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Environmental Geosciences. Human Interactions with the Environment. Organics and other compounds. Andrea Koschinsky. Characteristics of Organic Compounds. Vapour Pressure of Organics Given a mixture (ideal) of organics the partial pressure of component i is given by Raoult’s law:
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Environmental Geosciences Human Interactions with theEnvironment Organics and other compounds Andrea Koschinsky
Characteristics of Organic Compounds Vapour Pressure of Organics Given a mixture (ideal) of organics the partial pressure of component i is given by Raoult’s law: Pi = xi Pi,o where P0 is the vapor pressure of the pure substance. Solubility of Organics in Water The aqueous solubility will obey Henry’s law: Pi = ki Ciw where Ciw is the concentration in water and ki is the Henry’s Law constant. Estimating values for Koc The partitioning of organics between solid organic matter and water is given by Koc. The values for Koc can be predicted from the measured octanol-water partitioning for insoluble organics: Kow = [organic in octanol]/[organic in water] log Koc = 0.49 + 0.72 log Kow Sorption of organics onto soil organic matter The partitioning between soil and groundwater is found by scaling Koc by the fraction of organic matter (f =0.0001-0.02.): Distribution coefficient Kd = Kocfoc
Organic Compounds Aliphatic compounds
Organic Compounds Aromatic compounds BTEX is an acronym for benzene, toluene, ethylbenzene , and xylene . This group of volatile organic compounds (VOCs) is found in petroleum hydrocarbons, such as gasoline, and other common environmental contaminants.
Chemical structure of MTBE Organic Compounds Volatile organic compounds (VOCs) are compounds that have a high vapor pressure and low water solubility. Many VOCs are human-made chemicals that are used and produced in the manufacture of paints, pharmaceuticals, and refrigerants. VOCs typically are industrial solvents, such as trichloroethylene; fuel oxygenates, such as methyl tert-butyl ether (MTBE); or by-products produced by chlorination in water treatment, such as chloroform. VOCs are often components of petroleum fuels, hydraulic fluids, paint thinners, and dry cleaning agents. VOCs are common ground-water contaminants. Persistant bioaccumulative toxic chemicals (PBTs) are chemicals that are toxic, persist in the environment and bioaccumulate in food chains and, thus, pose risks to human health and ecosystems. The biggest concerns about PBTs are that they transfer rather easily among air, water, and land, and span boundaries of programs, geography, and generations. Polynuclear aromatic hydrocarbons (PAHs) are hydrocarbon compounds with multiple benzene rings. PAHs are typical components of asphalts, fuels, oils, and greases. They are also called Polycyclic Aromatic Hydrocarbons.
Organochlorinesare synthetic organic compounds that contain chlorine. A generally used term referring to compounds that contain mostly or exclusively carbon, hydrogen, and chlorine. Examples are DDT, chlordane, and lindane; PCBs; and some solvents that contain chlorine. Chemical structure of DDT, an insecticide formerly used to keep mosquito populations in check. Chemical structure of HCHs (hexachlorocyclohexane, Lindane), used as an insecticide Organic Compounds Persistent Organic Pollutants (POPs) are chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human population and the environment. There has been a realization that these pollutants, upon exposure of human population, can cause serious health effects ranging from increased incidence of cancers to disruption of hormonal system. These effects have also been observed and recorded for various animal species. Developing countries are particularly vulnerable due to often indiscriminate use and disposal of POPs.
Polychlorinated biphenyls (PCBs) are mixtures of up to 209 individual chlorinated compounds (known as congeners). PCBs are either oily liquids or solids that are colorless to light yellow. Some PCBs can exist as a vapor in air. PCBs have no known smell or taste. Polychlorinated biphenyls persist in the environment and are passed up the food chain, with the highest levels accumulating in predatory birds and mammals. Use:PCBs were predominantly used as coolant insulants and heat transfer agents in a number of electrical products such as transformers and capacitors. PCBs were also used in a wide variety of products including printing inks, adhesives and paints. There are no known natural sources of PCBs. Chemical Structure: General structure C12 H10-x Clx where x = 1 to 10 Organic Compounds
Dioxins- General name given to 210 organic compounds containing carbon, oxygen and hydrogen with one to eight chlorine atoms. Only 17 of the 210 dioxins are known to be toxic. Dioxins in trace quantities are created naturally (e.g. volcanoes) and as unwanted by-products in numerous combustion processes (e.g. forest fires, cigarettes, bonfires, car engines etc.), in metal smelting and recycling processes and in the manufacture of a few chlorine-containing chemicals. Organic Compounds
Organic Compounds in the Ecosystem TCDD = Tetrachlordibenzo-p-dioxine
Degradation of Organic Compounds Transformation processes of organic matter: Abiotic and biotic processes Chemical and biological transformation processes control the ultimate fate of hydrocarbons released into the environment. The transformation reactions differ depending on the environmental compartment within which the compounds reside and vary with chemical structure. When hydrocarbons are released to the atmosphere or surface waters, photochemical oxidation, an abiotic process, can occur. In soils and groundwater and surface waters, biologically mediated degradation of hydrocarbons is the most important transformation process. In the absence of light, chemical degradation reactions at Earth surface temperature and pressure are relatively unimportant compared to biologically mediated degradation reactions. Abiotic processes Approximately 25% of the average oil spill on the open ocean evaporates. In the gaseous state, hydrocarbons are readily photooxidized. The dissolved fraction of petroleum also is subect to photo-oxidation. The largest sink for alkanes in the atmosphere is reactions with OH and NO3 radicals (formation of photochemical smog). Mono-aromatic hydrocarbons react only with OH radicals, forming aldehydes, cresols, and in the presence of NO, benzylnitrates.
Aerobic processes Oxygen is the preferred electron acceptor by microorganisms because of the high-energy yield of these processes. Aerobic degradation of hydrocarbons can occur when indigenous populations of bacteria capable of aerobic degradation of hydrocarbons are supplied with molecular oxygen and nutrients required for cell growth. Studies involving complex mixtures of hydrocarbons have demonstrated that microorganims can degrade most of the hydrocarbons present in gasoline. Degradation of Organic Compounds Biotic processes In soils and groundwater, biologically mediated processes dominate. The more water-soluble components of crude oil and petroleum produces are most frequently reported in groundwater downgradients from spills and leaks. These hydrocarbons are biologically reactive and their fate in the subsurface is controlled by microbiological as well as physical and chemical processes. Certain microorganisms are able to degrade petroleum hydrocarbons and use them as a sole source of carbon and energy for growth.
Degradation of Organic Compounds Anaerobic processes Anoxic conditions frequently develop in subsurface environments affected by high concentrations of dissolved hydrocarbons because of rapid aerobic biodegradation rates and the limited supply of oxygen. In the absence of oxygen, the oxidized forms of other inorganic species, and some organic species such as humic substances, are used by microorganisms as electron acceptors. The most commonly available electron acceptors in subsurface environments include both solid (such as Fe and Mn oxides) and dissolved (such as nitrate and sulfate) species. In aquifers, as geochemical conditions change, a sequence of reactions occurs, reflecting the ecological succession of progressively less efficient modes of metabolism.
Degradation of Organic Compounds Landfill leachate
Degradation of Organic Compounds BIODEGRADATION OF PCBs As a result of their very stable properties, PCBs are synthetic compounds that are not readily degraded. The degradation of these compounds entails difficult mechanisms of chemical, biochemical or thermal destruction.Biodegradation, that is, the degradation of compounds by bacteria or other microorganisms, is a slow yet possible method for destroying PCBs in both aerobic and anaerobic environments. It is the only process known to degrade PCBs in soil systems or aquatic environments. The specific processes involved are aerobic oxidative dechlorination or hydrolytic dehalogenation and anaerobic reductive dechlorination. Theoretically, the biological degradation of PCBs should result to give CO2, chlorine and water. This process involves the removal of chlorine from the biphenyl ring followed by cleavage and oxidation of the resulting compound. Persistence of PCBs in the environment increases with the degree of chlorination of the congener. The position of chlorine atoms on the rings also affects the rate of biodegradation A possible pathway for the aerobic oxidative dehalogenation of PCBs
Degradation of Organic Compounds BIODEGRADATION OF pesticides: DDT Concentration of DDT and degradation products in southern Florida fishes in 1995. Fish at sites 6 and 7 had multiple DDT degradation products; total DDT at all other sites was principally p,p'DDE.
Transport and Sorption of Organic Compounds CFCs = Chlorofluorocarbons PCDD = polychlorinated dibenzo-p-dioxin, PCDF = polychlorinated dibenzofuran
