Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 253

orthophosphate, but more sensitive; nevertheless, the longer stability of the coloured sol
by the latter method made it more suitable for analysing pond waters for filtrate
orthophosphates. Concentration of filtrable orthophosphate changed with time of storage
at 25°C in polyethylene bottles for up to 48h; samples should ideally be analysed within
1h of collection, although storage for 2-8h does not greatly affect the concentration.
Recently, eutrophication in lakes and reservoirs has become an important problem.
Phosphorus is a critical nutrient aiding the eutrophication process. The principal sources
of phosphorus in environmental waters are agricultural effluents, municipal waste waters,
industrial waste waters, etc.
As the eutrophication of lakes, streams and reservoirs has increased in recent years,
sanitary engineers have become increasingly aware of the widespread use of phosphorus
in the environment and the important role it has in the eutrophication process. Phosphates
have been applied as plant fertilisers for many centuries in one form or another but the
development of synthetic fertilisers has greatly increased the amount applied.
Metaphosphates are often used to treat water used in cooling systems and boilers to
control corrosion. With the banning of alkyl benzene sulphonate for household detergents
in the mid 1960s, phosphate builders were used for synthetic detergents and this greatly
increased the phosphorus content of domestic wastewater. Phosphates occur naturally in
bodies of water and littoral sediments but their increased use and subsequent discharge
into the environment has greatly increased the concentrations in the environment in
recent years. Since phosphorus is an essential nutrient for the growth of aquatic plants
and organisms, the result in many instances had been the overgrowth of algae and aquatic
plants to the point that the usefulness of the body of water for other purposes has been
greatly impaired.
The importance of phosphorus in the eutrophication of surface waters is well known.
Extensive monitoring is needed to provide data on this nutrient for effective water quality
management. An indispensable key to the accomplishment of this objective are methods
for analysing phosphates that are accurate, specific, and reliable.
Most colorimetric determination procedures in common use are based on the formation
of 12-molybdophosphoric acid and its reduction to a blue heteropoly compound. There
are quite a few reductants that can be used for the formation of phosphomolybdenum
blue. A few are used for the high range determinations, such as
vanadomolybdophosphoric acid and amino acid. Stannous chloride has been most widely
used for low range determinations.
2.75.1 Spectrophotometric procedures
2.75.1.1 Methods based on formation of molybdenum blue
Pakalns and Stedman [597] have discussed the effect of surfactants on the
Spectrophotometric determination of phosphate by direct and by solvent