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Groundwater contamination by toxic metals and organic compounds is a serious environmental and public health problem (Crini 39). Many of the common contaminants in wastewater are known to be toxic or carcinogenic.
Common groundwater contaminants include heavy metal ions, aromatic compounds, and dyes. Additionally, heavy metals are not biodegradable and tend to bioaccumulate, leading to various diseases and disorders. Mercury and cadmium are among the most toxic metals and are very damaging to the environment. Additionally, chromium (VI) is a wide-spectrum toxin, as it is toxic to bacteria, plants, animals, and humans.
Organic compounds in groundwater are of several types. Widely used industrial solvents and aromatic hydrocarbons from petroleum products are among the most common organic contaminants found in groundwater (Mackay and Cherry 631). Most groundwater contamination by organic chemicals is a result of leakage, spillage, or improper disposal of water-immiscible organic liquids into the ground.
Chlorinated phenols are of particular concern as they harmful to living organisms and humans even at low concentrations. Their amphiphilic nature allows these compounds to accumulate within the body. As a result, even very low dosages over a period of time can lead to harmful concentrations within the body. This harmful potential – especially to human health – has led to this class of molecules being declared harmful pollutants (Crini 39).
Another major pollutant found in ground water is 2,4,6-trinitrotoluene (TNT), which is a nitro-aromatic molecule widely used in the weapons and mining industries. This compound is persistent in the environment and has been reported to be toxic and mutagenic to various organisms (Crini 39). Synthetic dyes are a similar class of molecules. Most synthetic dyes are – like natural dyes and TNT – made of an aromatic backbone, and highly toxic like other aromatic compounds. Many aromatic compounds show carcinogenic behaviour in addition to their toxicity. Unlike their natural counterparts, synthetic dyes are not biodegradable. This results in them being persistent in the environment. Dyes, by definition, are water-soluble and hence easily get washed into the groundwater. Synthetic dyes are used extensively in the textile, paper printing, and plastic industries. They are also used as additives in petroleum products (Crini 39).
The most common means of remediation for contaminated groundwater is the pump-and treat method. In this method, the groundwater is extracted by means of wells or drains. This is followed by treatment of the water prior to disposal or reintroduction to the aquifer (Mackay and Cherry 631). This method shows initial decrease in contaminant concentration; progressive treatment leads to a levelling of the contaminant concentration. This makes it unlikely to achieve stringent standards that conform to health and safety requirements. Additionally, such treatment methods are very expensive and time-consuming (Mackay and Cherry 631). Hence, it is imperative that wastewater be treated before it can contaminate groundwater. Current areas of research involve the removal of metal ions or the degradation of organic metals in wastewater (Crini 40). This is sometimes achieved by adsorbents, binding sites, or by mediated oxidation.
Works Cited
Crini, Gregorio. “Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment.” Progress in Polymer Science, vol. 30, 2005, 38-70.
Mackay, Douglas M. and Cherry, John A. “Groundwater contamination: Pump-and-treat remediation.” Environmental Science and Technology, vol. 23, no. 6, 1989, 630-636.
