137Cs and 210Po in Pacific walrus and bearded seal from St. Lawrence Island, Alaska

The activity concentration of Cesium-137 ((137)Cs) and naturally-occurring Polonium-210 ((210)Po) were measured in the muscle tissue, kidney and liver of Pacific walrus (Odobenus rosmarus divergens) and bearded seal (Erignathus barbatus) collected by native hunters from the Bering Sea during May 1996. The mean (137)Cs concentrations in muscle, liver and kidney of Pacific walrus were 0.07, 0.09 and 0.07 Bq kg(-1) (n=5, wet weight), respectively, and 0.17, 0.10, and 0.17 Bq kg(-1) (n=2, wet weight), respectively, in bearded seal. In general, (137)Cs tissue concentrations are significantly lower than those previously reported for mammals from other regions. By comparison, (210)Po activity concentrations are more variable and appear to be higher level compared with mammal data from other regions. The mean (210)Po concentration in the muscle tissue, liver and kidney of Pacific walrus (n=5, wet weight) were 28.7, 189, and 174 Bq kg(-1), respectively. This compares with (210)Po concentration values (n=2, wet weight) of 27, 207 and 68 Bq kg(-1) measured in the muscle tissue, liver and kidney, of bearded seal, respectively. Estimated concentration factors--as defined by the radionuclide concentration ratio between the target tissue to that in sea water--were two to three orders of magnitude higher for (210)Po that those of (137)Cs. We conclude from radiological dose estimates that ingestion of (137)Cs in foods derived from walrus and seal will pose no threat to human health. This work has important implications for assessment of risks of Alaskan coastal communities concerned about the dumping of nuclear waste in the Russia Arctic.     

210Po and 210Pb variations in fish species from the Aegean Sea and the contribution of 210Po to the radiation dose

In recent years, there has been increasing interest in the significance of natural radionuclides, particularly (210)Po, in the marine environment. (210)Po, a naturally occurring alpha emitter, accumulates in marine organisms and reflects differences in their diets. In the literature, there is no data for (210)Po and (210)Pb activity concentrations for fish species on the Turkish coast of Aegean Sea. Therefore, in this study, multiple fish species were collected from six stations seasonally on the Turkish coast of Aegean Sea and were analyzed for their (210)Po and (210)Pb content. The (210)Po and (210)Pb concentrations in the fish samples were found to vary from undetectable levels to 499 ± 44 Bq kg(-1) dry weight (dw) and from 1.0 ± 0.3 Bq kg(-1) to 35 ± 4.0 Bq kg(-1) (dw), respectively. There were no significant differences in the activity concentrations of (210)Po and (210)Pb in fish samples between seasons (ANOVA, P>0.05). The highest dose contribution of (210)Po to humans was calculated to be 10,530 μSv year(-1).     

Ecotoxicological effects of a semi-submerged municipal dump (Castle harbour, Bermuda) on the Calico scallop Argopecten gibbus

A biomarker study was undertaken using the Calico scallop Argopecten gibbus to assess the ecotoxicological effects of a semi-submerged municipal dump on the adjacent patch reef lagoon ecosystem (Castle harbour, Bermuda). Caged scallops were deployed in situ for 2 months at various distances from the dump (50 m, 900 m and 2.7 km) and at a reference site (14 km). A suite of biomarkers comprising metallothionein (MT), lipid peroxidation (LPO), vitellin-like proteins (Vn), glutathione S-transferase (GST), DNA strand breaks and condition factor (CF) were investigated in various tissues of the scallop (gill, digestive gland and gonad). Levels of heavy metals were also measured in the whole scallop soft tissue. While there was some variation in response between tissues, in general the results indicated that the dump was negatively impacting scallops deployed in the adjacent marine environment: elevated levels of MT, DNA strand breaks, Vn and GST and reduced condition factor were found for scallops deployed nearest to the dump and at the site 1.5 km from this point source of contamination (Tuckers town) in Castle harbour, with respect to the reference site, North Rock (although this exhibited some degree of metal contamination). The gills from scallops deployed at the dump site were the most responsive tissue, with the highest expression of MT, LPO and DNA damage. This study indicates the potential of the Calico scallop as a convenient bioindicator species in the marine tropical benthos.     

A large excess of 210Po in the overlying water of the Zhubi Coral Reef flat, in the South China Sea

The temporal variability of ²¹⁰Po and ²¹⁰Pb was examined in the overlying water of the Zhubi Coral Reef flat to detect nutrient-like behavior of ²¹⁰Po. Different mechanisms influencing their geochemical behaviors were observed. Excess ²¹⁰Po relative to ²¹⁰Pb revealed an additional input of ²¹⁰Po other than in situ production from ²¹⁰Pb. The ²¹⁰Po input comes from the reef flat sediment through diffusion. The diffusion contributes 62% of the total ²¹⁰Po. This diffusion of ²¹⁰Po directly highlights its nutrient-like behavior. No input, but the slight removal, of ²¹⁰Pb was observed. Fractionation factors indicate that particulate matter prefers to adsorb ²¹⁰Po rather than ²¹⁰Pb. In combination with particulate composition, ²¹⁰Po diffusion was closely related to organic matter. These results reveal that ²¹⁰Po might be a potential tracer for quantifying nutrient recycling in the Coral Reef system.     

Disequilibria between ~(210)Po and ~(210)Pb in surface waters of the southern South China Sea and their implications

Naturally occurring 210Po (half-life 138.4d) is the granddaughter of 210Pb (half-life 22.3a), both are members of 238U decay series and have been inten-sively utilized to study kinetic aspects of material cy-cling in the ocean[1]. Based on radioactive disequilibria in the 226Ra-210Pb-210Po system, oceanographical processes with different timescales have been widely studied. Rama et al.[2] first detected excess 210Pb rela-tive to its precursor 226Ra in surface waters, and considered this exc…     

Levels of Po and Pb in mussel and sediments in Candarlı Gulf and the related dose assessment to the coastal population

²¹⁰Po and ²¹⁰Pb in mussel (Mytilus galloprovincialis) and sediment samples collected at Candarl? Gulf during the period of 2010–2012 are presented and discussed. The activity concentrations of ²¹⁰Po and ²¹⁰Pb were measured by means of alpha spectrometry. Activity concentrations of ²¹⁰Po and ²¹⁰Pb in mussels are in the ranged of 332 ± 17–776 ± 23 Bq kg⁻¹ dw and 14 ± 1–40 ± 5 Bq kg⁻¹ dw, for sediments the ranges for 52 ± 5–109 ± 8 Bq kg⁻¹ dw and 38 ± 5–92 ± 9 Bq kg⁻¹ dw, respectively. The estimated consequent annual effective ingestion dose due to ²¹⁰Po and ²¹⁰Pb from mussel consumption in Candarl? Gulf coastal region were calculated. The highest dose due to ²¹⁰Po and ²¹⁰Po were calculated to be 4232 ± 126 μSv and 126 ± 16 μSv, respectively.     

Monitoring of DSP toxins in small-sized plankton fraction of seawater collected in Mutsu Bay,Japan, by ELISA method: relation with toxin contamination of scallop

Monitorings were conducted on DSP toxins in mid-gut gland of scallop (mouse assay), cell numbers of toxic dinoflagellate species of Dinophysis, and diarrhetic shellfish poisoning (DSP) toxins in small-sized (0.7-5 microm) plankton fraction of seawater collected from surface (0 m) and 20 m depth at a station in Mutsu Bay, Aomori Prefecture, Japan, in 2000. A specific enzyme-linked immunosorbent assay (ELISA) was employed for the analysis of DSP toxins in small-sized plankton fraction using a mouse monoclonal anti-okadaic acid antibody which recognizes okadaic acid, dinophysistoxin-1, and dinophysistoxin-3. DSP toxins were detected twice in the mid-gut gland of scallops at 1.1-2.3 MU (mouse units) g(-1) on 26 June and at 0.6-1.2 MU g(-1) on 3 July, respectively. Relatively high cell densities of D. fortii were observed on 26 June and 11 September, and may only contribute to the bivalve toxicity during late June to early July. D. acuminata did not appear to be responsible for the toxicity of scallops in Mutsu Bay in 2000. ELISA monitoring of small-sized plankton fraction in seawater could detect DSP toxins two weeks before the detection of the toxin in scallops, and could do so two weeks after the loss of the bivalve toxicity by mouse assay. On 17 July, toxic D. fortii was detected at only small number, <10 cells l(-1), but DSP toxins were detected by the ELISA assay, suggesting a presence of other toxic small-sized plankton in seawater. For the purpose of reducing negative impacts of DSP occurrences, monitorings have been carried out hitherto on DSP toxins of bivalve tissues by mouse assay and on cell densities of "toxic" species of Dinophysis. Here we propose a usefulness of ELISA monitoring of plankton toxicity, especially in small-sized fraction, which are possible foods of mixotrophic Dinophysis, as a practical tool for detecting and predicting DSPs in coastal areas of fisheries grounds of bivalve aquaculture.     

Possible effects of organotins on scallop recruitment

The adult populations of the scallop (Pecten maximus) and of flame shells (Lima hians) have declined in the North Water of Mulroy Bay on the north coast of Ireland. Settlements of these and some other bivalve species either failed or were reduced. These events relate well to the first introduction and subsequent increased use of organotin net-dips on salmonid farms in this Bay. The last use of these net-dips was during the spring of 1985. In 1986 these was a good settlement of scallops, and settlements of other bivalves were recorded except for flame shells. Levels of TBT in adult scallop tissue in the North Water are high, 0.7 μg g⁻¹ wet wt; levels determined in other species were much lower. Pacific oyster (Crassostrea gigas) shell thickening was used to monitor the presence of organotins in a number of areas including Mulroy Bay. In Kilkieran Bay, an area having a scallop fishery, this was greatest at the innermost station, suggesting higher levels there. Shell thickening and organotins in Pacific oysters were also measured in Cork Harbour.     

Carbon and nitrogen cycling in the Zhubi coral reef lagoon of the South China Sea as revealed by Po and Pb

The radionuclides ²¹⁰Po and ²¹⁰Pb were examined to trace the cycling of particulate organic carbon (POC) and particulate organic nitrogen (PON) in the Zhubi coral reef lagoon. The net export flux of POC to the open sea is 14 mgC m⁻² d⁻¹. However, the net exchange of PON has not yet been observed. On average, the vertical export fluxes in the lagoon of POC and PON, as derived from ²¹⁰Po/²¹⁰Pb disequilibria, are 43 mgC m⁻² d⁻¹ and 13.8 mgN m⁻² d⁻¹, respectively. The deficit of ²¹⁰Po relative to ²¹⁰Pb in particulate matter provides evidence for the degradation of particulate organic matter. According to the mass balance budgets, 310 mgC m⁻² d⁻¹ and 121 mgN m⁻² d⁻¹ were recycled into dissolved fractions. Based on a first-order kinetics model, the degradation rate constants of POC and PON are 0.28 and 0.30 m⁻¹, respectively. Thus, ²¹⁰Po and ²¹⁰Pb can quantify the cycling of carbon and nitrogen in this coral lagoon.     

Disequilibria between 210Po and 210Pb in surface waters of the southern South China Sea and their implications

Activities of the naturally occurring radionuclides, ²¹⁰Pb and ²¹⁰Po, were measured in both dissolved (<0.45 μm) and particulate (>0.45 μm) phases from surface waters of the southern South China Sea. The average activity of particulate ²¹⁰Pb, 0.23 Bq/m³ (n=23), accounted for about 12% of the total ²¹⁰Pb, which corresponds with values of open oceans. Particulate ²¹⁰Po, with an average activity of 0.43 Bq/m³, accounted for about 40% of the total ²¹⁰Po, which was much higher than those of open and eutrophic oceans. The residence times of total ²¹⁰Po and ²¹⁰Pb in surface waters estimated from an irreversible steady-state model were 0.82 a and 1.16 a, respectively. The consistently high fractionation factor calculated either by scavenging rate constants (5.42) or K_d values (6.69) suggested that a significant fractionation occurred between ²¹⁰Po and ²¹⁰Pb during their removal from solution to particles and that the two radionuclides had different biogeochemical cycling pathways in the oligotrophic South China Sea. Furthermore, our results indicated that there exist different fractionation mechanisms between ²¹⁰Po and ²¹⁰Pb in different marine environments: in eutrophic ocean, plankton detritus and fecal pellets are the main carrier of ²¹⁰Po and ²¹⁰Pb, by which ²¹⁰Po and ²¹⁰Pb have been scavenged and removed; while in oligotrophic ocean, microbes could become the main carrier of ²¹⁰Po and fractionate ²¹⁰Po and ²¹⁰Pb significantly as a result of scarce plankton detritus and fecal pellets. These results suggest the use of ²¹⁰Po to trace marine biogeochemical processes relating to microbial activities and the cycling of sulfur group elements (S, Se, Te and Po).     

Assessment of health safety from ingestion of natural radionuclides in seafoods from a tropical coast, India

The activities of ²¹⁰Po and ²¹⁰Pb were determined in commonly consumed seafoods to evaluate the internal exposure and risk to humans residing Kudankulam coast where a mega nuclear power plant is under construction. The concentration of ²¹⁰Po in seafoods ranged from 1.2 ± 0.7 to 248 ± 8.1 Bq kg⁻¹. Meanwhile, ²¹⁰Pb ranged between 1.1 ± 0.05 and 14.8 ± 1.6 Bq kg⁻¹. The committed effective dose (CED) due to ²¹⁰Po and ²¹⁰Pb varied from 11.04 to 515.6 and 3.93 to 23.5 μSv yr⁻¹, respectively. The lifetime cancer risk for the public due to ²¹⁰Po was in the range of 3.47 × 10⁻⁵-1.62 × 10⁻³ and it was 4.03 × 10⁻⁵-1.96 × 10⁻⁴ due to ²¹⁰Pb. The activity intake, effective dose and cancer risk was found lesser than international guidelines and the seafood intake was considered to be safe for human consumption.     

Present state and historical changes of trace metal pollution in Kaoping coastal sediments, southwestern Taiwan

Surface and gravity-cored sediments were collected from the Kaoping coastal area off southwestern Taiwan to determine particle size, organic carbon, trace metal concentration and enrichment factor (EF), 210Pb dating, and 206Pb/207Pb ratio for determining present and historical metal pollution. Surface distributions of trace metals ranged from 0.02 to 0.13 mg/kg for Cd (EF: 0.16-1.65), from 35 to 189 mg/kg for Cr (EF: 0.85-2.92), from 25 to 64 mg/kg for Ni (EF: 0.53-2.38), from 10 to 32 mg/kg for Pb (EF: 1.20-4.94), and from 29 to 129 mg/kg for Zn (EF: 1.18-3.50). Trace metal concentrations correlate closely with distributions of mud (<63 microm) and organic carbon which accumulate largely around river mouths and within the Kaoping Canyon. With the exception of Cd, Cr and Ni in certain areas with rather coarse sediments, metals were generally elevated above the baseline levels over the studied area. Metals were also relatively enriched in areas with high contents of mud and organic carbon. Sedimentation rates derived from the excess 210Pb data in core sediments sampled from the canyon illustrate metal pollution beginning around 1970 that is corresponding to the booming time of economic growth in Taiwan. Meanwhile, the status of Pb pollution in core sediments is verified by an inversed correlation between 206Pb/207Pb ratios and Pb concentrations. Anthropogenic Pb and other metals in the studied area were apparently derived primarily from the Kaoping River and accumulated around the river mouth and within the Kaoping Canyon. The Kaoping Canyon appears to act as a major sink for river borne trace metals.     

Integrated biomarker assessment of the effects exerted by treated produced water from an onshore natural gas processing plant in the North Sea on the mussel Mytilus edulis

The biological impact of a treated produced water (PW) was investigated under controlled laboratory conditions in the blue mussel, Mytilus edulis. Mussel health status was assessed using an integrated biomarker approach in combination with chemical analysis of both water (with SPMDs), and mussel tissues. Acyl-CoA oxidase activity, neutral lipid accumulation, catalase activity, micronuclei formation, lysosomal membrane stability in digestive cells and haemocytes, cell-type composition in digestive gland epithelium, and the integrity of the digestive gland tissue were measured after 5 week exposure to 0%, 0.01%, 0.1%, 0.5% and 1% PW. The suite of biomarkers employed were sensitive to treated PW exposure with significant sublethal responses found at 0.01-0.5% PW, even though individual chemical compounds of PW were at extremely low concentrations in both water and mussel tissues. The study highlights the benefits of an integrated biomarker approach for determining the potential effects of exposure to complex mixtures at low concentrations. Biomarkers were integrated in the Integrative Biological Response (IBR/n) index.     

Seasonal and pollution-induced variations in biomarkers of transplanted mussels within the Beagle Channel

The occurrence of biomarker variations linked to environmental factors makes it difficult to distinguish the effect of pollution. In an attempt to evaluate spatial and seasonal effects of environmental parameters on biomarker responses, mussels Mytilus edulis chilensis coming from an aquaculture farm were transplanted to several points within Ushuaia Bay (Beagle Channel) for 6 weeks in summer and winter. Activities of superoxide dismutase, catalase, glutathione-S-transferase and levels of lipid peroxidation were measured in gills and digestive gland. Cu, Zn, Fe, Cd and Pb concentrations were also assessed. Results indicated a significant effect of seasons on biological responses as well as in metal bioaccumulation showing the influence of natural factors such as dissolved oxygen, temperature and food availability. The interdependence of those environmental factors is important for the homeostasis of thermoconformers, especially regarding their oxidative metabolism and should also be taken into consideration to distinguish natural from pollution-induced variations.     

Natural radionuclides in the water of Narragansett Bay

The concentrations of radionuclides of the U-Th series (²³⁸U,²³⁴Th,²³⁴U,²³⁰Th,²²⁶Ra,²¹⁰Pb,²¹⁰Po, and²³²Th,²²⁸Ra,²²⁸Th) in the water of Narragansett Bay are reported. Analysis of the total, particulate, dissolved and colloidal forms of Th isotopes reveal a consistent removal behavior which is controlled mainly by the particulate matter concentration and the sediment resuspension rate. Half-removal times of Th from solution onto particles range from 1.5 to 15 days, and settling velocities of Th containing particles range generally between 1 and 11 m/day.²¹⁰Pb and²¹⁰Po concentrations are seasonally dependent, with higher concentrations and slower removal during the early summer (half-removal times from solution onto particles of 1–5 days in winter and up to 2 months in early summer).     

Geochemical behavior of 210Pb and 210Po in the nearshore waters off western Taiwan

Dissolved and particulate (210)Pb and (210)Po were determined at 15 stations along the coastline off western Taiwan in April 2007. The (210)Pb activities in dissolved and particulate phases fell within a relatively small range of 2.4-5.2 dpm 100 L(-1) and 1.0-3.2 dpm 100 L(-1), respectively. The dissolved and particulate (210)Po activities also fell within a small range of 0.8-3.4 dpm 100 L(-1) and 1.1-2.9 dpm 100 L(-1), respectively. The correlation of the distribution coefficients (K(d)) of (210)Pb and (210)Po with particle concentration in turbid waters are not as evident as in the open ocean. The mass balance calculation shows that the residence times of (210)Pb and (210)Po with respect to particle removal from the nearshore waters ranges from 3 to 15 days and from 14 to 125 days, respectively. The flux of particulate organic carbon was estimated by (210)Po proxy and ranged from 4.8 to 33.7 mmol-C m(-2) d(-1).     

Could a 1755-Like Tsunami Reach the French Atlantic Coastline? Constraints from Twentieth Century Observations and Numerical Modeling

The tsunami generated by the 1 November, 1755 earthquake off the coast of Portugal affected mainly the coastlines of the Iberian Peninsula and Northwest Morocco, but was also observed in some places along the North Atlantic coasts. To determine whether the event could have effected the French coastline, we conducted a study to search for signs of the tsunami in historical records from all tide gauge stations off the French Atlantic coast during the twentieth century, specifically for the 28 February, 1969 and the 26 May, 1975 tsunamis that were recorded by the Portuguese tide gauge network. Because many recordings are available in La Rochelle (located on the southwest coast of France), we focused our study on this harbor. The analysis of the tide gauge data shows no evidence for tsunamis in La Rochelle, neither in 1969 nor in 1975. To confirm this lack of tsunami signals, we used nonlinear, shallow water equations to compute the tsunami propagation to the French Atlantic coastline for both 1969 and 1975 events. Results obtained from these simulations confirm otherwise unnoticeable wave amplitudes at La Rochelle harbor. In a second step, tsunamis from three different scenarios for the 1755 earthquake were modeled to estimate the impact of such a tsunami on the French Atlantic coast, with a focus on La Rochelle harbor. A comparison of the functions of tide configuration was made in order to analyse the difference in impact. The results show that, while the harbor is poorly impacted, several areas (western part of the island of Ré and northern coast of the island of Oléron) may have experienced a moderate impact from 0.5 to 1 m, especially since the tide was high at the time of arrival, possibly causing local inundations in lowland areas.     

Carbon and nitrogen cycling in the Zhubi coral reef lagoon of the South China Sea as revealed by 210Po and 210Pb

The radionuclides (210)Po and (210)Pb were examined to trace the cycling of particulate organic carbon (POC) and particulate organic nitrogen (PON) in the Zhubi coral reef lagoon. The net export flux of POC to the open sea is 14 mg Cm(-2) d(-1). However, the net exchange of PON has not yet been observed. On average, the vertical export fluxes in the lagoon of POC and PON, as derived from (210)Po/(210)Pb disequilibria, are 43 mg Cm(-2) d(-1) and 13.8 mg Nm(-2) d(-1), respectively. The deficit of (210)Po relative to (210)Pb in particulate matter provides evidence for the degradation of particulate organic matter. According to the mass balance budgets, 310 mg Cm(-2) d(-1) and 121 mg Nm(-2) d(-1) were recycled into dissolved fractions. Based on a first-order kinetics model, the degradation rate constants of POC and PON are 0.28 and 0.30 m(-1), respectively. Thus, (210)Po and (210)Pb can quantify the cycling of carbon and nitrogen in this coral lagoon.     

Phosphorus retention and release by sediments in the eutrophic Mai Po Marshes, Hong Kong

This study examined the phosphorus retention and release characteristics of sediments in the eutrophic Mai Po Marshes in Hong Kong. Results of chemical fractionation show that the sum of inorganic P pools exceeded 50% of the total sediment P content, with the redox-sensitive iron-bound P (Fe(OOH) approximately P) being the dominant P fraction. Given the considerable average Fe(OOH) approximately P concentration of 912 microg g(-1), Mai Po sediments demonstrated a great potential to release bioavailable P under low sediment redox potentials. This was further supported by the high mean anaerobic P flux of 31.8 mg m(-2)d(-1) recorded in Mai Po sediment cores, indicating the role of bottom sediments as a net P source. Although sediments in Mai Po had appreciable Langmuir adsorption maxima (1642-3582 mg kg(-1)), the high zero equilibrium P concentrations (0.02-0.51 mg L(-1)) obtained suggest that sediment sorption processes would contribute to sustaining the eutrophic conditions in overlying water column even with a further reduction in external P load. Concerted efforts should be made to reduce internal loading of P, especially under reducing conditions, to complement the implementation of zero discharge policy for Deep Bay for effective eutrophication abatement and long-term water quality improvement in the Mai Po Marshes.     

210Po and210Pb distributions in the central and eastern Indian Ocean

Disequilibrium between²¹⁰Po and²¹⁰Pb and between²¹⁰Pb and²²⁶Ra has been mapped in the eastern and central Indian Ocean based on stations from Legs 3 and 4 of the GEOSECS Indian Ocean expedition.²¹⁰Po/²¹⁰Pb activity ratios are less than 1.0 in the surface mixed layer and indicate a residence time for Po of 0.6 years.²¹⁰Po and²¹⁰Pb are generally in radioactive equilibrium elsewhere in the water column except at depths of 100–500 m, where Po may be returned to solution after removal from the surface water, and in samples taken near the bottom at a few stations.²¹⁰Pb excesses relative to²²⁶Ra are observed in the surface water but these excesses are not as pronounced as in the North Pacific and North Atlantic. The difference is attributable to a lower flux of²¹⁰Pb from the atmosphere to the Indian Ocean. Below the main thermocline,²¹⁰Pb activities increase with depth to a broad maximum before decreasing to lower values near the bottom. Departures from this pattern are especially evident at stations taken in the Bay of Bengal (where²¹⁰Pb/²²⁶Ra activity ratios as low as 0.16 are observed) and near the Mid-Indian Ridge. The data suggest that removal of²¹⁰Pb at oceanic boundaries, coupled with eddy diffusion along isopycnals, can explain gradients in²¹⁰Pb near the boundary. Application of a simple model including isopycnal diffusion, chemical removal, production and radioactive decay produces fits the observed²¹⁰Pb/²²⁶Ra gradients for eddy diffusion coeffients of ～ 10⁷ cm²/s. High productivity in surface waters of the Bay of Bengal makes this region a sink for reactive nuclides in the northern Indian Ocean.