20. Agricultural Chemistry

supplementary (mostly) not in text, but see Chapt 14 sections: 14.14, 14.15

Protect the (Food Producing) Plants !

Natural 'enemies': 80,000diseases(viruses, bacteria, fungi, algae 30,000 species of weeds(a plant growing in the wrong place) 10,000 species of plant-eating insects

Food crop losses: ~30% world wide(>40% in developing countries) Estimated costs in US(2000): $15 billion ($4 billion to insects alone)

Out, Out Damned …. Pest

Pest = any organism that in some way reduces crop yields, or endangers human health, eg. malaria mosquitoes, tape worms, lice, cockroaches, rats(?) Pesticides = chemicals(?) used to control(kill, scare away) pests. Classified by 'pest', ie. Insecticide - kills insects Herbicide - kills weeds Fungicide - kills fungi

The Pesticide Business

Some numbers: 1995(world): 500 billion lbs pesticides(~$7.5 billion), 80% for agriculture 2007(USA): 700 million kg(400 million as herbicides)

There are ~1500 'active' ingredients

(down from ~2500 in 1980), in ~50,0000 different

'formulations' divided into 18 categories.

Pesticides - Risks

Cons: effects of biomagnification, esp. persistents since 1945 a 30X increase in pesticide use and slight increase(31- 37%) in crop loss USA(2007) - 45,000 'poisonings’, 200 fatalities Worldwide(1995) - 1 million & 20,000

Many pesticides have LD50s(rats) = 1-100mg/kg.

Pros: probably 'saves' ~35% of food crops yearly WHO estimates DDT has saved 25 million lives from malaria we consume ~1.5 g/day of 'natural' pesticides (49 in cabbage, 23 in lima beans); 10,000 x 'synthetics'

Pesticides - Benefits

Insecticide!?...but it was self-defense

Most common insecticides are non-selective (broad spectrum) and rated by 'reactivity'/ rate of breakdown from persistent (bioaccumulate!) non-persistent.

Many have LD50 of 1-300mg/kg(rat) but 'bugs' are much smaller than humans

We're surrounded! aphid, gypsy moth, corn borer, locust, spruce budworm, potato beetle, cotton weevil ….. plus ……. lice (typhus), mosquito(malaria), mites, ticks(Rocky Mtn. fever), tse tse fly(sleeping sickness).

DDT - from Dream to Nightmare in 30 yrsDichloroDiphenylTrichloroethane = 1st chlorinated HC

Discovered in 1938(Paul Muller, Swiss, >Nobel '48). Inexpensive, broad spectrum, 'low' toxicity = ideal.

Used extensively worldwide 1943-1965: (US -76 million kg/yr in '62) by '46 first 'problems' (resistance, bioaccumulation); Silent Spring by Rachel Carson) by 1975 banned in most developed countries.

Unreactivepersistent; fat solublebioaccumulates.

Chlorinated Hydrocarbon InsecticidesHydrocarbon skeleton with many chlorines, eg. aldrin, chlordane, toxaphene, heptachlor, methoxychlor

DDT = first 'endocrine disruptor', eg. 3-eyed fish, 1-leg frogs, thin bird's eggs. Probably saved more lives than any other chemical; still used for malaria but at 'a cost'(birds, fish, shrimp, plankton)

Cl Cl

CCl3

Cl Cl

Cl Cl

Cl Cl

Cl Cl

Cl

Cl

Cl

Cl

Cl

Cl Cl

Cl Cl

MirexLindane

DDT

Organophosphate InsecticidesFunction as 'neurotoxins'(wrt. acetylcholine); broad spectrum; somewhat 'fat-soluble'; decompose in days/weeks; rarely found in foods.(LD50, rats)

SP

S

CH3O

O

OCH2CH3

O

OCH2CH3OCH3

CH3CH2O P

S

O NO2

CH3CH2O

N

NOP

S

CH3CH2O

CH3CH2O

Malathion(1100)

Parathion(4)

Diazinon(285)

Cholinesterase inhibitors

• Acetylcholine conducts nerve impulses across the junction between the nerve and the muscle (the synapse)

• After an appropriate response, cholinesterase is released, breaking down the acetylcholine and terminating the response

Acetylcholine

• Is an ester!

Cholinesterase inhibition cont’d

• If this process is inhibited, muscle continues to move

• Can result in breathing difficulties, convulsions and death

• If humans get overexposed :mild (nausea); ranging to fatal if long term continuous

• Organophosphates, carbamates worst

Natural Insecticides/AntifeedantsProduced by plants to kill/deter insect predators; still commonly used but not 'industrial'-scale 1) Nicotine - since 1700 in France(Black Leaf 40) 2) Rotenone(tropical legumes) – used since 1850 as insecticide 3)Pyrethrum* (chrysanthemums) - Chinese in 0 AD; from Iran/Persia in 1800; commercial crop in Kenya; particularly for flying insects; degraded by air/sunlight,

very low mammalian toxicity(in household aerosols); now 'synthetics',eg. permethrin, dimethrin, allethrin * distinctive odour antifeedant(repels insects)

eg. citronellal, marigolds/nasturtiums in gardens

The Neem Tree - a 'New' Discovery

Native to Africa/Asia the oil from seeds of the neem tree have been used in India for centuries to deter(antifeedant) or kill insects, eg. locusts, aphids, cockroaches.

Azadirachtin, the major 'active ingredient, interferes with molting, reproduction,digestion and is 'non-toxic' to 'predators' and mammals. Effective against ~200 species. Somewhat unstable but looks good! Already on the shelves as Azatin/Margosan.

Some Natural Insecticides

OO O

O

OCH3

CH3O

CR

C

C O

O

O

O

OO

O

O

O

OH

OOHOO

OO

pyrethrins

rotenoneazadirachtin

Insect Predators - Big and Small

Organisms that feed on 'pesty' insects but 'do no harm' to the 'crop'. 1)Cane toads - introduced to Australia(1930) to control sugar-cane beetle; now 'invade' most of NE Australia

2)Lady bugs - for aphids in many parts of world

3)Bacillus thuringensis(Bt) - soil bacteria that releases a toxin that kills many insects(powder form), eg. against cotton weevil, gypsy moth; already 'resistance' is developing.

“BIOCONTROL” approach-sounds good,but………

“Biocontrol” can have disastrous consequences!!

Cane toad

2001: year of the aphid in Ontario

Lady bugs introduced to “solve” the aphid and leafhopper problem in

Ontario vineyards

Ladybug release:72,000 in a 1 gallon sack

Ladybugs love Aphids!

• Ravenous ladybugs attacked ripe grapes whose vines were also infected with Aphids

• Flotillas of ladybug carcasses capped fermentation tanks

• Once squished, ladybugs give off pyrazines, which occur naturally in Sauvignon Blanc

Chardonnays tasted like Sauvignon Blancs!

• In addition to this white wine flavour mixup, many 2001 Ontario reds were spoiled and eventually taken off the market

• But not all……………………….

Beware 2001 ON Red wines !!

Herbicides/ 'Weed' Killers - Generalities

Weed = plant in the wrong place, eg. grass in canola, mustard in potatoes, poison ivy/ragweed/dandelions

in urban setting, 'baddies' in cereal crops

Eliminate how? - manually, cultivate/till(erosion), spray

Species selective or non-selective, eg. inhibit essential a.a. production or photosynthesis. Contact or systemic; often defoliants(broad leaf) Exploit: different metabolism, timing, young vs mature

? Inorganics, eg. NaCl, urea(NH3)- fertilizer/ice melter Usually 'organics' acting as 'plant hormones'

Herbicides - specific examples

1) 2,4D (2,4-Dichlorophenoxy-

acetic acid), aka Killex Systemic(broad leaf) - plant

grows to death (can't get enough nutrients)

also 2,4,5T = Agent Orange(defoliant in Vietnam) and Mecoprop(MCPP)

2) Atrazine - shuts down photosynthesis Corn can deactivate, weeds do not. 'Persistent' - now 'polluting' lakes /ground water, eg. in eastern Ontario & US midwest

Killex

• At your neighborhood store

Text references (1003) see Pesticides under 'pollution'

Sec. 13.15 &13.16, pages 372 - 376

Pesticide Control - Biological/Chemical1) Pheromones - chemicals secreted by insects to 'send a signal' eg. mark a trail, signal alarm, attract

a mate. Sex pheromones(mostly synthetic analogs)

can limit reproduction by attracting males to kill/ sterilize (radiation) or to confuse. expensive; some success with gypsy moth. 2) Juvenile Hormones(and 'synthetics') - interrupt the maturation cyclecan't reproduce; expensive; some success with malarial mosquitoes & fleas. Limited application; clearly no use if caterpillar is the 'enemy' not moth. 3) Growth Hormones – for animals(natural peptides or synthetic) and plants (gibberellins)

Some 'Biologicals'

CO

OH

COOH

OH

(CH3)2CH(CH2)4CH CH(CH2)9CH3

O

COOCH3CH3CH2C

CH3

OCH3 CH3

gibberellic acid

A pheromone

juvenile hormone

Increase Food 'Production' - Various

Keep alive - use antibiotics on the factory farms; in USA 4.5 million kgs/yr used in agriculture (= 50% of annual production) Bigger(& better?) - use growth hormones for animals, plants(gibberellins) or milk(up 20% with BGH) Control/delay ripening - N2 in shipping containers to dilute ethylene buildup

Kentucky Fried Chicken Anyone?!

Alternative Agriculture–can/will we afford it?

Modern farming is specialized, energy intensive(13% of all energy consumption in NA), causes serious soil erosion/damage and increasing water pollution.

'New' changes: 1) crop rotations, 2) multiple crops in a field, 3) 'natural' fertilizer, 4) increasing 'biological'

pest control, 5) soil and water conservation.

Organic farming: ~50% less 'non-renewable energy', ~25% more labour, ~20% less production

30% of food costs in NA are for transport, eg. $6 x106 & 3.6 x106L of fuel per year to supply NY city with California broccoli!

Food Production by Genetic Modification - the Present -

Trait Crop Insect resistance

(Bt gene) Herbicide resistance (“RoundUp ready”) Virus resistance (tobaco mosaic virus) Specialty oils (less sat’d. fatty acids) Controlled ripening

corn, cotton, potato, rice

canola, soybean, cotton, squash squash

canola

flavr savr tomato

A Tale(Tail?) of Two Salmon

(18 months old)

GMO(growth hormone)

wild

Food Production by Genetic Modification - the Future/Present ?

Carotenoids in (golden)rice. Disease resistance in papayas(Hawaii),

bananas (Kenya) and sweet potatoes(Africa). Grapes + ‘antifreeze genes’ from salmon = ‘cool climate’ wines. ‘Kinder/gentler’ chickens (then pigs) for factory farms. New ‘drugs’ and polymers from ‘cloned’ sheep/goats raised on ‘pharms’.

Food preservation and safety

• What are the alternatives to chemical additives for preservation and prevention of microbial growth on foods?

Mould on Strawberries

• Can be prevented!

Food Irradiation (GRAS In UK)

• Short term exposure to High E gamma rays kills bacteria

(triage!) Would you buy them?

• Yes, no , maybe?

• What are your concerns?

Fears (legit or not)

• Food is radioactive

• Food constituents (hence taste) changed by the effect of the radiation

Agriculture Canada 1992

• “the safety of irradiated food, when carried out according to internationally accepted standards, has been established beyond a shadow of a doubt”

Market status of irradiated food

• GRAS in UK for all foods (must be labelled); used since 1980’s

• Canada: Irradiation is approved for use on potatoes, onions, wheat, wheat flour and spices

• USA: used for spices, chicken and ground beef (E. coli risk lowered!)

2007 E. coli in spinach

• Lettuce and spinach contaminated • Taco Bell & Taco John’s • Cause: feral pigs ate grubs in cow manure

in a “free range” pasture, wandered into spinach fields and caused contamination with their infected manure

• Pressure mounting to irradiate fresh produce

Washing your spinach

• Not necessarily effective:E coli can penetrate cells of produce

Experts agree

• Prof. Elena Perez (Texas A &M)

• “we should irradiate all fresh produce to eliminate microbial problems before they reach the consumer”

Irradiated hotdogs!

• USDA researching irradiation of vacuum sealed meat

So much for bad bacteria……..

• Some bacteria are beneficial and are critical to the human digestive process

• Bacteria living in the large intestine (intestinal flora!) are normal and helpful

• Finish the digestive process and the products (other than waste) such as short chain fatty acids, are returned to the liver for storage and further use

Elie Metchnikoff (1845-1916)

• Studied Bulgarian peasants who led long, healthy lives-linked to consumption of fermented milk products

• 1st to suggested in 1907, that consuming bacteria would have a beneficial health effect (prevent fouling of large intestine)

Elie Metchnikoff

• Russian Biologist/Microbiologist

• Nobel Prize 1908 for Medicine, shared with Paul Erlich

Probiotic bacteria: yogurt for breakfast!

• Functional foods-foods that promote health beyond their basic nutritional function

• “probiotic (pro-life)” bacteria are live organisms found in or added to fermented foods to optimize the bacterial environment of the intestine

Beneficial effects of probiotic bacteria

• Lactobacillus and/or bifidobacterium stick to the intestinal wall

• Tolerated by the lactose intolerant!

• May increase the number and activity of infection T lymphocyte cells.

• Improves regularity, used to treat diarrhea, IBS, gastric ulcers, urinary infections

• Reduces conversion of bile into carcinogens

A highly recommended food!

What to look for

• Not all yogurt is probiotic

• Label indicates : “live or active culture”

• Lactobacillus (L.) acidophilis is best

• Also L. bulgaricus

• Avoid if heat treated after culturing

• Daily consumption recommended