Distribution and budget of 137Cs in the China Seas

Abstract

Cesium-137 is one of the most abundant anthropogenic radionuclides released by atmospheric nuclear testing and nuclear accidents, and accordingly it may significantly impact the health of humans and marine environmental ecosystems. Documenting the distribution and inventory of 137 cs is thus a crucial task. In this study, we collected a large number of datasets with field observations of 137 cs in the China Seas, in order to provide an in-depth understanding of 137 Cs budgets and distributions. The activity and inventory of 137 Cs in China Seas' sediments showed large spatial variations, related to the 137 Cs source, sedimentation rates and the mineral composition of sediments. The 137 Cs concentration in sediments decreased with distance from the shore, generally tracing the distribution of sedimentation rates. High 137 Cs inventories in the water column indicated a high solubility and long mean residence times. The mean residence times of 137 Cs in the China Seas were determined to be 45.6 ± 3.8 years for the South China Sea (SCS), 36.8 ± 3.1 years for the East China Sea (ECS), and 12.0 ± 1.0 years for the Yellow Sea (YS). A 137 Cs mass balance suggests that oceanic input from the north Pacific is the dominant 137 Cs source to the China Seas, contributing about 96.9% of this substance. Furthermore, the bulk of 137 Cs remains dissolved in the SCS water column, while 137 Cs is mostly deposited to the sediments of the ECS and the YS. This new compilation of the activity level and inventory of 137 Cs help to establish background levels for future 137 Cs studies in the China Seas. The fission product 137 Cs (t 1/2 = 30.17 years) has been introduced into the marine environment by nuclear bombs, nuclear accidents, and nuclear power plants since the 1940s. The estimated 137 Cs inventory of the global ocean is ~603 PBq (1 PBq=10 15 Bq), accounting for over 60% of the total global fallout 1. Additionally, 137 Cs has high radiotoxicity and is easily absorbed by muscular tissues. Therefore, the environmental impact of 137 Cs has become of great concern to the society since the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, which occurred in 2011 2 .