Can compost applications affect metal and PAH contents in Mediterranean agricultural soils?

The effects on soil inorganic and organic pollution, due to long-term compost applications in Mediterranean agricultural soils, were investigated. Total and available metal (Cd, Fe, Mn, Ni, Pb, Zn) and polycyclic aromatic hydrocarbon (17 PAHs) concentrations were evaluated for three years, in two agricultural fields of CRA (Consiglio per la Ricerca e la Sperimentazione in Agricoltura) of Campania Region (Southern Italy), one in open-field and one in greenhouse. At each field, compost was annually incorporated into the soil to a depth of 20-25 cm, at the doses of 15, 30 and 45 t/ha (on dry weight basis). Three plots were amended with each dose and three plots not amended were used as controls. The soils of the two fields showed different metal baseline concentrations and comparable PAH values. Along the time, the differences in metal and PAH concentrations between sites and among samplings were wider than the differences attributable to the treatments. However, after three consecutive compost applications, treatments increased available metal concentrations rather than total concentrations, and the effects were more evident in soil under greenhouse, where higher available concentrations of Cd, Fe, Mn, Pb and Zn were found in the amended plots. At the open-field, after the last compost application, only available Zn increased. Compost amendment did not show long-term effects on soil total PAH concentrations at the investigated fields