PARAFAC Modeling of Fluorescence Excitation−Emission Spectra of Fish Bile for Rapid En Route Screening of PAC Exposure

Abstract

Polycyclic aromatic compound (PAC) metabolites in fish bile can be used as biomarkers for recent environmental exposure to PACs. Here, a novel method for rapid screening of nonhydrolyzed fish bile is presented. The method is based on excitation-emission fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) and may constitute an alternative to fixed wavelength fluorescence and synchronous fluorescence spectroscopy (SFS). PARAFAC was applied to excitation-emission matrices (EEMs) of bile samples of shorthorn sculpins and European eels collected in Greenland and Denmark. The EEMs were decomposed into a four-factor PARAFAC model. The comparison of the PARAFAC factors with the EEMs of PAC metabolites and amino acids suggests that two factors are related to PAC metabolites and two correspond to fluorescent residues of tryptophan and tyrosine in bile proteins. A new standardization procedure based on the mean of the scores for the biological factors was used to correct for feeding status and sample dilution and, upon such normalization, the score plots of PARAFAC factors showed a clear distinction between exposed and nonexposed fish. A good correlation was found between the factor scores and 1-hydroxypyrene equivalents determined by SFS for high contamination levels, whereas the sensitivity was better for the EEM method.