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Comparative study of radioactivity levels and radionuclide fingerprints in typical marine ecosystems of coral reefs, mangroves, and hydrothermal vents
Marine Pollution Bulletin 152 (2020) 110913
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Baseline
Comparative study of radioactivity levels and radionuclide fingerprints in typical marine ecosystems of coral reefs, mangroves, and hydrothermal vents
T
⁎
Wuhui Lina,b, Yu Fenga, Kefu Yua,b, , Yi Hana, Shiyue Wanga, Zhenni Moc, Qiuyun Ningc, ⁎⁎ Xinming Liuc, , Dingyong Huangd, Jianjia Wangd a
School of Marine Sciences, Guangxi University, Nanning 530004, China Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China Guangxi Academy of Oceanography, Nanning 530022, China d Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China b c
A R T I C LE I N FO
A B S T R A C T
Keywords: Coral reefs Mangroves Hydrothermal vents Radiation dose ERICA Non-human species
As a key environmental parameter to induce radiation dose and effect on non-human species, radioactivity level is rarely evaluated in typical ecosystems of coral reefs, mangroves, and hydrothermal vents. In this study, naturally occurring radionuclides (238U, 226Ra, 228Ra, and 40K) in carbonate, silicate, and sulfide sediments collected from coral reefs, mangroves, and hydrothermal vents were simultaneously measured using high purity germanium (HPGe) γ spectrometry. Radioactivity levels and radionuclide fingerprints (226Ra/238U and 228 Ra/226Ra) were interpreted and explored for tracking sources and formation processes of marine sediments in distinct marine ecosystems. Additionally, ionizing radiation dose rate on representative marine biotas (molluscbivalve, crustacean, polychaete worm, benthic fish, and pelagic fish) was evaluated using the ERICA tool with an increasing rank in coral reefs < mangroves < hydrothermal vents. Polychaete worm received the highest radiation dose relative to other marine biotas. We also emphasized the dominant contribution of 210Po to total radiation dose rate on marine biotas.
Radionuclides are recognized as invaluable tools for tracking and quantifying marine processes (Van der Loeff, 2001; Hong et al., 2011; Lin et al., 2014; Lin et al., 2016b). Meanwhile, radionuclides are widely dispersed in the Earth's system and impose ionizing radiation on human and non-human species (Lin et al., 2019b). Particularly, the impacts of ionizing radiation on human and marine environment were of great concern after the Fukushima Nuclear Accident (Lin et al., 2015; Lin et al., 2016a; Buesseler et al., 2017; Vives i Batlle et al., 2018). Therefore, radionuclides in marine environment were widely measured and compiled from the global seas and oceans by the international organizations of International Atomic Energy Agency (IAEA) and United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (UNSCEAR, 2000; IAEA, 2005). The physical settings are greatly variable in distinct marine ecosystems from the coastal sea to open ocean, from the tropical ocean to polar ocean, and from the surface ocean to interior ocean, resulting in the classifications of several tens of marine biogeographic realms in the
⁎
global ocean (Costello et al., 2017). Coral reefs, mangroves, and hydrothermal vents are well-known and very representative marine ecosystems in the ocean. As “rainforests” in the ocean, coral reefs are “hotspots” of high biodiversity and provide rich biological resources for humans (Moberg and Folke, 1999; Lin et al., 2019b). The mangrove ecosystems provide habitats and breeding areas for many marine endangered and commercial species in the tropical and subtropical seas (Primavera et al., 2019). The mangrove ecosystems are also recognized as the “Earth's kidney” due to its capacity to store wastes, such as nutrient and heavy metals (Lewis et al., 2011). The hydrothermal vent ecosystems are composed of chemolithotrophic bacteria, clams, and mussels in the absence of photosynthesis on the deep sea bottom. The extreme environment of hydrothermal vent ecosystems, which is characterized by high pressure, high temperature, low acid, and toxic gases, is analogous to the initial environment after the formation of the Earth. The hydrothermal vent ecosystems are recognized as the candidates of the origin of life (Martin et al., 2008) and “oases of the abyss”
Correspondence to: K. Yu, Office 1111#, Zonghe Shiyan Building, Guangxi University, Nanning City, Guangxi Province, China. Correspondence to: X. Liu, Office 206#, No. 74 Minzu Road, Guangxi Academy of Oceanography, Nanning City, Guangxi Province, China. E-mail addresses: [email protected] (K. Yu), [email protected] (X. Liu).
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https://doi.org/10.1016/j.marpolbul.2020.110913 Received 27 November 2019; Received in revised form 11 January 2020; Accepted 13 January 2020 Available online 20 January 2020 0025-326X/ © 2020 Elsevier Ltd. All rights reserved.
Marine Pollution Bulletin 152 (2020) 110913
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Fig. 1. Station map of marine Fe-Mn nodules (black rectangle in a), coral reefs (b), mangroves (c), and hydrothermal vents (red rectangles in a). Notice that several samples were collected from the same stations (e.g., 2 samples at station DY01, 2 samples at station DY03, 3 samples at station DY02). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
mangroves, and hydrothermal vents, respectively. The dominant component was ferromanganese oxides in marine Fe-Mn nodule. Particularly, the color of carbonate sediment (white color), silicate sediment (gray color), sulfide sediment (brown color), and ferromanganese oxides (black color) was significantly different. Notice that radioactivity data in marine sediments collected from the Beibu Gulf (30 samples from 30 stations, published data) was also used for discussing the sources of sediments (Lin et al., 2019a). All above-mentioned samples were measured using HPGe γ spectrometry in our laboratory. Although radioactivity data in marine sediments collected from coral reefs and Beibu Gulf had been published (Lin et al., 2019a; Lin et al., 2019b), radiation dose rate on marine biotas have not been evaluated using the ERICA tool in these previous studies. The thawed sediments were dried in an oven at a temperature of 60 °C. After discarding the exotic materials, the samples were pulverized into fine power and passed through an 80–100 mesh sieve. We took ~20 g powder and sealed the samples in a cylindrical container with parafilm over 30 days followed by the measurement of HPGe γ spectrometry. The secular equilibrium of parent radionuclides and their progenies was achieved to calculate the activities of 238U, 226Ra, and 228 Ra through their progenies at the photopeaks of 63.3 keV (234Th), 609.3 keV (214Bi), and 911.1 keV (228Ac), respectively. The 40K activity is quantified by a γ ray of 1460.8 keV. The standard sediment (IAEA384 and IAEA-385) was produced by the IAEA and used for the calibration of detection efficiency. The activity (A) and its associated uncertainty (δA) are calculated by Eqs. (1)–(2), respectively.
(Corliss and Ballard, 1977). Therefore, a wide range of biotas inhabit in distinct marine ecosystems with variable radioactivity levels. Although radioactivity level is one of key factors to induce radiation dose and effect (reproduction, mortality, and morbidity) on non-human species (Garnier-Laplace et al., 2008), there is scarce radioactivity data (activity and radiation dose) in marine ecosystems of coral reefs, mangroves, and hydrothermal vents. In this study, we simultaneously measured naturally occurring radionuclides (238U, 226Ra, 228Ra, and 40K) in carbonate sediments, silicate sediments, and sulfide sediments collected from distinct marine ecosystems of coral reefs, mangroves, and hydrothermal vents using high purity germanium (HPGe) γ spectrometry. The radionuclide fingerprints (226Ra/238U and 228Ra/226Ra) were explored for tracking the sources and formation processes of marine sediments. Finally, ionizing radiation on non-human species (mollusc-bivalve, crustacean, polychaete worm, benthic fish, and pelagic fish) was simultaneously evaluated in typical marine ecosystems of coral reefs, mangroves, and hydrothermal vents using the ERICA tool (Brown et al., 2016). Marine sediments in coral reefs (15 samples from 12 stations in Fig. 1b, published data), mangroves (13 samples from 10 stations in Fig. 1c, unpublished data), and hydrothermal vents (4 samples from 2 stations in Fig. 1a, unpublished data) were collected from the South China Sea (SCS), coastline of the north Beibu Gulf, Pacific Ocean (DY01 and DY05) and Indian Ocean (DY03 and DY12), respectively, during 2005–2019. Additionally, radionuclides in marine Fe-Mn nodules (3 samples from 1 station in Fig. 1a, unpublished data) collected from the north Pacific Ocean were also measured and discussed in this study. The shape of marine Fe-Mn nodules was spherical with a diameter of ~1 cm. The major components of marine sediments were carbonate, silicate, and sulfide sediments in the typical ecosystems of coral reefs,
A=
2
(nT − n 0 ) λ(t1− t0) e εm
(1)
Marine Pollution Bulletin 152 (2020) 110913
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δA = A ×
(nGT + nG0 ) T (nT − n 0 )2
radionuclides in mangroves from Brazil (de Paiva et al., 2016), India (Valan et al., 2016), and Thailand (Kaewtubtim et al., 2017). The results of 238U, 226Ra, 228Ra, and 40K in marine sediments collected from hydrothermal vents were 3.24–42.7 Bq/kg (19.5 ± 19.0 Bq/kg), 59.8–122 Bq/kg (86.3 ± 26.5 Bq/kg), 1.45–3.13 Bq/kg (2.30 ± 0.95 Bq/kg), and 16.6–135 Bq/kg (66.2 ± 55.6 Bq/kg), respectively. The activities of 238U, 226Ra, and 228Ra in sulfide sediments were comparable to other studies in hydrothermal vents of the Juan de Fuca Ridge (Pacific Ocean) and the Southwest Indian Ridge (Indian Ocean) (Kim and McMurtry, 1991; Münch et al., 2001). The activities of 238U, 226Ra, 228Ra, and 40K in marine Fe-Mn nodules were 45.2–59.1 Bq/kg (52.2 ± 6.94 Bq/kg), 85.1–500 Bq/kg (322 ± 214 Bq/kg), 67.7–93.2 Bq/kg (80.2 ± 12.8 Bq/kg), and 243–311 Bq/kg (283 ± 35.5 Bq/kg), respectively. Our results were also comparable to other studies in marine Fe-Mn nodules (Ku and Broecker, 1969; Krishnaswami and Cochran, 1978; Nozaki and Yang, 1985). Notice that the 40K activity was not reported in sulfide sediments from hydrothermal vents and marine Fe-Mn nodules in above-mentioned references. For comparison of radioactivity levels among distinct marine ecosystems, the results of 238U, 226Ra, 228Ra, and 40K in carbonate sediments from coral reefs were 22.1–38.2 Bq/kg (27.7 ± 5.02 Bq/kg), 1.06–9.39 Bq/kg (2.79 ± 2.03 Bq/kg), 0.5–14.4 Bq/kg (3.00 ± 3.46 Bq/kg), and 2.15–154 Bq/kg (18.9 ± 37.7 Bq/kg), respectively (Lin et al., 2019b). The activities of 238U, 226Ra, 228Ra, and 40 K in marine sediments collected from the Beibu Gulf were 5.06–43.2 Bq/kg (24.7 ± 11.6 Bq/kg), 4.33–42.2 Bq/kg (22.2 ± 10.7 Bq/kg), 7.75–88.8 Bq/kg (34.4 ± 18.7 Bq/kg), and 0.16–588 Bq/kg (253 ± 192 Bq/kg), respectively (Lin et al., 2019a). The average activities of radionuclides in distinct marine ecosystems are represented in Fig. 2. We also exhibit the average activities of radionuclides (238U, 226Ra, 228Ra, and 40K) in China soil (Wang, 2002). The 238U activity (20–52 Bq/kg) was relatively comparable in distinct marine ecosystems. The 226Ra activity ranged from low value (2.80 Bq/ kg) in coral reefs to high result (322 Bq/kg) in marine Fe-Mn nodules with respect to the average value of 37.6 Bq/kg in China soil. Extremely high 226Ra activity in marine Fe-Mn nodules was mainly attributed to the physical process of high activity of parent radionuclide 230Th (several hundreds to several thousands Bq/kg) to support the ingrowth of daughter radionuclide 226Ra (Ku and Broecker, 1969; Krishnaswami and Cochran, 1978; Nozaki and Yang, 1985). In this study, we also
(2)
where nT and n0 are the counting rates of the sample and background, respectively. ε and m represent the relative detection efficiency and the dry weight of the sample, respectively. λ is the decay constant. t1 and t0 are the detection date and sampling date. T refers to the instrumental measurement time of the sample. nGT and nG0 represent the total counting rate of the sample and background, respectively. The uncertainty originates from counting statistics and is represented as one standard deviation (1δ). For analytical quality control, the standard sediments of IAEA-384 and IAEA-385 were cross-validated using the relative detection efficiency derived from the standard sediments of SGPb-1014 (210Pb), SGU1014 (238U), and 4NSG-1014 (241Am, 226Ra, 137Cs, and 60Co) provided by the China National Institute of Metrology. The obtained value was consistent with the reference value of IAEA-384 and IAEA-385 corrected to April 18, 2017 (Lin et al., 2019b). The instrumental background and detection efficiency of 238U, 137Cs, and 60Co were periodically measured to guarantee the data quality. Additionally, we also participated in and passed the interlaboratory comparison of radionuclides (210Pb, 238U, 226Ra, 228Ra, 228Th, 40K, and 137Cs) in marine sediments organized by the National Marine Environmental Monitoring Center of China in October 2017. The typical marine ecosystems of coral reefs, mangroves and hydrothermal vents are recognized as the “marine rainforests”, “Earth's kidney”, and “origin of life/oases of the abyss”, respectively. These marine ecosystems have different ecosystem structures, functions, and services for human. Radionuclides in marine sediments from mangroves (13 samples) and hydrothermal vents (4 samples) ecosystems are presented in Table 1. Radionuclides in marine Fe-Mn nodules (3 samples) are also exhibited (Table 1) for discussing formation process of sulfide sediment and marine Fe-Mn nodules in the following section. It is noticed that radionuclides in marine sediments from coral reefs (15 samples) are referred to the previous studies and not presented in Table 1 (Lin et al., 2019b). As for mangroves, the activities of 238U, 226Ra, 228Ra, and 40K in silicate sediments were 6.16–70.7 Bq/kg (27.8 ± 19.8 Bq/kg), 7.33–55.3 Bq/kg (21.2 ± 13.9 Bq/kg), 10–94.1 Bq/kg (35.8 ± 24.8 Bq/kg), and 26.5–479 Bq/kg (177 ± 131 Bq/kg), respectively. Our results were comparable to other studies of
Table 1 Radionuclides in marine Fe-Mn nodules and marine sediments collected from mangroves and hydrothermal vents. (Unit: Bq/kg). Marine ecosystems
Station
238
Mangroves
DPP2~1 DPP2~2 DPP1~3 DPP1~4 SJH YZP YLW BC SH TH ZS ZJL WJ
6.16 15.5 13.3 14.1 17.7 19.4 17.2 22.8 25.0 35.2 40.4 64.3 70.7 27.8 42.7 3.24 4.68 27.5 19.5 59.1 45.2 52.4 52.2
Average Hydrothermal vents
Average Marine Fe-Mn nodules
Average
DY01 DY03 DY05 DY12 DY02 DY10 DY11
U
226
228
7.33 ± 0.46 7.93 ± 0.44 13.2 ± 0.52 17.1 ± 0.58 13.9 ± 0.82 11.9 ± 0.46 16.7 ± 0.66 17.0 ± 0.86 23.6 ± 1.22 21.4 ± 0.81 26.3 ± 0.71 43.6 ± 0.48 55.3 ± 1.67 21.2 ± 13.9 87.0 ± 1.87 76.2 ± 2.05 59.8 ± 1.69 122 ± 2.38 86.3 ± 26.5 381 ± 3.65 500 ± 4.59 85.1 ± 1.48 322 ± 213
10.0 13.4 14.6 24.7 25.3 21.9 27.0 33.0 32.3 51.4 42.8 74.9 94.1 35.8 1.45 3.12 1.50 3.13 2.30 93.2 67.7 79.6 80.2
Ra
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
2.34 2.67 2.40 2.42 4.10 2.43 3.05 3.98 4.81 3.81 3.18 2.01 6.40 19.8 4.86 4.50 4.48 5.53 19.0 7.77 9.63 5.09 6.94
3
40
Ra ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
1.25 1.24 1.12 1.34 2.19 1.20 1.58 2.21 2.61 2.09 1.64 1.02 3.48 24.8 1.35 1.56 1.91 1.99 0.95 3.36 3.58 2.36 12.7
K
26.5 ± 1.23 39.2 ± 1.60 60.3 ± 2.08 176 ± 4.24 141 ± 6.49 98.2 ± 2.84 115 ± 3.80 154 ± 6.02 208 ± 8.77 150 ± 4.94 310 ± 6.02 344 ± 3.41 479 ± 12.4 177 ± 131 86.8 ± 4.47 16.6 ± 1.24 135 ± 6.06 26.0 ± 1.93 66.2 ± 55.6 243 ± 8.64 311 ± 10.7 294 ± 7.09 283 ± 35.5
Marine Pollution Bulletin 152 (2020) 110913
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Fig. 2. Radionuclides in China soil, marine Fe-Mn nodules, and sediments from distinct marine ecosystems.
Fig. 4. Relationship between 228Ra and 226Ra in sediments from coral reefs, mangroves and hydrothermal vents. The k value represents the activity ratio of 228 Ra to 226Ra.
observed a significant γ ray at 67.7 keV derived from 230Th in γ spectrometry of marine Fe-Mn nodules, even through the emission intensity of γ ray is only 0.4%. By contrast, low 226Ra activity in carbonate sediments from coral reefs was determined by the biogenic process of reef-building coral to incorporate 226Ra into coral skeleton from seawater, which was characterized by low 226Ra activity (~3 Bq/m3) in seawater and CF value (~1000 L/kg) of 226Ra in coral skeleton (Lin et al., 2019b). The 228Ra activity was in a range of ~2 Bq/kg (coral reefs and hydrothermal vents) to 80.2 Bq/kg (marine Fe-Mn nodules). The range of 228Ra activity was also related to the biogenic process of carbonate sediments from coral reefs and the physical process of 228Ra ingrowth from its parent radionuclide 232Th in marine Fe-Mn nodules. The 40K activity ranged from 19 Bq/kg (coral reefs) to 584 Bq/kg (China soil), which was attributed to the biogenic process of carbonate sediment from coral reefs and geological process of silicate soil (Lin et al., 2019b). Overall, radioactivity levels were closely related to chemical components in distinct marine sediments. Source of sediment is a classical topic in marine sedimentology. Radionuclide fingerprints have been explored as potential proxies for tracking the sources of sediments (Lin et al., 2019b). In this study, the activity ratio of 226Ra/238U in distinct marine ecosystems is exhibited in Fig. 3. Generally, the 226Ra/238U ratio is extremely low (k = ~0.10) in marine sediments from coral reefs. This low 226Ra/238U ratio was related to the major component of calcium carbonate in sediments from coral reefs, attributing to the low 226Ra/238U ratio (< 0.10) in seawater and similar concentration factors (CF, ~1000 L/kg) of 226Ra and 238U in coral skeleton (Lin et al., 2019b). The 226Ra/238U ratio was in the range of 0.5–1.0 in marine sediments from mangroves (Fig. 3). A high consistency of the 226Ra/238U ratio in marine sediments from mangroves and the Beibu Gulf was observed, attributable to an internal linkage of
source and sink for sediments from mangroves and Beibu Gulf. It was reported that marine sediments in the north Beibu Gulf was dominantly derived from the coasts of Guangxi Province (e.g., beach, river, mangroves) (Li et al., 2012). Notice that sediments from mangroves and Beibu Gulf are characterized by the terrigenous materials with a major component of silicate minerals (Lin et al., 2019a). We found high 226 Ra/238U ratio (k > 2.0) in sulfide sediments from hydrothermal vents. The high 226Ra/238U ratio in sulfide sediments was also reported in other study (Kim and McMurtry, 1991). This high 226Ra/238U ratio was caused by the preferential precipitation of radium (226Ra) in sulfide sediments nearby hydrothermal vents. High 226Ra activity (59.8–122 Bq/kg) was observed in marine sediments from hydrothermal vents with respect to the average value of 37.6 Bq/kg in China soil. Therefore, the 226Ra/238U ratio was closely related to the major components of carbonate, silicate, and sulfide in coral reefs, mangroves, and hydrothermal vents, respectively. The activity ratio of 228Ra to 226Ra (228Ra/226Ra) had been studied in hydrothermal fluid and sulfide sediment (Kim and McMurtry, 1991; Kipp et al., 2018). In this study, we found extremely low 228Ra/226Ra ratio (k < 0.05) in sulfide sediment collected from hydrothermal vents (Fig. 4). The low 228Ra/226Ra ratio (k < 0.05) was attributed to low 228 Ra activity after a long elapsed time from the initial precipitation of sulfide sediment nearby hydrothermal vents. The extremely low 232Th activity in sulfide sediment cannot support the 228Ra activity (Kim and McMurtry, 1991; Münch et al., 2001), resulting in low 228Ra activity (1.45–3.13 Bq/kg) in this study. By contrast, the 228Ra/226Ra ratio in marine Fe-Mn nodules ranged from 0.13 to 0.94 in this study. The 232Th activity in marine Fe-Mn nodules supported relatively high 228Ra activity (67.7–93.2 Bq/kg) (Ku and Broecker, 1969; Krishnaswami and Cochran, 1978; Nozaki and Yang, 1985). Both of sulfide sediments and marine Fe-Mn nodules are in the group of authigenic minerals in the ocean. In the same condition of low available 232Th activity (< 10−2 Bq/m3) in surrounding seawater (Lin et al., 2016b), the contrasting 232Th activity (equivalent to the 228Ra activity in secular equilibrium) in sulfide sediments (1.45–3.13 Bq/kg) and marine Fe-Mn nodules (67.7–93.2 Bq/kg) was probably determined by distinct formation rates of authigenic materials. The sulfide was rapidly formed after the eruption of hydrothermal fluid because of steep chemical gradient between oxygenated seawater and reduced hydrothermal fluid (e.g., H2S, CH4). The low available 232Th in seawater resulted in a negligible 232Th activity in sulfide sediments during the rapid formation of sulfide sediments nearby hydrothermal vents (Münch et al., 2001). However, the formation rate of marine Fe-Mn nodules was much slow (~1 mm/106y) (Ku and Broecker, 1969). The 232Th activity will be slowly accumulated in marine Fe-Mn nodules, resulting in relatively high 232Th activity. Therefore, the formation rate may affect the radionuclides concentration in the authigenic minerals in the ocean.
Fig. 3. Relationship between 226Ra and 238U in distinct marine ecosystems. The k value represents the activity ratio of 226Ra to 238U. The shaded areas indicate typical marine ecosystems of coral reefs, mangroves, and coral reefs. 4
Marine Pollution Bulletin 152 (2020) 110913
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Table 2 Parameters used in the ERICA tool. Seawater (Bq/L) (Lin et al., 2016b)
238
U Ra 228 Ra 40 K 210 Po 226
0.044 0.01 0.01 12.0 0.01
Sediment (Bq/kg)
Concentration factors (L/kg) (IAEA, 2004; Hosseini et al., 2008)
Coral reefs
Mangroves
Hydrothermal vents
Mollusc bivalve
Crustacean
Polychaete worm
Benthic fish
Pelagic fish
27.7 2.80 3.00 18.9 10
27.8 21.2 35.8 177 100
19.5 86.3 2.30 66.2 148
32.0 65.0 65.0 0.30 6.40 × 104
3.61 86.0 86.0 0.07 2.13 × 105
991 140 140 180 4.62 × 105
8.80 140 140 1.00 8.00 × 104
8.80 140 140 1.00 8.00 × 104
Therefore, radiation dose rate of naturally occurring radionuclides and Po were discussed separately in this study (Table 3). Total radiation dose rate of 238U, 226Ra, 228Ra, and 40K had an increasing rank in coral reefs < mangroves < hydrothermal vents. Polychaete worm had its exposure to the highest total radiation dose rate in these marine ecosystems. Total radiation dose rate on these representative marine biotas was lower than the no-effects screening benchmark level of 10 μGy/h (Garnier-Laplace et al., 2008). However, radiation dose rate of 210Po on all representative marine biotas was generally two orders of magnitude higher than total radiation dose rate of 238U, 226Ra, 228Ra, and 40K on all representative marine biotas and was also higher than the no-effects screening benchmark level of 10 μGy/h (Garnier-Laplace et al., 2008). The contributions of radionuclides to total radiation dose rate are also exhibited in Figs. 5–7. Radiation dose rate of 226Ra played a dominant role in radiation dose rate on mollusc-bivalve, crustacean, benthic fish, and pelagic fish. By contrast, the contributions of 238U and 40 K were significant in polychaete worm. The distinct components of radiation dose rate on different marine biotas were mainly attributed to different CF value in specific marine biotas. Although radionuclides in marine biotas was roughly estimated on the basis of CF value and activity in seawater, the preliminary results will provide clues to the future choice of the key radionuclides (210Po, 226Ra, 238U, 40K) to be measured in specific marine biotas for an accurate and precise evaluation of radiation dose rate on representative marine biotas in distinct marine ecosystems. In this study, naturally occurring radionuclides of 238U, 226Ra, 228 Ra, and 40K were simultaneously measured in marine Fe-Mn nodules and marine sediments collected from coral reefs, mangroves, and hydrothermal vents using HPGe γ spectrometry. The radionuclide fingerprints of 226Ra/238U and 228Ra/226Ra were explored and interpreted in carbonate sediments, silicate sediments, and sulfide sediments collected from coral reefs, mangroves, and hydrothermal vents, respectively. Finally, radiation dose rate of 238U, 226Ra, 228Ra, and 40K on representative marine biotas (mollusc-bivalve, crustacean, polychaete worm, benthic fish, and pelagic fish) was evaluated using the ERICA tool. We also emphasized the dominant role of 210Po in radiation dose rate on marine biotas. This study not only filled the gap of radioactivity data (activity and radiation dose) in distinct marine ecosystems but also shed light on radionuclide fingerprints as potential proxies for tracking marine processes.
Recently, ionizing radiation on non-human species was gradually concerned (ICRP, 2003; ICRP, 2007). Several groups participated in the international comparisons of radiation dose rate on non-human species (Batlle et al., 2007; Batlle et al., 2011). The ERICA tool was a popular software constructed by European Union and was continually updated to evaluate radiation dose rate on non-human species (Brown et al., 2016). In this study, radiation dose rate on marine biotas was evaluated in marine ecosystems of coral reefs, mangroves, and hydrothermal vents using the ERICA tool. We mainly focused on radiation dose rate derived from naturally occurring radionuclides (238U, 226Ra, 228Ra, 40K, and 210Po), which would provide a baseline for the future comparison of radiation dose rate derived from artificial radionuclides (e.g., 137Cs, 90 Sr, 239+240Pu). Several parameters (e.g., activity in seawater and sediment, concentration factors) are provided in Table 2 and used in the ERCIA tool. The typical activities of radionuclides (238U, 226Ra, 228Ra, 40K, and 210 Po) in seawater were chosen from other study (Lin et al., 2016b). The concentration factors were derived from the IAEA document and the Wildlife Transfer Parameter Database (IAEA, 2004; Hosseini et al., 2008). The representative marine biotas encompassed mollusc-bivalve, crustacean, polychaete worm, benthic fish, and pelagic fish. These marine biotas could be commonly observed in coral reefs, mangroves, and hydrothermal vents. Notice that we had not considered phytoplankton and zooplankton due to their absence in hydrothermal vents without the availability of sunlight. Although activity in marine biotas was estimated using the ERICA tool, the estimation was generally comparable to direct measurements of activity in marine biotas from the coastal sea (Heldal et al., 2019), open ocean (Yu et al., 2018), and hydrothermal vents (Cherry et al., 1992; Boisson et al., 2001; Charmasson et al., 2009). Naturally occurring radionuclides of 238U, 226Ra, 228Ra, and 40K are the most common primordial radionuclides of uranium decay series, thorium decay series, and potassium, imposing dominant radiation dose on human and non-human species in the Earth's system (Liu and Lin, 2018; Lin et al., 2019b). Although artificial radionuclides were significantly produced and released into the Earth's system (Lin et al., 2015; Waters et al., 2015), the activity and associated radiation dose of artificial radionuclides were generally lower than that of naturally occurring radionuclides (Aarkrog et al., 1997; Yu et al., 2018; Heldal et al., 2019). Recently, radiation dose rate of 210Po were emphasized because of its dominant contribution to total radiation dose on human and non-human species (Johansen et al., 2015; Yu et al., 2018).
210
Table 3 Radiation dose rate on non-human species in coral reefs, mangroves, and hydrothermal vents using the ERICA tool. Total radiation dose rate of
Mollusc - bivalve Crustacean Polychaete worm Benthic fish Pelagic fish
238
U,
226
Ra,
228
Ra, and
40
K (μGy/h)
Radiation dose rate of
210
Po (μGy/h)
Coral reefs
Mangroves
Hydrothermal vents
Coral reefs
Mangroves
Hydrothermal vents
0.13 0.13 1.82 0.21 0.20
0.15 0.15 1.88 0.23 0.20
0.17 0.17 1.92 0.25 0.20
19.8 66.1 143 24.8 24.8
19.8 66.1 143 24.8 24.8
19.8 66.1 143 24.8 24.8
5
Marine Pollution Bulletin 152 (2020) 110913
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Fig. 5. Contributions of radionuclides to total dose rate of marine biotas in coral reefs.
CRediT authorship contribution statement
Declaration of competing interest
Wuhui Lin: Conceptualization, Methodology, Funding acquisition, Writing-original draft. Yu Feng: Data curation, Methodology, Software. Kefu Yu: Resources, Investigation, Funding acquisition, Project administration. Yi Han: Methodology, Data curation, Software. Shiyue Wang: Methodology, Data curation, Software. Zhenni Mo: Methodology, Data curation. Qiuyun Ning: Methodology, Data curation. Xinming Liu: Resources, Funding acquisition. Dingyong Huang: Resources, Methodology. Jianjia Wang: Resources, Methodology.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work is benefited from the IAEA/RCA Regional Training Course on Dose Assessment and Risk Analysis Modeling hosted by the IAEA and Third Institute of Oceanography, Ministry of Natural Resources of China. We thanked Dr. M.P. Johansen and Dr. N.A. Beresford for their lectures in the regional training course on ERICA tool. This study was financially supported by the National Natural Science Foundation of
Fig. 6. Contributions of radionuclides to total dose rate of marine biotas in mangroves. 6
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Fig. 7. Contributions of radionuclides to total dose rate of marine biotas in hydrothermal vents.
China (41906043 and 91428203), the National Key Basic Research Program of China (2013CB956102), and the Natural Science Foundation of Guangxi Province (2017GXNSFBA198096 and 2019GXNSFAA185006).
Hong, G.-H., Hamilton, T., Baskaran, M., Kenna, T., 2011. Applications of anthropogenic radionuclides as tracers to investigate marine environmental processes. In: Baskaran, M. (Ed.), Handb. Environ. Isot. Geochem. Springer, pp. 367–394. Hosseini, A., Thørring, H., Brown, J.E., Saxén, R., Ilus, E., 2008. Transfer of radionuclides in aquatic ecosystems – default concentration ratios for aquatic biota in the Erica Tool. J. Environ. Radioact. 99 (9), 1408–1429. IAEA, 2004. Sediment Distribution Coefficients and Concentration Factors for Biota in the Marine Environment. IAEA, Vienna. IAEA, 2005. Worldwide Marine Radioactivity Studies (WOMARS): Radionuclide Levels in Oceans and Seas. IAEA, Vienna. ICRP, 2003. A Framework for Assessing the Impact of Ionising Radiation on Non-human Species. ICRP, pp. 33. ICRP, 2007. Recommendations of the International Commission on Radiological Protection. ICRP Publ. 103. ICRP. Johansen, M.P., Ruedig, E., Tagami, K., Uchida, S., Higley, K., Beresford, N., 2015. Radiological dose rates to marine fish from the Fukushima Daiichi accident: the first three years across the North Pacific. Environ. Sci. Technol. 49 (3), 1277–1285. Kaewtubtim, P., Meeinkuirt, W., Seepom, S., Pichtel, J., 2017. Occurrence of heavy metals and radionuclides in sediments and seawater in mangrove ecosystems in Pattani Bay, Thailand. Environ. Sci. Pollut. Res. 24 (8), 7630–7639. Kim, K.H., McMurtry, G.M., 1991. Radial growth rates and 210Pb ages of hydrothermal massive sulfides from the Juan de Fuca Ridge. Earth Planet. Sci. Lett. 104 (2), 299–314. Kipp, L.E., Sanial, V., Henderson, P.B., van Beek, P., Reyss, J.-L., Hammond, D.E., Moore, W.S., Charette, M.A., 2018. Radium isotopes as tracers of hydrothermal inputs and neutrally buoyant plume dynamics in the deep ocean. Mar. Chem. 201, 51–65. Krishnaswami, S., Cochran, J.K., 1978. Uranium and thorium series nuclides in oriented ferromanganese nodules: growth rates, turnover times and nuclide behavior. Earth Planet. Sci. Lett. 40 (1), 45–62. Ku, T.-L., Broecker, W.S., 1969. Radiochemical studies on manganese nodules of deep-sea origin. Deep-Sea Res. Oceanogr. Abstr. 16 (6), 625–637. Lewis, M., Pryor, R., Wilking, L., 2011. Fate and effects of anthropogenic chemicals in mangrove ecosystems: a review. Environ. Pollut. 159 (10), 2328–2346. Li, J., Gao, J., Wang, Y., Li, Y., Bai, F., Cees, L., 2012. Distribution and dispersal pattern of clay minerals in surface sediments, eastern Beibu Gulf, South China Sea. Acta Oceanol. Sin. 31 (2), 78–87. Lin, W., Ma, H., Chen, L., Zeng, Z., He, J., Zeng, S., 2014. Decay/ingrowth uncertainty correction of 210Po/210Pb in seawater. J. Environ. Radioact. 137, 22–30. Lin, W., Chen, L., Yu, W., Ma, H., Zeng, Z., Lin, J., Zeng, S., 2015. Radioactivity impacts of the Fukushima Nuclear Accident on the atmosphere. Atmos. Environ. 102, 311–322. Lin, W., Chen, L., Yu, W., Ma, H., Zeng, Z., Zeng, S., 2016a. Radioactive source-term of the Fukushima Nuclear Accident. Sci. China Earth Sci. 59 (1), 214–222. Lin, W., Chen, L., Zeng, S., Li, T., Wang, Y., Yu, K., 2016b. Residual β activity of particulate 234Th as a novel proxy for tracking sediment resuspension in the ocean. Sci. Rep. 6, 27069. Lin, W., Feng, Y., Yu, K., Lan, W., Mo, Z., Ning, Q., Feng, L., He, X., 2019a. Characteristics of radionuclides in sediments collected from the Beibu Gulf and influence factors. Acta Oceanol. Sin (In Chinese), In Press. Lin, W., Yu, K., Wang, Y., Liu, X., Ning, Q., Huang, X., 2019b. Radioactive level of coral reefs in the South China Sea. Mar. Pollut. Bull. 142, 43–53. Liu, X., Lin, W., 2018. Natural radioactivity in the beach sand and soil along the coastline
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Mangroves, Gulf of Mannar, India. J. Radioanal. Nucl. Chem. 310 (3), 1277–1288. Van der Loeff, M.M.R., 2001. Uranium-thorium decay series in the oceans: overview. In: Steele, J.H., Turekian, K.K., Thorpe, S.A. (Eds.), Encycl. Ocean Sci. Elsevier, pp. 3135–3145. Vives i Batlle, J., Aoyama, M., Bradshaw, C., Brown, J., Buesseler, K.O., Casacuberta, N., Christl, M., Duffa, C., Impens, N.R.E.N., Iosjpe, M., Masqué, P., Nishikawa, J., 2018. Marine radioecology after the Fukushima Dai-ichi nuclear accident: are we better positioned to understand the impact of radionuclides in marine ecosystems? Sci. Total Environ. 618 (Supplement C), 80–92. Wang, Z., 2002. Natural radiation environment in China. Int. Congr. Ser. 1225 (01), 39–46. Waters, C.N., Syvitski, J.P.M., Gałuszka, A., Hancock, G.J., Zalasiewicz, J., Cearreta, A., Grinevald, J., Jeandel, C., Mcneill, J.R., Summerhayes, C., 2015. Can nuclear weapons fallout mark the beginning of the Anthropocene Epoch? Bull. At. Sci. 71 (3), 46–57. Yu, W., Johansen, M.P., He, J., Men, W., Lin, L., 2018. Artificial radionuclides in neon flying squid from the northwestern Pacific in 2011 following the Fukushima accident. Biogeosciences 15 (23), 7235–7242.
of Guangxi Province, China. Mar. Pollut. Bull. 135, 446–450. Martin, W., Baross, J., Kelley, D., Russell, M.J., 2008. Hydrothermal vents and the origin of life. Nat. Rev. Microbiol. 6 (11), 805–814. Moberg, F., Folke, C., 1999. Ecological goods and services of coral reef ecosystems. Ecol. Econ. 29 (2), 215–233. Münch, U., Lalou, C., Halbach, P., Fujimoto, H., 2001. Relict hydrothermal events along the super-slow Southwest Indian spreading ridge near 63°56′E—mineralogy, chemistry and chronology of sulfide samples. Chem. Geol. 177 (3), 341–349. Nozaki, Y., Yang, H.-S., 1985. Non-destructive alpha-spectrometry and radiochemical studies of deep-sea manganese nodules. Geochim. Cosmochim. Acta 49 (8), 1765–1774. Primavera, J.H., Friess, D.A., Van Lavieren, H., Lee, S.Y., 2019. The mangrove ecosystem. In: Sheppard, C. (Ed.), World Seas: An Environmental Evaluation, Second edition. Academic Press, pp. 1–34. UNSCEAR, 2000. Sources, Effects of Ionizing Radiation. Report to the General Assembly With Annex B. UNSCEAR. United Nations, New York. Valan, I.I., Maniyarasan, S., Mathiyarasu, R., Sridhar, S.G.D., Narayanan, V., Stephen, A., 2016. Seasonal observation on radionuclide concentration in Krusadai Island
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Baseline
Comparative study of radioactivity levels and radionuclide fingerprints in typical marine ecosystems of coral reefs, mangroves, and hydrothermal vents
T
⁎
Wuhui Lina,b, Yu Fenga, Kefu Yua,b, , Yi Hana, Shiyue Wanga, Zhenni Moc, Qiuyun Ningc, ⁎⁎ Xinming Liuc, , Dingyong Huangd, Jianjia Wangd a
School of Marine Sciences, Guangxi University, Nanning 530004, China Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China Guangxi Academy of Oceanography, Nanning 530022, China d Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China b c
A R T I C LE I N FO
A B S T R A C T
Keywords: Coral reefs Mangroves Hydrothermal vents Radiation dose ERICA Non-human species
As a key environmental parameter to induce radiation dose and effect on non-human species, radioactivity level is rarely evaluated in typical ecosystems of coral reefs, mangroves, and hydrothermal vents. In this study, naturally occurring radionuclides (238U, 226Ra, 228Ra, and 40K) in carbonate, silicate, and sulfide sediments collected from coral reefs, mangroves, and hydrothermal vents were simultaneously measured using high purity germanium (HPGe) γ spectrometry. Radioactivity levels and radionuclide fingerprints (226Ra/238U and 228 Ra/226Ra) were interpreted and explored for tracking sources and formation processes of marine sediments in distinct marine ecosystems. Additionally, ionizing radiation dose rate on representative marine biotas (molluscbivalve, crustacean, polychaete worm, benthic fish, and pelagic fish) was evaluated using the ERICA tool with an increasing rank in coral reefs < mangroves < hydrothermal vents. Polychaete worm received the highest radiation dose relative to other marine biotas. We also emphasized the dominant contribution of 210Po to total radiation dose rate on marine biotas.
Radionuclides are recognized as invaluable tools for tracking and quantifying marine processes (Van der Loeff, 2001; Hong et al., 2011; Lin et al., 2014; Lin et al., 2016b). Meanwhile, radionuclides are widely dispersed in the Earth's system and impose ionizing radiation on human and non-human species (Lin et al., 2019b). Particularly, the impacts of ionizing radiation on human and marine environment were of great concern after the Fukushima Nuclear Accident (Lin et al., 2015; Lin et al., 2016a; Buesseler et al., 2017; Vives i Batlle et al., 2018). Therefore, radionuclides in marine environment were widely measured and compiled from the global seas and oceans by the international organizations of International Atomic Energy Agency (IAEA) and United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (UNSCEAR, 2000; IAEA, 2005). The physical settings are greatly variable in distinct marine ecosystems from the coastal sea to open ocean, from the tropical ocean to polar ocean, and from the surface ocean to interior ocean, resulting in the classifications of several tens of marine biogeographic realms in the
⁎
global ocean (Costello et al., 2017). Coral reefs, mangroves, and hydrothermal vents are well-known and very representative marine ecosystems in the ocean. As “rainforests” in the ocean, coral reefs are “hotspots” of high biodiversity and provide rich biological resources for humans (Moberg and Folke, 1999; Lin et al., 2019b). The mangrove ecosystems provide habitats and breeding areas for many marine endangered and commercial species in the tropical and subtropical seas (Primavera et al., 2019). The mangrove ecosystems are also recognized as the “Earth's kidney” due to its capacity to store wastes, such as nutrient and heavy metals (Lewis et al., 2011). The hydrothermal vent ecosystems are composed of chemolithotrophic bacteria, clams, and mussels in the absence of photosynthesis on the deep sea bottom. The extreme environment of hydrothermal vent ecosystems, which is characterized by high pressure, high temperature, low acid, and toxic gases, is analogous to the initial environment after the formation of the Earth. The hydrothermal vent ecosystems are recognized as the candidates of the origin of life (Martin et al., 2008) and “oases of the abyss”
Correspondence to: K. Yu, Office 1111#, Zonghe Shiyan Building, Guangxi University, Nanning City, Guangxi Province, China. Correspondence to: X. Liu, Office 206#, No. 74 Minzu Road, Guangxi Academy of Oceanography, Nanning City, Guangxi Province, China. E-mail addresses: [email protected] (K. Yu), [email protected] (X. Liu).
⁎⁎
https://doi.org/10.1016/j.marpolbul.2020.110913 Received 27 November 2019; Received in revised form 11 January 2020; Accepted 13 January 2020 Available online 20 January 2020 0025-326X/ © 2020 Elsevier Ltd. All rights reserved.
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Fig. 1. Station map of marine Fe-Mn nodules (black rectangle in a), coral reefs (b), mangroves (c), and hydrothermal vents (red rectangles in a). Notice that several samples were collected from the same stations (e.g., 2 samples at station DY01, 2 samples at station DY03, 3 samples at station DY02). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
mangroves, and hydrothermal vents, respectively. The dominant component was ferromanganese oxides in marine Fe-Mn nodule. Particularly, the color of carbonate sediment (white color), silicate sediment (gray color), sulfide sediment (brown color), and ferromanganese oxides (black color) was significantly different. Notice that radioactivity data in marine sediments collected from the Beibu Gulf (30 samples from 30 stations, published data) was also used for discussing the sources of sediments (Lin et al., 2019a). All above-mentioned samples were measured using HPGe γ spectrometry in our laboratory. Although radioactivity data in marine sediments collected from coral reefs and Beibu Gulf had been published (Lin et al., 2019a; Lin et al., 2019b), radiation dose rate on marine biotas have not been evaluated using the ERICA tool in these previous studies. The thawed sediments were dried in an oven at a temperature of 60 °C. After discarding the exotic materials, the samples were pulverized into fine power and passed through an 80–100 mesh sieve. We took ~20 g powder and sealed the samples in a cylindrical container with parafilm over 30 days followed by the measurement of HPGe γ spectrometry. The secular equilibrium of parent radionuclides and their progenies was achieved to calculate the activities of 238U, 226Ra, and 228 Ra through their progenies at the photopeaks of 63.3 keV (234Th), 609.3 keV (214Bi), and 911.1 keV (228Ac), respectively. The 40K activity is quantified by a γ ray of 1460.8 keV. The standard sediment (IAEA384 and IAEA-385) was produced by the IAEA and used for the calibration of detection efficiency. The activity (A) and its associated uncertainty (δA) are calculated by Eqs. (1)–(2), respectively.
(Corliss and Ballard, 1977). Therefore, a wide range of biotas inhabit in distinct marine ecosystems with variable radioactivity levels. Although radioactivity level is one of key factors to induce radiation dose and effect (reproduction, mortality, and morbidity) on non-human species (Garnier-Laplace et al., 2008), there is scarce radioactivity data (activity and radiation dose) in marine ecosystems of coral reefs, mangroves, and hydrothermal vents. In this study, we simultaneously measured naturally occurring radionuclides (238U, 226Ra, 228Ra, and 40K) in carbonate sediments, silicate sediments, and sulfide sediments collected from distinct marine ecosystems of coral reefs, mangroves, and hydrothermal vents using high purity germanium (HPGe) γ spectrometry. The radionuclide fingerprints (226Ra/238U and 228Ra/226Ra) were explored for tracking the sources and formation processes of marine sediments. Finally, ionizing radiation on non-human species (mollusc-bivalve, crustacean, polychaete worm, benthic fish, and pelagic fish) was simultaneously evaluated in typical marine ecosystems of coral reefs, mangroves, and hydrothermal vents using the ERICA tool (Brown et al., 2016). Marine sediments in coral reefs (15 samples from 12 stations in Fig. 1b, published data), mangroves (13 samples from 10 stations in Fig. 1c, unpublished data), and hydrothermal vents (4 samples from 2 stations in Fig. 1a, unpublished data) were collected from the South China Sea (SCS), coastline of the north Beibu Gulf, Pacific Ocean (DY01 and DY05) and Indian Ocean (DY03 and DY12), respectively, during 2005–2019. Additionally, radionuclides in marine Fe-Mn nodules (3 samples from 1 station in Fig. 1a, unpublished data) collected from the north Pacific Ocean were also measured and discussed in this study. The shape of marine Fe-Mn nodules was spherical with a diameter of ~1 cm. The major components of marine sediments were carbonate, silicate, and sulfide sediments in the typical ecosystems of coral reefs,
A=
2
(nT − n 0 ) λ(t1− t0) e εm
(1)
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δA = A ×
(nGT + nG0 ) T (nT − n 0 )2
radionuclides in mangroves from Brazil (de Paiva et al., 2016), India (Valan et al., 2016), and Thailand (Kaewtubtim et al., 2017). The results of 238U, 226Ra, 228Ra, and 40K in marine sediments collected from hydrothermal vents were 3.24–42.7 Bq/kg (19.5 ± 19.0 Bq/kg), 59.8–122 Bq/kg (86.3 ± 26.5 Bq/kg), 1.45–3.13 Bq/kg (2.30 ± 0.95 Bq/kg), and 16.6–135 Bq/kg (66.2 ± 55.6 Bq/kg), respectively. The activities of 238U, 226Ra, and 228Ra in sulfide sediments were comparable to other studies in hydrothermal vents of the Juan de Fuca Ridge (Pacific Ocean) and the Southwest Indian Ridge (Indian Ocean) (Kim and McMurtry, 1991; Münch et al., 2001). The activities of 238U, 226Ra, 228Ra, and 40K in marine Fe-Mn nodules were 45.2–59.1 Bq/kg (52.2 ± 6.94 Bq/kg), 85.1–500 Bq/kg (322 ± 214 Bq/kg), 67.7–93.2 Bq/kg (80.2 ± 12.8 Bq/kg), and 243–311 Bq/kg (283 ± 35.5 Bq/kg), respectively. Our results were also comparable to other studies in marine Fe-Mn nodules (Ku and Broecker, 1969; Krishnaswami and Cochran, 1978; Nozaki and Yang, 1985). Notice that the 40K activity was not reported in sulfide sediments from hydrothermal vents and marine Fe-Mn nodules in above-mentioned references. For comparison of radioactivity levels among distinct marine ecosystems, the results of 238U, 226Ra, 228Ra, and 40K in carbonate sediments from coral reefs were 22.1–38.2 Bq/kg (27.7 ± 5.02 Bq/kg), 1.06–9.39 Bq/kg (2.79 ± 2.03 Bq/kg), 0.5–14.4 Bq/kg (3.00 ± 3.46 Bq/kg), and 2.15–154 Bq/kg (18.9 ± 37.7 Bq/kg), respectively (Lin et al., 2019b). The activities of 238U, 226Ra, 228Ra, and 40 K in marine sediments collected from the Beibu Gulf were 5.06–43.2 Bq/kg (24.7 ± 11.6 Bq/kg), 4.33–42.2 Bq/kg (22.2 ± 10.7 Bq/kg), 7.75–88.8 Bq/kg (34.4 ± 18.7 Bq/kg), and 0.16–588 Bq/kg (253 ± 192 Bq/kg), respectively (Lin et al., 2019a). The average activities of radionuclides in distinct marine ecosystems are represented in Fig. 2. We also exhibit the average activities of radionuclides (238U, 226Ra, 228Ra, and 40K) in China soil (Wang, 2002). The 238U activity (20–52 Bq/kg) was relatively comparable in distinct marine ecosystems. The 226Ra activity ranged from low value (2.80 Bq/ kg) in coral reefs to high result (322 Bq/kg) in marine Fe-Mn nodules with respect to the average value of 37.6 Bq/kg in China soil. Extremely high 226Ra activity in marine Fe-Mn nodules was mainly attributed to the physical process of high activity of parent radionuclide 230Th (several hundreds to several thousands Bq/kg) to support the ingrowth of daughter radionuclide 226Ra (Ku and Broecker, 1969; Krishnaswami and Cochran, 1978; Nozaki and Yang, 1985). In this study, we also
(2)
where nT and n0 are the counting rates of the sample and background, respectively. ε and m represent the relative detection efficiency and the dry weight of the sample, respectively. λ is the decay constant. t1 and t0 are the detection date and sampling date. T refers to the instrumental measurement time of the sample. nGT and nG0 represent the total counting rate of the sample and background, respectively. The uncertainty originates from counting statistics and is represented as one standard deviation (1δ). For analytical quality control, the standard sediments of IAEA-384 and IAEA-385 were cross-validated using the relative detection efficiency derived from the standard sediments of SGPb-1014 (210Pb), SGU1014 (238U), and 4NSG-1014 (241Am, 226Ra, 137Cs, and 60Co) provided by the China National Institute of Metrology. The obtained value was consistent with the reference value of IAEA-384 and IAEA-385 corrected to April 18, 2017 (Lin et al., 2019b). The instrumental background and detection efficiency of 238U, 137Cs, and 60Co were periodically measured to guarantee the data quality. Additionally, we also participated in and passed the interlaboratory comparison of radionuclides (210Pb, 238U, 226Ra, 228Ra, 228Th, 40K, and 137Cs) in marine sediments organized by the National Marine Environmental Monitoring Center of China in October 2017. The typical marine ecosystems of coral reefs, mangroves and hydrothermal vents are recognized as the “marine rainforests”, “Earth's kidney”, and “origin of life/oases of the abyss”, respectively. These marine ecosystems have different ecosystem structures, functions, and services for human. Radionuclides in marine sediments from mangroves (13 samples) and hydrothermal vents (4 samples) ecosystems are presented in Table 1. Radionuclides in marine Fe-Mn nodules (3 samples) are also exhibited (Table 1) for discussing formation process of sulfide sediment and marine Fe-Mn nodules in the following section. It is noticed that radionuclides in marine sediments from coral reefs (15 samples) are referred to the previous studies and not presented in Table 1 (Lin et al., 2019b). As for mangroves, the activities of 238U, 226Ra, 228Ra, and 40K in silicate sediments were 6.16–70.7 Bq/kg (27.8 ± 19.8 Bq/kg), 7.33–55.3 Bq/kg (21.2 ± 13.9 Bq/kg), 10–94.1 Bq/kg (35.8 ± 24.8 Bq/kg), and 26.5–479 Bq/kg (177 ± 131 Bq/kg), respectively. Our results were comparable to other studies of
Table 1 Radionuclides in marine Fe-Mn nodules and marine sediments collected from mangroves and hydrothermal vents. (Unit: Bq/kg). Marine ecosystems
Station
238
Mangroves
DPP2~1 DPP2~2 DPP1~3 DPP1~4 SJH YZP YLW BC SH TH ZS ZJL WJ
6.16 15.5 13.3 14.1 17.7 19.4 17.2 22.8 25.0 35.2 40.4 64.3 70.7 27.8 42.7 3.24 4.68 27.5 19.5 59.1 45.2 52.4 52.2
Average Hydrothermal vents
Average Marine Fe-Mn nodules
Average
DY01 DY03 DY05 DY12 DY02 DY10 DY11
U
226
228
7.33 ± 0.46 7.93 ± 0.44 13.2 ± 0.52 17.1 ± 0.58 13.9 ± 0.82 11.9 ± 0.46 16.7 ± 0.66 17.0 ± 0.86 23.6 ± 1.22 21.4 ± 0.81 26.3 ± 0.71 43.6 ± 0.48 55.3 ± 1.67 21.2 ± 13.9 87.0 ± 1.87 76.2 ± 2.05 59.8 ± 1.69 122 ± 2.38 86.3 ± 26.5 381 ± 3.65 500 ± 4.59 85.1 ± 1.48 322 ± 213
10.0 13.4 14.6 24.7 25.3 21.9 27.0 33.0 32.3 51.4 42.8 74.9 94.1 35.8 1.45 3.12 1.50 3.13 2.30 93.2 67.7 79.6 80.2
Ra
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
2.34 2.67 2.40 2.42 4.10 2.43 3.05 3.98 4.81 3.81 3.18 2.01 6.40 19.8 4.86 4.50 4.48 5.53 19.0 7.77 9.63 5.09 6.94
3
40
Ra ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
1.25 1.24 1.12 1.34 2.19 1.20 1.58 2.21 2.61 2.09 1.64 1.02 3.48 24.8 1.35 1.56 1.91 1.99 0.95 3.36 3.58 2.36 12.7
K
26.5 ± 1.23 39.2 ± 1.60 60.3 ± 2.08 176 ± 4.24 141 ± 6.49 98.2 ± 2.84 115 ± 3.80 154 ± 6.02 208 ± 8.77 150 ± 4.94 310 ± 6.02 344 ± 3.41 479 ± 12.4 177 ± 131 86.8 ± 4.47 16.6 ± 1.24 135 ± 6.06 26.0 ± 1.93 66.2 ± 55.6 243 ± 8.64 311 ± 10.7 294 ± 7.09 283 ± 35.5
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Fig. 2. Radionuclides in China soil, marine Fe-Mn nodules, and sediments from distinct marine ecosystems.
Fig. 4. Relationship between 228Ra and 226Ra in sediments from coral reefs, mangroves and hydrothermal vents. The k value represents the activity ratio of 228 Ra to 226Ra.
observed a significant γ ray at 67.7 keV derived from 230Th in γ spectrometry of marine Fe-Mn nodules, even through the emission intensity of γ ray is only 0.4%. By contrast, low 226Ra activity in carbonate sediments from coral reefs was determined by the biogenic process of reef-building coral to incorporate 226Ra into coral skeleton from seawater, which was characterized by low 226Ra activity (~3 Bq/m3) in seawater and CF value (~1000 L/kg) of 226Ra in coral skeleton (Lin et al., 2019b). The 228Ra activity was in a range of ~2 Bq/kg (coral reefs and hydrothermal vents) to 80.2 Bq/kg (marine Fe-Mn nodules). The range of 228Ra activity was also related to the biogenic process of carbonate sediments from coral reefs and the physical process of 228Ra ingrowth from its parent radionuclide 232Th in marine Fe-Mn nodules. The 40K activity ranged from 19 Bq/kg (coral reefs) to 584 Bq/kg (China soil), which was attributed to the biogenic process of carbonate sediment from coral reefs and geological process of silicate soil (Lin et al., 2019b). Overall, radioactivity levels were closely related to chemical components in distinct marine sediments. Source of sediment is a classical topic in marine sedimentology. Radionuclide fingerprints have been explored as potential proxies for tracking the sources of sediments (Lin et al., 2019b). In this study, the activity ratio of 226Ra/238U in distinct marine ecosystems is exhibited in Fig. 3. Generally, the 226Ra/238U ratio is extremely low (k = ~0.10) in marine sediments from coral reefs. This low 226Ra/238U ratio was related to the major component of calcium carbonate in sediments from coral reefs, attributing to the low 226Ra/238U ratio (< 0.10) in seawater and similar concentration factors (CF, ~1000 L/kg) of 226Ra and 238U in coral skeleton (Lin et al., 2019b). The 226Ra/238U ratio was in the range of 0.5–1.0 in marine sediments from mangroves (Fig. 3). A high consistency of the 226Ra/238U ratio in marine sediments from mangroves and the Beibu Gulf was observed, attributable to an internal linkage of
source and sink for sediments from mangroves and Beibu Gulf. It was reported that marine sediments in the north Beibu Gulf was dominantly derived from the coasts of Guangxi Province (e.g., beach, river, mangroves) (Li et al., 2012). Notice that sediments from mangroves and Beibu Gulf are characterized by the terrigenous materials with a major component of silicate minerals (Lin et al., 2019a). We found high 226 Ra/238U ratio (k > 2.0) in sulfide sediments from hydrothermal vents. The high 226Ra/238U ratio in sulfide sediments was also reported in other study (Kim and McMurtry, 1991). This high 226Ra/238U ratio was caused by the preferential precipitation of radium (226Ra) in sulfide sediments nearby hydrothermal vents. High 226Ra activity (59.8–122 Bq/kg) was observed in marine sediments from hydrothermal vents with respect to the average value of 37.6 Bq/kg in China soil. Therefore, the 226Ra/238U ratio was closely related to the major components of carbonate, silicate, and sulfide in coral reefs, mangroves, and hydrothermal vents, respectively. The activity ratio of 228Ra to 226Ra (228Ra/226Ra) had been studied in hydrothermal fluid and sulfide sediment (Kim and McMurtry, 1991; Kipp et al., 2018). In this study, we found extremely low 228Ra/226Ra ratio (k < 0.05) in sulfide sediment collected from hydrothermal vents (Fig. 4). The low 228Ra/226Ra ratio (k < 0.05) was attributed to low 228 Ra activity after a long elapsed time from the initial precipitation of sulfide sediment nearby hydrothermal vents. The extremely low 232Th activity in sulfide sediment cannot support the 228Ra activity (Kim and McMurtry, 1991; Münch et al., 2001), resulting in low 228Ra activity (1.45–3.13 Bq/kg) in this study. By contrast, the 228Ra/226Ra ratio in marine Fe-Mn nodules ranged from 0.13 to 0.94 in this study. The 232Th activity in marine Fe-Mn nodules supported relatively high 228Ra activity (67.7–93.2 Bq/kg) (Ku and Broecker, 1969; Krishnaswami and Cochran, 1978; Nozaki and Yang, 1985). Both of sulfide sediments and marine Fe-Mn nodules are in the group of authigenic minerals in the ocean. In the same condition of low available 232Th activity (< 10−2 Bq/m3) in surrounding seawater (Lin et al., 2016b), the contrasting 232Th activity (equivalent to the 228Ra activity in secular equilibrium) in sulfide sediments (1.45–3.13 Bq/kg) and marine Fe-Mn nodules (67.7–93.2 Bq/kg) was probably determined by distinct formation rates of authigenic materials. The sulfide was rapidly formed after the eruption of hydrothermal fluid because of steep chemical gradient between oxygenated seawater and reduced hydrothermal fluid (e.g., H2S, CH4). The low available 232Th in seawater resulted in a negligible 232Th activity in sulfide sediments during the rapid formation of sulfide sediments nearby hydrothermal vents (Münch et al., 2001). However, the formation rate of marine Fe-Mn nodules was much slow (~1 mm/106y) (Ku and Broecker, 1969). The 232Th activity will be slowly accumulated in marine Fe-Mn nodules, resulting in relatively high 232Th activity. Therefore, the formation rate may affect the radionuclides concentration in the authigenic minerals in the ocean.
Fig. 3. Relationship between 226Ra and 238U in distinct marine ecosystems. The k value represents the activity ratio of 226Ra to 238U. The shaded areas indicate typical marine ecosystems of coral reefs, mangroves, and coral reefs. 4
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Table 2 Parameters used in the ERICA tool. Seawater (Bq/L) (Lin et al., 2016b)
238
U Ra 228 Ra 40 K 210 Po 226
0.044 0.01 0.01 12.0 0.01
Sediment (Bq/kg)
Concentration factors (L/kg) (IAEA, 2004; Hosseini et al., 2008)
Coral reefs
Mangroves
Hydrothermal vents
Mollusc bivalve
Crustacean
Polychaete worm
Benthic fish
Pelagic fish
27.7 2.80 3.00 18.9 10
27.8 21.2 35.8 177 100
19.5 86.3 2.30 66.2 148
32.0 65.0 65.0 0.30 6.40 × 104
3.61 86.0 86.0 0.07 2.13 × 105
991 140 140 180 4.62 × 105
8.80 140 140 1.00 8.00 × 104
8.80 140 140 1.00 8.00 × 104
Therefore, radiation dose rate of naturally occurring radionuclides and Po were discussed separately in this study (Table 3). Total radiation dose rate of 238U, 226Ra, 228Ra, and 40K had an increasing rank in coral reefs < mangroves < hydrothermal vents. Polychaete worm had its exposure to the highest total radiation dose rate in these marine ecosystems. Total radiation dose rate on these representative marine biotas was lower than the no-effects screening benchmark level of 10 μGy/h (Garnier-Laplace et al., 2008). However, radiation dose rate of 210Po on all representative marine biotas was generally two orders of magnitude higher than total radiation dose rate of 238U, 226Ra, 228Ra, and 40K on all representative marine biotas and was also higher than the no-effects screening benchmark level of 10 μGy/h (Garnier-Laplace et al., 2008). The contributions of radionuclides to total radiation dose rate are also exhibited in Figs. 5–7. Radiation dose rate of 226Ra played a dominant role in radiation dose rate on mollusc-bivalve, crustacean, benthic fish, and pelagic fish. By contrast, the contributions of 238U and 40 K were significant in polychaete worm. The distinct components of radiation dose rate on different marine biotas were mainly attributed to different CF value in specific marine biotas. Although radionuclides in marine biotas was roughly estimated on the basis of CF value and activity in seawater, the preliminary results will provide clues to the future choice of the key radionuclides (210Po, 226Ra, 238U, 40K) to be measured in specific marine biotas for an accurate and precise evaluation of radiation dose rate on representative marine biotas in distinct marine ecosystems. In this study, naturally occurring radionuclides of 238U, 226Ra, 228 Ra, and 40K were simultaneously measured in marine Fe-Mn nodules and marine sediments collected from coral reefs, mangroves, and hydrothermal vents using HPGe γ spectrometry. The radionuclide fingerprints of 226Ra/238U and 228Ra/226Ra were explored and interpreted in carbonate sediments, silicate sediments, and sulfide sediments collected from coral reefs, mangroves, and hydrothermal vents, respectively. Finally, radiation dose rate of 238U, 226Ra, 228Ra, and 40K on representative marine biotas (mollusc-bivalve, crustacean, polychaete worm, benthic fish, and pelagic fish) was evaluated using the ERICA tool. We also emphasized the dominant role of 210Po in radiation dose rate on marine biotas. This study not only filled the gap of radioactivity data (activity and radiation dose) in distinct marine ecosystems but also shed light on radionuclide fingerprints as potential proxies for tracking marine processes.
Recently, ionizing radiation on non-human species was gradually concerned (ICRP, 2003; ICRP, 2007). Several groups participated in the international comparisons of radiation dose rate on non-human species (Batlle et al., 2007; Batlle et al., 2011). The ERICA tool was a popular software constructed by European Union and was continually updated to evaluate radiation dose rate on non-human species (Brown et al., 2016). In this study, radiation dose rate on marine biotas was evaluated in marine ecosystems of coral reefs, mangroves, and hydrothermal vents using the ERICA tool. We mainly focused on radiation dose rate derived from naturally occurring radionuclides (238U, 226Ra, 228Ra, 40K, and 210Po), which would provide a baseline for the future comparison of radiation dose rate derived from artificial radionuclides (e.g., 137Cs, 90 Sr, 239+240Pu). Several parameters (e.g., activity in seawater and sediment, concentration factors) are provided in Table 2 and used in the ERCIA tool. The typical activities of radionuclides (238U, 226Ra, 228Ra, 40K, and 210 Po) in seawater were chosen from other study (Lin et al., 2016b). The concentration factors were derived from the IAEA document and the Wildlife Transfer Parameter Database (IAEA, 2004; Hosseini et al., 2008). The representative marine biotas encompassed mollusc-bivalve, crustacean, polychaete worm, benthic fish, and pelagic fish. These marine biotas could be commonly observed in coral reefs, mangroves, and hydrothermal vents. Notice that we had not considered phytoplankton and zooplankton due to their absence in hydrothermal vents without the availability of sunlight. Although activity in marine biotas was estimated using the ERICA tool, the estimation was generally comparable to direct measurements of activity in marine biotas from the coastal sea (Heldal et al., 2019), open ocean (Yu et al., 2018), and hydrothermal vents (Cherry et al., 1992; Boisson et al., 2001; Charmasson et al., 2009). Naturally occurring radionuclides of 238U, 226Ra, 228Ra, and 40K are the most common primordial radionuclides of uranium decay series, thorium decay series, and potassium, imposing dominant radiation dose on human and non-human species in the Earth's system (Liu and Lin, 2018; Lin et al., 2019b). Although artificial radionuclides were significantly produced and released into the Earth's system (Lin et al., 2015; Waters et al., 2015), the activity and associated radiation dose of artificial radionuclides were generally lower than that of naturally occurring radionuclides (Aarkrog et al., 1997; Yu et al., 2018; Heldal et al., 2019). Recently, radiation dose rate of 210Po were emphasized because of its dominant contribution to total radiation dose on human and non-human species (Johansen et al., 2015; Yu et al., 2018).
210
Table 3 Radiation dose rate on non-human species in coral reefs, mangroves, and hydrothermal vents using the ERICA tool. Total radiation dose rate of
Mollusc - bivalve Crustacean Polychaete worm Benthic fish Pelagic fish
238
U,
226
Ra,
228
Ra, and
40
K (μGy/h)
Radiation dose rate of
210
Po (μGy/h)
Coral reefs
Mangroves
Hydrothermal vents
Coral reefs
Mangroves
Hydrothermal vents
0.13 0.13 1.82 0.21 0.20
0.15 0.15 1.88 0.23 0.20
0.17 0.17 1.92 0.25 0.20
19.8 66.1 143 24.8 24.8
19.8 66.1 143 24.8 24.8
19.8 66.1 143 24.8 24.8
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Fig. 5. Contributions of radionuclides to total dose rate of marine biotas in coral reefs.
CRediT authorship contribution statement
Declaration of competing interest
Wuhui Lin: Conceptualization, Methodology, Funding acquisition, Writing-original draft. Yu Feng: Data curation, Methodology, Software. Kefu Yu: Resources, Investigation, Funding acquisition, Project administration. Yi Han: Methodology, Data curation, Software. Shiyue Wang: Methodology, Data curation, Software. Zhenni Mo: Methodology, Data curation. Qiuyun Ning: Methodology, Data curation. Xinming Liu: Resources, Funding acquisition. Dingyong Huang: Resources, Methodology. Jianjia Wang: Resources, Methodology.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work is benefited from the IAEA/RCA Regional Training Course on Dose Assessment and Risk Analysis Modeling hosted by the IAEA and Third Institute of Oceanography, Ministry of Natural Resources of China. We thanked Dr. M.P. Johansen and Dr. N.A. Beresford for their lectures in the regional training course on ERICA tool. This study was financially supported by the National Natural Science Foundation of
Fig. 6. Contributions of radionuclides to total dose rate of marine biotas in mangroves. 6
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Fig. 7. Contributions of radionuclides to total dose rate of marine biotas in hydrothermal vents.
China (41906043 and 91428203), the National Key Basic Research Program of China (2013CB956102), and the Natural Science Foundation of Guangxi Province (2017GXNSFBA198096 and 2019GXNSFAA185006).
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