ABSTRACT
The most fundamental point concerning impurities in the aquatic environment is the distinction between
dissolved
and
particulate
forms. Although this is a simple concept in principle, distinguishing between these forms is not always straightforward (see later in this chapter).Water is a good solvent for many substances, especially inorganic salts, and the vast majority of dissolved impurities in natural waters are of this type. The
total dissolved solids
(
TDS)
value for most fresh waters is in the range of 50-1000 mg/L (g/ m
) of which at least 90% would normally be dissolved salts. For sea water, the TDS level is of the order of 35 g/L, most of which is sodium chloride, with other salts making up nearly all of the rest.
