Transcript No Slide Title

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
There are ~1500 'active'
ingredients
(down from ~2500 in 1980),
in ~50,0000 different
'formulations'
divided into 18 categories.
Some numbers:
1995(world): 500 billion lbs pesticides(~$7.5 billion),
80% for agriculture
2007(USA): 700 million kg(400 million as herbicides)
Pesticides - Risks
Many pesticides have
LD50s(rats) = 1-100mg/kg.
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
Pesticides - Benefits
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'
Insecticide!?...but
it was self-defense
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).
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
DDT - from Dream to Nightmare in 30 yrs
DichloroDiphenylTrichloroethane = 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.
Unreactivepersistent; fat solublebioaccumulates.
Chlorinated Hydrocarbon Insecticides
Hydrocarbon skeleton with many chlorines, eg. aldrin,
chlordane, toxaphene, heptachlor, methoxychlor
CCl3
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
DDT
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Mirex
Cl
Cl
Lindane
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)
Organophosphate Insecticides
Function as 'neurotoxins'(wrt. acetylcholine); broad
spectrum; somewhat 'fat-soluble'; decompose in
days/weeks; rarely found in foods.(LD50, rats)
S
CH3O P S
OCH3
O
OCH2CH3
OCH2CH3
Malathion(1100)
O
S
CH3CH2O P O
CH3CH2O
S
CH3CH2O P O
CH3CH2O
Diazinon(285)
NO2
Parathion(4)
N
N
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/Antifeedants
Produced 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
O
C O
O
C C
R
pyrethrins
O
O
O
O
OH
O
O
HO O
O
azadirachtin
O
O
O
O
O
O
O
CH3O
OCH3
rotenone
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-Dichlorophenoxyacetic 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/Chemical
1) 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 cyclecan'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
HO
COOH
gibberellic acid
(CH3)2CH(CH2)4CH
O
CH(CH2)9CH3
A pheromone
O
CH3
CH3
COOCH3
CH3CH2C
CH3
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
Insect resistance
(Bt gene)
Herbicide resistance
(“RoundUp ready”)
Virus resistance
(tobaco mosaic virus)
Specialty oils
(less sat’d. fatty acids)
Controlled ripening
Crop
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