Contaminants, when present above certain thresholds, can induce physiological constraints to organisms, namely diatoms, a model group representative of marine phytoplankton, triggering feedback mechanisms, such as changes in cell’s fatty acid profiles, that can be used as biomarkers towards xenobiotic exposure. Having this in mind and considering the ecological relevance of diatom fatty acid profiles as well as their recognized potential as biomarkers of contaminant exposure, the present work aims to develop and test the accuracy of an integrative multi-biomarker response index based on the fatty acid profiles of marine diatoms (using Phaeodactylum tricornutum as model diatom) exposed to several emerging contaminants.In terms of the impacts at the individual fatty acid level, it was possible to observe changes transversal to different contaminants, such as the reduction of C14:0 and C16:0 fatty acids, with increasing xenobiotic concentration, as observed, for example, under propranolol and fluoxetine exposure. Enhancement of C16:2n-7 and C16:3n-4 concentrations as well as complete disruption of the basal fatty acid profile was observed in diatoms exposed to copper nanoparticles. These individual diverse and intrinsically connected alterations in fatty acid concentrations depended on the type and dose of the xenobiotic applied, highlighting the need to address these profiles as a whole. The evaluation of the diatom cells’ fatty acids using a multivariate approach revealed a high degree of sensitivity of these biochemical traits to disclose the type of xenobiotic applied to the diatoms, as well as the exogenous concentration used. These biochemical profiles were later incorporated into a unifying numerical index (LipidTOX) using an integrated biomarker response approach. The LipidTOX index showed strong correlations with both the exogenous xenobiotic concentration applied as well as with the growth features assessed for the exposed cultures, revealing a very high efficiency in translating growth impairments imposed by each of the xenobiotics tested at the different test concentrations. The LipidTOX index proved to be an efficient tool for ecotoxicological assays with marine model diatoms and evidenced a high degree of reliability for classifying the exposure of the cells to emerging contaminants. The results and benefits of the LipidTOX index application can be easily communicated to non-expert audiences such as stakeholders, policymakers and environmental managers so that this approach can be used in future toxicological evaluations of the impacts of classical and emerging xenobiotics in marine primary producers.

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