Biliary Fish Proteomics Applied to Environmental Contamination Assessments: A Case Study in Southeastern Brazil

Variability of Bile Baseline Excitation-emission Fluorescence of Two Tropical Freshwater Fish Species

The quantification of pollutant metabolites in fish bile is an efficient approach to xenobiotic pollution monitoring in freshwaters since these measurements directly address exposure. Fluorescence excitation-emission matrix spectroscopy (EEMS) has demonstrated to be a highly specific and cost-effective technique for polycyclic aromatic hydrocarbon (PAH) and PAH-metabolite identification and quantification. EEMS ability to quantify these compounds strongly depends on the intensity and variability of the bile baseline fluorescence (BBF). We found large differences in BBF among Aequidens metae (AME) individuals and of these with Piaractus orinoquensis (PIO). Moreover, BBF was large enough that solvent dilutions of over 1:400 were needed to avoid inner filter effects. We used parallel factor analysis (PARAFAC) to model the intra- and inter-species BBF variability. PARAFAC successfully decomposed the EEMS set into three fluorophores present in all samples, although in concentrations spreading over ~ 3 orders of magnitude. One of the factors was identified as tryptophan. Tryptophan and Factor 2 were covariant and much more abundant in AME than in PIO, while Factor 3 was ~ 6 times more abundant in PIO than in AME. Also, tryptophan was ~ 10x more abundant in AME specimens immediately caught in rivers than in their laboratory-adapted peers. The PARAFAC decomposition effectiveness was confirmed by the positive proportionality of scores to dilution ratios. A large inner filter indicates that Factor 2 is as strong a light absorber as tryptophan. Our results stress the need to include bile matrix variable components for the detection and quantification of pollutant metabolites using PARAFAC.

Review: Fish bile, a highly versatile biomarker for different environmental pollutants

Ecotoxicological assessments encompass a broad spectrum of biochemical endpoints and ecological factors, allowing for comprehensive assessments concerning pollutant exposure levels and their effects on both fish populations and surrounding ecosystems. While these evaluations offer invaluable insights into the overall health and dynamics of aquatic environments, they often provide an integrated perspective, making it challenging to pinpoint the precise sources and individual-level responses to environmental contaminants. In contrast, biliary pollutant excretion assessments represent a focused approach aimed at understanding how fish at the individual level respond to environmental stressors. In this sense, the analysis of pollutant profiles in fish bile not only serves as a valuable exposure indicator, but also provides critical information concerning the uptake, metabolism, and elimination of specific contaminants. Therefore, by investigating unique and dynamic fish responses to various pollutants, biliary assessments can contribute significantly to the refinement of ecotoxicological studies. This review aims to discuss the multifaceted utility of bile as a potent biomarker for various environmental pollutants in fish in targeted monitoring strategies, such as polycyclic aromatic hydrocarbons, metals, pesticides, pharmaceuticals, estrogenic compounds, resin acids, hepatotoxins and per- and polyfluorinated substances. The main caveats of this type of assessment are also discussed, as well as future directions of fish bile studies.