Pharmaceuticals and personal care products in different types of sewage sludge

Resumen

Emerging pollutants (EPs), those for which there is no clear and specific legislation, constitute a large group of chemical compounds used in human and animal health. It includes pharmaceutical compounds and personal care products (PPCPs); medicines, clean-up products, cosmetics, fragrances and hormones both natural and synthetic. These compounds have been off the radar of environmental science, which is more concerned with apolar, toxic, persistent and bioaccumulative pollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorophenyls (PCBs) and dioxins. However, the development of new methods of analysis has made it possible to warn of the presence of these EPs, mainly due to the aggravation of the problems of storage and disposal of sludge from the Wastewater Treatment Plants (WWTPs) due to the increase in the volume of treated water and, consequently, the volume of sludge to be managed. The trend in urban waste management is towards recycling, with special emphasis on agricultural use as a fertilizer or soil amendment. However, the presence of PPCPs has raised enormous concern about the possible adverse effects on humans and wildlife, since despite their low concentrations in the environment (ng L-1 or µg L-1), there is evidence that at these levels they can produce serious damage to humans and ecosystems. It has been demonstrated that the purification procedures are not completely effective since the main objective of the WWTPs is the elimination of contaminants above mg L-1. In fact, many of these compounds have physical-chemical properties that favour their adsorption to waste sludge that is used as agricultural soil fertilizer to minimize the use of chemical fertilizers and improve soil quality. Studies in several WWTPs determined an increase in the discharge of pharmaceutical products and pesticides, among other compounds, into our waters and finally into rivers. The research developed in this Doctoral Thesis began with a review of the different analytical approaches for the determination of EPs, including PPCPs, in environmental matrices. Sample preparation techniques and instrumental methods proposed to evaluate PPCPs in sewage sludge were reviewed. Three main steps were examined: extraction, clean-up, and analysis. Sample preparation is critical as the compounds of interest are typically found at low concentrations in such complex matrices. In view of this, an analytical method was developed and validated for the simultaneous determination of 14 PPCPs in sewage sludge. The optimal experimental conditions for sample pre-treatment were established. As a result, microwave-assisted extraction (MAE) was combined with an in-situ clean-up stage and a filtration step. A combination of MilliQ®/MeOH 95:5 (v/v) water adjusted to pH 9 proved to be the optimal solvent mixture for the extraction. The instrumental part of the method presents an important novelty based on a fully automated sample preparation for the analysis of PPCPs. It consisted of a Direct Immersion Solid Phase MicroExtraction followed by On-fiber Derivatization coupled to Gas Chromatography – Mass Spectrometry (DI-SPME-On-fiber derivatization - GC-MS). The analytical method has been validated following international validation guidelines with excellent results in terms of accuracy (precision and veracity), sensitivity (limits of detection and quantification), selectivity, linearity and robustness. This analytical method is an ecological alternative for many routine analysis laboratories worldwide. In addition, the method was applied to different samples generated in both thermal hydrolysis (TH) and anaerobic digestion (AD) pilot scale plants. In thermal hydrolysed samples, the highest concentration values corresponded to salicylic acid (1,000 ng g-1). However, the highest concentrations of the contaminants of interest after AD corresponded to naproxen (9,355 ng g-1). In the case of implementing a TH stage prior to digestion, both salicylic acid (10,045 ng g-1) and triclosan (762 ng g-1) showed the highest concentrations in the TH influent. On the other hand, salicylic acid (4,267 ng g-1) and triclosan (417 ng g-1) were also the contaminants with the highest concentrations after AD. Finally, the last chapter of the Doctoral Thesis corresponds to a developed method for the simultaneous determination of 60 PPCPs (e.g., antibiotics, analgesic/non-steroidal anti-inflammatory drugs, hormones, lipid regulators, hormones, among others) in dewatered digested sludge samples. Sample pre-treatment consisted of ultrasound-assisted extraction (UAE) was combined with an in-situ clean-up stage and a filtration step. A combination of MilliQ® water/MeOH 95:5 (v/v) water adjusted to pH 9 was used as solvent mixture for the extraction. Instrumental part of the method consisted of an online Solid Phase Extraction (SPE) coupled Ultra-High-Pressure Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS). Excellent results were observed in terms of limit of detection and quantification for 31 compounds of interest. In these sludge samples, the highest concentrations corresponded to enrofloxacin (12,875 ng g-1), 4-hydroxybenzoic acid (4,027 ng g-1), sulfamethoxazole (1,267 ng g-1), and clofibrate (1,090 ng g-1).