Study of Ra desorption processes in an estuary system with high-turbidity at the Southeast China

Qiangqiang Zhong; Hao Wang; Qiugui Wang; Suiyuan Chen; Jing Lin; Dekun Huang; Tao Yu

doi:10.1016/j.jenvrad.2023.107108

Study of Ra desorption processes in an estuary system with high-turbidity at the Southeast China

J Environ Radioact. 2023 Apr:259-260:107108. doi: 10.1016/j.jenvrad.2023.107108. Epub 2023 Jan 11.

Authors

Qiangqiang Zhong¹, Hao Wang², Qiugui Wang³, Suiyuan Chen⁴, Jing Lin¹, Dekun Huang⁵, Tao Yu¹

Affiliations

¹ Third Institute of Oceanography, Ministry of Natural Resource, Xiamen, 361005, China.
² Third Institute of Oceanography, Ministry of Natural Resource, Xiamen, 361005, China; College of Marine Sciences, Shanghai Ocean University, Shanghai, 201306, China.
³ School of Environmental Science and Engineering, Guangzhou University, Guangzhou, 510006, China.
⁴ Third Institute of Oceanography, Ministry of Natural Resource, Xiamen, 361005, China; College of Ocean and Earth Sciences, Xiamen University, Xiamen, 361005, China.
⁵ Third Institute of Oceanography, Ministry of Natural Resource, Xiamen, 361005, China; Observation and Research Station of Island and Coastal Ecosystem in the Western Taiwan Strait, Ministry of Natural Resources, Xiamen, 361005, China; Fujian Provincial Station for Field Observation and Research of Island and Costal Zone in Zhangzhou, Zhangzhou, 363216, China; Key Laboratory of Global Change and Marine-Atmospheric Chemistry, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, 361000, China. Electronic address: dkhuang@tio.org.cn.

PMID: 36638725
DOI: 10.1016/j.jenvrad.2023.107108

Abstract

Radium (Ra) isotopes are extensively used as geochemical tracers for studying water mass mixing and submarine groundwater discharge in marginal and coastal seas. However, river-borne particles and seafloor sediments are an important source of Ra in marine systems due to Ra desorption. Therefore, it is necessary to study the desorption behaviors of Ra isotopes in river sediment or suspended particles. Here, the desorption behaviors of four Ra isotopes (²²³Ra, ²²⁴Ra, ²²⁶Ra, and ²²⁸Ra) in the Zhangjiang River sediments were investigated by a series of designed variable-controlling experiments in the laboratory. Within the designed salinity range, desorption amounts of Ra isotopes increased with increasing salinity, and when the salinity was greater than 15 ppt, Ra desorption reached an equilibrium state. Overall, desorption of Ra isotopes increased with the decrease of particle grain size, however, the desorption fractions of ²²⁴Ra and ²²⁸Ra decreased with decreasing particle size due to the increase of original Ra activities in smaller sediment particles. In the experiments, we found that two sediment samples with similar mean grain size (3.8 μm and 3.3 μm) and similar grain size distributions had significantly different Ra desorption under the same conditions. The results of mineral composition analysis based on X-ray diffraction showed that these two samples had different percentages of kaolinite, quartz, and plagioclase, which indicated that the mineral composition of particles had an important effect on Ra isotope desorption. In conclusion, salinity, particle grain size, and mineral composition all had significant effects on Ra desorption behaviors of sediment particles. Based on the above desorption experiments, the desorbed fluxes of four Ra isotopes from river-borne sediments to the Dongshan Bay were estimated to be (5.95 ± 1.47) × 10⁷ Bq yr^-1 for ²²³Ra, (1.95 ± 0.27) × 10⁹ Bq yr^-1 for ²²⁴Ra, (2.73 ± 0.47) × 10⁸ Bq yr^-1 for ²²⁶Ra, and (1.26 ± 0.20) × 10⁹ Bq yr^-1 for ²²⁸Ra, respectively.

Keywords: Desorption behavior; Grain size; Mineral composition; Radium isotopes; Salinity; Source of radium.

MeSH terms

China
Environmental Monitoring / methods
Estuaries
Geologic Sediments
Radiation Monitoring*
Radium* / analysis
Water Pollutants, Radioactive* / analysis

Substances

Radium
Water Pollutants, Radioactive