Is the long-term application of sewage sludge turning soil into a sink for organic pollutants?: evidence from field studies in the Czech Republic

Purpose Long-term microscale field experiments established at four sites in the Czech Republic (since 1996) were used for an assessment of the severity of the wide-scale contamination of treated soils by persistent organic pollutants (POPs) and pharmaceuticals and personal care products (PPCPs) as a result of the long-term regular pollutant load via sewage sludge and farmyard manure applications and for an estimation of the potential environmental risk caused by long-term pollutant inputs to agricultural soils. Material and methods The experimental plots were treated as follows: (i) NPK mineral fertilization (NPK); (ii) sewage sludge (SS1); (iii) sewage sludge applied at three times the rate compared to SS1 (SS2); (iv) farmyard manure (FYM); and (v) untreated control. Except for antibiotics, which showed results for all analyses below the detection limit, all groups of the analyzed compounds showed measurable contents in the treated soils. Results and discussion Among the POPs, the levels of organochlorine pesticides (OCPs) were detected at two locations at levels exceeding the Czech preventive values for their contents in agricultural soils (7.5 mu g/kg for dichlorodiphenyl trichloroethane family, 20 mu g/kg for hexachlorbenzene, and 10 mu g/kg for alpha-hexachlorocyclohexane), regardless of the treatment. Similarly, elevated contents of polycyclic aromatic hydrocarbons (PAHs) were occasionally observed without any substantial relationship to the fertilizer application scenario. Thus, these contaminants are connected with atmospheric deposition in the given areas (PAHs) and their long-term stability (OCPs) even several decades after their ban; the role of the fertilizer composition was negligible. Conclusions The levels of per- and polyfluoroalkylated substances, brominated flame retardants, and synthetic musk compounds tended to increase in the sewage sludge-treated plots, indicating that sewage sludge can contribute to the abundance of these compounds in soil, although the contaminant levels determined do not represent a direct environmental risk. The levels of these contaminants in sewage sludge and sludge-treated soils should be regularly monitored in further research.