Environmental fate studies of Fullerene C60: Sorption to soil, desorption from soil, biodegradation and plant uptake
Buckminster fullerene (C60) is the most representative among all fullerenes. It has been widely studied for its potential applications. Because its use in the medical, electronic, and materials industries is ever expanding, its release into the environment is inevitable. Studying the environmental fate of C60 fullerene is essential in order to better assess its potential for exposure to aquatic and terrestrial organisms. Our goal was to determine the basic environmental fate processes for C60 including sorption to soil, desorption from soil, biodegradation, and uptake into plants. Information on the fate of C60 in the environment and its potential transport to other trophic levels were critical data gaps that we addressed. Aqueous suspensions of 14C-labeled C60 were prepared by two methods 1) extended mixing in water and 2) solvent exchange with THF. The aqueous suspensions of 14C60 were characterized using a filtration experiment. It was observed that the aqueous suspension produced by extended mixing in water did not have aggregates in the nanometer range, whereas a majority (~60%) of aggregates in the aqueous suspension prepared by solvent exchange was in the nanometer range. The aqueous solution prepared by solvent exchange was used for all subsequent fate studies. Sorption and desorption parameters in three different soil types (sandy loam, silt loam, and a loam) were studied using the batch equilibrium method. Koc values for sandy loam (3684.8 mL/g) and silt loam (3719.65 mL/g) showed the expected consistency, while the Koc value for C60 in the loam was dramatically higher (10083.4 mL/g). Desorption from these soil types was determined as a percentage of the sorbed C60. We found maximum desorption from sandy loam (85% at 24 h). The loam and silt loam showed around 35% C60 desorption at 24 h. Plant uptake experiments in sand and a hydroponic substrateshowed very low uptake of C60 (< 10%). 14C60 was distributed in the root > tuber > stem
leaf. Biodegradation of C60 in the sandy loam and the silt loam was monitored for more than a year. No mineralization of C60 was observed. Our results on some basic environmental fate parameters for C60 have helped to fill data gaps related to the potential for fullerene nanomaterials to impact the environment. As is the case in nanomaterials research, there are some uncertainties in the results we obtained owing to the ability of C60 to aggregate and subsequently behave as a particulate.