Ève Belzile-Dugas Winter 2015 Topic 5: Agriculture Agricultural Science I - From 70% of the world involved in agriculture to 2% in thirty years - Conventional agriculture stopped being sufficient for the growing world’s needs - Pesticides are necessary - Justus Von Liebig (1803-1873) looked first in chemical fertilizers o Various nutrients are needed by plants o Elements: N, P, K o Different fertilizers with different ratios for different plants - Fritz Haber (1868-1934) o N 2 + 3H 2 2NH 3 o NH 3 + HNO 3 NH 4 NO 3 Ammonium nitrate (rich source of nitrogen in fertilizers) Can also be used as an explosive NH 4 NO 3 N 2 O (nitrous oxide, greenhouse gas associated with global warming) - Fertilizer allows to not use soil (soilless gardening, hydroponics ) o Cucumbers, tomatoes o Hydroponic farms on top of buildings (year-round) - Agriculture fights: o 10,000 insects Crop is inedible/cannot be sold because portion of the plant has been eaten o 8,000 fungi Fruit produce has cosmetic defects such as scabs or discoloration o 2,000 weeds Crop production is lower because growth is affected by weeds competing for soil nutrients - Ex: Apple scab have nothing wrong in the health, but is an esthetical problem - Ex: Botrytis Fruit rot on strawberries - Ex: Stem rust on wheat (cosmetic and health) - Ex: Black spots fungi on roses - Ex: Nematodes destroy apple roots - How do we control these insects? o Sulfur (S) occurs in nature in its elemental form (S 2 ) When burnt, SO 2 is produced = insecticide
Ève Belzile-Dugas Winter 2015 o Tobacco plant produces nicotine = insecticide o Copper acetoarsenate (arsenic trioxide + copper acetate) = Paris Green One of the first artificial insecticide Also used in paint (e.g. in wallpaper) o DDT Very effective, many versions Used during the war to prevent infections WHO: 25 million lives were saved because of use of DDT Paul Muller (Nobel Prize medicine 1948) Farmers and communities overused DDT Eggshells broke too frequently Rachel Carson: Silent Spring introduced the idea that pesticides were not that good It builds up in the food chain because it is not biodegradable Banned in Canada in 1969 Banned in the US in 1972 WHO suggested in 2006 that DDT helps prevent malaria, a considerable problem in Africa How dangerous is DDT? Rats exposed to traces DDT develop fewer liver tumors than unexposed rats (DDT generates detoxicating enzymes in rats, this doesn’t happen in humans) Berkeley Public Health Institute: among women who were under 14 years of age during heaviest DDT exposure (1945-1959) blood levels of DDT were found to correlate with future breast cancer risk Long Island Study: no relationship between breast cancer and blood levels of DDT - Nocebo effect : believe that something is going to be harmful, there are physical harmful symptoms - Ex: Schools where pesticides were put in fruits and children died o Monocrotophos (pesticide) were accidently put in food o 1.2g is a potentially lethal dose - There may be a connection between insecticide/pesticides and Parkinson’s disease o Paracoid (pesticide) has similarity to contaminant (China white, drug on
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