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Hazardous Chemicals Handbook 2 Episode 11

Tham khảo tài liệu 'hazardous chemicals handbook 2 episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | POLLUTION MONITORING STRATEGIES IN INCIDENT INVESTIGATION 389 Generally sampling of waterways should be at the fastest flowing part of the stream river usually mid-depth unless the contaminant is less dense than water and could float or is more dense and could accumulate near the river bed. For lakes representative samples should be taken near to the inflow outflow and other locations. If two phases are present both may require sampling. Sample preservation by refrigeration pH adjustment elimination of light filtration and extraction may be important. Table 10.34 summarizes the information to be recorded during an investigation. A code of practice for the identification of potentially contaminated land and its investigation is given in British Standard DD 175 1988. Consideration should be given to the application of appropriate quality control and quality assurance procedures such as those advocated by good laboratory practice or ISO 17025 to ensure the sampling the analysis and interpretation reporting of data are robust since results will dictate action and may be subject to scrutiny by third parties. Duplicate samples may need to be retained for disclosure to third parties. There may be legal requirements to notify results to relevant authorities. 11 Radioactive chemicals The main chemical elements are listed in Chapter 18. Each comprises a nucleus of positively-charged protons and neutral neutrons orbited by negative electrons. The mass number A is given by A Z N where Z is the number of protons or atomic number N is the number of neutrons. Atoms with the same value of Zbut different values of A are isotopes Table 11.1 . Many isotopes are stable but others are naturally or artificially radioactive i.e. their atomic nuclei disintegrate emitting particles or radiation. This changes the nuclear structure of the atom and often results in the production of a different element. Table 11.1 Nuclear composition of selected istopes Element Symbol Atomic number Protons .