Environmental Distribution and Source Analysis of Organochlorine Pesticides in the Soils of the Sarno River Basin, Southern Italy

The Sarno River Basin (SRB) is among the most polluted in Europe, with contamination deriving from industrial activities, including tanneries and canneries, as well as intensive agriculture and dense urbanization. It is located in the Campania region in Southern Italy, in the southwestern portion of the Campania Plain, between the Somma–Vesuvius volcanic complex to the west and the Lattari Mountains carbonate reliefs to the south.

The SRB is characterized by the presence of high concentrations of some priority organic pollutants, deriving from their use in various processes linked to human activities (e.g., agriculture, industry, mining, vehicular traffic). The soils of the basin, predominantly fine-grained alluvial and volcanic deposits, provide an ideal matrix for the retention of these pollutants, further enhanced by the high organic matter content.

Organochlorine pesticides (OCPs) are synthetic organic compounds extensively utilized in agriculture as insecticides and fungicides during the mid-20th century and, subordinately, in the medical field. These chemicals are among the most common soil contaminants, especially in highly industrialized and anthropized areas; they show a high environmental persistence and are generally characterized by a marked tendency towards bioaccumulation and biomagnification along trophic chains due to their lipophilic character.

The study aims to assess the geochemical-environmental conditions of the SRB, through GIS-based maps and univariate statistical analysis, also establishing the nature of their potential emission sources. For the purpose, over an area of about 500 km² a total of 42 topsoil samples were collected to be analyzed to determine the concentration levels of 24 OCPs.

To investigate the distribution pattern of concentrations, the compounds were grouped into six classes:

• I) dichloro-diphenyl-trichloroethane (DDT) and its isomers and metabolites (DDE, DDD), whose Ʃ₆DDTs concentrations represent on average 68.7% of the total OCPs and ranges from a minimum of 0.021 µg/kg to a maximum of 339 µg/kg;
• II) hexachlorocyclohexane (HCH) isomers (α, β, γ, δ), with Ʃ₄HCHs representing 2.64% and ranging from 0.013 µg/kg to 7.84 µg/kg;
• III) aldrin, dieldrin, and endrin, whose Ʃ₃Drins varies from 0.010 µg/kg to 71.7 µg/kg and constitutes the 6.61%;
• IV) heptachlor, chlordane (α, γ), and nonachlor (cis, trans), constituting on average 1.39% with Ʃ₅Chlors from 0.016 µg/kg to 0.94 µg/kg;
• V) Endosulfan (α, β), and Endosulfan sulfate, whose Ʃ₃Endos varies from 0.010 µg/kg to 19.3 µg/kg and represents 14.5%;
• VI) mirex, methoxychlor and hexachlorobenzene, constituting 6.18%, with total values from 0.010 µg/kg to 7.01 µg/kg.

Because some OCPs tend to degrade over time and the technical pesticides (i.e., DDT, HCH, chlordane, endosulfan) consist of precise percentage of the different molecules, the ratio between the parent compound and its metabolites can be used as pollution sources indicators. This helps identify whether the concentrations are attributable to fresh or historical use of these substances. The analyzed isomeric ratios showed that, although most OCPs are banned, recent applications of pesticide mixtures still contribute to high soil concentrations in some parts of the study area.