PREDICTION OF SOIL PCBs CONTENT IN A HISTORICALLY CONTAMINATED SITE OF THE SIN OF TARANTO (SOUTHERN ITALY)

Soil contamination is a widespread problem in the World, especially in the more developed and industrialized Countries. In Italy, about 12000 potentially contaminated sites were recorded in 2004 by the regional environmental bureaus and by the National Environmental Protection Agency (APAT), now Italian National Institute for Environmental Protection and Research (ISPRA). Fifty-eight of these sites, subsequently reviewed and reduced to forty-one, have been recognised by the Italian Ministry of the Environment, Land and Sea (MATTM) as Sites of National Interest (SIN), on the basis of their characteristics, the quantity and hazardousness of pollutants, the extent of the health and ecological risks, and the detriment to cultural and environmental heritage. A site of particular attention, because of the high risk of soil contamination, includes the SIN of Taranto (Apulia Region, Southern Italy) and a surrounding area of about 564 km2 (Area di Crisi Ambientale). Soil contaminants on this site are both organic or inorganic elements and compounds. The main organic contaminants include polychlorinated biphenyls (PCBs), dioxins (polychlorinated dibenzo-p-dioxins, PCDDs), furans, polycyclic aromatic hydrocarbons (PAH) and volatile compounds, while the main inorganic contaminants are heavy metals. Soil reclamation of these compounds needs careful analysis in order to define their concentrations and spatial distribution. Conventional laboratory analyses, although useful and practically irreplaceable for a precise and detailed evaluation of soil contaminants, are costly and time-consuming. Thus, there is a need to assess alternative, rapid and cost-effective methods for the characterization of these contaminants, to use as substitutive or integrative of conventional laboratory analysis. In recent years, reflectance spectroscopy, that is the ratio of the spectral radiant flux reflected from a soil surface to the spectral radiant impinging on it in the visible-Near Infrared (vis-NIR) domain (350-2500 nm), has proved to be a useful technique for the prediction of various soil pollutants and other soil properties. It is based on the principle that the characteristics of radiation reflected from a material are a function of the chemical and physical properties of the material, thus, observations on soil reflectance can provide information on its properties. To date, many studies pertaining to the use of reflectance spectroscopy for the prediction of soil contaminants have been focused on heavy metals. Some research has regarded organic contaminants and limited research has ever covered polychlorinated compounds and, in particular, PCBs. Therefore, a preliminary study was carried out in a study area to assess the capability of vis-NIR spectroscopy, combined with Partial Least Square Regression (PLSR) analysis, for the prediction of PCBs and extractable organic halogen content (EOX), which is an expression of the total content of halogen in organochlorine compounds, including the PCBs. These compounds are very dangerous for both environment and human health, because of their toxicity and tendency to bioaccumulate; they tend to persist for long periods in the environment and they can easily cycle between air, water, and soil because of their resistance to acids, bases, oxidation and hydrolysis. The investigated area, contiguous the SIN of Taranto, falls within the so-called area "PIP" (Production Settlement Plan) of the municipality of Statte and specifically, it regards an area outside the ex-MATRA, a former engineering industry, within 100 m from it. For fourteen years (from 1984 to 1998) the ex-MATRA has been involved in the maintenance of electrical transformers and, during its activity, significant quantities of waste containing PCBs have been stored in the soil, in a totally inadequate way, causing soil and subsoil contamination. Diffuse vis-NIR reflectance was measured in the laboratory on twenty-eight soil samples for the determination of eighteen PCBs congeners (i.e. twelve dioxin-like PCBs and six "indicators" PCBs non-dioxin-like), their sum (PCBs18), and EOX, previously determined through conventional laboratory analysis. Using PLSR, after pre-processing the reflectance spectra, excellent models were calibrated for the prediction of PCBs18 (R2adj = 0.91; RPD = 3.47), EOX (R2adj = 0.909; RPD = 3.40) and Hepta-CB (R2adj = 0.897; RPD = 3.24), while a good model was calibrated for Penta-CB (R2adj = 0.798; RPD = 2.27). The combined analysis of the PLSR regression coefficients and the Variable Importance in the Projection (VIP) allowed determining important wavelength for the prediction of the investigated variables. The results of the present study demonstrated that vis-NIR reflectance spectroscopy, coupled with PLSR, can be considered a promising, useful method for the rapid and low-cost prediction of PCBs18, as well as of Hepta-CB and Penta-CB congeners and EOX.