Chemical availability of fallout radionuclides in cryoconite

Atmospheric deposition on glaciers is a major source of legacy fallout radionuclides (FRNs) accumulating in cryoconite, a dark granular material with surface properties that efficiently bind FRN contaminants (specifically 137Cs; 210Pb; 241Am). Cryoconite-bound FRNs in glaciers can be released when they interact with and are transported by glacial meltwater, resulting in the discharge of amassed particulate contaminants into aquatic and terrestrial environments downstream. The environmental consequences of FRN release from the cryosphere are poorly understood, including impacts of cryoconite-sourced FRNs for alpine food chains. Consequently, there is limited understanding of potential health risks to humans and animals associated with the consumption of radiologically-contaminated meltwater. To assess the chemical availability of cryoconite-adsorbed FRNs we used a three-stage sequential chemical extraction method, applied to cryoconite samples from glaciers in Sweden and Iceland, with original FRN activity concentrations up to 3300 Bq kg-1 for 137Cs, 10,950 Bq kg-1 for unsupported 210Pb (210Pbun) and 24.1 Bq kg-1 for 241Am, and orders of magnitude above regional backgrounds. Our results demonstrate that FRNs attached to cryoconite are solubilized to different degrees, resulting in a stage-wise release of 210Pbun involving significant stepwise solubilization, while 137Cs and 241Am tend to be retained more in the particulate phase. This work provides an insight into the vulnerability of pristine glacial environments to the mobilization of FRN-contaminated particles released during glacier melting, and their potential impact on glacial-dependent ecology.

The English Channel: Contamination status of its transitional and coastal waters

The chemical contamination (organic compounds, metals, radionuclides, microplastics, nutrients) of English Channel waters has been reviewed, focussing on the sources, concentrations and impacts. River loads were only reliable for Pb, whereas atmospheric loads appeared robust for Cd, Pb, Hg, PCB-153 and γ-HCH. Temporal trends in atmospheric inputs were decreasing. Contaminant concentrations in biota were relatively constant or decreasing, but not for Cd, Hg and HBCDD, and deleterious impacts on fish and copepods were reported. However, data on ecotoxicological effects were generally sparse for legacy and emerging contaminants. Intercomparison of activity concentrations of artificial radionuclides in sediments and biota on both Channel coasts was hindered by differences in methodological approaches. Riverine phosphate loads decreased with time, while nitrate loads remained uniform. Increased biomass of algae, attributable to terrestrial inputs of nutrients, has affected benthic production and shellfisheries. A strategic approach to the identification of contaminant impacts on marine biota is recommended.

Persistence and metallic composition of paint particles in sediments from a tidal inlet

Concentrations of Cu, Pb, Sn and Zn have been determined in sediment (<500 μm) and macroscopic paint particles (>500 μm) retrieved from sections of two cores collected from a tidal inlet of the Plym estuary, southwest England. Paint particles contributed up to about 0.2% of the total mass retrieved from each section and were most abundant towards the base of the cores where, according to (210)Pb dating, deposition took place about a decade prior to sampling. Metal concentrations in the paint particles pooled from the sections were highly variable, typically spanning two orders of magnitude in each core, and were greatest for Cu and Zn (up to 460,000 and 170,000 μg g(-1), respectively) due to their use in contemporary antifouling formulations applied to boat hulls. Concentrations of metals in the sediment were, however, relatively invariant, an effect attributed to the abundance and dispersion of microscopic paint particles throughout the cores.

Metals and nutrients in the Severn Estuary and Bristol Channel: contemporary inputs and distributions

The contemporary inputs of total metals to the Severn Estuary and the inner Bristol Channel from land-based sources have declined over the past 25 years, with the possible exception of chromium. Coherent measurements of dissolved and suspended particulate and sedimentary metals, dissolved nutrients and master variables, including salinity, suspended particulate matter (SPM) concentration, dissolved oxygen saturation and chlorophyll concentration, were made in the Severn Estuary and inner Bristol Channel during 2004 and 2005. Concentrations of total inorganic nitrogen (TIN) were comparable with values reported 20 years ago but were dominated by nitrate, possibly from diffuse sources. Sediments had total metal concentrations similar to the World averages for riverine particulate material, except for Cu which had elevated values in 2004. Concentrations of suspended particulate As, Cr and Zn showed little spatial variability. Dissolved concentrations of most metals were generally below their respective environmental quality standards, although high concentrations of dissolved Cu, and possibly As, appeared to be emanting from a sedimentary source. The K(D)s for As, Cr, Cu and Zn displayed an inverse relationship with SPM concentration, whereas the K(D)s for Hg increased with SPM. The results show that there is a need for a sediment inventory of metals to account for metal release during sediment resuspension events.

Metal concentrations in Kandalaksha Bay, White Sea (Russia) following the spring snowmelt

Elevated concentrations of dissolved and particulate Cd, Cu, Pb and Zn have been determined in the waters of Kandalaksha Bay (White Sea, Russia), following the ice melt in the spring of 2000. Dissolved metal maxima in the surface waters were observed at some stations and concentrations generally decreased with depth. The suspended particulate matter (SPM) comprised a non-lithogenic fraction in the range 12-83%, and had elevated metal concentrations that showed no trend with depth or salinity and was compositionally distinct from the sediments. A log-linear relationship existed between the concentrations of metals in sediments and in SPM and their respective Al concentrations, indicating a source of metal-rich particles, with low Al content, to the Bay. The results suggest that Kandalaksha Bay has been impacted by industrial activity on the Kola Peninsula and that restricted water exchange will hinder its recovery from metal contamination.

Transient oceanic and tidal contributions to water exchange and residence times in a coastal upwelling system in the NE Atlantic: the Pontevedra Ria, Galicia

An analysis of the intra-annual variability of hydrographic residence times, tau, is presented for the Pontevedra Ria--a large coastal system in NW Spain with a deep, unobstructed connection with the Atlantic Ocean. Ria-offshore water exchange and tau were quantified with an iterative approach to the fraction of freshwater method using 23 quasi-steady state water-salt budgets. Excluding prolonged flushing due to downwelling events at the end of the upwelling season, mean was 6 +/- 2 day in the central ria and 2 +/- 1 day in the internal ria. The tidal contribution, equal to 10-25% of total water renewal, was quantified for the first time for a Galician ria with the hydrodynamic model estuarine contaminant simulator (ECoS). The relationship between tau and residual freshwater input, Qz, was atypical, since Qz played a minor role in water exchange in comparison to periodic upwelling of East North Atlantic Central Water (ENACW) from the continental shelf mainly during spring and summer. During positive upwelling stress, the intrusion of ENACW into the ria produced enhanced flushing and tau < 4 day in the central ria and < 2 days in the internal ria. Under downwelling favourable conditions, water was retained and tau prolonged to >8 and >5 days, respectively. A quantitative parameterisation of tau with upwelling and Qz was weakly significant, due to the short-term variability in ria salinity. This paper elucidates problems associated with the use of water budgets to transient coastal systems such as the Pontevedra Ria.

Determination of arsenic species in fish, crustacean and sediment samples from Thailand using high performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS)

Suitable techniques have been developed for the extraction of arsenic species in a variety of biological and environmental samples from the Pak Pa-Nang Estuary and catchment, located in Southern Thailand, and for their determination using HPLC directly coupled with ICP-MS. The estuary catchment comprises a tin mining area and inhabitants of the region can suffer from various stages of arsenic poisoning. The important arsenic species, AsB, DMA, MMA, and inorganic arsenic (As III and V) have been determined in fish and crustacean samples to provide toxicological information on those fauna which contribute to the local diet. A Hamilton PRP-X100 anion-exchange HPLC system employing a step elution has been used successfully to achieve separation of the arsenic species. A nitric acid microwave digestion procedure, followed by carrier gas nitrogen addition- (N2)-ICP-MS analysis was used to measure total arsenic in sample digests and extracts. The arsenic speciation of the biological samples was preserved using a Trypsin enzymatic extraction procedure. Extraction efficiencies were high, with values of 82-102%(As) for fish and crustacean samples. Validation for these procedures was carried out using certified reference materials. Fish and crustacean samples from the Pak Pa-Nang Estuary showed a range for total arsenic concentration, up to 17 microg g(-1) dry mass. The major species of arsenic in all fauna samples taken was AsB, together with smaller quantities of DMA and, more importantly, inorganic As. For sediment samples, arsenic species were determined following phosphoric acid (1 M H3PO4) extraction in an open focused microwave system. A phosphate-based eluant, pH 6-7.5, with anion exchange HPLC coupled with ICP-MS was used for separation and detection of AsIII, AsV, MMA and DMA. The optimum conditions, identified using an estuarine sediment reference material (LGC), were achieved using 45 W power and a 20 minute heating period for extraction of 0.5 g sediment. The stability and recovery of arsenic species under the extraction conditions were also determined by a spiking procedure which included the estuarine sediment reference material. The results show good stability for all species after extraction with a variability of less than 10%. Total concentrations of arsenic in the sediments from the Pak Pa-Nang river catchment and the estuary covered the ranges 7-269 microg g(-1)and 4-20 [micro sign]g g(-1)(dry weight), respectively. AsV was the major species found in all the sediment samples with smaller quantities of AsIII. The presence of the more toxic inorganic forms of arsenic in both sediments and biota samples has implications for human health, particularly as they are readily 'available'.

Modelling solute transport in the Tweed Estuary, UK using ECoS

Predictions of the tidal variation in water elevation and the advection-dispersion of solutes have been made for the Tweed River Estuary (UK) by application of a modelling package called ECoS. The estuarine model consisted of a one-dimensional hydrodynamic scheme with tidally variable channel cross-sectional area. The model was driven by predicted tidal elevation at the mouth of the estuary, and combined fluvial inputs observed for the River Tweed at the head of the estuary and the River Whiteadder, a tributary within the tidal reaches. Model results were compared to field data collected during routine surveys of the river estuary, conducted as part of Natural Environment Research Council Land-Ocean Interaction Study (LOIS). Validation protocols showed that the model reproduced tidal- and river flow-driven changes in surface elevation, and explained over 90% of the variation in salinity when field data were averaged through the water column. The study demonstrates that ECoS can be used to model tidal hydrodynamic processes, and that in a stratified estuary a depth-averaged model is able to replicate depth-averaged data. However, in rapidly rising and partially stratified estuaries with highly variable river flows, sufficient and appropriate data must be available for model set-up and validation. This has implications for how field studies should be planned and conducted.

Modelling metal desorption kinetics in estuaries

The kinetics of desorption of Cd, Cu, Ni and Zn from riverine and estuarine sediments have been determined in deionised water and seawater (salinity=30). The time-dependent release of Cd, Cu and Ni from riverine sediments in both media showed an increase in dissolved metal concentrations within a few minutes, followed by a plateau after several hours of incubation. Desorption of Zn from riverine sediments in seawater was characterised by a maximum dissolved concentration after several minutes, followed by readsorption onto the suspended sediment. The extent of metal desorption from estuarine sediment (relative to a chemical digest of available particulate metal), in both deionised water and seawater, was less than that from the fluvial sediments, even though the available particulate metal concentrations were higher. The desorption kinetics of the metals were modelled using a mechanism consisting of reversible, first-order consecutive reactions. The dissolved metals were assumed to desorb into the bulk solution from exchangeable surface sites and from binding sites located within the particle matrix. A reasonable fit to the observed time-dependent desorption behaviour was simulated by integrating the differential equations resulting from the mechanism, assuming that the exchangeable particulate metal was defined by the chemical digest. The results are discussed within the context of improved understanding of the non-conservative behaviour of dissolved metals in estuaries.

Influence of organic complexation on the adsorption kinetics of nickel in river waters

The kinetics of Ni adsorption in rivers of widely different chemical characteristics have been studied by monitoring the uptake of 63Ni by suspended sediment particles. The rate and extent of adsorption was critically dependent on the presence and concentration of dissolved organic matter (DOM), defined analytically as the concentration of dissolved organic carbon (DOC). Thus, adsorption was greatest in experiments in which the DOM was decomposed by UV-oxidation and least in experiments in which Ni was preequilibrated with filtered river water before addition of particles. The extent of adsorption arising from the latter approach displayed a clear, inverse dependency on the concentration of DOC in the sample. These observations were interpreted and modeled in terms of the competing effects of DOM and particle sorption sites for dissolved Ni. Adsorption onto suspended particles in the absence of dissolved complexing ligands was adequately described by a reversible, two-stage reaction and a single set of adsorption rate constants. Forward and reverse rate constants defining Ni complexation with DOM of about 8 x 10(4) h(-1) M(-1) and 10 h(-1), respectively, were derived from data-fitting. The experimental and model results indicate that the toxicity, availability, and transport of Ni in freshwater environments are largely dictated by the concentration of DOM and the speciation of Ni entering the watercourse.

Sediment-water partitioning of inorganic mercury in estuaries

The sediment-water partitioning and speciation of inorganic mercury have been studied under simulated estuarine conditions by monitoring the hydrophobicity and uptake of dissolved 203Hg(II) in samples from a variety of estuarine environments. A persistent increase in the distribution coefficientwith increasing salinity is inconsistent with inorganic speciation calculations, which predict an increase in the concentration of the soluble HgCl4(2-) complex (or reduction in sediment-water distribution coefficient) with increasing salinity. Partition data are, however, defined by an empirical equation relating to the salting out of nonelectrolytes via electrostriction and are characterized by salting constants between about 1.4 and 2.0 L mol(-1). Salting out of the neutral, covalent chloro-complex, HgCl2(0), is predicted but cannot account for the magnitude of salting out observed. Since Hg(II) strongly complexes with dissolved (and particulate) organic matter in natural environments, of more significance appears to be the salting out of Hg(II)-organic complexes. Operational measurements of the speciation of dissolved Hg(II) using Sep-Pak C18 columns indicate a reduction in the proportion of hydrophobic (C18-retained) dissolved Hg(II) complexes with increasing salinity, both in the presence and absence of suspended particles. Ratios of hydrophobic Hg(ll) before and after particle addition suggest a coupled salting out-sorption mechanism, with the precise nature of Hg(II) species salted out being determined bythe characteristics and concentrations of dissolved and sediment organic matter.

Partitioning of mercury onto suspended sediments in estuaries

Radiochemical partitioning experiments using 203Hg have been undertaken with mixtures of river, seawater and sediment samples taken from three geochemically contrasting UK estuaries: the Plym, Beaulieu and Mersey. Species of dissolved Hg were determined using reversed-phase C18 chelating columns and particulate species were determined by sequential leaching with 1 M NH4OAc and 1 M HCl. Mercury had a high particle reactivity with partition coefficients, KDs, ranging from 10(4) to 5 x 10(5) ml g(-1), depending on salinity, the chemical composition of the end-member waters, and on the physico-chemical characteristics of the sediment. Dissolved organic matter present in the waters (humic substances and/or anthropogenic compounds) was found to be the main factor governing the forms of dissolved Hg and their reactivity. From the spiked 203Hg, up to 95% of the dissolved metal was retained on the C18 columns for the Mersey waters, whereas this fraction was < 60% in the Plym and Beaulieu waters. Quasi-irreversible adsorption of Hg onto particles from each estuary was observed over a time-scale of a few hours and < 20% of total particulate Hg was released by the sequential leach. In this paper, physico-chemical processes are proposed to explain the estuarine behaviour of Hg and the results are discussed in terms of Hg availability in estuarine systems.

Uptake and depuration of 63Ni by Mytilus edulis

The uptake and depuration of Ni (as radioisotope 63Ni) by Mytilus edulis (Mollusca: Bivalvia) has been investigated in a laboratory mesocosm. Nickel was reversibly held on low energy surface sites of estuarine suspended particulate matter (SPM), with a partition coefficient of the order 10(3) ml g-1, resulting in approximately 80% of radioisotopic Ni being in the dissolved phase. Mussels were fed a diet of radio-labelled estuarine SPM for 30 h in a flow-through exposure period and for a further 24 h in a static exposure period. Following exposure, the mussels were allowed to depurate in particle-free seawater. Pseudofaeces and faeces were collected throughout the experiment and tissues were dissected after 48 h of depuration. The 63Ni activity in the faeces was approximately 50% of that in the feedstock SPM, while the activity in the tissues was 2-29% of SPM activity. Tissue-specific accumulation occurred in the order viscera > byssus > mantle > adductor muscle > gill > foot. The results are discussed in the context of the bioavailability of Ni to mussels.

Heavy metal content of oysters from the Lynher Estuary, U.K

The concentrations of As, Cd, Hg, Pb and Zn have been determined in oysters and sediments from the Lynher Estuary, U.K. The sediments contained high levels of Cu, Fe, Pb and Zn probably associated with run off from a metalliferous catchment area and high Hg associated with a local sewage input. In contrast, the analyses of the oyster tissue showed that only Cu and Zn were concentrated in the flesh. The majority of samples contained coliform bacteria in excess of 1000 organisms per ml of tissue. It is concluded that the quality of the oysters from this fishery was limited by the bacteriological cleanliness rather than toxic metal content.