Cycling of rare earth elements in the atmosphere in central Tokyo Yoshinari Suzuki, Shimpei Hikida and Naoki Furuta * Received 22nd July 2011, Accepted 26th September 2011 DOI: 10.1039/c1em10590f Concentrations of 14 rare earth elements (REEs) in six size classes of airborne particulate matter (APM) (<0.43, 0.43–0.65, 0.65–1.1, 1.1–2.1, 2.1–11, and >11 mm) and in two different phases (suspended particulate and dissolved) in rainwater were determined by inductively coupled plasma mass spectrometry (ICP-MS). Positive Eu and Tb anomalies were observed in size-classified APM. These anomalies may be due to large emissions of Eu and Tb to the atmosphere resulting from the recent change in Japan from the use of cathode-ray tubes to plasma displays in television sets (Eu and Tb) and from the widespread use of magneto-optical disks (Tb). The light REEs were enriched in fine APM particles (diameter < 1.1 mm). Because compositions of La/Ce/Sm in fine APM (diameter < 1.1 mm) were similar to those in automobile catalyst, the light REE enrichment was attributed to automobile emissions. In contrast, the REE distribution pattern in the suspended particulate phase in rainwater was similar to that in coarse APM (diameter > 2.1 mm), and a positive Tb anomaly was observed, suggesting that coarse particles easily become trapped in rain droplets. A negative Eu anomaly was observed in the dissolved phase in rainwater, but not in APM or in the suspended particulate phase in rainwater. Unlike other REEs, Eu can exist as both bivalent and trivalent ions in nature, and Eu-selective dissolution from or adsorption onto the trapped particles of Eu might account for the negative anomaly. These results show that atmospheric REE cycling is affected by the physico- chemical properties of APM. Introduction All of the rare earth elements (REEs) have similar physico- chemical properties, and they have become technologically, environmentally, and economically important materials because of their versatility and specificity. Nowadays, REEs are used in various industrial and medical materials, including in ceramics for superconductors, catalysts for automobiles (La and Ce), lasers (Nd), permanent magnets (Nd, Sm, Gd, Dy, and Pr), fluorescent imaging by color televisions (Y, Eu, and Tb), fluo- rescent lamps (Y, La, Ce, Eu, Gd, and Tb), contrast media for magnetic resonance imaging (Gd), and fiber optic telecommu- nication cables (Er). As a result, large amounts of REEs are consumed. 1,2 Because about 97% of REEs are produced in China, 3 all other countries must import them from China. The expansion of demand for REEs due to industrial development has led to the development of technologies for REE recycling from used products. Because of the widespread use of REEs, it is probable that large amounts of REEs are emitted into the atmosphere. Airborne particulate matter (APM) has become a serious air pollution problem. Many studies have investigated organic, metallic, and ionic contaminants in size-classified APM. Unlike organic compounds, heavy metals and trace elements are not biochemically decomposed and thus persist for a long time in the environment. Elements of anthropogenic origin that have been identified in APM include toxic elements such as As, Cd, Cr, Pb, Faculty of Science and Engineering, Department of Applied Chemistry, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo, 112-8551, Japan. E-mail: nfuruta@chem.chuo-u.ac.jp Environmental impact In this paper, we determined concentrations of 14 rare earth elements (REEs) in six size classes and two different phases of rainwater, and then we clarified REE cycling in atmospheric environment from the physico-chemical aspect. Some REEs were enriched in APM and suspended particulate phase of rainwater because of human activities. Coarse APMs were easily trapped in rain droplet. Eu anomalies were observed only in the dissolved phase of rainwater, because of Eu-selective dissolution from or adsorption onto the trapped particles. As far as known, these are the most precise data of REE concentrations in six size classes and two different phases of rainwater at the same time. 3420 | J. Environ. Monit., 2011, 13, 3420–3428 This journal is ª The Royal Society of Chemistry 2011 Dynamic Article Links C < Journal of Environmental Monitoring Cite this: J. Environ. Monit., 2011, 13, 3420 www.rsc.org/jem PAPER Downloaded by CHUO-KENKYUJO LIB on 02 December 2011 Published on 28 October 2011 on http://pubs.rsc.org | doi:10.1039/C1EM10590F View Online / Journal Homepage / Table of Contents for this issue