Isotopic fingerprinting as an effective tool for polluter apportionment in environmental crimes involving groundwater

One pillar of the protection of groundwater established by the EU legislation is the “polluter pays principle”. Following this principle, the costs for the remediation of contaminated sites must be in charge of the responsible of the environmental crime. Compound Specific Isotope Analysis (CSIA), also known as “isotopic fingerprinting”, is a robust tool to apportion the source of groundwater contamination and eventually the polluter. The isotopic composition of the contaminant molecule may reflect the production process of a compound or the origin of the raw materials used in the production. Here we present the effective and decisive application of isotopic fingerprinting of carbon stable isotopes in the molecule of chlorinated hydrocarbons (chlorinated ethenes PCE-Perchloroethylene and TCE-Trichloroethylene) for the source apportionment in two contaminated sites in Italy, namely Ferrara (Emilia-Romagna region, Northern Italy) and Bussi sul Tirino (Abruzzo region, Central Italy). In both cases, industrial wastes from a production of chloromethanes, using methane and chlorine, were disposed illegally in unlined dumps resulting in a severe contamination of groundwater. The companies responsible for the contamination are different in the two sites but the production process is the same, resulting in a similar isotopic signature of the wastes. In both cases, the isotopic fingerprinting was critical to identify the chlorometane production as the source of contamination among other possible sources, despite two different hydrogeological settings (a large alluvial plain in the Ferrara site and a narrow valley with macroclastic alluvial deposits and travertines in the Bussi site). In both cases, PCE and TCE showed strongly depleted values of δ¹³C (isotopic ratio of the fraction of ¹³C respect to ¹²C isotopes of carbon) ranging between  -87 and -65‰ for PCE and between -79 and -64‰ for TCE. The very depleted isotopic values are related to the use of methane in the production process instead of coal, this last one being commonly adopted in the synthesis of PCE and TCE for commercial use (e.g. for laundry of textiles or metal degreasing). The groundwater contamination in the two sites had serious implications in terms of sanitary risk due to vapour intrusion into residential buildings (Ferrara site) or water ingestion by local citizens (Bussi site) from a public water supply well field site serving about 300.000 inhabitants and affected for more than 20 years by the contamination (from the opening in 1984 to the decomissioning in 2007). In both cases, complex legal issues arose either below penal or civil jurisdiction and the isotopic fingerprinting was used as the most relevant proof in order to identify the polluters.