Volatile Organic Compounds

Volatile organic compounds (VOCs), such as benzene, toluene, xylenes, trichloroethane, dichloromethane, and trichloroethylene (TCE), are common soil pollutants in industrialized and commercialized areas. One of the more common sources of these contaminants is leaking underground storage tanks. Improperly discarded solvents and landfills, built before the introduction of current stringent regulations, are also significant sources of soil VOCs. Many of organic substances are classified as priority pollutants such as PCBs, polycyclic aromatic, acetaldehyde, formaldehyde, 1,3‐butadiene, 1,2‐dichloroethane, dichloromethane, hexachlorobenzene, etc. In Table 3.2, a list of typical inorganic and organic substances present in industrial effluents is presented.

Heavy Metal Discharges

Several industries discharge heavy metals, 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. As shown in Figure 3.1, many of the pollutants entering aquatic ecosystems (e.g. mercury lead, pesticides, and herbicides) are very toxic to living organisms. They can lower reproductive success, prevent proper growth and development, and even cause death.

Table 3.2 Substances present in industrial effluents.

Source: From Bond and Straub (1974).

However, chromium 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 sulfur and disrupt enzyme function by forming bonds with sulfur 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 catalyze their decomposition.