenyls

• Commercially attractive since chemically inert, difficult to burn, low vapor pressure and inexpensive

• Before 1974, PCBs were used as coolant in capacitors, transformers, heat transfer fluids, plasticizers, surface coatings, inks, adhesives, and carbonless duplicating paper

• After 1974, use of PCBs was restricted to the production of capacitors and transformers

• Manufacture discontinued in 1976, uses and disposal strictly controlled

http://www.epa.gov/ttn/atw/hlthef/polychlo.html

PCBsThe numbering system

The unprimed ring is chosen to be the one that will give a substituent with the lowest numbered carbon

Rotation around C-C bond produces congeners

PCBsPollution in Hudson River

GE began using PCBs for a wide range of industrial purposes in the late 1940s. From 1947 to 1977, GE plants north of Albany poured more than 1.3 million pounds of PCBs into the upper Hudson.

200 miles is now designated NPL site

Source: http://www.nrdc.org/water/pollution/hhudson.asp

By the mid-1970s, a growing number of studies had found links to premature births and developmental disorders, and had shown that PCBs caused cancer in lab animals.

Today, the federal government classifies PCBs as probable human carcinogens. They are also associated with reproductive problems, low birth weight, reduced ability to fight infections and learning problems.

EPA orders General Electric to dredge PCBs from Hudson River (Source: Pollution Online newsletter, 12/4/2001)

WASHINGTON, Dec 04, 2001 (AP WorldStream via COMTEX) –

The Bush administration ordered tons of PCBs removed from New York's upper Hudson River, setting in motion one of the largest dredging operations in the nation's history. General Electric Co. dumped 1.3 million pounds (585,000 kilograms) of PCBs into the river before the federal government banned the pollutants in 1977. The company bitterly opposes dredging, which expected to cost GE dlrs 500 million.

….

PCBs, used as insulation and a coolant, have been linked to cancer in laboratory animals. The EPA classifies the oily substance as a probable carcinogen and says PCBs pose risks to wildlife and to people who eat fish from the Hudson. GE released PCBs from its plants in Fort Edward and Hudson Falls, about 40 miles (64 kilometers) north of Albany. The cleanup will include locations in that stretch, reaching almost down to the capital city.

…..

PCBsCycling in the Environment

• PCBs are highly resistant to degradation

• Due to low solubility, most of the PCBs in water are bound to the soil and sediments

• Biodegrade very slowly!

• Widely dispersed, e.g. polar regions, bottom of oceans

• Approximately 30% in environment, 70 % remaining in equipment

Question

The PCB concentration in Lake Michigan is declining according to a first-order rate constant of 0.078 yr-1. If the PCB concentration averaged 0.047 ppt in 1994, what will it be in 2010? In what year will the concentration fall to 0.010 ppt? What is t1/2?

Find t when C = 0.010 ppt

0.010/0.047 = e-0.078t

t = 19.8, concentration declines to 0.010 ppt by the year 2014

t1/2 = ln2 / k = 8.9 y

C = C0e-kt

Let 1994 be equivalent to t = 0

2010 will be t = 16 y

C = 0.047e-0.078 x 16 = 0.047e-1.248 = 0.013 ppt

PCB Levels - Great Lakes Aquatic Food Chain

PCB concentration in herring gull eggs in Toronto Harbor (1991)

50,000 x

PCB Levels - Great Lakes Aquatic Food Chain

Slow and erratic decline in fish

PCB concentration in Coho Salmon

…the good news

Levels have fallen steadily in bird eggs…

PCB concentration in herring gull eggs in Toronto Harbor

Note different scales

Since PCBs with less chlorine are metabolized faster the relative concentrations of PCB congeners changes with time

Health EffectsAccidental Exposures of PCBs

NYT, August 2nd 1988

‘epidemic of birth defects’

‘contaminated cooking oil’

‘discolored skin, deformed nails and developmental delays’

Japan/Taiwan PCB poisoning episodes 1968/79

‘the Taiwanese experience does not prove one way or another” that lower levels of exposure to PCB’s are dangerous to fetuses’

Why?

Health EffectsEffects in Utero

• Exposure to low levels results in impaired intellectual development

NYT, September 12th 1998

Health EffectsEffects in Utero

• Lake Michigan study – 212 children– long-lasting deficits in a child’s intellectual

development– prenatally exposed group had lower birth

weight, smaller head size, slightly more premature

• Severity increases with exposure– Age 7 months – visual recognition– 4 yrs – lower weight – lower mental

functioning (verbal + memory)– 11 yrs – 6 point IQ deficit in high exposure

group – ADHD

Jacobson et al. 2002

Radionuclides

Radionuclides

• Radium-226, an alpha emitter from decay of uranium-238, an important contaminant in some drinking water supplies

• Iodine-131, 8-day half-life beta and gamma emitter, goes to thyroid and can cause thyroid cancer, product of nuclear fission and one of the more dangerous radionuclides released by the Chernobyl nuclear reactor fire in the former Soviet Union

• Cobalt-60, a gamma emitter from uranium fission and non-fission reactions in nuclear reactors

• Radiation causes adverse health effects by breaking bonds in biomolecules including nucleic acids

Radioactive Decay

Decay Chains

Radioactive isotopesundergo decay untilthey reach a stablespecies

All isotopes of allelements with atomicnumber 84 (Po) andhigher are radioactive

RadionuclidesInteraction with DNA

• Can irradiate sensitive cells

• Radiation can alter the cells, increasing the potential for cancer

Double Strand Breaks

+ ionize water to produce free radicals

Radioactivity

Half-life: the time required for half the radionuclide to decay

e.g. caesium-137t1/2 = 30.3 yr

Radionuclides

Radioactivity

• Rate of decay is proportional to amount remaining

dN N , let λ = constant dN = -λN

dt dt

• Solve for N,

N = Noe-λt

• Where N = no. nuclei at time t, N0 = no. nuclei at start, λ = decay constant

• Half-life t1/2 when N = N0

2

Question

N = Noe-λt

Solve for t1/2, N = N0 /2

N0 / 2 = Noe-λt

1/2 = e-λt

ln(1/2) = ln(2-1) = -ln2 = - λ t1/2

λ = ln 2

t1/2

Rule of logs

ln ab = b lna

Question

Derive the expression for the time to decay:

t = t1/2 ln (N / N0) from N = Noe-λt

-0.693

Radioactivity

• t1/2 is related to probability of any one nuclei decaying

• Larger the λ, the higher the probability of decay, the shorter the half-life

• With a mix of radioactive waste there is a progression from highly active, short half-life isotopes to less active, long-lived isotopes

Radionuclide λ (s-1) t1/2

Lead-210 9.86 x 10-10 22.3 yr

Radon-222 2.11 x 10-6 3.8 d

More active,

More disintergrations

Radionuclides

• Radium-226, an alpha emitter from decay of uranium-238, an important contaminant in some drinking water supplies

• Naturally occurring

• Maximum contaminant level (MCL) is 5 pCi/L

• Removed by conventional water softening processes