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Introduction to environmental analysis - Reeve R.

Reeve R. Introduction to environmental analysis - Wiley publishing , 2002. - 312 p.
ISBN 0-471-49295-7
Download (direct link): introductiontoenvironmental2002.pdf
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Sediment will need more pretreatment to remove potential interferences. Concentrations will vary greatly from site to site and even from sample to sample and so a large number of samples would need to be taken to obtain an average concentration. Seaweed will also need pretreatment and will only be found in specific locations. On the other hand, sediment and seaweed samples are ideal for investigating localized pollution. In each case, the effect of enrichment or bioaccumulation make it easier to detect the species since they will be present at higher concentrations than in the surrounding water.
Fish are not static and so it is difficult to relate concentrations found to specific locations. There may be large variations in concentration from specimen to specimen. However, shellfish are more static and measured concentrations may be more easily related to localized pollution.
264
Introduction to Environmental Analysis
Response 5.7
All of the solids discussed in this chapter have complex structures and there will be a range of binding sites for the analyte. Some of the analyte can be so very strongly bound that it may be unavailable for uptake by organisms. It is quite possible that with length of time the pollutant becomes more tightly bound within the solid. We have considered this in Sections 5.4 and 5.7 for the related problem of metal availability in solids.
Chapter 6
Response 6.1
The definition of the term for gas concentrations is very precise, referring to measurements made as volumes. An atmosphere containing 20 ppm sulfur dioxide would contain 20 ^l of gas per litre of atmosphere. A complete statement of the unit should be parts per million (volume/volume).
When the term is applied to aqueous concentrations, it is often used interchangeably with mg l-1. This would give the complete statement of the unit as parts per million (weight/volume)! Since 1 l of water containing little dissolved material has a mass of 1000 g, this would become:
1 ppm = 1 mg of analyte per 1000 g of water, i.e.
parts per million (weight/weight) for water samples.
Response 6.2
Atmosphere Typical pollutant concentrations (volume/volume)
External atmospheres parts per billion (ppb) - parts per million (ppm)
Internal atmospheres parts per million
Exhausts or flue gases parts per million - parts per hundred (%)
1. Different Concentration Ranges. The concentrations in the two atmospheres span a range of 106. It is not surprising that some methods are more readily applicable to the low concentrations and others to higher concentrations.
2. Different Analytes. Unless you are concerned with highly localized pollution, the number of gaseous pollutants which can build up to detectable levels in the external atmosphere is small. Although Figure 6.1 presents by no means a comprehensive list, it does give an indication of the type of compounds which may be present - simple inorganic gases, a few stable organic compounds, and a number of photochemically generated species. A greater diversity can build up in internal atmospheres, and in particular, many organic compounds. These will require different monitoring techniques.
Responses to Self-Assessment Questions
265
3. Concern over Human Health. You might expect, since internal atmosphere monitoring is largely concerned with human health, that instantaneous concentration measurements (or short-term, time-averaged concentrations) will be important, alongside longer-term, time-averaged values. Longer-term averaged values often predominate for external atmospheres. Different methods may be needed for the two types of determination.
4. Sampling Difficulties. We have not discussed this point before, but you should realize that air currents are usually lower and more stable indoors than in the external environment. Representative samples may be easier to obtain in an internal environment. We will find that both the accuracy and the precision of at least one of the methods we will be discussing is lowered by strong air currents. When a new analytical technique is introduced, there is sometimes a progression of validation, first for internal atmospheres and only subsequently for external atmospheres.
Response 6.3
1. Hydrogen peroxide solution is readily available.
2. The reaction product may be estimated by volumetric titration (e.g. using sodium hydroxide), removing the necessity of spectrometers and well-equipped laboratories.
3. The method is, however, non-specific. Any atmospheric component which will dissolve to form a strong acid or can be oxidized to a strong acid will be included in the final analysis.
For ambient air monitoring, potential interferences are likely to be at lower concentrations than the sulfur dioxide but for other analyses (e.g. flue gases) this may not necessarily be the case.
Response 6.4
Passive sampling techniques will require longer sampling times than the corresponding active sampling techniques, since they rely on gas diffusion. The minimum sampling time is several hours even for internal atmospheres, and so would be of little use in short-term monitoring.
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