AGROCHEMICALS

Population: 1B in 1830; 5B in 1986; > 6.76B today (Jan 09)Crop Yields: ~ 25 bushels/acre (1800) to >110 b/a today

~ 1.68 tonnes/hectare (1800); 7.39 tonnes/hecate today

FERTILIZERS

NITROGEN: plants require N as NO3-, either from natural sources or

by symbiotic N2 fixing bacteria

Legume crops have root nodules that contain bacteria capable of converting N≡N to nitrate (via Mo, V based nitrogenase enzymes)

egs. alfalfa, lover, most beans and peas

ALL others need nitrate – add as fertilizer BUT water soluble so much washes into lakesand streams causing algal blooms

PHOSPHORUS

Phosphate rock (and bone meal) is mostly Ca3(PO4)2 very insolubleTreatment with sulfuric acid gives more soluble SUPERPHOSPHATE

Ca(H2PO4)2 + 2CaSO4

more easily absorbed by plants BUT more easily washed in to lakesTRIPLE SUPERPHOSPHATE uses phosphoric acid to give Ca(H2PO4)2

POTASSIUM

Potash: technically this is K2CO3 from wood ashes but the term now applied to any potassium deposit such as KCl

Global ~ 36M tonnes/y (as K2O equivalents)Canada 32% (Saskatchewan and Alberta)NB: Saskatchewan led Canada in jobs, economic growth in2008 due largely to potash, uranium and oil industries

MIXED BAG FERTILIZERS N - P - K13-10- 6

13% N, as elemental N10% P, as P2O5 (‘real’ %P = P number x 0.44)6% K, K2O (‘real’ %K = K number x 0.83)

so 13-10-6 is really 13-4.4-5.0 !

ASIDE:THE ENERGY PROBLEMCorn uses ~ 950L fuel per hectare so to get 4 kg of corn uses about1 kg of fuel

ENERGY IN: 45 MJ for fuel ENERGY OUT: 10-60 MJ (depending on efficiency of processes)

Diverting corn to fuel use may not make energy sense!

What is alternative to more fertilizers?

Plant Growth Hormones (>100 M$)Auxins cause enlargement of cellsGibberellins stimulate division and enlargementCytokinins stimulate division

OH

COOH

CO

O

HO

Gibberellic acid

Treatment of sugar cane with 100 g gibberellin per hectare, increases yield ~ 12 tonnes/hectare

Good on grapes - larger

No good on cabbage - makes it flower

Monsanto’s Polaris HOOCCH2N(CH2PO3H2)2 = Glyphosphine is an aminoacid derivative which increases sugar content 10-20% at harvest (introduced in sugar shortage of 1974, enormous profits) – very similar to structure to their herbicide Roundup:LD50 = 4 g / kg body mass!Very low toxicity to mammals (inhibitsplant protein synthesis, specificallyof aromatic amino acids)

Cyanamid’s Cycocel (Me3NCH2CH2Cl)+Cl-

also ripens sugarcane, but reduces the stem length of cereal crops like wheat- reduces fall over in heavy wind/rain

Ethephon ClCH2CH2PO3H2 stimulates latex flow in rubber trees, stimulates flowering in pineapples...

HERBICIDES (> 15B $ World, > 7B US alone) ~ ½ B kg /yWeeds compete for fertilizer and water; reduce crop yields90% corn, soya-beans, cotton, pea-nuts, rice treated; 75% of herbicides go on farm crops

ClCl

OCH2COOHOH

ClCl

ClCl

OCH2COOHCl

O

OCl

Cl

Cl

Cl

Cl

Cl Cl

Cl Cl

Cl Cl

OHHO-

2,4-D (1946) and 2,4,5-T (late 50’s) (mixture = Agent Orange):

2,4-D

2,4,5-T

‘Dioxin’

2,4-D (1946) kills broadleaf plants at 200 g – 2.5 kg per hectare (much less than the inorganic defoliants used to that point)

Cheap (use >100M kg/y); Low mammalian toxicity ~0.5 g / kg orally, 1.5 g / kg dermally; degrades quickly in soil, does not concentrateCan use on wheat, barley, corn, sugar, rice, GRASS (home use)

then the relative 2,4,5-T was found to be more effective on brush, blackberries: used around power lines AND THE VIETNAM JUNGLE

US used ~70M L of 50:50 2,4-D/2,4,5-T (AGENT ORANGE) Vietnam

sprayed neat, not diluted as used commercially in NA

Causes puss oozing acne and birth defects due to the Dioxin impurity in 2,4,5-T - stopped use in 1970

EPA permitted use on rice, rights of way, home use till 1985 (later in Canada)

Viktor Yushchenko, Ukrainian Presidential Candidate 2004, Poisoned by ‘dioxin’ (?)Shows the classic disfigurement Caused by severe chloracne

ATRAZINE (Ciba-Geigy, Shell, Syngenta)

Used at 2-5 kg / hectare LD50 ~5 g / kg

Corn is able to remove -Cl and deactivate so atrazine is widely used

Disrupts photosynthesis

Controversy: It was one of the more widely used, but Banned in EU in 2004 because detected in ground waters. Some associate the feminization of frogs to atrazine; US disagrees:http://www.syngentacropprotection-us.com/prod/herbicide/Atrazine/ http://www.epa.gov/safewater/contaminants/dw_contamfs/atrazine.html http://www.pan-uk.org/pestnews/Actives/atrazine.htm

Major herbicides in use today•Imazapyr, is a non-selective herbicide used for the control of a broad range of weeds including terrestrial annual and perennial grasses and broadleaved herbs, woody species, and riparian and emergent aquatic species. •Imazapic, is a selective herbicide for both the pre- and post-emergent control of some annual and perennial grasses and some broadleaf weeds. Imazapic kills plants by inhibiting the production of branched chain amino acids, which are necessary for protein synthesis and cell growth. •Glyphosate, a systemic nonselective (it kills any type of plant) herbicide used in no-till burndown and for weed control in crops that are genetically modified to resist its effects. It is an example of an EPSPs inhibitor. •Paraquat, a nonselective contact herbicide used for no-till burndown and in aerial destruction of marijuana and coca plantings. More acutely toxic to people than any other herbicide in widespread commercial use. •2,4-D, a broadleaf herbicide in the phenoxy group used in turf and in no-till field crop production. Now mainly used in a blend with other herbicides that act as synergists, it is the most widely used herbicide in the world, third most commonly used in the United States. It is an example of synthetic auxin. •clopyralid, is a broadleaf herbicide in the pyridine group, used mainly in turf, rangeland, and for control of noxious thistles. Notorious for its ability to persist in compost. It is another example of synthetic auxin. •metoalachlor, a pre-emergent herbicide widely used for control of annual grasses in corn and sorghum; it has largely replaced atrazine for these uses. •dicamba, a persistent broadleaf herbicide active in the soil, used on turf and field corn. It is another example of synthetic auxin. •picloram, a pyridine herbicide mainly used to control unwanted trees in pastures and edges of fields. It is another synthetic auxin. •atrazine, a triazine herbicide used in corn and sorghum for control of broadleaf weeds and grasses. Still used because of its low cost and because it works as a synergist when used with other herbicides, it is a photosystem II inhibitor.

Pesticide residues on fruit and vegetables are very small

Natural carcinogens, eg. aflatoxin in the mould on peanuts and corn is much more dangerous

Risk from carcinogens:1/3000 motor cycle1/300 smoking1/25 car driving25x strike by lightening!

Pesticides and Insecticides

Before 1989, BC and Washington apples were sprayed with ALARto stops premature falling and bruising

Feb 1989: ‘60 Minutes’ aired a report that ALAR was found in apple juice and caused tumors in rats – at the equivalent to 20,000 L of apple juice per day per rat!

Uniroyal took ALAR off market voluntarily (Apple growers filed a libel suit against CBS, dismissed in ‘94) Now apples can develop a natural fungus inbruises that produces the mycotoxin patulin:An antibiotic but also a carcinogen that may bemore potent than ALAR!

Daminozide (ALAR)Uniroyal (1963)

INSECTICIDES

500 BC Burning Sulfur;1500 Arsenic1800 Nicotine (Sulfate)1900’s Lead Arsenate

1900 Extract of dried chrysanthemum = PYRETHRUM

Have to hit insectDecomposes in sunlight (no good for crops)Low mammalian toxicity

By 1949 had developed more stable synthetic ones:

H

Cl Cl

O O

O

H O

O

O

Allethrin Permethrin

O

O OO

O

Piperonyl butoxide

Allethrin could be used in sunlight but needs a synergist, piperonyl butoxide, to prevent insect recovery - used in RAID and expensive

Since 1970, for agricultural use, Permethrin (Ambush, Pounce) is better, need only 100g/hectare – more stable, cheaper, BUT still relatively expensive LD50 = 2g/kg - low – known as PYRETHROIDS

THE CHLORINATED PESTICIDESDDT first made in 1873 in Germany (Baeyer) but insecticidal properties not recognized until 1939 (Geigy labs in Switzerland)

Cl

CCl3

ClCl Cl

CCl3

CHOacid

ALL CHEAP CHEAP < 50c/kg in 1940

dichlorodiphenyltrichlorethane

Wartime: pyrethrum supply cut off by Japan (troops were lice/tick infested)

Tried DDT as 10% powder mixed with talc directly on millions of troops: 3M people treated in Naples in 1943 alone!

DDT THE GOOD DDT THE BADCheap Cheap - used indiscriminatelyEffective against all insects Kills ‘good’insectsExtremely persistent Stays around for >20 yearsLow toxicity to non-insects Estrogenic effect on birds

[LD50 300-500 mg/kg, 2-3 g/kg dermally, but about 10 mg/kg to insects]

Insects do not need to eat - absorbed through cuticles: allows Na+ to leak into nerve channels, continuous transmission of nerve impulses, overload, death

Crop yields went up

Stopped Gypsy Moth in East, Spruce Budworm in West

Reduced malaria in tropics (1g/m2 on house walls), also kills louse (Typhoid), Flea (Plague), Tetse Fly (Sleeping sickness)

Peak production in 1961 ~ 400 Mkg/y; World total production >3B kg, i.e. > 3M tons or about ½ kg per person alive today!

Insect Resistance – overrated! Some insects have developed DDT-ase which dehydrochlorinates DDT to DDE; however that is easy to overcome by blocking the enzyme, eg. with chlorofenthol

Cl Cl

Cl Cl

Cl Cl

OH

DDE Chlorofenthol

Non-selectivity is bad – most insects not pests!SOLUBLE IN FAT: passes up food chainALSO VERY PERSISTENT: half life ~ 20 years!

UVIC students 1970: ~12 ppm in tissuesNOW: ~2-3 ppm even though use in NA was stopped in 1972!

BIRDS: DDE and DDT metabolites mimic diethylstilbestrol and have weakly estrogenic activity: affect Ca transport – thin egg shells

See: ‘Silent Spring’ by Rachel Carson (1962)for one view of DDT

In Canada, Methoxychlor is widely used – degrades more quickly

MeO

CCl3

OMe

Methoxychlor

Cl

ClCl

Cl

Cl

Cl

CCl2 O

Cl

ClCl

Cl

Lindane Dieldrin

But many much more toxic ones were also made:

Lindane LD50 100 mg/kg

Dieldrin LD50 50 mg/kg highly toxic to fish and mammals

Most have been phased out now but residues remain buried in soils, ocean muds, lake bottoms, etc.

ORGANOPHOSPHATE NERVE AGENTS

Less environmentally persistent insecticides (hydrolyze)Acetylcholine esterase inhibitors

Malathion LD50 = 1 g/kg

Diazinon LD50 = 80 mg/kg

Parathion LD50 = 8 mg/kg

Sarin LD50 = 10 g/kg

RelativeToxicity

1

12.5

125

100,000

All species use acetylcholine as a nerve transmitter:

Botulinus toxin prevents synthesis of acetylcholine - no impulses - paralysis of muscles, etc.

Organophosphates block acetylcholine esterase: prevents break down of acetylcholine - nerve impulses continuously sent, overload, convulsions, death

~300,000 farm workers per year suffer from pesticide poisoning!!

Other important strategies not covered here:

Insect biology strategies:pheromonesinterfere with sexual developmentinterfere with maturation

Genetic engineering of crops:disease resistanceinsect resistance (kill insects when feed on plant)herbicide resistance (to kill weeds but not plant)better climate tolerance (drought, heat, cold)