Owing of their wide-range of commercial applications, fullerene (C-60) nanoparticles, are likely to reach environments through the application of treated sludge (biosolids) from wastewater treatment plants to soils. We examined the release behaviour of C-60 from contaminated biosolids added to soils with varying physicochemical characteristics. Incubation studies were carried out in the dark for up to 24 weeks, by adding biosolids spiked (1.5 mg/kg) with three forms of C-60 (suspended in water, in humic acid, and precipitated/particulate) to six contrasting soils. Leaching of different biosolids + soil systems showed that only small fractions of C-60 (<5% of applied amount) were released, depending on incubation time and soil properties (particularly dissolved organic carbon content). Release of C-60 from unamended soils was greater (at least twice as much) than from biosolids-amended soils. The form of C-60 used to spike the biosolids had no significant effect on the release of C-60 from the different systems. Contact time of C-60 in these systems only slightly increased the apparent release up to 8 weeks, followed by a decrease to 24 weeks. Mass balance analysis at the completion of the experiment revealed that 20-60% of the initial C-60 applied could not be accounted for in these systems; the reasons for this are discussed. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.