2.Sources.11

2.Sources.11 - Chemical Sources – Why are they Important?...

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Unformatted text preview: Chemical Sources – Why are they Important? Introduction – Definitions Revisited What is Normal? Sources – Why are they Important? Chemical Sinks in the Environment Environmental Compartments Fate of Chemicals in the Environment Summary and Conclusions I. Introduction – Definitions Revisited Toxicant – a chemical that causes an adverse effect at a dose or concentration of interest. Contaminant – a chemical present at an abnormal concentration. Pollutant – a toxic contaminant. Chemistry – the study of chemical properties and reactions. Environmental chemistry – the study of chemical movement and reactions in the environment, as influenced by their properties II. What is Normal?? Normal is a defined concept – it can be more difficult to grasp than “abnormal.” Normal can be defined according to place – “spatial.” Normal can be defined according to time in history – “temporal.” Typical interest is to “clean up” the environment to what it once was – but where and when?? Current Atmospheric Composition Earth’s Original Atmosphere The original atmosphere is thought to have been a “reducing environment.” It contained C, N, S, in their reduced forms – CH4, NH3, and H2S. Today, the atmosphere is considered to be an “oxidizing environment,” containing CO2, N2, SO2 and – O2. In reducing atmospheric pollution, what is the goal? “Normal” Definition by Convenience The advent of the industrial revolution has led to dramatic changes in environmental quality. Therefore, by convention “normal” is usually referred to as representing conditions prior to the industrial revolution, or about 1750 AD. More Concepts of Importance Environmental fate – the study of the sources, transport, partitioning, transformations, and targets of chemicals in the environment. Source – place of origin of a chemical in the environment. Target – the organism(s) impacted by a chemical. Sink – a long-term repository for a chemical. III. Sources – Why are they Important? Some chemicals have only anthropogenic sources – freons (chlorofluorocarbons). Many have natural and anthropogenic sources – SO2. Managing chemical inputs to the environment requires an understanding of sources and their contributions. Values in teragrams Point Sources Represented by sites where concentrated amounts are released from relatively small areas. They are relatively easy to manage. Non-Point Sources Represented by sites where diffuse amounts are released from relatively large areas. They are difficult to manage. IV. Chemical Sinks in the Environment Areas of long-term storage. Characterized by large volumes and/or long turnover times. Represented by physical and/or chemical forms. Physical forms include oceans, glaciers, groundwater and adipose tissues. Chemical forms include limestone (calcium carbonate). Examples of Sinks V. Environmental Compartments Hydrosphere – water in any of its physical states. Lithosphere – the mineral surface of the earth (soils). Atmopshere – blanket of gases that surround the earth. Biosphere – all forms of life, from viruses to whales. The Hydrosphere – Typical Motions The Lithosphere – Typical Soil Horizons The Atmosphere – Typical Motions VI. Environmental Fate Processes Dissolution – dissociation in water to discrete – adherence to particle surfaces – evaporation as a gas. – degradation via loss-gain of molecules. Adsorption (soils). Volatilization Oxidation-reduction - e s. Hydrolysis – degradation via nucleophilic reaction with water. Chemicals Run a “Gauntlet” of Processes VII. Summary and Conclusions A pollutant is a contaminant with a demonstrable adverse effect (above a threshold). Normal may be defined either temporally or spatially. Primary sources must be identified to manage inputs. Sinks involve large volumes or long turnover rates. Chemical fate involves four compartments. ...
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2.Sources.11 - Chemical Sources – Why are they Important?...

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