Sediment in Frierfjord, Southern Norway is polluted by heavy metals, PAH, PCB, dibenzo-p-dioxins and dibenzofurans. Levels of toxicity in sediment cannot be determined through chemical analyses alone due to biological, chemical and physical interactions with the sediment and biota. This study aimed to assess toxicity through exposure of Arenicola marina to the sediment. Sub-lethal effects in oxidative stress resistance (total oxyradical scavenging capacity- TOSC) and alterations to the energy budget (cellular energy allocation- CEA) were determined and related to sediment exposure. In addition to contaminated sediment, two reference sediments with different grain sizes were collected from outer Oslofjord. Effects were measured after 1, 2, 4 and 8 weeks of exposure in a microcosm experiment. Differences in bioaccumulation factors and energy budgets were detected in two Frierfjord sediments with similar levels of contamination. This demonstrated discrepancies in bioavailability of sediment-bound contaminants from the same area highlighting the need to consider spatial heterogeneity in sediment assessments. Two control sediments also affected A. marina differently, possibly due to dissimilar particle size, organic content and/or estrogenicity. Two Contaminated sediments were found not to affect the TOSC for three oxyradical agents (peroxyl radicals, hydroxyl radicals and peroxynitrite anions). Effects were discovered in the CEA of the exposure group with the highest levels of bioaccumulated toxicants. Exposure to one of the contaminated sediments was found to cause temporary increases in all measured energy storage parameters (protein, carbohydrate, lipids). Exposure to contamination also resulted in decreased levels of lipids and total available energy during the final 4 weeks, relative to one control group. It was concluded that effects in the energy budget due to contaminated sediment, were not caused by suppression of oxidative stress resistance in Arenicola marina.