(171 Oenio, A. A., J. CHeM. Eouc., 56,30 (19791. (181 Oenio,A.A.,J.CHeM. EDUC.57.272 (19801. (19) "The Merek Index? 10th ed.,Merek and Co., lnc., Rahway, N.J., 1983. (201 Sax, N. I. "Cancer , Causing Chemicala:Van Nostrand Reinhold Co.,NewYork, 1981. (211 MeCann. M., "Artists Beware", Watson-GuptillPubliatitititi, New York. 1979. 1221 "Handbmk of Organic IndusUial Solvents: 5th ed.,Alliance of Ameriean Inaurera, Chicago, IL. 1980. (231 $reen.M. E..andTmk,A.,"Safetyin WorkingwithChemieals,"MaemillsnPuhlishmg Co., Ine.. New York, 1978. (24) M-,C., Purdhsm, J.. Bowhay, D., and Hosein, R., "Health and SafeLy InPrintmskine Alberta Labour, Occumtional Health and Safety Div.. Edmonton, Alberta,
canads, 1978. 1984.
(251 Seeger. N., '"Alternatives for the Artist," The An Institute of Chicago, Chicago, IL, (261 '"Health Hanards in An" Wve color slide setr and Film Bureau, Chicago, IL,1984.
audioea&ttal, lntematiod
Agricultural Chemicals for Consumer Use Edward Maslowsky, Jr. Loras College Dubuque, IA 52001
Chemicals play a very important role in the agricultural industry. One major group included in this category is fertilizers, over 250 billion pounds of which were used in 1983 by developing and developed countries of the world. Also included in this category are pesticides. According to one report, the total loss to worldwide food produhion from pests amounts to an estimated 45% of total annual food production. Imagine the increase in global food availability that would result if such pests could he controlled. Chemicals are often the weapons of choice in this battle. Pesticides (herbicides, fungicides, and insecticides) are important in controlling not only many types of agricultural pests, but also insects that are vectors of disease such as the mosquitoes that carry encephalitis, yellow fever, and malaria; body lice that carry typhus; and fleas that can spread plague. Pesticides also play a very important part in the lives of consumers. Althoueh home and earden use of ~esticides constituted only 8% of the US marcet for such p;oducts in 1983. this amounted to 97 million nounds at a total cost of $377million. The importance of chemicals in increasina worldwide food productiok and controlling diseases cannot be overestimated. These chemicals are, therefore, a worthy topic for inclusion in any chemistry-for-the-consumer course. Often, however, it is difficult to maintain student interest when talking in such general terms. They do not get excited when told of the critical role that chemicals play in growing corn or soybeans on an Iowa farm or in controlling malaria in India. This is especially true of students with an urban as opposed to a rural aericultural backeround. " Many of these same fertilizers and pesticides, however, are also available to and used by nonagricultural consumers, and their use provides a means to discuss them in a way that is more interesting- to students with a nonaaricultural hackground. Ferllllzers
Fertilizers are used not onlv .bv" farmers but also bv backyard gardeners, those trying to make their lawn the greenest on the block. and bv aDartment dwellers and colleee dorm students hoping to keep their indoor plants health; during the dream and dark davs of winter. The thiee numbers ok a bag of fertilizer or a container of ~ l a nfood t indicate the relative percentaaes of the macronutrients nitrogen, phosphorus (calculated as PzOs), and potassium (calculated as K20). The relative amounts of each vary depending on the purpose for which the fertilizer is intended. Products high in nitrogen, including those used on lawns, evergreens, shrubs, and some house plants or leafy vegetables are intended to promote leaf growth. Fertilizers 774
Journal of ~hernicai Education
high in phosphorus are intended for use on bulb plants such as tulips and plants that produce flowers, fruit;, and nonleafy vegetables. Com~oundsused as sources of nitrocen. nhos~horus.and potassLm are often inorganic salts thaiare Feadiiy soluble in water. Exceptions include the organic nitrogen-containing compounds urea and urea-formaldehyde that decompose slowly and provide a source of nitrogen over a long period of time; natural materials such as bone meal that act as a slow release source of phosphorus; and fish or seaweed by-products that are sources of nitrogen. Some fertilizers also provide the micronutrients copper, manganese, iron, and zinc. These metal ions are found as soluble salts or, in the case of iron, as chelates that are more efficiently used by plants. Available as an alternative source of nitrogen with leguminous plants is a legume innoculaut that is applied to seeds before planting. I t contains bacteria that take up residence in the root systems of leguminous plants such as peas and produce nitrogen compounds for them by fixing nitrogen directly from the air. Herbicides
Herbicides are an important class of pesticides that are used to destroy unwanted weeds not only on farms, in forests, and along roadsides, but also in home gardens and lawns. One of the most commonly used organic herbicides is (2,4-dichlorophenoxy)aceticacid, or its salts, d s o known as 2,4-D, a compound that belongs to the phenoxyaliphatic acid family. 2,4-D wasused during the Vietnam war as one of the active ingredients in the defoliant Agent Orange. Now i t is used to remove dandelions and other broad-leaf weeds that areactively growinginlawns. Arelated compound, 242methyl-4-chlorophenoxy) propionic acid or its salts are often used in combination with 2,4-D. Other compounds, called preemergence herbicides, are used to prevent seeds from germinating. Of these, Dacthal is one of the most commonly used. n
O\
,O-CHa
rn
6 OH
24-D
"0-CH,
Daethal
(2.4.diehlorophenoxy metie acid)
Fungicides
Fungicides help to control the diseases that wither the leaves of our fruit trees, cucumber vines, or rose bushes. Among the most common and safest organic fungicides are the dicarboximides Captan and Folpet. Also very important are the dithiocarhamates Maneb and Zineb, which have a chelated structure. In mixtures or alone, fungicides are used on lawns, gardens, and fruit trees, and to pretreat seeds to prevent them from rotting in the soil.
Insecticides
If our plants are not choked by weeds or dried up by fungal infections, they are eaten by insects. Many insecticides are availahle to deal with those outdoor insects that eat cahbage leaves or suck the juice from flower huds-catapillars, aphids, spider mites, among others-or that move into our homes t o live on indoor plants. Some insects such as mosquitoes enjoy using us as a source of their diets; others, including yellow jackets, bees, and wasps, may decide that we are unwelcome euests. There are the ticks and fleas that make our pets71iv& miserable, as well as the head lice that become a problem for manv children a t the start of each school vear. ~ a s t lthere ~ , are chose insects that invade our homeswen though we may have never owned and indeed may even hate plants, cats, and dogs. Silverfish, ants, flies, termites, and of course many varieties of roaches could care less about whether or not we enjoy plants or pets. Many insects are, therefore, not only a nuisance hut also a hazard t o our property or health if not properly controlled. First among the insecticides came the organochlorine compounds, of which DDT is the grandfather and most famous. It and many of its relatives are now banned from further use in the U S . Exceptions include Clordane which is used to treat termites, and Kelthane, Lindane, and Methoxychlor that are reserved primarily for outdoor applications.
DDT
Chlordane
DDW
Malathion
Another important group of insecticides that has replaced many organochlorine compounds is the organocarbamates. The most commonly available of these to the consumer are Sevin and Baygon. The former is often used for gardens and in flea and tick powders and sprays, while the latter is used to treat household ants and roaches. Both may also he used in flea and tick collars.
All of the insecticides discussed so far are manmade. Another very important group, however, called pyrethrins may be derived frommanmade or natural sources. Natural pyrethrins, obtained from the flower heads of chrysanthemums, are among the safest insecticides known to man and his pets and act very rapidly on insects. They are, therefore, the ideal insecticide for many indoor applications. They are a mixture of mainly four compounds, with pyrethrin I being the most effective of the four. Because of the instability of natural pyrethrins, especially in sunlight, more stable synthetic pyrethrins have been produced and are now the active ingredients in several commercial products. Natural ovrethins
Organochlorine pesticides have been replaced largely by organophosphates. These compounds are generally not very persistent but are, as a group, the most toxic of all pesticides to vertebrates. The most popular organophosphate insecticide and one of the safest is DiazinonAt i&sed-in concentrations of less than 1%in sprays for house plants and in treating home pests such as roaches and ants. In higher concentrations, i t is used to control outdoor insects on vegetables, flowering plants, and lawns. Other important organophosphates are Malathion, which has been used to treat fruit fly infestations in California among other places, Dy-syston, and DDVP. Dy-syston is a systemic that is used on indoor plant bug-darts, while DDVP is used in no-pest strips because of its highvapor pressure, which gives it a slow-release aualitv . " that is important. For the same reason, other closely related organophosphates are the active ingredients in many brands of flea and tick collars.
Synthetic pyrethins
wsthrio (Ally1 analog of Cinerio I)
Volume 62
Number 9
September 1985
775
