Lecture 4

Second Lecture for Chapter 2

PesticidesA chemical, physical or biological agent that destroys or controls pest organisms

Common: insecticides, herbicides, fungicidesApproximately 500,000 tons applied in the U.S. each yearPublic health: disease prevention (malaria, typhus, yellow fever) and increased agricultural production

PesticidesDDT Story

Saved lives through prevention of malaria, DDT kills mosquito’sBanned later as a result of bioaccumulation in the food chainDDT was found in marine sediments, wildlife, and human lipidsCaused thinning of eggshells in birds

PesticidesMany 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 NomenclatureCommon and Trade names used most often

The farm chemicals handbook The following is an introduction to different Pesticides

PesticidesInsecticides

Natural products were used for centuries (nicotine, rotenone)Until the “first generation”

Metals – lead arsenate and methylarsenateSecond Generation

Synthetic organic insecticides• Organochlorine compounds, DDT 1939• Organophosphorus ester insecticides,

PesticidesInsecticides

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

PesticidesOrganochlorine 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

PesticidesCommon organochlorine insecticides include:

DDT, methoxychlor, lindane, aldrin, dieldrin, and endosulfan

Organophosphorus estersNonselective, broad spectrum insecticides that inhibit acetyl cholinesterase, an important enzyme for neurological function

PesticidesOrganophosphorus 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

PesticidesInsecticides

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

PesticidesInsecticides

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

PesticidesHerbicides

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

PesticidesHerbicides

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

PesticidesHerbicide families

1. Acid Amides – alachlor, propanil, Exact mechanism of kill unknown, appears to interrupt protein

synthesis and nucleic acid replication

2. Aliphatics – Glyphosate (Roundup), Methyl Bromide Interference with amino acid synthesis

3. 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

PesticidesHerbicides

4. Substituted UreasUrea – a bound form of N excreted by animalsCommon diuron and linuron

5. TrazinesPredominantly N-alkylated derivatives of 2-chloro-4,6-diamino-s-triazineMost common are atrazine, cyanazine, and senecorWork by interfering with photosynthesisWork well because they lose their phytotoxicity within one growing season and are not very toxic to humans

PesticidesFungicides

Destroys fungi and molds to prevent the deterioration of fruit, grain, and vegetables70% of fungicides used are from ethylene-bis-dithiocarbamates (EBDC’s), captan, and benzimidazolesSome contain manganese and zinc (Mancozeb and EBDC)

PesticidesFungicides

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

PesticidesSoil Fumigants

Used to control a range of pestsEarly fumigants include (HCN) hydrogen cyanide and carbontetrachlorideResulted in GW contamination

ExplosivesExplosive

A quasi stable chemical that rapidly changes from a solid or a liquid to a gas following activation or detonationPressure from expanding gases release energy of the compound seeking equilibriumUsually made of aliphatic or aromatic rings with nitro substituent groups

ExplosivesUses

Mining, construction and warfareMilitary 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

ExplosivesCharacteristics

Low explosive – reacts slowly, burns rapidly instead of detonatingHigh 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 IntermediatesAliphatic and aromatic compounds used for the synthesis of market chemicalsMost common, benzene and derivatives of benzene, phthalate esters, chlorobenzenes, chlorophenols, and chlorotoluenes

Benzene - styrene, cyclohexane, phenolics, xylenespolymers, 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)PCB’s

Heat stable oils once used as transformer and hydraulic fluidsNon flammable transformer dielectric cooling oilMineral oil was used but PCB was more stableAlso used as a plasticizer and lubricant until banned in 1979Basic unit aromatic hydrocarbon biphenyl, 10 possible Cl positions on two rings207 Congeners – compounds formed from the same process

Polychlorinated Dibenzodioxins and Dibenzofurans

PCDD’s and PCDF’sNot produced for a potential useWaste 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 NonmetalsMetal defined as an element that:

1. Conducts electricity2. Has a high thermal conductivity3. Has a high density4. Characterized by malleability and ductility

Metals and Inorganic NonmetalsMost metals wastes is produced during electroplatingArsenic (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 NonmetalsCadmium (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 NonmetalsLead (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 NonmetalsCyanides (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 NonmetalsAsbestos

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