Formatted Title
Evolution of Hexachlorocyclohexane Concentrations in the Sacco River Sediments (Italy) over a 15-Year Period
Background/Objectives
The Sacco River flows in the Lazio Region, Italy, and the river banks have been used for agricultural purposes for decades. In 2005 exceedances of the threshold values for hexachlorocyclohexane isomers (HCH) were detected in samples of milk produced in the area. The environmental investigation activities performed in the period 2006-2008 identified the presence of HCH in the sediments of the Sacco River over a length of 70 km, through the collection and analysis of sediment samples at 85 locations. A former HCH production plant was present along the Sacco River; activities were implemented in the period 2007-2010 in order to interrupt the input of HCH-impacted sediments into the Sacco River from the plant, but no remediation activities have been directly performed on the Sacco River sediments. The aim of the work was to assess changes in HCH concentrations in the Sacco River sediments in the period 2006-2023, and to collect evidences of naturally-occurring remediation processes which could lead to a more sustainable approach for sediment remediation (compared to a traditional approach based on sediment dredging).
Approach/Activities
In August 2023 ERM analyzed for HCH sediment samples collected at 20 locations close to those of 2006-2008 (in most cases at a distance < 100 m), accessible on foot. It was not possible to collect samples at other areas due to H&S issues and/or the need for accessing private areas. Samples were collected manually in river calm areas by means of a piston sampler, at different depths (0-20/30 cm, 20/30–50 cm), as done in 2006-2008. Sediments were analyzed for HCH isomers by means of analytical method EPA 3550C 2007 + EPA 8270E 2018. Analytical results were compared with the 2006-2008 data to identify changes in HCH concentrations in sediments over an approximately 15-year period.
Results/Lessons Learned
In general, 2023 data showed an appreciable decrease in HCH concentrations compared to 2006-2008 data. With regard to shallow sediment samples (0-20/30 cm), HCH concentrations decreased at 15 sampling locations out of 19 (one sample was not analyzed for the shallow sediment). Considering all the analyzed shallow samples, the average 2023 total HCH concentration was approximately 70% lower than the 2006-2008 total HCH concentration. In 2023 HCH isomers were below the detection limit at 50% of the sampling locations (while in 2006-2008 they were detectable at >90% of the sampling locations). Deep sediment (20/30-50 cm) was present at seven sampling locations only and was collected and analyzed at six locations; HCH concentrations were detectable at five locations out of six and decreased in 50% of the cases compared to 2006-2008 data. Considering all the analysed deep samples, the average 2023 total HCH concentration was approximately 55% lower than the 2006-2008 total HCH concentration. The observed reduction in HCH concentrations may be related to natural HCH degradation and/or deposition of clean sediments coming from upstream, non-impacted areas.