Perfluorinated alkylated substances (PFAS) are persistent compounds with many uses, for example impregnation of fabrics and leather and as fire-retardants. Recently, it has focused on these compounds, because of their wide environmental distribution and the lack of knowledge about their behaviour in the environment. Since they have been detected in the Nordic marine environment, two PFAS were chosen as test compounds. Tributyltin (TBT) has been used in anti-fouling paints since the mid-1960s and has proven to have adverse effects on many species. This study aimed at clarifying effects of a 56 day exposure to perfluorooctane sulfonate (PFOS), perfluorononanoic acid (PFNA) and tributyltin (TBT) on the cellular energy allocation (CEA) in the polychaete Hediste diversicolor. Avoidance behaviour, survival and growth were also recorded. The CEA biomarker assay involves using colorimetric biochemical methods to quantify the energy reserves available (Ea) and the energy consumption (Ec). This information can then be integrated into a single value expressing an overall net-energy budget value. The assay was initially developed for use in short-term toxicity assays with Daphnia magna. The compounds spiked in the sediment had not been present in the concentrations intended during the exposure. PFOS was not detected in any of the sediment samples, and was probably washed out of the sediment when it was added to the aquaria. PFNA was detected in sediments not spiked with the compound, probably because it already was present in the sediment to some extent. The compound perfluorooctanoic acid (PFOA) was also found in the sediment samples. There was not observed any significant differences in cellular energy allocation or any other parameters measured between the control group and the treatments. No significant effects were seen with respect to avoidance behaviour, survival or growth, nor did it seem that low actual contaminant concentrations in the sediment significantly affected the cellular energy allocation parameters of the test organisms.