Jianhua He

Distribution and risk assessment of radionuclides released by Fukushima nuclear accident at the northwest Pacific.

In order to understand the impact of Fukushima Nuclear Accident (FNA) on the marine environment, seawater and a composite squid (Ommastrephe bartrami) sample were collected on the monitoring cruise XT01 during June 16-July 4, 2011. The concentration levels of Cesium-134, Cesium-137, Strontium-90, Silver-110 m, Cobalt-58 and Cobalt-60 were measured both for the seawater and squid samples. The elevated activity levels of Cesium-134 and Cesium-137 were found in the sampling area. Cesium-134 and Silver-110 m, which were usually undetectable before FNA, were also found in the squid sample, with the activity levels of 1.65 ± 0.13 Bq/kg-wet and 0.07 ± 0.01 Bq/kg-wet, respectively. The radiological assessment result showed that the radioactive release from the FNA would not have a significant adverse effect on marine biota at the population level.

Radioactive status of seawater in the northwest Pacific more than one year after the Fukushima nuclear accident

To understand the impact of Fukushima Nuclear Accident(FNA), eight cruises were performed from 2011-2014. This paper reports the seawater monitoring results of the third cruise, which was conducted in May-June 2012.The northwest Pacific was clearly influenced even more than one year after FNA. However, compared to the monitoring results of the first and second cruises, which were performed in 2011, the seawater radioactivity of the third cruise decreased greatly. The highest value and the highest average of 137Cs and 134Cs were found in the 200u2005m layer, which suggested that 137Cs and 134Cs were most likely transported to a depth of 200u2005m or deeper. At 21.50°N, 125.00°E, 134Cs was found at a depth of 200u2005m, which is 430u2005km away from the southernmost point of Taiwan Island. The formation and subduction of Subtropical Mode Water is the most reasonable explanation for this process. The coastal water of China was not impacted by the radioactive pollutants released from the FNA. The radiation increments from 137Cs, 134Cs and 90Sr are only one-thousandth to one-millionth of the screening rate (10u2005μGy/h) according to the estimation using ERICA tools.

Determining coastal mixing rates of western Taiwan Strait using 224Ra

Abstract224Ra concentrations in the coastal sea water of western Taiwan Strait in winter were measured using Mn-fiber adsorption—successive emanation scintillation method. 224Ra activities in the seawater of the western Taiwan Strait varied from 0.90 to 16.25xa0Bq/m3 with an average of 4.60xa0Bq/m3. The horizontal and vertical distributions of 224Ra were studied. The distributions of 224Ra in the surface water decreased gradually with increasing distance offshore. The apparent horizontal and vertical eddy diffusion coefficients estimated from the one dimensional steady state model of 224Ra were (5.0–55.4)xa0×xa0106cm2/s and (4.0–51.7) cm2/s, respectively.

Optimization of an underwater in-situ LaBr3:Ce spectrometer with energy self-calibration and efficiency calibration

An underwater in-situ gamma-ray spectrometer based on LaBr3:Ce was developed and optimized to monitor marine radioactivity. The intrinsic background mainly from 138La and 227Ac of LaBr3:Ce was well determined by low background measurement and pulse shape discrimination method. A method of self-calibration using three internal contaminant peaks was proposed to eliminate the peak shift during long-term monitoring. With experiments under different temperatures, the method was proved to be helpful for maintaining long-term stability. To monitor the marine radioactivity, the spectrometers efficiency was calculated via water tank experiment as well as Monte Carlo simulation.

Preliminary identification of palaeofloods with the alkane ratio C31/C17 and their potential link to global climate changes.

A major challenge in palaeohydrology is the extraction of continuous palaeoflood information from geophysical records. A high-resolution sediment core off the Minjiang estuary area in the Taiwan Strait, SE China, records the sedimentation history from approximately 1660 to the present. The alkane ratio C31/C17, a classic organic geochemical indicator of terrestrial/aquatic matter, peaks in the layers dating as 1876-1878 and 1968-1970, suggesting the large terrestrial input to the Minjiang estuary area by huge flood transporting during the each peak interval. Historical archives are consistent with this interpretations and record catastrophic floods in the Minjiang River during both intervals. Furthermore between 1876-1878 there were floods in southern China and droughts in northern China, as well as throughout Asia, Africa, Australia, and the Americas. The 1876-1878 catastrophic flood of the Minjiang River may therefore has been the local response to global climate anomalies during that time interval.

Decay/ingrowth uncertainty correction of (210)Po/(210)Pb in seawater.

Due to increasing application of (210)Po/(210)Pb in studying particle dynamics, a consistent procedure and calculation to derive accurate and precise result of (210)Po and (210)Pb in seawater should be proposed in the framework of intercalibration by GEOTRACES. The associated uncertainty of radioactivity, which is a significant component of data report, plays a vital role in intercomparison and should be well evaluated. Although measurement uncertainty of laboratory result was well defined in ISO standards and IAEA technical documents, the decay/ingrowth uncertainty correction from laboratory result to in-situ result was less studied. It was demonstrated that the relative uncertainty of in-situ (210)Pb activity was independent of elapsed time and equal to relative uncertainty of laboratory measuring (210)Po activity at second spontaneous deposition date. The relative uncertainty of in-situ (210)Po activity decreases with in-situ activity ratio of (210)Po to (210)Pb and increases with elapsed time between sampling date and separation date, relative uncertainty of laboratory measuring (210)Po activity at first spontaneous deposition date and relative uncertainty of in-situ (210)Pb activity. It was more important to improve precision of (210)Po at first spontaneous deposition date than that of (210)Po at second spontaneous deposition date. To obtain a desirable relative uncertainty of in-situ (210)Po activity, the maximum allowing elapsed time for (210)Po, which was important for sampling strategy making and quality assurance, was calculated by in-situ activity ratio of (210)Po to (210)Pb and precision of analytical method for (210)Po. The methodology of decay/ingrowth uncertainty correction could also be applied for other radionuclide pairs ((234)Th/(238)U, (90)Y/(90)Sr, (210)Bi/(210)Pb), sample matrixes (aerosols), and disciplines.

An integrated device for coprecipitation and filtration of radiocesium in seawater.

To improve the pretreatment efficiency of radiocesium in seawater, a prototype machine based on a new design of an integrated device for coprecipitation and filtration was developed and tested in the laboratory for its possibility and efficiency, the results show the that the efficiency of pretreatment of radiocesium can be improved more than one orders of magnitude compared to traditional methods. And the results from experiments on effect of settle time show that immediately filtration of solution after reaction will not affect the absorption of AMP to radiocesium in seawater.

234 Th-derived particulate organic carbon export in the Prydz Bay, Antarctica

Abstract234Th activities in sea water were measured using Fe(OH)3 co-precipitation and beta counting at six stations in Prydz Bay in March 2008 during the 24th Chinese National Antarctic Research Expedition. Total 234Th activities ranged from 0.96 to 2.44xa0dpmxa0L−1 with an average of 1.61xa0dpmxa0L−1, showing an apparent deficit with respect to 238U due to scavenging and export with particles. With a one-dimensional steady state model, 234Th export fluxes were converted to particulate organic carbon (POC) export using bottle ratios of POC concentrations to particulate 234Th activities on suspended particles. POC fluxes at the depth of 100xa0m varied between 33 and 297xa0mmolxa0m−2xa0day−1, comparable to prior work in the same region and higher than those of some other sea areas in the Southern Ocean, and indicated efficient running of biological pump in Prydz Bay. The results could be helpful to expand the knowledge of carbon cycle in seasonally ice-covered coastal regions around Antarctica.

Radioactive impacts on nekton species in the Northwest Pacific and humans more than one year after the Fukushima nuclear accident

This study investigated the radioactive impacts on 10 nekton species in the Northwest Pacific more than one year after the Fukushima Nuclear Accident (FNA) from the two perspectives of contamination and harm. Squids were especially used for the spatial and temporal comparisons to demonstrate the impacts from the FNA. The radiation doses to nekton species and humans were assessed to link this radioactivity contamination to possible harm. The total dose rates to nektons were lower than the ERICA ecosystem screening benchmark of 10μGy/h. Further dose-contribution analysis showed that the internal doses from the naturally occurring nuclide 210Po were the main dose contributor. The dose rates from 134Cs, 137Cs, 90Sr and 110mAg were approximately three or four orders of magnitude lower than those from naturally occurring radionuclides. The 210Po-derived dose was also the main contributor of the total human dose from immersion in the seawater and the ingestion of nekton species. The human doses from anthropogenic radionuclides were ~ 100 to ~ 10,000 times lower than the doses from naturally occurring radionuclides. A morbidity assessment was performed based on the Linear No Threshold assumptions of exposure and showed 7 additional cancer cases per 100,000,000 similarly exposed people. Taken together, there is no need for concern regarding the radioactive harm in the open ocean area of the Northwest Pacific.

Underground measurements of artificial radioactivity in squids from the western Pacific Ocean

To investigate the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accidents radiological effect on marine ecosystem, ash samples of squids from the western Pacific Ocean were collected in May 2014 and measured using an underground gamma-ray spectrometer in the underground laboratory JinPing. Low levels of 108mAg, 110mAg, 134Cs and 137Cs were detected, which indicates that the influence of the FDNPP accident on marine ecosystem is lasting but decreasing.