Investigating fish eye lenses as chemical archives of organic pollutant exposure

To target pollution remediation efforts and predict pollutant impacts on fisheries and food security, new tools are needed to reconstruct lifetime exposure histories for endangered and commercially valuable fishes. However, current methods used to quantify chemical burden typically use soft tissues which lack temporal information and can miss pulse exposures. Fish eye lenses are proteinaceous structures that form metabolically inert layers (laminae) through life. Their isotopic chronologies are widely used to track lifetime habitat use and diet, but organic pollutants have not previously been quantified in this tissue for fish. Other metabolically inert archival tissues, such as otoliths, are also popular for isotopic life history reconstruction, but almost entirely comprise calcium carbonate with very low protein or lipid content compared with the eye lens, which we show here contain low but measurable levels of lipids, as much as 3.5% w/w in European eels, and so have a greater affinity to bind organic chemicals. To reconstruct pollutant exposure events, a key first step is to show which, if any, chemicals bind to eye lenses. Hence, the present study developed methods to detect organic pollutants in the eye lenses of common dab (Limanda limanda) and European eel (Anguilla anguilla) using GC-MS/MS. For the first time, multiple polycyclic aromatic hydrocarbons were detected in lens tissue, with total concentrations positively correlated to those measured in paired liver samples. However, eye lenses generally contained fewer analytes, likely reflecting a lower bioaccumulation capacity compared with lipid-rich livers. More targeted analysis is needed to achieve lamina-level (chronological) resolution, and controlled exposure experiments to validate relationships with ambient concentrations and establish the underlying pathway(s). Nevertheless, eye lenses show potential as archives of historical organic pollutant exposure.