acidic in scrubbers through the absorption of SOx, creating sulfuric acid (Ülpre et al., 2013; Koski et al., 2017). OL-scrubbers use the natural alkalinity of seawater to neutralize the acids, whereas CL-scrubbers use either seawater or freshwater that is re-circulated in the scrubber together with an alkaline solution to neutralize the accumulating acids (Linders et al., 2019). A certain fraction of the re-circulated water is drained off (bleed-off water), commonly stored on board after a treat- ment step and finally discharged into the sea. The average discharge water volumes are 90 m3/MWh from OL-operation and 0.45 m3/MWh from CL-operation (Hermansson et al., 2021). Scrubbers do not only remove SOx from the exhaust gas but also other combustion (pyrogenic) and fuel derived (petrogenic) species like heavy metals, particularly vanadium (V) and nickel (Ni), and polycyclic aromatic hydrocarbons (PAH). PAH are known to have toxic, mutagenic, and/or carcinogenic properties and are ubiquitous in environmental samples (Chen et al., 2021). PAH molecules consist of two or more fused benzene rings, and the high-molecular weight PAH (e.g. benzo[a]pyr- ene) are more toxic. PAH bio-accumulate particularly in biological systems due to their high lipid solubility. The scrubber discharge water can hence be harmful to the marine environment, giving rise to concern (Ytreberg et al., 2019; Endres et al., 2018; Linders et al., 2019; Her- mansson et al., 2021; Thor et al., 2021; Marin-Enriquez et al., 2023). Frequently studies are limited to the 16 US EPA PAH (Keith, 2015) but previous ones on scrubber discharge water have indicated the presence of more than the 16 EPA PAH that contribute significantly to the mixture toxicity (Koski et al., 2017, Linders et al., 2019, Schmolke Table 1 PAH standard compounds used in this study, their abbreviations and suppliers. Asterisked (*) compounds cannot be sufficiently ionized with atmospheric pressure laser ionization (APLI); m/z: mass-to-charge ratio. No PAH Substance Abbreviaon m/z Suppl. No PAH Substance Abbreviaon m/z Suppl. 1 Naphthalene Nap 128 1 45 Benzo[a ]?uoranthene BaFlu 252 3 2 2-Methylnaphthalene 2-Mnap 142 1 46 Benzo[e ]pyrene BePyr 252 1 3 2,6-Dimethylnaphthalene 2,6-DMNap 156 2 47 Benzo[a]pyrene BaPyr 252 1 4 1,3-Dimethylnaphthalene 1,3-DMNap 156 3 48 Perylene Per 252 1 5* Acenaphthylene* Acy 152 1 49 3-Methylcholanthrene 3-MCho 268 1 6 1,8-Dimethylnaphthalene 1,8-DMNap 156 6 50 6-Methylbenzo[a ]pyrene 6-MBaPyr 266 1 7 Acenaphthene Ace 154 1 51* Indeno[1,2,3-cd ]?uoranthene* Ind-1,2,3-cdFlu 276 3 8 2,3,6-Trimethylnaphthalene 2,3,6-DMNap 170 3 52 Dibenzo[a,j ]anthracene DBajAnt 278 3 9 Fluorene Fl 166 1 53 Indeno[1,2,3-cd]pyrene Ind-1,2,3-cdPyr 276 1 10 1-Methyl?uorene 1-MFl 180 1 54 Dibenzo[a,c ]anthracene DBacAnt 278 6 11 Phenanthrene Phe 178 1 55 Dibenzo[a,h]anthracene DBahAnt 278 1 12 Anthracene Ant 178 1 56 Benzo[b ]chrysene BbChr 278 3 13 3-Methylphenanthrene 3-MPhe 192 3 57 Benzo[ghi]perylene BghiPer 276 1 14 2-Methylphenanthrene 2-MPhe 192 3 58 Anthanthrene Anthan 276 1 15 9-Methylphenanthrene 9-MPhe 192 1 59 Naphtho[1,2-b ]?uoranthene N-1,2-bFlu 302 5 16 1-Methylphenanthrene 1-MPhe 192 3 60 Naphtho[1,2-k ]?uoranthene N-1,2-kFlu 302 5 17 9-Methylanthracene 9-MAnt 192 1 61* Naphtho[2,3-j ]?uoranthene* N-2,3-jFlu 302 5 18 Fluoranthene Flu 202 1 62 Naphtho[2,3-b ]?uoranthene N-2,3-bFlu 302 5 19 9,10-Dimethylanthracene 9,10-DMAnt 206 1 63 Dibenzo[a,e ]?uoranthene DBaeFlu 302 1 20 Pyrene Pyr 202 1 64 Dibenzo[a,l ]pyrene DBalPyr 302 1 21 Retene Ret 234 4 65 Naphtho[2,3-k ]?uoranthene N-2,3-kFlu 302 5 22 2-Methyl?uoranthene 2-MFlu 216 3 66 Naphtho[2,3-e ]pyrene N-2,3-ePyr 302 5 23 1-Methyl?uoranthene 1-MFlu 216 3 67 Dibenzo[a,e ]pyrene DBaePyr 302 1 24 3-Methyl?uoranthene 3-MFlu 216 3 68 Coronene Cor 300 3 25 Benzo[a ]?uorene BaFl 216 3 69 Naphtho[2,3-a ]pyrene N-2,3-aPyr 302 5 26 Benzo[b ]?uorene BbFl 216 3 70 Dibenzo[a,i ]pyrene DBaiPyr 302 1 27 1-Methylpyrene 1-MPyr 216 1 71 Dibenzo[a,h ]pyrene DBahPyr 302 1 28 7H -Benzo[c ]?uorene BcFl 216 1 29 Benzo[ghi ]?uoranthene BghiFlu 226 1 30 Benzo[c ]phenanthrene BcPhe 228 1 No Heterocyclic Substance m/z Suppl. 31 Benzo[a]anthracene BaAnt 228 1 1 Benzofuran 118 4 32* Cyclopenta[cd ]pyrene* CycdPyr 226 1 2 2-Methylbenzofuran 132 4 33 Triphenylene Tri 228 3 3 Benzothiophene 134 2 34 Chrysene Chr 228 1 4 Quinoline 130 4 35 6-Methylbenzo[a ]anthracene 6-MBaAnt 242 1 5 2-Methylquinoline 144 4 36 2-Methylchrysene 2-MChr 242 3 6 Indole 117 4 37 5-Methylbenzo[a ]anthracene 5-MBaAnt 242 5 7 Dibenzofuran 168 4 38 6-Methylchrysene 6-MChr 242 3 8 Dibenzothiophene 184 4 39 5-Methylchrysene 5-MChr 242 1 9 Acridine 179 4 40 4-Methylchrysene 4-MChr 242 3 10 Naphtho[2,3-b ]thiophene 184 2 41 Benzo[b]fluoranthene BbFlu 252 1 11 4-Methyldibenzo[b,d ]thiophene 198 2 42 Benzo[k]fluoranthene BkFlu 252 1 12 Carbazole 167 4 43 7,12-Dimethylbenzo[a ]anthracene 7,12-DMBaAnt 256 1 13 2,3-Dimethyldibenzo[b,d ]thiophene 212 2 44* Benzo[j ]?uoranthene* BjFlu 252 1 14 Benzo[b]naphtho[1,2-d ]thiophene 234 2 16 EPA PAH Pairs of coeluon in GC-APLI-MS * not ionized by APLI Coeluon in GC-MS Supplier 1 2 3 4 5 6 Single standard soluons, Fluka, Germany Single pure substances, Prof. Jan Andersson, Instute of Inorganic and Analycal Chemistry, University of Münster Custom-made PAH-mixture, Chiron, Norway Single standard soluons, Neochema, Germany Single standard soluons, Dr. Ehrendorfer, Germany Single standard soluons, Chiron, Norway C. Achten et al. Marine Pollution Bulletin 208 (2024) 116790 2