Environmental Chemistry Lecture Notes PDF

TOXIC INORGANIC CARBON COMPOUNDS 1. Cyanide (CN) Hydrogen cyanide has numerous uses: Ingredients of pest poisons. Metal (silver) polishes. Photographic chemical solutions. Cyanide salt solutions are used to: Metal refining. Metal plating. Salvaging silver from exposed photographic and x-ray film. So...

TOXIC INORGANIC CARBON COMPOUNDS 1. Cyanide (CN) Hydrogen cyanide has numerous uses: Ingredients of pest poisons. Metal (silver) polishes. Photographic chemical solutions. Cyanide salt solutions are used to: Metal refining. Metal plating. Salvaging silver from exposed photographic and x-ray film. Some plants contain cyanogenic glycosides, saccharidal substances that contain the –CN group and that may hydrolyze to release cyanide. Such substances, called cyanogens, The release of cyanide by the enzymatic or acidic hydrolysis of amygdalin in the digestive tract is shown below: Biochemical action of cyanide 1. Cyanide deprives the oxygen of body by acting as a chemical asphyxiant (that simply displace oxygen in respired air). 2. Cyanide inhibits an enzyme involved in a key step in the oxidative phosphorylation pathway, by which the body utilizes oxygen in cell mitochondria. The overall process is represented as follows: Cyanide bonds to the iron(III) of the ferricytochrome enzyme, preventing its reduction to iron(II) in the first of the two reactions above. Anti-dotes 1. Thiosulfate, S2O32- The detoxification of cyanide involves conversion to the less toxic thiocyanate by a reaction requiring thiosulfate or colloidal sulfur as a substrate: 2. Nitrite, NO2- Administered intravenously as sodium nitrite solution or inhaled as amyl nitrite,C5H11NO2, an ester which hydrolyzes to NO2– in the blood, functions as an antidote to cyanide poisoning. 2. Carbon monoxide (CO) Toxic industrial gas produced by the incomplete combustion of carbonaceous fuels. Biochemical action of carbon monoxide Carbon monoxide enters the bloodstream through the lungs and reacts with oxy-hemoglobin (O2-Hb) to produce carboxyhemoglobin (CO-Hb): Carboxyhemoglobin is several times more stable than oxyhemoglobin and ties up the hemoglobin so that it cannot carry oxygen to body tissues. Anti-dotes CO poisoning can be cured by exposing the affected person to fresh O2, TOXIC INORGANIC NITROGEN COMPOUNDS Nitrogen Oxides (NOx) The two most common oxides of nitrogen are: Nitrous oxide (NO). Nitrogen dioxide (NO2). Effects of NO2 1. severe irritation of the inner most parts of the lungs. 2. disruption of some enzyme systems, such as lactic dehydrogenase. 3. acts as an oxidizing agent and form free radicals, particularly the hydroxyl radical HO and causes lipid peroxidation. Effect of NO 1. It is a central nervous system depressant 2. can act as an asphyxiant. A possible antidote is antioxidant vitamin E. TOXIC INORGANIC SULFER COMPOUNDS Sulfur dioxide (SO2) Effects of atmospheric sulfur dioxide On human 1. Irritation and increasing airway resistance. 2. Increased effort to breathe and stimulated mucus secretion. On plants Acute exposure to high levels of atmospheric sulfur dioxide kills leaf tissue (leaf necrosis). Chronic exposure of plants to sulfur dioxide causes chlorosis. Acid rains Sulfur dioxide in the atmosphere is converted to sulfuric acid, so that in areas with high levels of sulfur dioxide pollution, plants may be damaged by sulfuric acid aerosols. Such damage appears as small spots where sulfuric acid droplets have impinged on leaves. TOXIC OXIDANTS Ozone (O3) and Peroxyacetyl nitrate (PAN) The most toxic environmental pollutants present in polluted atmospheres, especially under conditions where photochemical smog is present. Toxic effects: 1. ozone in the body produces free radicals that can cause lipid peroxidation or reaction with sulfhydryl (–SH) groups. 2. A deep lung irritant. 3. Strongly irritating to the upper respiratory system and eyes. 4. chromosomal damage. 5. PAN can attack the sulphur-containing amino acid (cysteine). 6. Ozone is notable for being phytotoxic (toxic to plants) Anti-dotes Radical-scavenging compounds. Antioxidants. Compounds containing sulfhydryl groups. TOXIC PESTICIDES The biological action of DDT: ❑ The central nervous system is the target of DDT. ❑ DDT dissolves in lipid (fat) tissue and accumulates in the fatty membrane surrounding nerve cells. ❑ Interference with the transmission of nerve cells. ❑ The net result is disruption of the central nervous system killing the target insect. ❑ DDT is fairly stable and persists in the environment. The other groups like organophosphates and carbamates can degrade quite rapidly in the environment and can react with O2 and H2O, undergoing decomposition within a few days in the environment and the products are not toxic. Mode of Action of Insecticides The pesticides can inhibit acetylcholin estearase enzyme. Acetylcholine is a neurotransmitter and triggers nerve cells. The enzyme acetylcholinesterase, which decomposes acetylcholine and prevents the nerve cell from firing. An organophosphate or carbamate insecticide can mimic acetylcholine and induce the formation of a phosphoryl and carbaryl enzymes (intermediate). The breakdown of this intermediate is much slower than that of the acetyl enzyme. Acetylcholinestearase inhibition by organophosphate insecticide Methyl Isocyanate (MIC) Methyl isocyanate, CH3NCO (MIC), is the raw material for the production of carbamate pesticide. MIC is synthesized by 2 steps as following: The reaction of primary amine with phosgene (COCl2). The product is decomposed by heating with lime (CaO). CH3NH3Cl + COCl2 ====> CH3NHCOCl + 2HCl 2CH3NHCOCl + 2CaO ====> 2CH3NCO + CaCl2 + Cl2 Workers exposed to MIC suffer from chest tightness and breathing troubles due to irritation of the respiratory tract beacouse COCl2 is deadly gas.