Groundwater Contaminants

Aquifer contamination occurs following a release of chemical compoundsin groundwater exploited for human consumption which poses a health risk to theconsumers. There is a variety of anthropogenic causes of contamination, spanningfrom discharge of wastewater to the ground, to industrial or mining activities, fromaccidental spills to agricultural activities. The wide range of sources of contamina-tion is reflected on the extremely broad and diverse set of contaminants, includingbiological, chemical and radioactive constituents. This chapter is dedicated to thechemical, physical and toxicological classification and characterization of chemicalcontaminants. Chemically, compounds can be broadly categorized as inorganic (e.g.,metals, certain anions and cations, metalloids) or organic (i.e., containing at least oneorganic carbon). The main organic groups are described, including hydrocarbons,halogenated hydrocarbons, phenols, chlorobenzenes, nitroaromatic compounds, anda class of recently identified hazardous compounds, named emerging organic con-taminants, is presented. A physical characterization of contaminants is essential forthe prediction of their behavior once they are released to the ground and migrateeither across the unsaturated zone towards the saturated medium, or directly in theaquifer. The most important physical characteristics affecting contaminant migrationand illustrated in this chapter are physical state, miscibility with water, mass density,solubility in water and volatility. Finally, a toxicological classification of contami-nants is provided, which categorizes them as threshold or non-threshold compounds,depending on whether their health effects are manifested only above a certain concen-tration or are independent of the exposure level (i.e., they induce genetic mutationswhich lead to cancer development). This classification lays the foundations for thedefinition of threshold concentration values in drinking water prescribed by nationaland international health agencies and regulatory authorities. A comparison of theguideline or regulatory values defined by the WHO, the US-EPA, the EU and theItalian law is provided.