A feature of this analytical scheme is the marked reliance on infrared spectrometry and titrimetry. The
former is particularly applicable to the qualitative characterization of unknown organic materials whilst
titrimetry provides a rapid, precise and cheap means of quantitative analysis. The routine titrimetric
determination of water, total acid (acid number) and total base (base number) forms a significant
proportion of the work load in some analytical laboratories. It is instructive to consider how other
techniques might have been applied to the solution of this particular problem, e.g. NMR spectrometry
and chromatography.
The Assessment of the Heavy Metal Pollution in a River Estuary
Example 12.2.3
Many heavy metals (e.g. Pb, Tl, Zn, Hg) which are known poisons are present in industrial wastes. The
effluents from most factories, after some degree of pretreatment, are discharged into rivers.
Atmospheric contaminants from smelting works or combustion processes eventually enter the natural
drainage system as 'fall out', and are carried into the rivers. It is probable that the deposition of
sediments and the higher pH of marine water, which leads to precipitation, results in a build-up of the
heavy metal pollutants in the river estuary. An assessment of this build-up is essentially an analytical
problem.
The natural levels of heavy metal pollutants in the environment vary considerably, but are generally low
(less than 100 ppm). In the cases of lead and mercury very low levels are normal (less than 1 ppm) and
concentrations of a few parts per million in food are known to be dangerous. The analytical methods
used must, therefore, be able to cope with concentrations of hundreds of ppm and have a potential
sensitivity well below 1 ppm. The characteristics of a number of techniques which will meet these
requirements are summarized in Table 12.3. The practical part of the problem, as always, starts with
sampling. A systematic programme of sampling, including the bed and banks of the river as well as the
water, and estuarine life would generate an enormous number of samples, especially as the analysis of
repetitive samples taken over a year would be essential to give the survey perspective. Although such
surveys have been attempted, various 'short cut' expedients have been devised. An important example of
such a 'short cut' is based on an assessment by marine biologists, who say that it is the degree to which
pollutants enter the food chain which is even more important than the overall level of pollution. Thus,
analysis concentrated on 'pollution indicators' such as shellfish which are low down in the food chain
will serve as a measure of the overall build-up of pollutants in estuarine life. To this end, extensive
analyses of limpets and mussels have been made. Samples were taken from various parts of the estuary
at different depths. Careful note was taken of the materials supporting the shellfish. In addition, similar
samples were obtained from 'open sea' sites to provide a comparison with the estuarine samples and an
indication of the natural levels. Other important pollution indicators for this type of site are