The concentration of 1,2,4-trichlorobenzene that is additionally required within an organism for lethality, after long-term exposure to sediments, is evaluated as an endpoint for risk assessment. This additionally required body burden for lethality after 2 months of exposure to sediments from different locations, was significantly lower in sticklebacks exposed to the more polluted sediments. In two sediments a series of chemicals was analyzed; risk assessment using these data in combination with biota-to-sediment accumulation factors and supposing concentration-addition severely underestimated the ecotoxicological risk. The lethal body burden (LBB) of seawater acclimated sticklebacks did not differ from that of fish acclimated to fresh water. However, the LBB was significantly influenced by temperature. The use of the lethal body burden in risk assessment of sediments is discussed and compared to more conventional techniques.