Photochemical Transformation of Aqueous C₆₀ Clusters in Sunlight

C60 is emerging in a variety of potential applications; however, its environmental fate remains largely unknown. Photochemical transformation may be an important fate process of C60 in the aquatic environment due to its strong light absorption within the solar spectrum. In this study, the photochemical transformation of aqueous C60 clusters (nC60) in sunlight (West Lafayette, IN, 86 degrees 55' W, 40 degrees 26' N) and in lamp light (300-400 nm wavelengths) was investigated. When exposed to light, the brown to yellow color of nC60 was lost gradually, and the cluster size decreased as the irradiation time increased. TOC analysis on the water phase of centrifuged samples indicated that water soluble products formed and that with continued light exposure, these intermediates eventually mineralized, volatilized, or were converted to other products not quantified by TOC after centrifugation and filtration. In sunlight at approximately 1 mg/L C60, the decay rate of C60 in small clusters (diameter = 150 nm) was greater than for C60 in larger (500 nm) clusters, with half-lives of 19 and 41 h, respectively. The presence of fulvic acid, changes in pH, and the preparation method of the clusters had minimal effects on the phototransformation rate. Deoxygenated samples resulted in negligible loss after 17 h of lamp exposure, indicating O2 played a role in the phototransformation mechanism. These findings suggested that release of nC60 into surface waters will result in photochemical production of currently unknown products.