Sampling and analysis of environmental media

The ranges of concentration which may be commonly encountered in environmental samples are summarized in Table 8.2. These data should assist in determining the necessary sample size, or the optimum analytical method. 

In high volume sampling air is drawn through large (20 cm X 26 cm) glass fibre filters at a rate of some 2000 dm min L Sampling times are rather prolonged (usually 24 h) to overcome the lead blank of the filter material. It is rare to analyse the whole of these filters for lead usually a square (about 3 cm X 3 cm) or strip is cut from the filter for lead analysis. 

polluted, or in mineralized areas Vegetation, background (dry weight) Vegetation, polluted (dry weight) Small mammals (dry weight) Tetraalkyllead in air 

Lead may exist in many forms in waters, both dissolved and suspended. As indicated in Chapter 3 there is no clear cut-off point between dissolved and suspended material and the arbitrary standard of a 0.45 jJim membrane filter is usually adopted to separate filterable and non-filterable lead. 

Filterable metal may be analysed directly by AAS. Except in highly polluted waters, the use of flameless techniques will be necessary and research has shown that reliable results are obtained only by use of the method of standard additions to minimize matrix interferences. The sensitivity of flame methods may be enhanced if the lead is preconcentrated by extraction with ammonium pyrolidine dithiocarbamate in methyl isobutyl ketone (APDC/MIBK). This also eliminates many interferences, but prior heating of the sample with acid may be necessary to release complexed lead [8]. The use of ASV for analysis of filterable lead in water is rather more complex than might appear at first sight, since ASV is only sensitive to labile (weakly-bound) lead, and not to that strongly bound in complexes. Reduction of the sample pH by addition of an appropriate acid may cause release of most of the lead enabling analysis to be carried out. In general, AAS is to be preferred. 

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