Exposure to tritiated water at an elevated temperature: Genotoxic and transcriptomic effects in marine mussels (M. galloprovincialis)

Abstract

Temperature is an abiotic factor of particular concern for assessing the potential impacts of radionuclides on marine species. This is particularly true for tritium, which is discharged as tritiated water (HTO) in the process of cooling nuclear institutions. Additionally, with sea surface temperatures forecast to rise 0.5-3.5 °C in the next 30-100 years, determining the interaction of elevated temperature with radiological exposure has never been more relevant. We assessed the tissue-specific accumulation, transcriptional expression of key genes, and genotoxicity of tritiated water to marine mussels at either 15 or 25 °C, over a 7 day time course with sampling after 1 h, 12 h, 3 d and 7d. The activity concentration used (15 MBq L) resulted in tritium accumulation that varied with both time and temperature, but consistently produced dose rates (calculated using the ERICA tool) of <20 Gy h, i.e. considerably below the recommended guidelines of the IAEA and EURATOM. Despite this, there was significant induction of DNA strand breaks (as measured by the comet assay), which also showed a temperature-dependent time shift. At 15 °C, DNA damage was only significantly elevated after 7 d, in contrast to 25 °C where a similar response was observed after only 3 d. The transcription profiles of two isoforms of hsp70, hsp90, mt20, p53 and rad51 indicated potential mechanisms behind this temperature-induced acceleration of genotoxicity, which may be the result of compromised defence. Specifically, genes involved in protein folding, DNA double strand break repair and cell cycle checkpoint control were upregulated after 3 d HTO exposure at 15 °C, but significantly downregulated when the same exposure occurred at 25 °C. This study is the first to investigate temperature effects on radiation-induced genotoxicity in an ecologically relevant marine invertebrate, Mytilus galloprovincialis. From an ecological perspective, our study suggests that mussels (or similar marine species) exposed to increased temperature and HTO may have a compromised ability to defend against genotoxic stress.

Mixtures of tritiated water, zinc and dissolved organic carbon: Assessing interactive bioaccumulation and genotoxic effects in marine mussels, Mytilus galloprovincialis

“…Mussels were transferred to 2 L glass beakers 48 h prior to exposure at a density of 4.5 mussels L -1 (i.e. 9 mussels -1 beaker) in order to acclimate and in line with our previous study (Dallas et al, 2016b). Nine mussels were exposed to one of 8 treatments (Figure 1), comprising a seawater-only control, 383, 1915 or 3830 nM Zn, and 4 treatments containing 5 MBq L -1 HTO, which has previously shown consistent genotoxic effects in haemocytes across numerous experiments [Jha et al, 2005;Jaeschke et al, 2011;Dallas et al 2016 a].…”

Relative comparison of tissue specific bioaccumulation and radiation dose estimation in marine and freshwater bivalve molluscs following exposure to phosphorus-32

“…Adult MG and DP were collected from Trebarwith strand (Dallas et al, 2013) and Bude, Cornwall, UK (50.828059, -4.549053), respectively. Maintenance of the mussels has been described in detail in previous publications (Dallas et al 2013;Dallas et al 2016a;Pearson et al 2018). As Hilbish et al (2002) reported the occurrence and distribution of Mytilus edulis, M. galloproviancialis and their hybrids in the coastal regions of south-west England, we ensured species homogeneity in our experiments based on the method of Inoue et al (1995).…”

“…Activity concentrations in water were calculated from preliminary experiments (data not included). Water changes (50 %) were carried out on days 3, 5, 7 and 9 and mussels were fed during this exposure (2 hours before each water change), as described in detail elsewhere (Dallas et al 2016a). MG were fed a solution of Isochrysis galbana algae (1.05 x 10 -5 cells mL -1 , Reed Mariculture, Campbell, CA, USA), DP fed on dried Chlorella powder (3.2 mg/mussel per feed, Naturya, Bath, UK).…”

“…5 Bioaccumulative abilities in aquatic bivalves, an important group of invertebrates of ecological and economic importance, has been identified in scientific literature. This is notably to ubiquitous, long-lived radionuclides such as 134 Cs,210 Po,210 Pb and 3 H (Evans 1984;Jha et al 2005;Kalaycı et al 2013;Feroz Khan et al 2014;Dallas et al 2016a;Metian et al 2016;Pearson et al 2018). However whole body accumulation and dose are often (but not always) the focus of such studies.…”

“…Whole-body determination of radionuclide bioaccumulation levels is important for risk assessments, however for biomonitoring and biological response studies (including sensitive transcriptomics and proteomics studies), it is important that tissue specific information is generated. Radionuclide uptake disparity amongst tissues has been highlighted in studies from Jha et al (2005), Jaeschke et al (2011), Dallas et al (2016a) and Pearson et al (2018) where tritium accumulation in bivalve (Mytilus sp.) tissues were observed to be highly specific.…”