7
Chemicals Chapter in Our Bodies and Our Environment
Good Effects, Bad Effects
Copyright W. H. Freeman and Company New York
Chemistry Applied
Vitamins Food Additives Pesticides Dioxin and PCB's Synthetic hormones in the environment
Copyright W. H. Freeman and Company New York
Vitamins
Vitamins are essential, noncaloric nutrients. Vitamins are needed in very small amounts. Our bodies cannot synthesize vitamins; they are obtained entirely from our diet or from vitamin supplements. A healthy diet containing fresh vegetables, fruits, whole grains and complete protein sources provides the recommended daily amount of vitamins and minerals. Vitamins are divided into two classes: water soluble and fat soluble. A vitamin's class determines how it is absorbed into the bloodstream and transported, whether it can be stored in the body, and how easily it is lost from the body.
Copyright W. H. Freeman and Company New York
Vitamins
1. Vitamin C and members of the vitamin B family are water soluble.
Water soluble vitamins are absorbed directly into the bloodstream where they travel freely. They are not stored in the tissues to any great amount so are not toxic. Excess amounts are secreted in the urine. Water soluble vitamins are diminished in foods cooked in water.
Copyright W. H. Freeman and Company New York
Vitamins
Vitamin C is water soluble because it contains many hydroxyl groups.
Vitamin C is required for the production of collagen, an important connective tissue. A deficiency of vitamin C results in the disease, scurvy, characterized by skin lesions and tooth loss. Vitamin C is found in fresh fruits and vegetables, especially citrus fruits.
Copyright W. H. Freeman and Company New York
Vitamins
A deficiency of vitamin C leads to the disease scurvy, characterized by skin lesions and tooth loss. Vitamin C is an antioxidant and is also involved in the body's immune response against infection. Many people ingest large amounts of vitamin C to try to ward off colds. Its effectiveness is inconclusive and people are advised to refrain from taking massive doses of vitamin C. The other water soluble vitamins are all members of the B family. The B vitamins all act as coenzymes, molecules that cannot be synthesized by the body but are required for the activity of certain enzymes.
Copyright W. H. Freeman and Company New York
Vitamins
Copyright W. H. Freeman and Company New York
Vitamins
Copyright W. H. Freeman and Company New York
Vitamins
1. Vitamins A, D, E, and K are fat soluble.
The fat soluble vitamins are carried by fattransporting proteins in the blood. Fat soluble vitamins can accumulate in fatty tissue, so levels of fat soluble vitamins can build up to toxic doses if megadoses are taken. Fat soluble vitamins may be missing from the diet for weeks since reserves are generally stored in the fatty tissues.
Copyright W. H. Freeman and Company New York
Vitamins
Vitamin E is an antioxidant. It is present in eggs, vegetable oil, nuts, and other fatty plant based foods. A deficiency of vitamin E leads to scaly skin, sterility and decay of muscle tissue. When O2 is used by the body, small amounts of highly reactive molecules called free radicals are formed. Free radicals damage living cells by disrupting cell membranes. They are also damaging to proteins and DNA. Vitamin E and other antioxidants prevent this damage from happening.
Copyright W. H. Freeman and Company New York
Vitamins
Vitamin A is present in mild, eggs, and liver and in the form of betacarotene, found in vegetable sources. Betacarotene is converted to vitamin A once inside the body. Vitamin A is involved in vision and is required for proper growth in children. Lack of vitamin A leads to night blindness. Vitamin D can be made in the body by the action of UV light on the skin. It is routinely added to milk as a vitamin supplement. Vitamin D is involved in the uptake of calcium through the intestinal wall. Vitamin D deficiency leads to a disease called rickets.
Copyright W. H. Freeman and Company New York
Vitamins
Vitamin K is required to make the proteins involved in blood clotting. A routine injection of vitamin K is given to newborn infants.
Copyright W. H. Freeman and Company New York
Vitamins
Copyright W. H. Freeman and Company New York
Vitamins
Copyright W. H. Freeman and Company New York
Food Additives
1. Antioxidants prevent foods from becoming rancid.
When food spoils, it is often the result of the oxidation of unsaturated fatty acids. Antioxidants added to the food prevent this process from occurring by interfering with one of the first steps in the process. Vegetable oils come with their own antioxidant, vitamin E.
Copyright W. H. Freeman and Company New York
Food Additives
Several vitamin E mimics have been synthesized and are used in packaged food products susceptible to oxidation. These include BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene), and Propyl Gallate. Small numbers of metal ions in food catalyze the oxidation reactions in food. Sequestrants are often added to foods to bind these metal ions in order to reduce their reactivity. Citric acid and EDTA (ethylenediaminetetraacetic acid) are typical sequestrants.
Copyright W. H. Freeman and Company New York
Food Additives
1. Dehydration and certain chemicals act as food preservatives.
The simplest way to preserve foods is to dehydrate them. Microbes cannot grow in the absence of water. Adding common table salt acts to dehydrate foods because it draws water to itself and thus out of the food. Concentrated sugar solutions work in the same way. The principle involved is called osmosis, the movement of water across a membrane from a dilute solution to a more concentrated solution. Freeze drying is a second way to dehydrate foods. All water is removed by placing frozen foods in a vacuum.
Copyright W. H. Freeman and Company New York
Food Additives
Organic acids Many food preservatives are toxic to microorganisms, but not toxic to humans. Benzoic acid, in the form of sodium benzoate, is a commonly added preservative.
Propionic acid (calcium or sodium propionate) is added to baked goods, cheeses, and other noliquid products. Sorbic acid (calcium, sodium, or potassium sorbate) is added to the same foods, but is only useful against molds and fungi, not bacteria.
Copyright W. H. Freeman and Company New York
Food Additives
Sulfites Sodium bisulfite, NaHSO3, kills bacteria and is used to protect wine and other grape products. Some people are allergic to sulfites so foods and beverages containing them must include a warning label. Bisulfites can be produced by reacting sulfur dioxide or a sulfite with water. SO2(g) + H2O(l) H2SO3 H+ + HSO3 SO3 + H2O HSO3 + OH
Copyright W. H. Freeman and Company New York
Food Additives
Nitrites Sodium nitrite is used to preserve cooked and cured meats such as ham, bacon, hot dogs, sausages, and luncheon meats. Nitrites prevent the growth of the bacteria which causes botulism and causes the meats to assume a pink or reddish color which is more appealing than their natural brown or gray color. Nitrites occur naturally in the body and react with hemoglobin preventing it from carrying oxygen. About 12% of our hemoglobin is tied up in this way. Enzymes keep the level of nitrites low in most people, but in some people, this enzyme is defective and nitrite poisoning can occur.
Copyright W. H. Freeman and Company New York
Food Additives
A major concern is whether or not nitrites can be converted into carcinogenic nitrosamines in the body. This issue is still controversial.
Copyright W. H. Freeman and Company New York
Food Additives
1. Some additives are used to enhance the appearance, texture, and flavor of food.
Another category of food additives includes colors and bleaching agents. Currently used coloring additives in the US are:
Copyright W. H. Freeman and Company New York
Food Additives
Thickening agents and texture modifies are also added to foods. These include carrageenan, a carbohydrate extracted from Irish moss; xanthan gum; locust bean gum; propylene glycol alginate and various cellulose derivatives. Flavor enhancers such as MSG or monosodium glutamate, disodium guanylate, and disodium inosinate are added to allow manufacturers to use inferiorquality ingredients but still produce a pleasing taste. MSG can cause headaches in some people
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
1. Pesticides kill undesirable organisms but are also toxic to humans.
A pesticide is a substance that kills or otherwise controls an organism that humans find undesirable. Pesticides function by blocking a vital metabolic process in the organism for which they are toxic. Pesticides are generally toxic to organisms, including humans, other than the target organism. The most important forms of pesticides are Insecticides DDT, matlathion kill insects Insecticides DDT, matlathion kill insects Herbicides 2,4D kills plants, especially weeds. Herbicides 2,4D kills plants, especially weeds.
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
About one billion kilograms of pesticides are used annually in North About one billion kilograms of pesticides are used annually in North America. Almost half of this is used in agriculture. Pesticides (along with Almost half of this is used in agriculture. Pesticides (along with inorganic fertilizers) allow the production of large amounts of food on relatively small amount of land. The greatest agricultural use of insecticides occurs in the growing of The greatest agricultural use of insecticides occurs in the growing of cotton, and of herbicides in the growing of corn and soybeans. Fungicides are used to protect seed during storage, and to kill fungi Fungicides are used to protect seed during storage, and to kill fungi on plants before the penetrate the leaves or stem. About half the foods eaten in the US contain measurable amounts of About half the foods eaten in the US contain measurable amounts of at least one pesticide. For this reason many pesticides have been banned or their use restricted. Living plants themselves sometimes produce natural pesticides which Living plants themselves sometimes produce natural pesticides which are no less toxic to humans than synthetic ones.
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
Pesticides often migrate from where they are applied to the rest of the Pesticides often migrate from where they are applied to the rest of the environment and often show up in our water supplies. Some common persistent pesticides are: Some common persistent pesticides are:
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
1. DDT is an infamous insecticide whose effects are still with us.
In the 1940's through the 1960's DDT was commonly used as an insecticide against mosquitoes which can carry malaria and yellow fever mosquitoes which can carry malaria and yellow fever body lice which can transmit typhus body lice which can transmit typhus fleas which can carry the plague. fleas which can carry the plague.
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
1. DDT is an infamous insecticide whose effects are still with us.
DDT was part of the WW2 malaria reduction program that saved the DDT was part of the WW2 malaria reduction program that saved the lives of more than 5 million people worldwide. In 1962, Rachel Carson wrote "Silent Spring" in which the role of DDT In 1962, Rachel Carson wrote "Silent Spring" in which the role of DDT in decreasing the populations of many birds was documented. DDT has been banned in developed countries since the early 1970,s DDT has been banned in developed countries since the early 1970,s due to its persistence in the environment and its negative effect on the reproduction of insect eating birds.
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
1. Organochlorine molecules accumulate in living matter.
Organochlorine compounds tend to accumulate in fish in concentrations millions of time greater than in the water in which them swim Bioconcentration of these materials occur because they a fish's blood is directly exposed to organochlorine compounds dissolved in the water in which they swim. After accumulating in the fatty tissues of small fish, the organochlorines become biomagnified when larger fish eat smaller fish. The organochlorine concentrations are typically highest at the top of the food chain.
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
DDT biomagnification in the food chain:
Copyright W. H. Freeman and Company York
Pesticides: New An Introduction
1. Organophosphate and carbamate insecticides do not bioaccumulate but are toxic.
Organophosphate compounds consist of a central phosphorous atom forming five bonds to: A doubly bonded oxygen or sulfur (P=O or A doubly bonded oxygen or sulfur (P=O or P=S) Two singly methoxy (OCH3) or ethoxy ( OC2H5) groups, (OR) A longer, more complicated R group A longer, more complicated R group attached through an oxygen or sulfur atom ( OR or SR)
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
Carbamate insecticides contain a central carbonyl group rather than a phosphorous atom.
Both organophosphate and carbamate insecticides function by reacting with and inhibiting enzymes in the central nervous systems of the insects targeted. These insecticides are nonpersistent in the environment and decompose within days are weeks. They are seldom found in the food chain. Organophosphate and carbamate insecticides are much more toxic to humans than are organochlorines. Exposure during application can result in immediate health problems.
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
Common organophosphate pesticides include: Malathion (low toxicity to mammals) Malathion (low toxicity to mammals) Diazinon (toxic to birds) Diazinon (toxic to birds) Parathion (very toxic to humans, birds, and other nontargeted Parathion (very toxic to humans, birds, and other nontargeted organisms. It has been banned in some developed countries. Dichlorvos (A volatile insecticide used in flea collars and some Dichlorvos (A volatile insecticide used in flea collars and some aerosol insecticides) Common carbamate pesticides include: Common carbamate pesticides include: Carbaryl (low toxicity to mammals, toxic to honeybees) Carbaryl (low toxicity to mammals, toxic to honeybees) Aldicarb (very toxic to humans) Aldicarb (very toxic to humans)
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
1. Some insecticides are natural products or substances derived from them.
Many plants synthesize their own natural insecticides: nicotine, rotenone, pheromones, and juvenile hormones. Another group of natural pesticides are the pyrethrins which paralyze insects, but generally do not kill them.
Copyright W. H. Freeman and Company New York
Pesticides: An Introduction
Rotenone is derived from the roots of certain bean plants and is used as a crop insecticide. It is also used to kill fish. Both pyrethrins and rotenone are destroyed by sunlight. Synthetic pyrethrins which are more stable have been developed.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. Phenoxy herbicides are used to kill broadleaf weeds and brush.
Phenoxy herbicides are based on a benzene ring connected by an ether oxygen to a short chain carboxylic acid. Two or three chlorine atoms replace ring hydrogens in commercial herbicides.
The two herbicides based on this system are 2,4D (2,4 dichlorophenoxyacetic acid) and 2,4,5T (trichlorophenoxy acetic acid).
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
2,4D is used to kill broadleaf weeds in lawns, golf courses, etc. while 2,4,5T is used for clearing brush from roadsides and power line corridors. Farmers who mix and use large quantities of 2,4D have an increased incidence of noHodgkin's lymphoma.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. Dioxin is a highly toxic byproduct of 2,4,5T production.
A trace contaminant, dioxin, is produced during the manufacture of 2,4,5T. During the Vietnam War, large amounts of Agent Orange (a mixture of 2,4D and 2,4,5T) was used as a defoliant.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
Civilians and soldiers who were exposed believe the their chronic health problems resulted from the dioxin in this substance. This is still a controversial issue. The manufacture and use of 2,4,5T were phased out in North America in the mid 1980's.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. Glyphosate is a herbicide that kills almost all plants.
The most widely used herbicide is glyphosate. It is the herbicide in Roundup and is rather nontoxic. It kills almost all plants.
Recently, genetically engineered soybeans have been produced that are resistant to Roundup. This is controversial because of possible allergenic problems from soybean derived foods, and the possibility of resistance moving naturally from soybeans to other plants.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. PCBs are multiuse organochlorine compounds.
Polychlorinated biphenyls, or PCB's, were a major environmental concern in the 1970's and 80's. They are a major environmental contaminant due to careless dispose practices. They persist for a very long time in the environment. PCB's are implicated in problems with human growth and development. Examples of PCB's are:
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
PCB's find application in coolant fluids in power transformers, plasticizers, carbonless copy paper, deinking solvent used to recycle newspaper, heattransfer fluids, and waterproofing agents.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. PCBs released into the environment will be recycled for years.
PCB's are widespread and persistent environment contaminants. US Production of PCB's was halted in 1977, however old supplies still remain in use in many electrical transformers.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
Biomagnification of PCB's in the food chain:
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. PCBs are contaminated by furans.
Strong heating of PCBs in the presence of oxygen can produce small amounts of dibenzofurans:
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. There are many environmental sources of dioxins and furans.
Many industrial processes produce PCDFs and PCDDs as by products. Contributors include bleaching of paper pulp, incineration of garbage, and recycling of metals. Most pulp and paper mills have switched from Cl2 to chlorine dioxide, ClO2, which produces much smaller levels of furan and dioxin. Incineration is now the largest source of dioxins in the environment.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. We are exposed to dioxins, furans, and PCBs mainly via our diet.
More than 90% of human exposure to dioxins is through the food we eat. Meat, fish, and dairy products contribute the most. The combined concentrations of organochlorines is reported as the equivalent amount of 2,3,7,8 TCDD, that by itself, would produce the same toxic effect. The TEQ scale is used for reporting this toxicity. A value of 1.0 on this scale is defined as the toxicity of pure 2,3,7,8 TCDD.
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
Copyright W. H. Freeman and Company New York
Herbicides, PCB's, Dioxins, and Furans
1. The health effects of PCBs, furans, and dioxins are still controversial.
Conclusions about the extent to which PCBs, furans, and dioxins cause toxic reactions in humans are still tentative and controversial. Most PCBs are not acutely toxic to humans. Heavy exposure of workers in electrical capacitor plants has not resulted in a higher overall death rate, however. Of greater concern is the toxic ef...