Presentation on theme: "Toxins in Food Chains. Feeding the human population is a big business, economically. To prevent foods from being eaten by pests, we put chemical substances."— Presentation transcript:
Feeding the human population is a big business, economically. To prevent foods from being eaten by pests, we put chemical substances called pesticides on farmer’s fields. They either kill the insects or prevent them from reproducing. Another solution is to apply herbicides, which are chemicals that destroy or inhibit the growth of unwanted plants (weeds). In small quantities, pesticides are not harmful, but when they enter the food chain, they accumulate to dangerous levels and cause undesirable effects in the upper trophic levels. Crop - sprayer
Bio-magnification: An accumulation of toxic substances in a food chain. The biggest quantity of toxins is found in top carnivores (tertiary consumers). Bioaccumulation – “The biological sequestering of a substance at a higher concentration than that at which it occurs in the surrounding environment or medium.” - U.S. Geological Survey, 2007 Bioaccumulation – “Bioaccumulation (or bioconcentration) is the uptake of organic compounds by biota from either water or food. Many toxic organic chemicals attain concentrations in biota several orders of magnitude greater than their aqueous concentrations, and therefore, bioaccumulation poses a serious threat to both the biota of surface waters and the humans that feed on these surface-water species.” – Smith and others, 1988 Bioaccumulation – “General term describing a process by which chemicals are taken up by an organism either directly from exposure to a contaminated medium or by consumption of food containing the chemical.” – U.S. Environmental Protection Agency, 2010 Bioaccumulation – “Bioaccumulation is defined as the accumulation of chemicals in the tissue of organisms through any route, including respiration, ingestion, or direct contact with contaminated water, sediment, and pore water in the sediment.” – U.S. Environmental Protection Agency, 2000 Bioaccumulation – “Progressive increase in the amount of a substance in an organism or part of an organism which occurs because the rate of intake exceeds the organism’s ability to remove the substance from the body.” – International Union of Pure And Applied Chemistry, 1993
DDT A pesticide used in the 50’s and 60’s to control populations of pests on crops. It is only when we started spraying DDT commercially onto farms that we began to see the severe effects it had on the ecosystem.
1. What is DDT? 2.How was DDT used in Canada the 50’s and 60’s? 3.When was DDT use banned in Canada? 4. How was DDT used in Mexico? 5. Explain why DDT is “persistent”: 6. Explain what is meant by “DDT is not easily metabolized” 7. What is the “grasshopper effect”? 8. Explain how DDT negatively affects birds. 9. Explain how DDT negatively affects humans. 10. Draw a food chain, showing DDT traveling through.