Heavy metals and inorganic species
Heavy metal discharges
Several industries discharges heavy metals (Table 18.2).
It can be seen that of all of the heavy metals chromium
is the most widely used and discharged to the
environment from different sources. However, it is not
the metal that is most dangerous to living organisms.
Much more toxic are cadmium, lead and mercury.
These have a tremendous affinity for sulphur and
disrupt enzyme function by forming bonds with
sulphur groups in enzymes. Protein carboxylic
acid (-CO2H) and amino (-NH2) groups are also
chemically bound by heavy metals. Cadmium, copper,
lead and mercury ions bind to cell membranes, hindering
transport processes through the cell wall. Heavy
metals may also precipitate phosphate bio-compounds
or catalyse their decomposition.