Assessing emerging and priority micropollutants in sewage sludge: environmental insights and analytical approaches

Abstract

The application of sewage sludge (SS) in agriculture, as an alternative to manufactured fertilizers, is current practice worldwide. However, as wastewater is collected from households, industries, and hospitals, the resulting sludge could contaminate land with creeping levels of pharmaceuticals, pesticides, heavy metals, polycyclic aromatic hydrocarbons, and microplastics, among others. Thus, the sustainable management of SS requires the development of selective methods for the identification and quantification of pollutants, preventing ecological and/or health risks. This study presents a thorough evaluation of emerging and priority micropollutants in SS, through the lens of environmental insights, by developing and implementing an integrated analytical approach. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction method, coupled with gas chromatography and liquid chromatography, was optimized for the determination of 42 organic compounds. These include organophosphorus pesticides, organochlorine pesticides, pyrethroid pesticides, organophosphate ester flame retardants, polybrominated diphenyl ethers, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. The optimization of the dispersive-solid phase for clean-up, combined with the optimization of chromatographic parameters, ensured improved sensitivity. Method validation included assessments for recovery, reproducibility, limit of detection (LOD), and limit of quantification (LOQ). Recoveries ranged from 59.5 to 117%, while LODs ranged from 0.00700 to 0.271 µg g^-1. Application of the method to seven SS samples from Portuguese wastewater treatment plants revealed the presence of sixteen compounds, including persistent organic pollutants. The quantification of α-endosulfan, an organochlorine pesticide, was consistently observed in all samples, with concentrations ranging from 0.110 to 0.571 µg g^-1. Furthermore, the study encompasses the analysis of agronomic parameters, as well as the mineral and metal content in SS samples. The study demonstrates that the levels of heavy metals comply with legal limits. By conducting a comprehensive investigation into the presence of micropollutants in SS, this study contributes to a deeper understanding of the environmental and sustainable implications associated with SS management.

Keywords: Flame retardants; Micropollutants; PAHs; PCBs; POPs; Pesticides; QuEChERS; Sewage sludge.

Fig. 1

Color removal with different d-SPE mixtures applied to samples A and B in the first set of clean-ups. The d-SPE tube contained a typical mixture of 150 mg of MgSO₄, 50 mg of PSA, and 50 mg of C18 with A-I — 3 mg of CB; A-II — 10 mg of CB; A-III — 20 mg of CB; A-IV — 20 mg of CB and 10 mg of Z-Sep; A-V — 50 mg of CB; B-I — 3 mg of CB; B-II — 6 mg of CB; B-III — 10 mg of CB; B-IV — 10 mg of CB and 10 mg of Z-Sep; B-V — 50 mg of CB

Fig. 2

RE (%) (a) and ME (b) obtained with the different formulations of d-SPE sorbents (VI–IX) used in the clean-up of the sludge mixture. The d-SPE tube contained a typical mixture of 150 mg of MgSO₄, 50 mg of PSA, and 50 mg of C18 combined with VI – 10 mg of CB and 10 mg of Z-Sep; VII – 5 mg of CB and 15 mg of Z-Sep; VIII– 5 mg of CB and 20 mg of Z-Sep; IX – 5 mg of CB and 25 mg of Z-Sep