Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 17. Aromatic Compounds.
Herbicides are being used at increasing levels in order to enhance production of various crops by controlling competing vegetation. Atrazine, a toxic herbicide, is not only one of the most widely used herbicides in the United States, but in the global scheme of agriculture as well. Many organizations, such as the Office of Children's Health Protection Advisory Committee, have recently dedicated a vast amount of research to understanding the detrimental effects of this chemical, as well as to how it is degraded, the maximum contaminant level, and methods to reduce/remove this harmful chemical from our environment.
Atrazine, 2-chloro-4-ethylamino-6-isopropylamino-s-triazine, is a member of the symmetrical triazine class of pesticides and serves to selectively control broadleaf weeds. This chemical is absorbed by roots and leaves of plants, then transported up through the plant where it builds up in the leaves. The weed killer acts by inhibiting photosynthesis in the plant. Tolerant plants metabolize atrazine to hydroxyatrazine and amino acid conjugates. The hydroxyatrazine is further degraded by dealkylation and hydrolysis. Research has yet to identify an organism which contains all of the required enzymes to completely degrade atrazine into harmless by-products. The net result of widespread use and resistance to degradation facilitates long-term environmental contamination and increased levels of this chemical in surface and ground waters due to runoff from nearby fields. These findings prompted the Environmental Protection Agency to place a federal mandate on the maximum contaminant level at three parts per billion (ppb). This is extremely liberal considering many European countries, including Switzerland where this weed killer is manufactured, have a safe level designated at no more than 0.1ppb, or they have implemented an absolute ban on the use of atrazine. Thus far, research has shown the main degradation pathways of this herbicide are biological dealkylation, chemical hydrolysis, and biological hydrolysis of which they consecutively break down into urea which is broken down further into carbon dioxide and ammonia.
Studies have shown that laboratory animals exposed to high concentrations of this herbicide over an extended period of time suffer from liver, kidney, lung, or cardiovascular damage. Health effects on humans range from weight loss to muscle degradation and cancer. Atrazine is a known carcinogen and an endocrine disrupting toxin as is DDT. Moreover, bottle-fed babies from several Midwestern communities ingest over twenty six percent of their lifetime allowable dose of this chemical before reaching the age of one. In light of this knowledge concerning water contamination, the Environmental Working Group claims that routine tap water has been contaminated with these weed killers for at least twenty-five years. As a result, initiatives to protect drinking water sources from contamination with atrazine have been called forth by the American Water Works Association.
It is clear that atrazine poses serious problems to our environment and to
us, but banning this herbicide could increase other risks not associated
with atrazine as well as inducing soil erosion from increased tillage.
Not to mention, treating water with activated charcoal to purify it within
municipal water treatment facilities would be a costly measure.
Pertinent Text References
Chapter 17. Reactions of Aromatic Compounds.
Chapter 6-3. Pesticides.
Chapter 20-8. Formation and Hydrolysis of Nitriles.
Chapter 19-18. Reactions of Arenediazonium Salts.
Question 1: What are the detrimental environmental and health effects of atrazine?
Question 2: Describe the reaction and reagents used in the first step of the biological degradation pathway to convert atrazine to hydroxyatrazine.
Question 3: How is atrazine similar to DDT? Why do these chemicals appear to have compound effects?
Question 4: When and why do atrazine levels peak in the water supply? It's ironic that this is the same time most babies are born.
Why do other countries have tougher standards than the United
States? Do we need to tighten our federally mandated levels of
Answer 1: It causes many kinds of cancer, including cancer of the breast, ovaries, uterus, testicles, as well as leukemia and lymphoma, it is an endocrine disrupter, it interrupts regular hormone function, congestion of heart, lungs and kidneys, low blood pressure, muscle spasms, weight loss, damage to the adrenal glands, muscle degradation, it is active in soil for 5 to 7 months, it can easily move in soil and runoff may pollute surface water
1. Diazotization to alkane diazonium salt using NaNO2
2. Hydrolysis using H2SO4, heat, and H2O to obtain Ar-OH, N2(g), and HCl
Answer 3: Both DDT and atrazine are long-lasting so that their residues may accumulate in the environment, both chemicals are chlorinated and toxic, and ironically enough, they were both invented by the same chemist.
Answer 4: Since atrazine is applied before or shortly after plant growth begins, these levels are the highest during spring time. The fresh herbicide is frequently carried out of fields into sources of water by rain runoff. This is compounded by the fact that most rain falls during the spring increasing runoff.
Answer 5: This question is to your own discretion.