ABSTRACT
The major dissolved phase constituents include those substances that are abundant as dissolved ions in natural waters, namely calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), iron (Fe2+), manganese (Mn2+), carbonate species (H2CO3, HCO3-, and CO32-), chloride (Cl-), and sulphate (SO42-). Together with dissolved silica (SiO2), these ions generally account for most of the total dissolved solids (TDS) in subsurface and surface waters. Aluminium (Al3+) may also occur as a dissolved ion, but only under exceptionally acid conditions. Since they occur in natural waters (see Section 1.2.2) these major dissolved constituents are usually not considered as pollutants. Nevertheless, they may cause contamination of soil and water, because they are often released into the environment together with other polluting substances. Consequently, the major dissolved constituents may be an important indicator of pollution when they occur in abnormal concentrations, so knowledge of their behaviour and patterns may help when interpreting the occurrence and dispersal of other, more harmful, pollutants.
