The charged end is attracted by water and provides a kind of hydrophilic handle to the remaining hydrophobic alkane.The charged end is attracted by water and provides a kind of hydrophilic handle to the remaining hydrophobic alkane.

The alkane hydrophobic portion attracts oil and greases and other hydrophobic alkanes and attaches them to the hydrophobic tail.

Soaps precipitate with alkaline earth elements such as Ca and Mg and form "soap scum" and are usually found as precipitates in the environment as Ca or Mg solids that are easily decomposed by bacteria. Ca and Mg are the main ions contributing to water "hardness."

2C₁₇H₃₅COO^-Na⁺ + Ca²⁺ <---> Ca(C₁₇H₃₅COO)_(s) + 2Na⁺

Detergents

Synthetic detergents do not form insoluble precipitates with Ca and Mg and have excellent hydrophobic attraction properties also making them exceptional surfactants.

Surfactants are surface-active agents that affect the water's "wetting" ability especially at the liquid and air interface.

This is especially important for cleaning oil and grease since these molecules "self-assemble" and float to the surface.

A modern example of a popular detergent is Sodium dodecylsulfate and alpha-benzenesulfonate:

Sodium dodecylsulfate

Linear alkyl sulfonate (LAS)

This detergent is biodegradable and has relatively short durability in the environment.

From the 1930's to the 1960's, many of the detergents were not biodegradable such as alkyl benzene sulfonate (ABS). It is a relatively non biodegradable surfactant and persists for such a long time in the environment that it caused foam at outfalls of sewage treatment plants that was obvious and undesirable. This type of detergent is also toxic to many fish.

Alkyl benzene sulfonate (ABS)

The tertiary carbon tends to make this type of molecule not readily biodegradable and is a good indicator of non-biodegradability.

Detergent Builders

Builders are still a significant problem as water pollutants. Detergents are only 10-30% surfactants and the rest are detergent builders.

Detergent builders are other ingredients that increase the effectiveness of the surfactant or add other desirable properties to the detergents. Some of these ingredients are complexing agents such as polyphosphates which complex Ca and Mg and enhance the surfactant's ability to function by "softening" the water (removing the ability of the hardness factors Ca and Mg to bind to the surfactant).

Other Builders are bleaches, fabric softeners, enzymes, optical brightners, dyes, anticorrosive sodium silicates, foam stabilizers, inert suspended solids such as carboxymethylcellulose.

Pesticides: Water & General Environmental Pollutants

Non-agricultural applications of pest control, gardening, industrial and home pest control consume the rest of the pesticides and insecticides each year.

There are several general types and categories of pesticides.

• Naturally occurring, their derivatives and anthropogenic copies
  
• Polychlorinated hydrocarbons (chlorinated hydrocarbons)
  
• By-Products of Pesticide Manufacture
• Organophospate Compounds
• Carbamate Compounds
• Bipyridilium Compounds
• Chlorophenoxy Compounds
• Amides and Nitrogenated Compounds

Many pesticides are derived from natural compounds in plants such as Nicotine, Rotenone and Pyrethrin.

These are among the more biodegradable and environmentally friendly of the pesticides.

Pesticides Naturally occurring (cont)

Examples of these extracted natural pesticides are:
Three naturally occurring insecticides:

Nicotine - Extracted from tobacco

Rotenone - Extracted from some legume roots

Pyrethrin I - Extracted from chrysanthemum flower heads

(known for over 2,000 years as an insecticide)

Once a class of compound is found in nature, synthetic analogues are produced that also produce similar reactions as pesticides such as Allethrin and Fenvalerate. These synthetic analogues are easily metabolized by mammals and because of a metabolic and enzymatic degradation pathway already established pose little threat to food protected by these natural pesticides and synthetic natural analogues.

Allethrin - Modern synthetic analogue of Pyrethrin I

Fenvalerate - Modern synthetic analogue of Pyrethrin I

Pesticides:

Organochlorine Insecticides have hydrogens replaced with chlorine. They are frequently as a class of compounds called Polychlorinated hydrocarbons or Polychlorinated aromatics.

This class of compounds was used heavily in the 1960s and was the subject of the book by Rachel Carson "Silent Spring" that focused attention on their general toxicity, and bioaccumulation. Eventually they were discontinued (DDT banned in 1972) in the US but are still manufactured in other countries and shipped from the US to these countries for use.

Generally, there are no metabolic pathways which exist for chlorinated organic molecules. They are fat or lipid soluble and not water soluble and bioaccumulate to toxic levels over long time periods.

The most famous of these was dichloro-diphenyltrichloroethane or 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane known as DDT. All of the following organochlorine insecticides are now banned but still persist in the environment due to their low biodegradability.

DDT

Methoxychlor

Dieldrin/Endrin,

Chlordane

Aldrin

Heptachlor

Toxaphene is about 68% Cl as a result of a mixture of a possible 177 compounds from the chlorination of camphene a terpene isolated from pine trees. One form marketed as Lindane (gamma isomer).

Toxaphene

1,2,3,4,5,6-Hexachlorocyclohexane, Gamma isomer (Lindane)

1,2,3,4,5,6- Hexachlorocyclohexane, Gamma isomer (Lindane)

Chlorophenoxy Herbicides

2, 4 - D is one of the most widely used domestic broad leaf weed killers. It was also contaminated with a byproduct TCDD (2,4,5,-T)

2,4 - Dichlorophenoxyacetic acid, "2,4-D"

2,4,5-Trichlorophenoxyacetic acid, (2,4,5-T)

Chlorinated organic by-products

Manufacturing by-products intermediates are also hazards.
Hexachlorobenzene is one starting material that sometimes remains in the final product and is very non-biodegradable.

Hexachlorobenzene

75 different dioxin compounds are created as chlorine occupies positions 1 through 8 on Dibenzo-o-dioxin. TCDD is the most infamous dioxin. Until 1960, dioxin was a by-product of many chlorinated phenyl compounds especially herbicides of this type.

Dibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)

TCDD has an mp of 305 °C and a high degree of chemical and thermal stability of up to 700 °C. It is very non-biodegradable and highly toxic to most mammals (an LD₅₀ of only 0.6 µg/kg body mass, guinea pigs). TCDD has been identified in some municipal incineration emissions and is found in other waste disposal environments.

Environmental Disaster

An example of disastrous chlorinated hydrocarbon pesticide contamination occurred in Hopewell Virginia in the mid 1970s. As much as 53,000 kg of Kepone may have been dumped into the Hopewell sewage system and the James River. It was essentially sterilized and has been estimated to require several billion dollars and the removal of over 135 million cubic meters of river sediment.

Kepone

Polychlorinated Biphenyls (PCBs)

There are 209 different PCB compounds

Example of a 5-chlorinated biphenyls

Biodegradation of PCBs

{CH₂O} + H₂O + 2Cl-PCB -------> CO₂ + 2H⁺ + 2Cl^- + 2H-PCB

Final PCB products after normal biodegredation are mono- chlorinated biphenyls.

If oxygen is supplied, the final product is a dechlorinated hydrocarbon starting from the natural final mono-chlorinated degradation product.

Organophosphate Insecticides

Orthophosphoric acid

Paraoxon

A special sub-group are the phosphorothionate compounds due to the phosphorous double bonded to a sulfur (P=S) in these compounds.

Methyl Parathion

Chlorpyrifos (sold as Dursban)

These organophosphate compounds differ dramatically in toxicity due to their structure and metabolic pathways in mammals.

For example, parathion has been linked to over 200 deaths since its introduction. Between 2 to 120 mg is fatal to a child or adult.

Dermal absorption is a very real danger with organophosphate pesticides as they permeate the skin at higher rates as compared to other compounds.

The two carboxyester linkages on malathion are removed by carboxylase enzymes and render it relatively nontoxic to humans.

Malathion Hydrolysis: metabolic pathway that detoxifies it in mammals.

Malathion is approximately 100 times less toxic to mammals than Parathion.

The organoposphates do not bioaccumulate since they are water soluble (not lipid or fat soluble) and are metabolized in established pathways.

Carbamate Pesticides

The toxic effect stems from the fact that carbamate compounds inhibit acetylcholinesterase. Acetylcholinesterase breaks down Acetylcholine after it has transmitted a nerve impulse from one cell to another. Inhibition of acetylcholinesterase essentially leaves the nerve connection open and prevents the nerve from being used again. This is a relatively reversible toxin and has no carcinogenic or biocumulative effects.

Carbamic acid	Carbaryl
Carbofuran	Primicarb

Bipyridilium Herbicide Compounds

Paraquat                                                         Diquat
               

Food and water are sometimes contaminated with residues from these herbicides due to their ubiquitous use.

Nitrogen Compounds as Herbicides

Triazine compounds are heterocyclic (a compound containing two or more different elements in the ring) that have both carbon and nitrogen in the ring. Triazines inhibit photosynthesis.

Atrazine - used on weeds near corn crops

Metrabuzin - used on weeds near soybeans, sugarcane, and wheat.

Substituted Amide Herbicides

Many herbicides, including propanil for weed control for rice fields and alachlor (Lasso) for killing germinating grasses and broad-leaf weed seedlings.

Propanil

Alachlor

Nitrogen Compounds as Herbicides

Nitroaniline herbicides have nitro groups and substituted amines on benzene rings exemplified by trifluralin.

Trifluralin

Other diverse alterations such as substituted urea, carbamates and thiocarbamates also kill unwanted plants and weeds.

3-(4-Chlorophenyl)-1,1-dimethylurea

Isopropyl carbanilate

Sodium N-methyldithio carbamate

Radionuclides in the Aquatic Environment

Three (common) particles or energies emitted in nuclear reactions

	Helium nucleus (2 protons, 2 neutrons)
	conversion of neutron to proton in nucleus
	electromagnetic radiation: very short wavelength, high energy

An inverse relationship exists between the particle size and depth of penetration into matter.

Size of particle:

Alpha particle > Beta particle > Gamma rays

Depth of penetration of particle or ray:

Alpha particle < Beta particle < Gamma rays

Ionization of particle or ray per path length:

Alpha particle > Beta particle > Gamma rays

Natural Radioactivity

Uranium

Radon

Structure and energy of particles and rays

Alpha-particle>

The Alpha particle is easily understood from a matter standpoint

How do you get an electron from the nucleus when there are no electrons in the nucleus (Beta particle)? Neutron is converted to a proton within the nucleus and an electron is emitted.

Gamma ray

The energy of a gamma ray depends on the frequency of the electromagnetic radiation. For example:

Radioactive decay follows first-order kinetics; that is, the number of nuclei disintegrating in some period of time is directly proportional to the number of radioactive nuclei present.

Where:
N - is the number of radioactive nuclei present

- is the rate constant with units of reciprocal time

Another useful term is the half-life - the time period in which one-half of the given number of radionuclides decay.

Thus it will take 10 half-lives for the concentration of radionuclides to reach < 99.9% of the present concentration. By multiplying the half-life by 10 one can estimate the 99.9% decay of the radionuclide.

Naturally occurring radionuclides in water, soil, and air are uranium, radium, radon and potassium-40. The unit of measurement is typically the curie, and for low levels the picocurie.

Where:
Ci = 1 curie is 3.7 x 10¹⁰ disintegrations per second
pCi = 1 picocurie is 3.7 x 10^-2 disintegrations per second

The maximum level of radionuclides in drinking water for Radium-226 and Ra-228 is 5 pCi/L.
Several states have naturally higher levels of radium such as Iowa, Illinois, Wisconsin, Missouri, Minnesota, Florida, North Carolina, Virginia and the New England states.

The half-lives of anthropogenic nuclides range from seconds and minutes to 24,000 years for Plutonium (Pu-239).

Anthropogenic Contributions of Radionuclides

There have been many instances of anthropogenic contamination.

For example:
The deliberate sinking of 11 nuclear submarines with fuel on board off the coast of Norway in the fishing grounds (1989-1990). Nuclear fuel isotopes now find their way into fish and ocean water.

Post World War II testing of nuclear weapons by the US, Russia, China, and France.

A standard US nuclear power plant produces approximately 1,000 cubic meters (1,300 cubic yards) of radionuclide contaminated waste per year. Nuclear energy production plus other sources such as medical, research, and industrial applications produce an estimated total of 100,000 cubic meters annually. Some of this waste has been, and is, disposed of in landfills where it may leache into water.

A large nuclear reactor discharges about 30 metric tons of spent fuel each year. This waste occupies the space of a small automobile.

The April 26, 1986 Chernobyl nuclear plant accident spread nuclear waste over much of the Ukraine, Russia and some of Europe. Chernobyl is located 130 km north of Kiev in the Ukraine. Large quantities of nuclear debris were released into the air and water in a 30 km radius of Chernobyl. Thirty one people died immediately, several hundred followed in weeks or months, and thousands still live on contaminated soil and drink water with higher than previous levels of radionuclides.

Radionuclides in Water

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Revised 5/12/99.