Lecture 4

1. Lecture 4 Second Lecture for Chapter 2

2. Pesticides • A chemical, physical or biological agent that destroys or controls pest organisms • Common: insecticides, herbicides, fungicides • Approximately 500,000 tons applied in the U.S. each year • Public health: disease prevention (malaria, typhus, yellow fever) and increased agricultural production

3. Pesticides • DDT Story • Saved lives through prevention of malaria, DDT kills mosquito’s • Banned later as a result of bioaccumulation in the food chain • DDT was found in marine sediments, wildlife, and human lipids • Caused thinning of eggshells in birds

4. Pesticides • Many hazardous waste sites have been created as a result of pesticide use • Abandoned pesticide manufacturing plants • Mixing and loading areas, surface and GW contamination • Pesticide Nomenclature • Common and Trade names used most often • The farm chemicals handbook • The following is an introduction to different Pesticides

5. Pesticides • Insecticides • Natural products were used for centuries (nicotine, rotenone) • Until the “first generation” • Metals – lead arsenate and methylarsenate • Second Generation • Synthetic organic insecticides • Organochlorine compounds, DDT 1939 • Organophosphorus ester insecticides,

6. Pesticides • Insecticides • Second generation continued • Thousands created from 1940-1970 • Now they are banned • More than 400 insect species have developed resistance • Third generation • Natural products and pheremones • Use of these with 2nd generation is called integrated pest management

7. Pesticides • Organochlorine Insecticides • Chlorinated aliphatic and aromatic compounds • May contain O and S • Highly lipophilic (fat loving • Disrupt the Na+ and K+ balance of cellular membranes and neurological pathways • Though banned in the U.S. and Europe, still found in the environment • Degrading slowly in U.S., still manufactured here and sold overseas

8. Pesticides • Common organochlorine insecticides include: • DDT, methoxychlor, lindane, aldrin, dieldrin, and endosulfan • Organophosphorus esters • Nonselective, broad spectrum insecticides that inhibit acetyl cholinesterase, an important enzyme for neurological function

9. Pesticides • Organophosphorus esters • Discovered in 1854, use didn’t start until the 1970’s when the organochlorines were banned • Very low half-life, persist for days or weeks, not years like organochlorines • Acutely toxic however • 3 drops of parathion applied to the skin will kill the average adult • Common names • Parathion most widely used, Methyl Parathion, Malathion, and Diazinon

10. Pesticides • Insecticides • Carbamate Esters • N-methyl carbamates modeled after the natural product physostigmine, a neurotoxic alkaloid • First developed in 1954, by 1985 25 carbamates had been developed • Derivatives of carbamic acid, which is so unstable that it does not exist HO-C-NH2 O

11. Pesticides • Insecticides • Carbamate Esters • However, replacing the H attached to the oxygen with an alkyl group and one H attached to the amino group with a methyl • Creates a stable molecule • Carbamates also interfere with acetyl cholinesterase • Common names include: carbaryl, carbofuran, and aldicarb

12. Pesticides • Herbicides • Agents that destroy vascular plants and are employed mainly as weed killers • Most widely used class of pesticides • Last in the environment from a few days to over a year • Degradation rates are a function of the herbicide structure and the environmental conditions

13. Pesticides • Herbicides • Kill through a variety of mechanisms • Interference with DNA replication • Mimicking growth hormones • 120 different compounds • 20 families • Review of five families

14. Pesticides • Herbicide families • Acid Amides – alachlor, propanil, • Exact mechanism of kill unknown, appears to interrupt protein synthesis and nucleic acid replication • Aliphatics – Glyphosate (Roundup), Methyl Bromide • Interference with amino acid synthesis • Phenoxy Herbicides – 2,4-D, 2,4,5-T and Silvex • Phenyl ethers with an oxygen link to the benzene ring • 27,000 tons of 2,4-D used per year in U.S. • Agent Orange used in Vietnam was 50:50 mixture of 2,4-D and 2,4,5-T • Mimics auxins – growth regulators produced by plants

15. Pesticides • Herbicides • Substituted Ureas • Urea – a bound form of N excreted by animals • Common diuron and linuron • Trazines • Predominantly N-alkylated derivatives of 2-chloro-4,6-diamino-s-triazine • Most common are atrazine, cyanazine, and senecor • Work by interfering with photosynthesis • Work well because they lose their phytotoxicity within one growing season and are not very toxic to humans

16. Pesticides • Fungicides • Destroys fungi and molds to prevent the deterioration of fruit, grain, and vegetables • 70% of fungicides used are from ethylene-bis-dithiocarbamates (EBDC’s), captan, and benzimidazoles • Some contain manganese and zinc (Mancozeb and EBDC)

17. Pesticides • Fungicides • Pentachlorophenol (penta or PCP) • Used to preserve telephone poles and railroad ties • Also as an insecticide, fungicide, aracacide, herbicide, disenfectant, etc • Hundreds of Hazardous Waste sites are contaminated with PCP • PCP is only moderately toxic, but when degraded dioxins are produced from it and they are highly toxic and biorefractory

18. Pesticides • Soil Fumigants • Used to control a range of pests • Early fumigants include (HCN) hydrogen cyanide and carbontetrachloride • Resulted in GW contamination

19. Explosives • Explosive • A quasi stable chemical that rapidly changes from a solid or a liquid to a gas following activation or detonation • Pressure from expanding gases release energy of the compound seeking equilibrium • Usually made of aliphatic or aromatic rings with nitro substituent groups

20. Explosives • Uses • Mining, construction and warfare • Military production and storage has caused most of the problems with the environment • Pink water – TNT contaminated pit or production water • Explosives are environmentally persistent and toxic • Inhibit life through defeating the process of oxidative phosphorylation – ATP production

21. Explosives • Characteristics • Low explosive – reacts slowly, burns rapidly instead of detonating • High explosive – rapid detonation, more stable • Three groups of high explosive • Aliphatic nitrate esters – produced by treating polyhydric alcohols with nitric acid (nitroglycerine) • Nitramines – RDX, HMX, Tetryl, Military explosives • Nitroaromatics – TNT, Picric acid, biodegraded under anaerobic conditions

22. Industrial Intermediates • Aliphatic and aromatic compounds used for the synthesis of market chemicals • Most common, benzene and derivatives of benzene, phthalate esters, chlorobenzenes, chlorophenols, and chlorotoluenes • Benzene - styrene, cyclohexane, phenolics, xylenespolymers, phenol  chlorophenols, resins • Phthalate esters – plasticizers in plastics production • Chlorobenzenes and chlorophenols – pesticides, pharmaceuticals, antiseptics and plastics • Chlorinated toluenes – pesticides, drugs, peroxides, and dyes • Anilines are aminobenzenes – inks, dyes, drugs, photographs

23. Polychlorinated Biphenyls (PCBs) • PCB’s • Heat stable oils once used as transformer and hydraulic fluids • Non flammable transformer dielectric cooling oil • Mineral oil was used but PCB was more stable • Also used as a plasticizer and lubricant until banned in 1979 • Basic unit aromatic hydrocarbon biphenyl, 10 possible Cl positions on two rings • 207 Congeners – compounds formed from the same process

24. Polychlorinated Dibenzodioxins and Dibenzofurans • PCDD’s and PCDF’s • Not produced for a potential use • Waste products of production • Trace impurities formed during the chlorination or combustion of organic compounds • Extremely toxic compounds • A low concentration can be found in burning wood • Aromatic and non-planar • 75 possible congeners

25. Metals and Inorganic Nonmetals • Metal defined as an element that: • Conducts electricity • Has a high thermal conductivity • Has a high density • Characterized by malleability and ductility

26. Metals and Inorganic Nonmetals • Most metals wastes is produced during electroplating • Arsenic (As) • Has a complex chemistry • Used to make herbicides to control weeds • Used to make glass, growth stimulants for plants and animals, and fungicides • Used in semiconductor production

27. Metals and Inorganic Nonmetals • Cadmium (Cd) • Found in plastics, household batteries, electronics, pigments and appliances • Metals finishing • Highly toxic, range of health effects from hypertension to cancer • Chromium (Cr) • Used in electroplating, leather tanning, wood preservation, catalysts and commercial electronics

28. Metals and Inorganic Nonmetals • Lead (Pb) • Used in autobatteries, electronics, plastics and glass • Ubiquitous in the environment after use in gas and paint • Nickel (Ni) • Used in stainless steel, iron ferrous alloys, electroplating, catalysts, ceramics, and salt • Mercury (Hg) • Found in three forms, elemental, inorganic, and organic • Used to make electrical products, dental supplies, caustic soda, chlorine, instruments ,and paints

29. Metals and Inorganic Nonmetals • Cyanides (CN-) • An inorganic nonmetal anion • HCN  CN- + H+ Ka = 7.94 x 10-10 • Hydrogen cyanide, highly toxic, acute poison • HCN produced by mixing ammonia and methane under controlled conditions • Used in electroplating, stored in ponds, caused dead wildlife and GW contamination

30. Metals and Inorganic Nonmetals • Asbestos • Generic label attached to fibrous metal silicates of sodium, magnesium, calcium, and iron • Asbestos is a commercial label given to six mineral fibers made from magnesium silicates • Uses: roofing products, friction products, asbestos cement pipe, packing, and paper