20' Agricultural BioChemistry

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20. Agricultural (Bio)Chemistry
supplementary ie.(mostly) not
in text, but see sec.14.14, 14.15(4th ed.)
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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(gt40 in
developing countries)

Estimated costs in US(2000) 15 billion

(4 billion to insects alone)
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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
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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)
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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
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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'
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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
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DDT - from Dream to Nightmare in 30 yrs
DichloroDiphenylTrichloroethane 1st chlorinated
HC Discovered in 1938(Paul Muller, Swiss,
gtNobel '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.

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Chlorinated Hydrocarbon Insecticides
Hydrocarbon 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)
DDT
Lindane
Mirex
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Organophosphate Insecticides
Function as 'neurotoxins'(wrt. acetylcholine)
broad spectrum somewhat 'fat-soluble' decompose
in days/weeks rarely found in foods.(LD50, rats)


Malathion(1100)
Diazinon(285)
Parathion(4)
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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

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Acetylcholine

• Is an ester!

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Cholinesterase inhibition contd

• 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

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Carbamate Insecticides
Since 1956 some selectivity(narrow-spectrum)
don't bioaccumulate breakdown in hours/days
more . Sevin is extremely toxic to honey
bees(millions killed).

Pirimicarb
Carbaryl(sevin)
Carbofuran
Aldicarb
LD50(rats,mg/kg)carbaryl/pirimicarb200aldicarb/
carbofuran5
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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) - since 1650
as fish poison(SA), 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
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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.
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Some Natural Insecticides
pyrethrins
azadirachtin
rotenone
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Insect Predators - Big and Small
Organisms that feed on 'pesty' insects but 'do no
harm' to the 'crop'.
1)Cane
toads(10", 4lb) - introduced to Australia(1930)
to control sugar-cane beetle now 'invade'
most of NE Australia(insecticide for the
'beetle')
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.
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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'
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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
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Killex

• At your neighborhood store

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Fungicides
200(of 100,000) fungal species cause plant
damage, eg. molds, powdery mildew. Fungicides
applied to seeds, foliage or during storage. Many
inorganics still used, eg. containing sulfur,
mercury, copper(arsenic). Organics include
dithiocarbamates(Thiiram) and benzimidazoles(Benom
yl)
thiram
(a dithiocarbamate)
benomyl
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Text references (1003)
see Pesticides

under 'pollution'
Sec. 13.15 13.16, pages
372 - 376
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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)
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Some 'Biologicals'
gibberellic acid
A pheromone
juvenile hormone
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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
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Compound released by ripening fruit

• Is ethylene!

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Kentucky Fried Chicken Anyone?!
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Alternative Agriculturecan/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!
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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
satd. fatty acids) Controlled ripening
corn, cotton, potato, rice canola, soybean,
cotton, squash
squash

canola
flavr savr tomato
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A Tale(Tail?) of Two Salmon (18 months old)
GMO(growth hormone)
wild
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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.
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Food preservation and safety

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

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Mould on Strawberries

• Can be prevented!

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Food Irradiation (GRAS In UK)

• Short term exposure to High E gamma rays kills
  bacteria

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(triage!) Would you buy them?

• Yes, no , maybe?
• What are your concerns?

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Fears (legit or not)

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

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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

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Market status of irradiated food

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

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2007 E. coli in spinach

• Lettuce and spinach contaminated
• Taco Bell Taco Johns
• 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

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Washing your spinach

• Not necessarily effectiveE coli can penetrate
  cells of produce

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Experts agree

• Prof. Elena Perez (Texas A M)
• we should irradiate all fresh produce to
  eliminate microbial problems before they reach
  the consumer

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Irradiated hotdogs!

• USDA researching irradiation of vacuum sealed meat

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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

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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)

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Elie Metchnikoff

• Russian Biologist/Microbiologist
• Nobel Prize 1908 for Medicine, shared with Paul
  Erlich

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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

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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

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A highly recommended food!
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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