30 Organics II - Toxic Bioaccumulative Chemicals Mercury...

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Unformatted text preview: Toxic Bioaccumulative Chemicals Mercury Most mercury enters aquatic environments from the atmosphere Hg2+ Hg2+ sediments - charge Negatively charged particles bind mercury And retain it in bottom sediments. Under anaerobic conditions, Hg2+ can be converted to organic methylmercury which is more toxic and persistent in organisms. Mercury Methylation Hg Organisms (CH Hg ) methylmercury Methylmercury is strongly accumulated in the body 2+ 3 + and is generally more toxic than inorganic Hg The following are required for mercury methylation Inorganic Mercury (Hg ) 2+ Carbon Source (food) C H O Anaerobic Conditions + 3SO42- + 3H = 6HCO + 3HS Sulfate/Sulfate-Reducing Bacteria 6 12 6 + 3- The addition of sulfate to water stimulates the inadvertent methylation of inorganic mercury Sulfate concentrations in EAA runoff and Lake Okeechobee average more than 50 times background concentrations than in the pristine Everglades Fertilizers Potassium Sulfate Calcium Sulfate Elemental Sulfur Sulfate Methylmercury is more directly toxic and remains in the tissues of organisms longer than inorganic Hg2+. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost from the body. Bioaccumulation allows for biomagnification, which is the increase in concentration of a chemical in organisms higher up in the food chain. Biomagnification: concentration of a chemical in organisms as it moves up the food chain. Organisms near the top of the food chain may have concentrations of mercury millions of times greater than in the aquatic environment Other Bioaccumulative Toxins Synthetic Organic Chemicals Dioxin DDT C H O2Cl4 11 18 C H Cl5 14 22 PCB C H Cl8 12 21 Principally carbon, hydrogen Generally poorly soluble in water Dioxin Dioxin water solubility: 0.2 µg/L Dioxin DDT 0.2 µg/L < 0.1 µg/L PCB 10 µg/L Uncharged and principally carbon, hydrogen Organic Solvents carbon carbon Dioxin carbon Organic solvents carbon Carbon-based compounds dissolve more easily in carbonbased solvents. water Extra Credit: 1. Concentration of a chemical in organisms as it moves up the food chain is called _________ 2. An example of a synthetic organic chemical is ___ 3. Many synthetic organic chemicals are poorly or easily soluble in water. 4. Synthetic organic chemicals are composed of what two main chemical elements? What is the most common solvent used every day? Detergents SO4SO4hydrophilic hydrophobic SO4- SO4- SO4 SO4- SO4SO4SO4- High Carbon Concentration Detergent Micelles Vegetable Oil (insoluble in water) Synthetic Organics and Organisms Synthetic organic chemicals can be acutely toxic In high doses, but they also can bioaccumulate creating chronic toxicity at lower doses Their ability to bioaccumulate is related to their poor water solubility. Bioaccumulation in Organisms Lipid Tissue in Organisms carbon Principally Carbon and Hydrogen Bioaccumulation in Organisms Dioxin carbon The chemical essentially dissolves into the lipid tissues Synthetic organic chemicals are poorly soluble in water They are soluble in organic solvents and lipids Lipids are found in all organisms Despite low levels of organic chemicals in water due to their low water solubility, high amounts can accumulate in the tissues of living organisms Bioaccumulation Water Concentration = 0.2μg/L Zooplankton concentration = 160 μg/L Magnification of 800 x Bio-Magnification Water and phytoplankton to zooplankton: 800 x Zooplankton to fish: 31 x Fish to eagle: 4.8x Overall: 120,000 times original concentration in water Bioaccumulative Organics PCBs and Pesticides PCBs Used as insulating fluids and coolants in electrical equipment and machinery from 1929-1977. Electrical equipment plasticizers in paints, plastics and rubber products pigments, dyes and carbonless copy paper EPA estimates that 150 million pounds of PCBs are dispersed throughout the environment, including air and water supplies; an additional 290 million pounds are located in landfills in this country some PCBs act like hormones, and other PCBs are nerve poisons PCBs were “banned” in 1979 Killer Whales (1000 ppm) PCBs in Marine Mammals High on food chain Lipid tissues Hazardous Waste level (Canada) Toxaphene (670 chemicals) 400,000 tons: 1946 to 1974 carbon lipid Seawater Arctic cod muscle Narwhal blubber 0.0003 ppb 14 - 46 ppb 50,000 X 2440 - 9160 ppb ~8MX Toxaphene and Mirex: 1959 - 1976 highest levels ever recorded in a living organism. Many synthetic organic chemicals, particularly those like PCBs and DDT are very persistent in the environment. They last for decades. They become stored in organic materials that naturally occur in aquatic and terrestrial systems Where in these environments do we find high levels of carbon? Environmental Persistence Water DDT Solubility of < 0.1 μg/L Organic Sediments Organic chemicals become stored in organic sediments This protects them from degradation and increases their lifetime in the environment ½ Life and Organochlorines PCBs 1 month 2-6 years > 60 years 1 - 30 years (7 years in humans) 28 days 15 – 20 years up to 150 years Dioxin DDT Muck: high in organic carbon Lake Michigan PCBs “banned” in 1979 EPA 2004 N Organic Carbon Concentration mg Carbon /g sedimen PCBs µg PCB/Kg sediment (parts per billion) Open water PCB concentration = < 1 part per trillion Lake Erie PCB levels PCBs EPA, 2004 After 30 years, PCBs continue to persist in the Environment Persistence in the Environment Old sediments Homework IV Emerging Contaminants Due Friday, December 4 in class. th ...
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