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Exploring phenomena that affect the fate and impact of radioactive materials in the blue mussel
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. (Marine Ecotoxicology)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Current protection of the marine environment from radiation is based largely on measuring, estimating and modelling accumulation and impact(s) of radionuclides in a few marine species. Using a relevant marine organism, this thesis focusses on investigating some poorly described phenomena that could cause deviations from predicted measurements.

Paper I investigated the biological transformation of tritium (radioactive hydrogen) into an organic compound. The resulting organically bound tritium (OBT) showed increased accumulation in mussels, unique incorporation into a key biological molecule (DNA), extended persistence in tissues, and greater toxicity than the inorganic form. Paper II demonstrated significant disparity in OBT accumulation between functionally similar microalgae species and that OBT in algae is readily transferred to a consumer.

Highly radioactive particles are a complex issue in radioecology due to their concentrated dose geometry, potentially inducing very different impacts in organisms, compared to external irradiation. Paper III developed a method to introduce radioactive particles that would facilitate their recovery, improve dose-calculation, and aid the measurement of toxicological endpoints. It also showed that such particles can be incorporated into mussel tissues, causing significant effects.

In Paper IV, hypoxia – another major ecological hazard in the marine environment – was expected to reduce radiosensitivity. The minimal observable effect from radiation prevented identification of such an interaction, and indicates drawbacks in the (otherwise sensitive) endpoints used. It appears that stressors like hypoxia may be more of a health hazard to marine organisms than environmental levels of ionising radiation.

By understanding such causes of variation in accumulation and impact, it is possible to improve risk assessment, providing more justification for regulations chosen and minimising conservatism in setting environmental standards.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2013. , 93 p.
Keyword [en]
Radioecology, ionising radiation, environmental protection, Mytilus edulis, bioaccumulation, dose-response, ecotoxicology, tritium, particle, hypoxia
National Category
Biological Systematics
Research subject
Marine Ecotoxicology
Identifiers
URN: urn:nbn:se:su:diva-83404ISBN: 978-91-7447-616-3 (print)OAI: oai:DiVA.org:su-83404DiVA: diva2:575585
Public defence
2013-01-18, DeGeersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of doctoral defense, the following papers were not published and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2012-12-27 Created: 2012-12-10 Last updated: 2013-01-02Bibliographically approved
List of papers
1. Tissue-specific incorporation and genotoxicity of different forms of tritium in the marine mussel, Mytilus edulis
Open this publication in new window or tab >>Tissue-specific incorporation and genotoxicity of different forms of tritium in the marine mussel, Mytilus edulis
2011 (English)In: Environmental Pollution, ISSN 0269-7491, E-ISSN 1873-6424, Vol. 159, no 1, 274-280 p.Article in journal (Refereed) Published
Abstract [en]

Marine mussels (Mytilus edulis) were exposed to seawater spiked with tritiated water (HTO) at a dose rate of 122 and 79 mu Gy h(-1) for 7 and 14 days, respectively, and tritiated glycine (T-Gly) at a dose rate of 4.9 mu Gy h(-1) over 7 days. This was followed by deputation in clean seawater for 21 days. Tissues (foot, gills, digestive gland, mantle, adductor muscle and byssus) and DNA extracts from tissues were analysed for their tritium activity concentrations. All tissues demonstrated bio-accumulation of tritium from HTO and T-Gly. Tritium from T-Gly showed increased incorporation into DNA compared to HTO. About 90% of the initial activity from HTO was depurated within one day, whereas T-Gly was depurated relatively slowly, indicating that tritium may be bound with different affinities in tissues. Both forms of tritium caused a significant induction of micronuclei in the haemocytes of mussels. Our findings identify significant differential impacts on Mytilus edulis of the two chemical forms of tritium and emphasise the need for a separate classification and control of releases of tritiated compounds, to adequately protect the marine ecosystem.

Keyword
Bio-accumulation, Tritiated glycine, Tritiated water, DNA, Genotoxicity
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-69713 (URN)10.1016/j.envpol.2010.08.033 (DOI)000285129600036 ()
Note

authorCount :4

Available from: 2012-01-15 Created: 2012-01-15 Last updated: 2017-12-08Bibliographically approved
2. Bioaccumulation of tritiated water in phytoplankton and trophic transfer of organically bound tritium to the blue mussel, Mytilus edulis
Open this publication in new window or tab >>Bioaccumulation of tritiated water in phytoplankton and trophic transfer of organically bound tritium to the blue mussel, Mytilus edulis
2013 (English)In: Journal of Environmental Radioactivity, ISSN 0265-931X, E-ISSN 1879-1700, Vol. 115, 28-33 p.Article in journal (Refereed) Published
Abstract [en]

Large releases of tritium are currently permitted in coastal areas due to assumptions that it rapidly disperses in the water and has a low toxicity due to its low energy emissions. This paper presents a laboratory experiment developed to identify previously untested scenarios where tritium may concentrate or transfer in biota relevant to Baltic coastal communities. Phytoplankton populations of Dunaliella tertiolecta and Nodularia spumigena were exposed at different growth-stages, to tritiated water (HTO; 10 MBq l(-1)). Tritiated D. tertiolecta was then fed to mussels, Mytilus edulis, regularly over a period of three weeks. Activity concentrations of phytoplankton and various tissues from the mussel were determined. Both phytoplankton species transformed HTO into organically-bound tritium (OBT) in their tissues. D. tertiolecta accumulated significantly more tritium when allowed to grow exponentially in HTO than if it had already reached the stationary growth phase; both treatments accumulated significantly more than the corresponding treatments of N. spumigena. No effect of growth phase on bioaccumulation of tritium was detectable in N. spumigena following exposure. After mussels were given 3 feeds of tritiated D. tertiolecta, significant levels of tritium were detected in the tissues. Incorporation into most mussel tissues appeared to follow a linear relationship with number of tritiated phytoplankton feeds with no equilibrium, highlighting the potential for biomagnification. Different rates of incorporation in species from a similar functional group highlight the difficulties in using a 'representative' species for modelling the transfer and impact of tritium. Accumulations of organic tritium into the mussel tissues from tritiated-phytoplankton demonstrate an environmentally relevant transfer pathway of tritium even when water-concentrations are reduced, adding weight to the assertion that organically bound tritium acts as a persistent organic pollutant. The persistence, potential for biomagnification and the increased toxicity of organic tritium increases the potential impact on the environment following a release of HTO; current legislation does not adequately take into account the nature of organic forms of tritium and therefore may be underestimating accumulation and toxic effect of tritium in the environment. Such information is necessary to accurately assess the distribution of tritium following routine releases, and to adequately protect the environment and humans.

Keyword
HTO, Organically bound tritium, Bioaccumulation, Phytoplankton, Mussel
National Category
Biological Systematics
Identifiers
urn:nbn:se:su:diva-84814 (URN)10.1016/j.jenvrad.2012.07.008 (DOI)000311527800004 ()
Note

AuthorCount:2;

Available from: 2013-01-02 Created: 2013-01-02 Last updated: 2017-12-06Bibliographically approved
3. Retention of radioactive particles and associated effects in the filter-feeding marine mollusc Mytilus edulis
Open this publication in new window or tab >>Retention of radioactive particles and associated effects in the filter-feeding marine mollusc Mytilus edulis
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Radioactive particles are aggregates of radioactive atoms formed by, e.g., condensation or precipitation of radionuclides or breakdown of larger radioactive materials, and can contain significant radioactivity. They have been released into the environment from nuclear weapons tests, and from accidents and effluents within the fuel nuclear cycle.

Aquatic filter feeders can be expected to take up and potentially retain radioactive particles, which could then provide concentrated localised doses to nearby tissues. Despite the high potential for accumulation and the potency of radioactive exposure, studies of the retention of radioactive particles in filter feeders are scarce. This study experimentally investigated the retention and effects of radioactive particles in the blue mussel, Mytilus edulis.

The spent fuel particles, collected in the field, comprised of a U and Al alloy containing fission products such as 137Cs and 90Sr/90Y. The particles were introduced into mussels in suspension with plankton food or through implantation under the mantle tissue. Induced effects of the particle exposure were measured using micronucleus and Comet assays on haemocytes. Of those particles introduced with food, 37.5 % were retained for 70 h, and were found in the siphons and gills, with the notable exception of one particle that was ingested, found in the stomach. Those not retained seemed to have been actively rejected by the mussels. In several cases where particles were retained or implanted, white marks suggesting necrosis were seen in the tissues near the particles; these are thought to be caused by radiation and physical irritation. The largest and most radioactive particle (estimated dose rate 3.18 ±0.06 Gy.h-1) caused the largest such mark in the mantle tissue; in this case, increased micronucleus frequency and Comet tail DNA % was also observed in the haemolymph collected from the muscle, implying that non-targeted effects of radiation were induced by the high dose particle.

The results showed that radioactive particles can potentially be retained by blue mussels and retained high activity particles can potentially induce negative effects, particularly in tissues close to such particles. Thus, current methods which are used for risk assessment that calculate “no-effect dose” estimates and are based upon the absorbed dose equivalent limit are inadequate for radioactive particle exposures. In addition, knowledge is lacking about the ecological implications of radioactive particles, for example potential recycling within a population, or trophic transfer in the food chain.

National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-83399 (URN)
Available from: 2012-12-10 Created: 2012-12-10 Last updated: 2012-12-11Bibliographically approved
4. The relative impact of the combined stresses hypoxia and ionising radiation in the marine bivalve, Mytilus edulis
Open this publication in new window or tab >>The relative impact of the combined stresses hypoxia and ionising radiation in the marine bivalve, Mytilus edulis
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A key requirement to accurate risk assessment of the impact of radioactive materials in the environment is the ability to assess the interactions and combined effects of other existing stresses or contaminants. Hypoxia is a common and growing hazard in the world’s oceans. Hypoxia is known to cause radioresistance in tumorous tissues of patients undergoing radiotherapy, however the impacts of radiation on marine organisms exposed to hypoxia is largely untested. The hypoxia tolerant bivalve – the blue mussel, Mytilus edulis - was exposed to a range of doses of gamma radiation (0.04Gy – 4Gy), following acclimatisation to either normoxia (10mgoxygen.l-1) or moderate hypoxia (3mgoxygen.l-1). Oxidative stress (lipid peroxidation) and antioxidant enzyme (catalase and superoxide dismutase) analyses were performed on tissues taken from these mussels. Very little or no effects were observed resulting from irradiation regardless of oxic treatment, however large increases in oxidative stress and antioxidant response were observed in the tissues of mussels acclimatised to hypoxia. The results suggest that the mussels are more impacted by the moderate level of hypoxia than the high doses of radiation, indicating that the endpoints or the species is not sensitive to irradiation and that historical exposure has led to adapted responses to hypoxia.

National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-83401 (URN)
Available from: 2012-12-10 Created: 2012-12-10 Last updated: 2012-12-11Bibliographically approved

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