Transcript Slide 1
Exam: Wednesday, April 2 Study Guide: today Review: Monday, March 31 Student numbers on Exam drainage basin 12,000 km2 Dairy and Beef Sugarcane production contributes twothirds of the economic production of Everglades agriculture, and uses nearly 80% of the crop land in the EAA Sugar, Rice, Veg. Phosphorus Eutrophication Phosphorus Photosynthetic life O2 bacteria Effectiveness of P controls Above Target SWIM target: 397 tons Phosphorus concentrations in the Lake remain at about 117 ppb The target level is 40 ppb. Internal Loading Fe3+ high oxygen Fe2+ low oxygen Dissolved phosphorus combines with oxidized iron (Fe3+) to create an insoluble compound that becomes buried in lake sediments. Fe3+ + PO43- = Fe(PO4) solid Fe3+ If oxygen contents are reduced (anoxic bottom sediments) the converts to Fe2+ which solubilizes the compound returning P to water. 2+ Fe (PO4) 3- to water P released by sediments is taken up by photosynthetic algae faster than it can be returned to the sediments Mercury Mercury is naturally occurring (coal, volcanism, rock weathering) Anthropogenic sources include: •combustion of coal (#1) •oil product combustion •cement production •lead production •zinc production •iron and steel production •mercury production •gold production. Enters water bodies principally from the atmosphere Forms of Mercury The dominant forms of mercury are Hgo and Hg2+ which often occurs as HgCl2 (mercuric chloride) in many aqueous environments. Hg2+ interacts with soil and sediment particles becoming part of lake bottom sediments (limits availability) Mercury, however, can undergo chemical changes in lakes which render mercury more environmentally dangerous Mercury as a persistent, bioaccumulative toxin Bioaccumulation: concentration of a chemical in organisms as it moves up the food chain. Methylation: conversion of inorganic forms of mercury Hg2+ to an organic form: methyl mercury (CH3Hg+) Methylmercury attaches to proteins in animals (enters food chain) Methylmercury has a half-life in human blood of about 50 days. Mercury Methylation Methylation occurs in the absence of oxygen (anoxic or anaerobic conditions) but in the presence of organic carbon and sulfate (SO42-) Occurs primarily in bottom sediments as a byproduct of the life processes of sulfate-reducing bacteria (SO4 to H2S) that live in high sulfur, low oxygen environments. +4 0 0 O2 + Carbon (C) -2 x 2 = -4 CO2 Carbon loses electrons (oxidized), oxygen gains electrons (reduced). Oxygen is the electron acceptor. +6 SO4 -2 microbes -2 H2S Sulfur is the electron acceptor. The exact role of sulfate-reducing bacteria In mercury methylation is poorly understood However, bacterial sulfate reduction requires sulfate. The addition of sulfate to water stimulates the metabolic activity of sulfate-reducing bacteria and the inadvertent methylation of inorganic mercury Sulfate concentrations in EAA runoff and Lake Okeechobee average more than 50 times background concentrations in the pristine Everglades Hg2+ from coal, volcanism, rock weathering Water Sediments (Bound) Sulfur reducing bacteria, low O2 methylmercury Food Chain bioaccumulation Bioaccumulation Factors BAF = Methylmercury is rapidly taken up but only slowly eliminated from the body by fish and other aquatic organisms, so each step up in the food chain (bio)magnifies the concentration from the step below. Bioaccumulation factors (BAF's) of up to 10 million in largemouth bass have been reported for the Everglades. Fish-eating birds, otters, alligators, raccoons and panthers can have even higher bioaccumulation factors. Methylmercury in the organs and tissues causes birth defects & disorders of the brain, reproductive system, immune system, kidney, and liver at extremely low levels in food. Concentration in organism Concentration in water Sidebar: Fluorescent Lights A typical fluorescent lamp is composed of a phosphor-coated glass tube with electrodes located at either end. The tube contains mercury, of which only a very small amount is in vapor form. When a voltage is applied, the electrodes energize the mercury vapor, causing it to emit ultraviolet (UV) energy. The phosphor coating absorbs the UV energy, causing the phosphor to fluoresce and emit visible light. Each year, an estimated 600 million fluorescent lamps are disposed of in US landfills amounting to 30,000 pounds of mercury waste. Other Bioaccumulative Toxins Synthetic Organic Chemicals Organochlorines Dioxins Pesticides PCBs Organic Solvents Cleaning agents Chlordane DDT Dioxin PCB Why do they bioaccumulate? Solubility Organochlorines as well as many other synthetic organic compounds are poorly soluble in water Dioxin 0.2 µg/L PCB 10-31 µg/L (50% Cl) DDT insoluble Principally carbon, hydrogen Ionic Compounds NaCl Na+ + Cl- Sodium Chloride 350 g/L Potassium Chloride 280 g/L Why? Liquid water - Vibration and rotation NaCl Na+ + Cl- Dioxin PCBs Water Solubility Aroclor 1221 (21% Chlorination) 500-1500 ppb Aroclor 1230 (30% Chlorination) 85-92 ppb Aroclor 1240 (40% Chlorination) 40-170 ppb Aroclor 1254 (54% Chlorination) 10-31 ppb Aroclor 1260 (60% Chlorination) <1 ppb Improving Solubility Organic Solvents Soap/detergents Structural similarity between the chemical and the solvent. Hexane Lipids and Solubility Structural similarity between the chemical and the solvent. Solubility A chemical’s solubility in lipids is inversely proportional to its solubility in water. Lipid (Carbon/hydrogen) Carbon/hydrogen water Bio-Accumulation Water and phytoplankton to zooplankton: 800 x Zooplankton to fish: 31 x Fish to eagle: 4.8x Overall: 120,000 times original concentration PCBs Spokane River Nov. 2002 Banned in 1979 Smallmouth bass - 1100-1800 ppb Round gobies - 200-800 ppb Zebra mussels - 100 ppb Toxaphene Biomagnification Seawater Arctic cod muscle Narwhal blubber 0.0003 ppb 14 - 46 ppb 2440 - 9160 ppb Mirex highest levels ever recorded in a living organism.