Hydrocarbon contamination in waters and sediments of the Pertusillo freshwater reservoir, Val d'Agri, Southern Italy

In order to determine hydrocarbon contamination of drinking water in the Southern Italian region of Basilicata and to identify its source, we sampled water and subaqueous surface sediments from Lake Pertusillo, a freshwater, highly dynamic, artificial reservoir located entirely within the largest oil field in Italy (Val d'Agri, Basilicata). Monitoring by the Basilicata Agency for Environmental Protection (ARPAB) is infrequent and insufficient to determine temporal variability of water quality. In the present study, metals and hydrocarbons were identified and quantified in 4 water samples and in 10 subaqueous grab sediment samples. Our data were integrated with other 7 sediment samples collected by ARPAB. Total hydrocarbon concentrations ranged from 97 to 6458 mu g/1 in water samples and from 6.6 to 559 mg/kg in sediment samples, with values exceeding the threshold limits of Italian legislation, when present. The areal distribution of hydrocarbons in subaqueous surface lake sediments reveals a strong asymmetry between the northeastern and southwestern subaqueous lake margins. Higher levels of hydrocarbons were recorded along the northeastern side of Lake Pertusillo, at the mouth of stream tributaries and of the Agri River. 25 oil-producing wells are located on the northeastern side of Val d'Agri. River runoff represents thus an important pathway for hydrocarbons in the freshwater reservoir. Hydrocarbon concentrations along the southwestern subaqueous side of the reservoir were marked by lower values; the corresponding subaerial margin is more populated and urbanized than the northeastern one, with no oil-producing operations. There is evidence that urban runoff of street or agriculture waste is the less important hydrocarbon source, since the northeastern industrialised subaerial margin is much less populated and urbanized than the opposite one. Temporal high variability of water quality, asymmetric hydrocarbon distribution in sediments of subaqueous lake margins, and the occurrence of well-defmed hydrocarbon-rich beds, indicate that most hydrocarbon deposition in Pertusillo reservoir was episodic, from the catchment basin trough northeastern lake tributaries and Agri River. This scenario is compatible with sources mainly related to oil industry of Val d'Agri.