Assessment of Hg Pollution Released from a WWII Submarine Wreck

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Assessment of Hg pollution released from a WWII submarine wreck (U-864 ) by Hg isotopic analysis of sediments and Cancer pagurus tissues Ana Rua-Ibarz, Eduardo Bolea Fernandez, Amund Maage, Sylvia Frantzen, Stig Valdersnes, and Frank Vanhaecke Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b02128 • Publication Date (Web): 09 Sep 2016 Downloaded from http://pubs.acs.org on September 13, 2016

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Assessment of Hg pollution released from a WWII submarine

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wreck (U-864 ) by Hg isotopic analysis of sediments and Cancer

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pagurus tissues

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Ana Rua-Ibarza, Eduardo Bolea-Fernandeza, Amund Maageb, Sylvia Frantzenb, Stig Valdersnesb and

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Frank Vanhaeckea,*

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a

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Ghent, Belgium

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b

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*

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Ghent University, Department of Analytical Chemistry, Campus Sterre, Krijgslaan 281-S12, 9000

National Institute of Nutrition and Seafood Research, Strandgaten 229, 5002 Bergen, Norway

Corresponding author

Supporting Information ABSTRACT

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Hg pollution released from the U-864 submarine sunk during WWII and potential introduction of that

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Hg into the marine food chain have been studied by a combination of quantitative Hg and MeHg

14

determination and Hg isotopic analysis via cold vapor generation multi-collector inductively coupled

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plasma-mass spectrometry (CVG-MC-ICP-MS) in sediment and Cancer pagurus samples. The

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sediment pollution could be unequivocally linked with the metallic Hg present in the wreck. Crabs

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were collected at the wreck location and 4 nmi north and south and their brown and claw meat were

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analyzed separately. For brown meat, the δ202Hg values of the individuals from the wreck location

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were shifted towards the isotopic signature of the sediment and thus, the submarine Hg. Such

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differences were not found for claw meat. The isotope ratio results suggest direct ingestion of metallic

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Hg by C. pagurus, but do not offer any proof for any other introduction of the submarine Hg into the

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marine food chain.

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INTRODUCTION

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At the end of World War II (February 9th, 1945), the German submarine U-864 was torpedoed and

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sunk by the British submarine HMS Venturer in the proximity of Bergen (Norway). According to the

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cargo list, the U-boat was transporting 67 tons of metallic mercury (Hg) in almost 2000 steel

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containers in its keel. In 2003, the wreckage was discovered by the Royal Norwegian Navy at 150 m

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depth and 2 nautic miles (nmi) west of Fedje island. Some of the containers were broken and Hg has

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contaminated the surrounding sediments. This has aroused serious concern about the corresponding

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environmental impact.1 Since 2004, the Hg levels in seafood have been monitored by the National

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Institute of Nutrition and Seafood Research (NIFES) on behalf of the Norwegian Coastal

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Administration to evaluate potential introduction of this Hg into the marine food chain.2, 3

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Hg is a highly toxic heavy metal that can be globally distributed due to its capacity for traveling long

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distances in the atmosphere, and it readily biomagnifies through the trophic chain.4,

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strongly depends on its chemical form, and although both inorganic (IHg) and organic Hg have a

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deleterious effect on human health, methylmercury (MeHg) poses the greatest risk. This Hg species is

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prevalent in fish, the consumption of which is the primary source of human MeHg exposure.4, 6, 7 Hg in

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the environment is mainly attributed to anthropogenic sources, e.g., fossil fuel combustion, mining-

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related emissions, and industrial activities;8-10 although also natural sources, e.g., volcanic emissions,11

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contribute. Hg deposition in aquatic systems and sediments enables the conversion of IHg into MeHg

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via microbial methylation,12 thus favoring its bioaccumulation through the aquatic food web. Previous

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studies have found a strong correlation between the Hg levels in sediments and in biota,13,

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suggesting such processes as the main source of Hg in the aquatic food web. However, atmospheric

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deposition15 and/or MeHg accumulation in the water column particles, have also been suggested as

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possible sources.16

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Next to elemental and speciation analysis,17, 18 determination of the isotopic composition of Hg has

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emerged as a key tool for providing a better understanding of the biogeochemical cycling of this

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element and for evaluating its environmental risk.19-22 However, although its applicability has already

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been demonstrated in some real-life case-studies during the last years,8, 13, 23, 24 important knowledge

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Hg toxicity

14


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gaps concerning the chemical transformations that Hg can undergo in complex environmental systems

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and the corresponding effects on its isotopic composition remain. This remark is especially valid for

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the unusual context of this work, characterized by the presence of a massive amount of elemental Hg.

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In addition, Hg isotopic analysis is not free from challenges and multi-collector inductively coupled

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plasma mass spectrometry (MC-ICP-MS) instrumentation is required due to the small range of natural

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variation in the isotopic composition of Hg. Cold vapor generation (CVG) of Hg(0) enables accurate

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and precise Hg isotopic analysis as a steady signal without isotope fractionation is generated via

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complete reduction of the Hg(II) in the sample digest using SnCl2. Also, compared to conventional

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pneumatic nebulization, CVG provides a 20-fold improvement in Hg+ signal intensity, allowing the

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measurement of environmental samples in which Hg concentrations tend to be low.25-27

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Hg isotopes display fractionation as its isotopes may engage in physical processes and/or bio-

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geochemical reactions to a slightly different extent. In the case of mass-dependent fractionation

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(MDF), the observed change in the isotope ratio is linearly dependent on the difference in mass

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between nominator and denominator isotope.28, 29 The resulting differences in the isotopic composition

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are typically reported as δ202Hg and have already been measured in several sample types, e.g., coal,

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soil, rock, lichen, peat, snow, rainfall, sediment and biological materials,19-21 and many environmental

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processes and reactions, e.g., evaporation, biotic methylation and demethylation,30-32 were shown to be

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accompanied by MDF. This renders Hg isotopic analysis a viable tool for the identification of Hg

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pollution sources and for tracing Hg emitted into the environment.8, 33

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In addition to MDF, the isotopic composition of Hg may also be affected by mass-independent

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fractionation (MIF),34, 35 reported as ∆199Hg and ∆201Hg. Although the origin of MIF has not been fully

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understood yet, it has been tentatively explained in terms of nuclear volume and magnetic isotope

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effects.36, 37 Berquist and Blum38 and Malinovsky et al.39 reported MIF for the odd-numbered isotopes

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of Hg as a result of photochemical reduction in aqueous medium, while this “odd-MIF” was not

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observed when the reduction was carried out in dark abiotic conditions. Berquist and Blum38 showed

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that fish samples collected from three different lakes displayed a wide range of MIF (expressed as

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∆199Hg) and used these data to estimate the extent of MeHg photodegradation prior to MeHg uptake



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by organisms from the lowest level within the food web, assuming that MIF is not modified by trophic

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transfer to fish. Although this assumption has been experimentally documented in several studies,13, 23,

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40

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“odd-MIF”, recent studies have also reported MIF of the even-numbered isotopes of Hg. This "even-

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MIF" has been observed for samples of atmospheric origin, e.g., rain water and snow; photo-initiated

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oxidation of Hg(0) in the tropopause has been suggested as the possible origin of this MIF.43-45

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Clearly, the complementary information provided by MDF and MIF of Hg isotopes may help in

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understanding the chemistry of Hg in the environment and in tracking Hg sources. In this work,

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quantitative Hg determination and MeHg speciation have been combined with high-precision MC-

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ICP-MS Hg isotopic analysis with the aim of evaluating the Hg pollution in the vicinity of the U-864

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wreck and the potential introduction of metallic Hg released from the wreck into the marine food

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chain.

Jackson et al.41 and Das et al.42 suggested that ∆199Hg values can be modified in vivo. In addition to

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EXPERIMENTAL SECTION

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Area of study and sample collection

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Metallic Hg from the U-864 wreck was retrieved from an intact steel container found in the sediment

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near the wreckage. Core sediments (n = 14) were sampled in the immediate vicinity of the wreck at

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different depths (0 – 2.4 m) in January 2013 using an ROV (Solhjell & Lunne, 2013). Cancer pagurus

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crabs (n = 74) were caught in June 2014 at three sites – the wreck location and about 4 nmi north and 4

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nmi south – from the M/K Vikingfjord H-1-A vessel using deep-water pots (Figure S1 of the

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Supporting Information shows the sampling zones). Sample preparation at NIFES was done as

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described in detail by Julshanm et al.46 Claw meat (muscle) and brown meat (mainly hepatopancreas

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and gonads) were analyzed separately. From the complete set of samples, claw meat and brown meat

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from 13 individual crabs from each location were selected for the purpose of this work (n = 78). C.

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pagurus, also referred to as brown crab, is abundant in northern European coastal waters, is night

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active and known to prey on mussels, snails, barnacles, sea urchins and polychaetes that it can crush

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with its claws. It might also eat softer species like algae, jellyfish and ascidians.47, 48 In Norway, C.


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pagurus is exploited for consumption both commercially and recreationally,49 and both the claw meat

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and the brown meat are consumed.

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THg and %MeHg determination

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The metallic Hg from the submarine was dissolved in 14 M HNO3 (ChemLab, Belgium) and diluted

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appropriately for isotopic analysis (without prior quantification) with high-purity water (resistivity >

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18.2 MΩ.cm) obtained from a Milli-Q Element water purification system (Millipore, France). The

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total mercury (THg) concentration was determined in all sediment and crab tissue samples using a

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ThermoScientific (Germany) Element XR single-collector sector field ICP-MS (SF-ICP-MS)

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instrument, equipped with a 100 µL min-1 concentric nebulizer mounted onto a cyclonic spray

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chamber for sample introduction. Quantification was accomplished via external calibration with Rh (1

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µg L-1) as an internal standard and KBrO3 (0.009 mM) for inhibiting Hg evaporation and minimizing

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memory effects. Acid digestion was accomplished with a 3:1 mixture of 14 M HNO3 and 9.8 M H2O2

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(Fluka, Belgium) and of 7 M HNO3 and 9.8 M H2O2, for sediment and crab tissue samples,

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respectively. The digestion was carried out in closed Teflon® Savillex Beakers, pre-cleaned with

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HNO3 and HCl (ChemLab, Belgium) and subsequently rinsed with Milli-Q water. The samples were

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heated on a hot plate at 110 °C overnight to complete the digestion and diluted subsequently for ICP-

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MS analysis. For the sediment samples, multiple digestion replicates were obtained (n = 2 – 3),

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whereas for the crab tissue samples, only one digestion was possible due to the limited sample mass,

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low Hg concentration and subsequent high sample intake required for isotopic analysis. The entire

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procedure was validated using the following certified reference materials (CRMs) with a matrix

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composition similar to that of the samples of interest: BCR CRM 464 (tuna fish), NIST SRM 2704

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(Buffalo river sediment), NRC-CNRC DORM-1, DORM-2 and DORM-4 (fish protein), and NRC-

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CNRC TORT-2 and TORT-3 (lobster hepatopancreas). The results thus obtained are summarized in

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Table S2 of the Supporting Information. In addition to THg determination, for the crab tissue samples,

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MeHg speciation was performed via isotope dilution gas chromatography ICP-MS (GC-ICP-IDMS).

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The method was validated in a previous work with the CRMs ERM CE 464 (tuna fish), NIST SRM



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1566B (oyster tissue) and NIST SRM 2977 (blue mussel), NRC-CNRC DOLT-4 (dogfish liver),

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DORM-3 and TORT-2, as reported by Valdersnes et al.50

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Hg isotopic analysis

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Hg isotopic analysis was carried out using a ThermoScientific (Germany) Neptune multi-collector

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ICP-MS (MC-ICP-MS) unit, equipped with nine Faraday cups (instrumental parameters are shown in

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Table S1 of the Supporting Information). The sample introduction system was based on the

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combination of CVG – using an HGX-200 Cold Vapor & Hydride Generation unit (Teledyne Cetac

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Technologies, US) – and pneumatic nebulization (PN) – using a concentric nebulizer (100 µL min-1)

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fitted onto a dual (cyclonic and Scott-type) spray chamber – for Hg (analyte) and Tl (internal standard

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selected for mass discrimination correction purposes), respectively.27 Hg was reduced to Hg(0) by

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SnCl2 (3% SnCl2.2H2O in 1.2 M HCl) in the gas liquid separator (GLS) of the CVG unit, and the

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resulting Hg vapor was carried away with an Ar gas flow and admixed with the wet aerosol of the Tl

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standard solution produced by PN prior to its introduction into the plasma. Instrumental mass

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discrimination was corrected for by using Tl (NIST SRM 997) as an internal standard in the “Baxter

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approach”,51 followed by external correction relying on NIST SRM 3133, measured in a sample-

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standard bracketing (SSB) approach. External standard and sample solutions were matched in both the

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Hg (5 ± 0.5 µg L-1) and acid (0.7 M HNO3) concentration. Data acquisition was carried out using 5

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blocks of 10 cycles and 4 s of integration time. Blank solution intensities were less than 1 % of the

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sample intensities, and therefore, no blank subtraction was performed because its effect on the δxxxHg

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results was demonstrated to be of the order of ~0.01 ‰ only, which was considered negligible within

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the precision attainable. MDF is reported in delta notation (δxxxHg ‰), referring to NIST SRM 3133:

(‰) =

⁄

⁄

− 1 ∗ 1000 #$%&'()* 1

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where xxx = 199, 200, 201 or 202.

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MIF signatures are expressed using the capital delta notation (∆xxxHg ‰), as the difference between

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the measured δxxxHg and the theoretically calculated value, assuming purely kinetic MDF:28 ∆

=

− ,-, ∗ 0.2520 #$%&'()* 2


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∆ ,-- = ,-- − ,-, ∗ 0.5024 #$%&'()* 3 ∆ ,- = ,- − ,-, ∗ 0.7520 #$%&'()* 4

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An in-house Hg standard solution (Inorganic Ventures, The Netherlands, Lot: F2-HG02105)27 was

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measured approximately every five samples as a measurement quality control sample (Table S3 of the

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Supporting Information). Its associated uncertainty – expressed as standard deviation (SD, n = 40) –

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can be used as the uncertainty in those cases in which the SD calculated for the sample is smaller than

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that associated to the in-house Hg standard solution. In addition, the same CRMs selected for

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validation of the Hg quantification were also used to validate the isotopic analysis of Hg in the

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samples of interest. The isotopic compositions obtained for these CRMs are provided in Table S2 of

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the Supporting Information, in which δ202Hg and ∆199,201Hg are compared to values reported in

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literature. The entire procedure was also validated in a previous work, in which an in-depth evaluation

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of accuracy and precision in Hg isotopic analysis was performed.27

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RESULTS AND DISCUSSION

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THg concentration in sediments

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The THg concentration in sediments collected close to the submarine wreck as a function of depth (n =

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2 – 3 at each depth) ranged from ~60 to ~24,000 mg Kg-1 (wet weight – w.w.). The complete data set

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is provided in Table S4 of the Supporting Information. Previous studies have documented THg

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concentrations in marine sediments coming from, e.g., the Gulf of Trieste (0.1 – 23.3 mg Kg-1),8 the

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central Portuguese Margin (0.018 – 0.594 mg Kg-1),52 and the South China Sea (12 – 84 µg Kg-1).53

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The THg background in ocean sediments is 20 – 100 µg Kg-1.54 Both the high THg concentration and

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the wider range obtained here indicate important Hg contamination, as was previously reported on by

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Uriansrud et al.,55 who obtained IHg levels in surface sediments next to the U-864 wreck of up to

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108,000 mg Kg-1. The THg distribution as a function of depth, provided in Figure 1 (left y-axis),

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demonstrates high heterogeneity, with peak values at 1 and 2.6 m depth, corresponding with samples

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containing visible metallic Hg droplets. The depth profile does not reveal information on origin (or

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timing) and/or changes in Hg pollution. The heterogeneity can be related to the explosion that

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occurred during the torpedoing/sinking, the possibility of metallic Hg sinking down through the sand 7 ACS Paragon Plus Environment


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and clay particles, and the fact that the location suffers from landslides,56 preventing time-resolved

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information to be obtained from the variation in THg as a function of depth. THg and MeHg concentration in crab tissue samples

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THg and MeHg concentrations in the two types of tissues for the crab samples (n = 78), as well as the

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average and the SD for each type of meat are provided in Table S5 of the Supporting Information for

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the three locations studied. Within the entire area, the THg concentration varied from 0.033 to 0.220

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mg Kg-1 (w.w.) with a mean of 0.094 mg Kg-1 in brown meat and from 0.036 to 0.290 mg Kg-1 (w.w.)

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with a mean of 0.11 mg Kg-1 in claw meat. Previous results for C. pagurus caught along the entire

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Norwegian coast were in the range of 0.015 to 0.35 mg Kg-1 (mean of 0.067 mg Kg-1) and 0.021 to

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0.40 mg Kg-1 (mean of 0.095 mg Kg-1) for brown and claw meat, respectively.57 Concentrations of

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THg in brown meat of crabs were higher near the submarine wreck than background levels for the

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Norwegian coast. Claw meat, on the other hand, showed levels similar to background levels. In other

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studies using the same crab species in different marine ecosystems, the THg concentration determined

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ranged from 0.10 to 0.23 mg Kg-1 (dry weight – d.w.) for hepatopancreas and from 0.16 to 2.04 mg

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Kg-1 (d.w.) for muscle.58-60 In agreement with literature values, the THg concentrations reported in this

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work are higher for the claw meat than for the brown meat (Figure S2A – average values), although

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the differences are not statistically significant (texp = 1.81 < tcrit = 2.02). In addition, the THg

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concentration was established to be slightly higher in samples from the north compared to samples

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from the other two locations, as indicated via ANOVA (Fexp = 9.28 > Fcrit = 3.12), which could be

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tentatively explained by the North Atlantic oceanic current going from the south to the north in this

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region.

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MeHg speciation was carried out to determine the fraction of THg present as MeHg (expressed as the

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MeHg fraction in %) in the two types of crab meat and at the three different locations. Clearly, the

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MeHg fraction (%) was distributed differently between the two tissue types (texp = 2.01 < tcrit = 13.58)

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with ranges of 53 to 62% and of 89 to 99% for brown and claw meat, respectively (see Figure S2B and

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Table S4 of the Supporting Information). Such difference in bioaccumulation of IHg and of MeHg in

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different tissues has been documented in the literature and possible accumulation routes have been 8 ACS Paragon Plus Environment

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described. Previous studies concluded that the dominant input of Hg in marine organisms comes from

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the food, although also direct uptake from the water column contributes.61-63 After Hg ingestion, both

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IHg and MeHg are rapidly transferred to the visceral organs, i.e. brown meat in crab, and from there,

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the Hg species are further distributed. In crustaceans, the hepatopancreas acts as the main reservoir for

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IHg when contamination comes from the food. IHg remains in the brown meat, whereas MeHg is

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accumulated in muscle tissue (claw meat), which is characterized by high MeHg storage capacity and

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low depuration rates.18 In addition, the Assimilation Efficiency (AE) is considerably higher for MeHg

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than for IHg,17 while the excretion is favorable for the latter,64 which is in good agreement with the

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results reported in this work.

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In contrast to the differences in THg concentration, ANOVA indicates no significant variations in the

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MeHg fraction (%) between the 3 locations studied (Fexp = 0.46 < Fcrit = 3.12), as is shown in Figure

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S2B and Table S5 of the Supporting Information. However, neither the THg concentration, nor the

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MeHg fraction (%), provides any insight into origin of the Hg pollution, thus necessitating Hg isotopic

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analysis.

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Isotopic composition of metallic Hg

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Isotopic analysis of metallic Hg salvaged from the submarine wreck was carried out aiming to

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elucidate whether this contamination source could be correlated with the Hg pollution observed in the

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surrounding area. The resulting isotopic composition reported as delta (δxxxHg ‰) and capital delta

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(∆xxxHg ‰) notation (average ± SD, n = 10) is shown in Table S6 of the Supporting Information. The

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δ202Hg value is -0.58 ± 0.06 ‰ and the isotopic composition seems to be affected by a slight extent of

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MIF (∆199Hg = -0.06 ± 0.04 ‰ and ∆201Hg = -0.07 ± 0.04 ‰). These values are similar to those

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reported in literature for UM-Almaden metallic Hg (δ202Hg = -0.58 ± 0.08 ‰ and ∆199Hg = -0.01 ±

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0.01 ‰),27, 65 although with a slightly higher degree of negative MIF. This low-extent MIF ( tcrit = 1.99), which

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is attributed to the smaller fraction of Hg present as MeHg (%) in brown meat compared to claw meat,

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due to the capacity of the latter as reservoir of MeHg.72 Figure 3 (A, B and C) shows three-isotope

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plots of δ199Hg vs δ202Hg, δ200Hg vs δ202Hg and δ201Hg vs δ202Hg. The isotopic composition of Hg

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varies profoundly across the different sample types i.e., metallic Hg, sediments, brown meat and claw

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meat. Moreover, in contrast to metallic Hg and sediments, both tissue types demonstrate a clear effect

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of MIF on the odd-numbered Hg isotopes, that is more remarkable for the claw meat than for the

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brown meat (vide infra).

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The δ202Hg values follow the trend: metallic Hg (-0.58 ± 0.06 ‰) < sediments (-0.45 ± 0.12 ‰)
Fcrit = 3.26). Figure 3D shows δ200Hg as a function of δ202Hg for the complete brown

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meat data set. As can be seen, no significant differences were found between the locations north and

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south of the wreck (texp = 0.95 < tcrit = 2.06), whereas statistically significant differences were observed

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between these two locations on the one hand and the wreck location on the other (texp = 3.03 > tcrit =

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2.06 and texp = 4.07 > tcrit = 2.06 for north-of-wreck and south-of-wreck, respectively). Also, it is

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clearly shown that the isotopic signatures of brown tissue for the individual crabs collected at the

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wreck location are shifted in the direction of that of the submarine Hg and the sediments (see Figure

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3D), which suggests that they are affected by metallic Hg from the U-864. Due to the feeding habits of

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this crab species (see experimental section),48 we hypothesize that this difference most likely stems

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from the direct intake of metallic Hg by C. Pagurus, demonstrating that the determination of Hg


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isotopic signatures of visceral organs from C. pagurus is a valuable tool for tracking Hg pollution in

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the marine ecosystem studied and for evaluating the corresponding environmental risk.

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As previously indicated, the isotopic composition of Hg in the crab tissue samples testify of MIF

315

(expressed as ∆xxxHg notation). Figure S4 of the Supporting Information shows the ∆199Hg (A) and

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∆201Hg (B) vs δ202Hg. Significant differences were found between the two tissue types (texp = 8.64 >

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tcrit = 1.99), with ∆199Hg values ranging from 0.22 to 0.25 ‰ for brown meat and from 0.40 to 0.44 ‰

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for claw meat (average ∆199Hg as a function of location and tissue type). These differences are also

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related with the MeHg fraction (%) and a significant correlation (r = 0.707, p = 0.000) was found

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between %MeHg and ∆199Hg within the entire data set (n = 78). However, in contrast to δ202Hg, for

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∆199Hg ANOVA indicates no significant variation between the three sampling zones (Fexp = 0.34 < Fcrit

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= 3.26 and Fexp = 0.55 < Fcrit = 3.26, for brown and claw meat, respectively). ∆199Hg has been used in

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many studies to discern specific processes, such as photochemical reduction of Hg(II) and MeHg,19

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and to study biogeochemical transformations of the bioavailable pools of Hg.14 Das et al.42 suggested

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that MIF in fish from the first two trophic levels might occur during the bioaccumulation and

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biomagnification of Hg. However, several works to date reported on the photochemical reactions

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involving Hg(II) and MeHg as the only processes yielding MIF in aquatic organisms.38, 40, 73, 76 Next to

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the NVE, the other mechanism for explaining MIF of Hg isotopes is the magnetic isotope effect

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(MIE). Bergquist and Blum38 came to the conclusion that photochemical reduction of aqueous Hg(II)

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and of MeHg is most likely accompanied by MIE, and that the participation of either Hg(II) or MeHg

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can be distinguished based on the slope of the straight line obtained by plotting ∆199Hg versus ∆201Hg

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(slopes of 1.0 and 1.3 for Hg(II) and MeHg photoreduction, respectively). In this work, ∆199Hg is

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plotted as a function of ∆201Hg in Figure 4 for the complete data set. A regression line (R2 = 0.83) with

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a slope of 1.02 ± 0.05 was obtained. This value is not significantly different from that for

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photochemical reduction of Hg(II), suggesting that the MIF evidenced in crab tissue samples can be

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mainly attributed to MIE accompanying photoreduction of the IHg in the aquatic ecosystem studied.

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Environmental impact



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Overall, the data obtained in this work provide an expected, but now undeniable link between the Hg

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pollution in the sediments and the metallic Hg leaking from the U-864 wreck. Due to the low content

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of organic matter in the sediments, there is little microbial methylation activity at the wreck location,

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suggesting that the Hg pollution from the U-864 submarine may predominantly remain in the form of

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metallic Hg, which is characterized by a lower bioavailability than other Hg species. We hypothesize

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that the feeding habits of this crab species may allow for direct ingestion of this metallic Hg, and that

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the presence of metallic Hg in the digestive system (and thus, in the brown meat) of C. pagurus is

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most likely the responsible for the differences observed at the wreck place. However, except for this

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variation, the Hg isotope ratio results do not offer any proof for the introduction of the submarine Hg

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into the marine food chain.

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ASSOCIATED CONTENT

349

Supporting Information

350

Additional information is indicated in the text. This material is available free of charge via the Internet

351

at http://pubs.acs.org.

352

AUTHOR INFORMATION

353

Corresponding Author

354

Phone: +3292644848; Fax: +3292644960; E-mail: [email protected]

355

Notes

356

The authors declare no competing financial interest.

357

ACKNOWLEDGMENT

358

All authors would like to acknowledge the efforts of Dr. Daniel Fliegel in initiation this cooperation

359

and the Norwegian Coastal Administration for financial support.

360


Page 17 of 30


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565 566 567


Page 25 of 30


THg δ202Hg

27000

202

δ

0.0

Hgmetallic (U- 864) 202

SD δ

Hgmetallic (U-864)

-0.1

24000

-0.2

18000 -0.3 15000 -0.4

12000 9000

δ202Hg (‰)

-1

THg (mg Kg )

21000

-0.5

6000 -0.6

3000 0 0.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

Sediment depth (m)

568 569

Figure 1. Total Hg concentration (THg, blue squares, left y-axis) and δ202Hg (red circles, right y-

570

axis) as a function of depth for sediment samples collected in the immediate vicinity of the U-864

571

submarine wreck. The error bars indicate the SD for 2 or 3 digestion replicates. The solid and

572

dashed green lines show the δ202Hg (average ± SD, n = 10) for the metallic Hg salvaged from the

573

submarine wreck.

574



0.0

0.0

δ202Hgsediments

δ202Hgsediments

-0.1

SD - δ

Hgmet

δ202Hg (‰)

-0.4 -0.5

-0.3

-0.5 -0.6

-0.7

-0.7 10000

15000

20000

25000

r = 0.762 p = 0.000

-0.4

-0.6

5000

± SD

SD - δ202Hgmetallic

-0.2

-0.3

0

δ202Hgmetallic

Hgmet 202

-0.2

-0.1

± SD

202

δ

δ202Hg (‰)

Page 26 of 30

10

100

THg (mg Kg-1)

1000

10000

THg (mg Kg-1)

575 576

Figure 2. δ202Hg vs THg for sediment samples (all digestion replicates) collected in the immediate

577

vicinity of the U-864 submarine using (A) a linear scale and (B) a logarithmic scale for the

578

abscissa. The solid and dashed green lines show the δ202Hg (average ± SD, n = 10) for metallic Hg

579

salvaged from the submarine wreck.

580


Page 27 of 30


0.8

A

0.6

0.4

0.4

δ200Hg (‰)

0.6

0.2

199

δ Hg (‰)

0.8

0.0 -0.2

North brown Wreck brown South brown Metallic Hg Sediments

-0.4

-0.6

-0.4

-0.2

0.0

0.2

0.2 0.0 -0.2

North claw Wreck claw South claw Theoretical MDF line

0.4

B


-0.4

0.6

-0.6

-0.4

-0.2

δ202Hg (‰) 0.8

0.2

0.4

0.6

δ202Hg (‰)

C

0.2

0.6

D

0.1

δ200Hg (‰)

0.4 0.2

201

δ Hg (‰)

0.0


0.0

0.0 -0.1 -0.2

-0.2


-0.4

-0.6

-0.4

-0.2

0.0

0.2


0.4

0.6

North brown Wreck brown South brown Metallic Hg Sediments Theoretical MDF line

-0.3 -0.4 -0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

δ202Hg (‰)

δ202Hg (‰)

581 582

Figure 3. Three-isotope plots δ199Hg vs δ202Hg (A), δ200Hg vs δ202Hg (B) and δ201Hg vs δ202Hg (C)

583

for metallic Hg from the U-864 wreck (green, n = 10), sediments from the wreck location (grey

584

field, n = 14) and C. pagurus tissues – averages for brown (brown field) and claw meat (pink

585

field), n = 78 in total – from the three sampling zones: north (blue), south (black) and wreck

586

(red). The error bars indicate the SD for each group of samples. Figure 3D shows the three-

587

isotope plot δ200Hg vs δ202Hg for the brown meat from the three locations (one point per

588

individual, n = 39) and the average values for sediment samples (n = 33) and the metallic Hg

589

from the U-864 wreck (n = 10).

590



Page 28 of 30

591

North brown Wreck brown South brown North claw Wreck claw South claw

0.7 0.6

∆199Hg

0.5 0.4 0.3

± SD

0.2 0.1

slope = 1.02 ± 0.05, R2 = 0.83

0.0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

201

∆ Hg

592 593

Figure 4. ∆199Hg vs ∆201Hg for the complete C. pagurus data set for both tissues from the three

594

locations studied: north (blue), south (black) and wreck (red). The black solid line is the best-

595

fitting straight line through the experimental data and its slope (1.02 ± 0.05) serves as an

596

indicator of the type of mass-independent fractionation (MIF): the black dashed lines represent

597

the slopes calculated by Bergquist and Blum38 for MeHg (1.3) and Hg2+ photoreduction (1.0)


Page 29 of 30


graphical abstract 254x190mm (300 x 300 DPI)



graphical abstract 8 x 4.76 79x47mm (300 x 300 DPI)


Page 30 of 30

Assessment of Hg Pollution Released from a WWII Submarine Wreck

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