## 3 Results and Discussion
### Pharmaceuticals Extracted from Sludge  
In a previous work dealing with surface water containing matrix components, we have determined which isotopic labelled standard that best compensates for losses caused by ion suppression and sample preparation losses for a specific API ([PERSON] et al., 2016; [PERSON] et al., 2016). The pairing of labelled standard and API can be found in Table S2. The quantification in ug/kg sludge dry matter of a single API in the different sludge samples was calculated as described in Section 2.6.2. In total, 23 APIs were analysed. They have a molecular range from 236 to 734 D and contain 1-3 aromatic rings. A negative charge might be expressed from oxygenated substituents (e.g., diclofenac) and/or positive charge from nitrogen substituents (e.g., metoprolol). The results from the chemical analysis are presented in Table 2 together with various physicochemical parameters. Additionally, wastewater influent and effluent samples were collected at Kristianstad STP and the concentrations of all APIs were analysed and included in Table 2. Finally, results from a previous National Swedish Screening of API contents in sludge from the three Swedish cities Skovde, Stockholm and Umea (2016) are given for comparison at the end of Table 2 as are values from scientific articles on sludge published the last decade. All 23 investigated compounds, except sulfamethoxazole, could be detected and quantified in sludge--with both extraction methods. In total, the content of APIs was 1042 ug/kg using the Espresso method and 5027 ug/kg using the PHWE method, i.e., nearly 5 times higher drug levels were estimated using PHWE. Average standard deviations were 22% for the Espresso method and 17% for the PHWE method. An ANOVA comparison of the two methods showed a significant difference (F\({}_{\text{critical}}\) = 7.7) for 15 of the 23 investigated compounds and is marked in bold text in Table 2. One of the compounds, fluconazole, showed higher concentration with the Espresso method, while the remaining 14 compounds all were higher in the PHWE method. These differences can be explained, despite higher ion suppression as discussed earlier, by a more efficient extraction process using PHWE as it operates at a much higher temperature compared to Espresso. [PERSON] et al. 2010 [PERSON] et al. 2010 [PERSON] et al. 2010 describes this in a clear way writing that: \"Higher temperatures decrease the viscosity of liquid solvents, thus allowing better penetration of the matrix particles and enhancing extraction. In addition to reducing viscosity, high temperatures also decrease the surface tension of the solvent, the solutes and the matrix, allowing the solvent to \"wet\" the sample matrix more thoroughly\". It has also been concluded that the time of operation have a strong influence on extraction efficiency, as stated by [PERSON] et al. : \"The long exposure to the solvent allows the matrix to swell, thus improving penetration of solvent into the sample interstices and contact between solvent and analyte\" [PERSON] et al. (2010). In our study, the PHWE method operates under a longer time period, 13 min, as compared to the Espresso method extracting only for 10 s. As a consequence, more API molecules are likely liberated from the sewage sludge. Turning to individual compounds, _five_ compounds stands out; ciprofloxacin, citalopram, ketoconazole, metoprolol and venlafaxine, which all were detected in concentrations higher than 180 \(\upmu\)g/kg using the _PHWE method_, all other APIs being below 70 \(\upmu\)g/kg (Table 2, Figure 4). We would here like to make the reader aware of the logarithmic scale applied in Figure 4 due to the concentration range of APIs spanning three orders of magnitude  
The concentration found of ketokonazole in sludge using the _PHWE method_ was 3009 \(\upmu\)g/kg, which was 15 times higher as compared to the results from the _Espresso method_.