Groundwater Contaminants

Abstract

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