Second Lecture for Chapter 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

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

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

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,

Pesticides Insecticides Second generation continued Third generation 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

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

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

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

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

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

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

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

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

Pesticides Herbicides Substituted Ureas Trazines 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

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)

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

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

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

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

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

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

Polychlorinated Biphenyls (PCBs) 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

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

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

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

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

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

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

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