## 2 Materials and Methods
### Test with Lumbriculus variegatus  
The laboratory culture of _Lumbriculus variegatus_ ([PERSON], 1774) originated from the University of Joensuu (Department of Biology) Finland. The oligochaetes were reared in several 1 L-beakers containing 200 mL of clean sand and 700 mL of reconstituted water prepared according to United States Environmental Protection Agency (USEPA) methodology [35] by dissolving the following salts in deionized water: 0.05 g L\({}^{-1}\) CaSO\({}_{4}\), 0.05 g L\({}^{-1}\) CaCl\({}_{2}\), 0.03 g L\({}^{-1}\) MgSO\({}_{4}\), 0.096 g L\({}^{-1}\) NaHCO\({}_{3}\), 0.004 g L\({}^{-1}\) KCl. The reconstituted water had the following characteristics: hardness 106 \(\pm\) 4 mg L\({}^{-1}\) as CaCO\({}_{3}\), alkalinity 1.2 \(\pm\) 0.1 meg L\({}^{-1}\), conductivity 318 \(\pm\) 34 \(\upmu\)s cm\({}^{-1}\), and pH 8.07 \(\pm\) 0.42. The beakers were held in a temperature-controlled water bath at 20 \(\pm\) 1 \({}^{\circ}\)C under a 16:8 h light:dark photoperiod at about 150 lux. The worms were fed with approximately 100 mg ground fish food (Tetramin(r), TetraWerke, Melle, Germany) twice a week. Overlying water in the beakers was continuously aerated with a Pasteur pipette and it was manually renewed at the same time as feeding. Water renewal was necessary to prevent bacterial and fungal growth as well as excess levels of ammonia due to the accumulation of excess food and excretory products. A whole-sediment bioaccumulation test was conducted based on standard methods [35; 36; 37] with minor modifications. The photoperiod, temperature and aeration were the same used for the laboratory culture. Exposures were conducted in 3-L glass vessels (22 cm i.d., 9 cm ht) containing 0.6 L of whole sediment and 2.4 L of reconstituted water that was continuously aerated (1 bubble per second). The vessels were covered to limit the loss of overlying water. Before worm addition, sediments in test vessels were conditioned for 7 days at test temperature to stabilize ammonia concentration in the overlying water. The overlying water lost via evaporation or collected for overlying water quality analysis was filled up with deionised water. Oligochaetes were not fed during the sediment exposures. Control vessels were prepared as described above using sand and USEPA reconstituted water. The worms in the control vessels were fed three times a week with approximately 150 mg ground fish food (Tetramin(r)). The difference in the amount of added food with respect to the laboratory culture (see above) account for the different dimensions of the vessels and the different numbers of worms in the vessels. Half volume of the overlying water of the control vessels was manually renewed at the same time as feeding for the reasons already explained for the culture of _L. variegatus_. On the day before the start of the exposures (day-1), mixed-age oligochaetes were manually removed from the culture, rinsed to remove most of the debris and placed into 1 L beakers containing aerated USEPA reconstituted water. On day 0, the oligochaetes were combined into a glass pan and rinsed to break up the masses of oligochaetes and remove any remaining debris. Weighted aliquots of oligochaetes (mean percent dry weight \(14\pm 0.4\) mg), which were fixed according to ratio of total organic carbon in sediment (Table 1) to organism dry weight \(\geq\)50 [35], were transferred to the different exposure units (see Table S1 for the number of replicates used for different sediments). The weight of the aliquots of worms were carried out by gently filtering them (\(-\)0,8 kPa, 60 s) on a pre-weighed polycarbonate filter (Nuclepore 3.0 \(\upmu\)m, 47 mm i.d.) in order to remove the excess water [38]. Operation of the exposure system, dissolved oxygen, temperature and behaviour of oligochaetes were checked daily. Conductivity, pH, total hardness, alkalinity and total ammonia of the overlying water were measured at the beginning of the exposures (before adding the organisms) and then three times a week.