Preliminary Screening of Soils Natural Radioactivity and Metal(loid) Content in a Decommissioned Rare Earth Elements Processing Plant, Guangdong, China

Radiological aspects such as natural radioactivity of U-238, Th-232, Ra-226, K-40 combined with potentially toxic metal(loid) (PTM) distribution features were seldom simultaneously investigated in rare earth element (REE) processing activities. This work was designed to investigate the distribution levels of natural radioactivity, air-absorbed dose rate of gamma radiation as well as PTMs at a typical REE plant in Guangdong, China. Ambient soils around REE processing facilities were sampled, measured and assessed. The natural radioactivity of radionuclides of the samples was determined using a high-purity germanium gamma-energy spectrometer while the air-absorbed dose rate of gamma radiation was measured at a height of 1 m above the ground using a portable radiometric detector. The PTM content was measured by inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the specific activities of the radionuclides ranged from 80.8 to 1990.2, 68.2 to 6935.0, 78.4 to 14,372.4, and 625.4 to 2698.4 Bq.kg(-1) for U-238, Ra-226, Th-232, and K-40, respectively, representing overwhelmingly higher activity concentrations than worldwide soil average natural radioactivity. The radium equivalent activity and external hazard index of most samples exceeded the limits of 370 Bq.kg(-1) and 1, respectively. The measured air-absorbed dose rate of gamma radiation was in a range of 113 similar to 4004 nGy.h(-1), with most sites displaying comparatively higher values than that from some other REE-associated industrial sites referenced. The content levels of PTMs of Cu, Ni, Zn, Mn, Pb, Cd, Cr, and As were 0.7 similar to 37.2, 1.8 similar to 16.9, 20.4 similar to 2070.5, 39.4 similar to 431.3, 2.3 similar to 1411.5, 0.1 similar to 0.7, 6.7 similar to 526.1, and 59.5 similar to 263.8 mg.kg(-1), respectively. It is important to note that the PTM contents in the studied soil samples were 2.1 similar to 5.4 times higher for Zn-As and 1.4 times higher for Pb than the third level of the China soil standard while 2.5 similar to 13 times higher for Zn-As and 1.2 times higher for Pb than Canadian industry standard. The findings call for subsequent site remediation to secure the ecological environment and human health after the REE processing plant was decommissioned.

Automated summary

Rare earth element processing activities are often associated with high levels of natural radioactivity and potentially toxic metal distribution in the surrounding environment. The specific activities of radionuclides in the soil samples were found to be significantly higher than worldwide soil averages, with some samples exceeding safety limits. Remediation efforts may be necessary to protect ecological and human health post-decommissioning of the processing plant.