239 + 240Pu concentration and isotope ratio (240Pu/239Pu) in aerosols during high dust (Yellow Sand) period, Korea

Abstract

Concentration and isotope ratio of Pu were analyzed for aerosols collected at Anmyeondo located in the western coast of Korea using multiple collector inductively coupled plasma mass spectrometer equipped with desolvated micro-concentric nebulizer. Aerosols were collected from June 2001 to April 2002 using high volume air sampler. The samples consist of high dust samples (Yellow Sand), and also low dust samples; maximum Al concentration was 74.2 μg/m3 and minimum was 0.17 μg/m3.Pu was concentrated using 0.1 ml TEVA resin columns after conc. HNO3 extraction. Isotope dilution using 242Pu spike and mass bias correction using 233U and 236U mixed solution enabled the quantification of Pu and measurement of isotope ratio simultaneously. The contribution of 238U from both spikes and samples was minimized by careful chemical separation and optimization of spike concentration. The 238U1H and tail contribution on 239Pu peak were about 0.75×10−5 and 1×10−5 of 238U intensity, respectively, and they were corrected from 239Pu using externally determined (238U1H+tailing)/238U ratio and 238U measurement during acquisition. The detection limits of this analytical procedure were 0.61 fg/ml and 0.56 fg/ml for 239Pu and 240Pu, respectively (4 nBq/m3 and 12 nBq/m3 for 239Pu and 240Pu, respectively). The precision of isotope ratio measurement was better than 2% for larger quantity than 20 fg of 239Pu.In spring, maximum concentration of 0.580 μBq/m3 for 239Pu and 0.404 μBq/m3 for 240Pu was observed when Al concentration was maximum, so called as Yellow Sand event. Pu concentrations in aerosols are well correlated with Al, a tracer of soil dust. The ratios of Pu/Al were 0.0082 (μBq/μg) and 0.0055 (μBq/μg) for 239Pu/Al and 240Pu/Al, respectively. Isotope ratios of Pu (240Pu/239Pu) in Yellow Sand samples show 0.191±0.014 close to those of global fallout. These facts indicate that Yellow Sand plays an important role in the behavior of Pu in the environment like other concomitant metals such as Al, Fe etc.