After magnetically collecting the SPIONs from water, they were transferred to 10 mL of hexane and sonicated for 10 min at 25 °C in a Sonocool 255 from Bandelin to wash off any biphenyl or PCB. Aliquots of 1.5 mL were centrifuged at 15,000 rpm at 20 °C for 10 min in a Mikro