Polonium-210 in marine mussels (bivalve molluscs) inhabiting the southern coast of India

Highlights

• Polonium-210 was quantified in two species of Mytilid mussels inhabiting southern coast of India.

• Polonium-210 activity showed significant variation among size classes, between seasons and sampling site.

• The internal dose rate to mussels and the dose assessment to the adult population were performed.

Abstract

The present study focused on the determination of the alpha-emitter, ²¹⁰Po, in two species of marine mussels (bivalve molluscs) commonly available in the southern coastal region of India. The brown mussel, Perna indica was collected from the west coast and the green mussel, Perna viridis from the east coast. The concentration of ²¹⁰Po was related to the allometry (length of shell, wet/dry weight of shell/soft tissue) of the mussels and significant results were found. The study period focused on three seasons namely, pre-monsoon, monsoon and post-monsoon for a 1-year period (2010–2011). The results revealed higher activity levels in smaller-sized mussels compared to larger ones. Marked variation in ²¹⁰Po activity concentration was noted in the whole-body soft tissues between seasons and sampling site (p < 0.05). The dose rate assessment for mussels was performed using the ERICA Assessment tool. The chronic exposure to mussels due to ²¹⁰Po was found to be lesser than the global benchmark dose rate of 10 μGy h⁻¹. The effective ingestion dose to adults who intake mussels was estimated to be in the range 5.1–34.9 μSv y⁻¹. The measurement contributes to the furthering of knowledge of ²¹⁰Po, since no data exist in this region.

Introduction

Assessment of radioactive elements in the natural environment, their effects on living organisms and their safety has been one of the most important issues in radioecology and radiological protection in recent years. Of the various marine invertebrates, molluscs have been used extensively as biological indicators of metal contamination of the marine environment (Goldberg, 1975, Farrington et al., 1983). They are creatures living on sea beds and rocks, and are mostly found in intertidal regions. Bivalve molluscs have been recognized as first-order biological indicators of metal and radioactive pollution, since they ingest detritus and phytoplankton which has a high degree of radionuclide association and accumulation (Phillips and Rainbow, 1994, Elliotta et al., 2008). Radionuclides, toxic metals and organic contaminants (petroleum hydrocarbons and pesticides) have been reported to be accumulated by these species. Thus they are useful for assessing the contamination and ecotoxicology of any marine region (Francioni et al., 2007, Zorita et al., 2007, Carvalho et al., 2010, Mearns et al., 2013). Besides these, bivalve molluscs have been used as test species in vivo to understand the uptake mechanism, kinetics and transformation of contaminants in the marine ecosystem (Wildgust et al., 1998; Yu et al., 1997).

In addition to their use in environmental monitoring programmes, mussels are considered to be a nutritious and delicious food in many countries (Boyle, 1981). Certain species of the family Mytilidae comprise one of the important seafood sources to the public living around coastal regions and have high export value too; their consumption reported leading to higher radiation dose (Somasundaram, 1998; Štrok and Smodiš, 2011; Khan and Welsey, 2012, Khan et al., 2011). Marine bivalves such as the brown mussel, Perna indica and green mussel, Perna viridis are considered to be important protein source along the southern coast of India. Brown mussels represent the west coast and green mussels represent the east coast of southern India. Brown mussel is also cultured by local fishermen using rafts along the coastal regions.

Rather than the quantification of radionuclides alone, the assessment of radiation dose to the species assumes importance for the sustainability of the species as well as the environment. Establishment of a baseline benchmark for radiation dose helps us to measure any addition dose due to industrial operations. Although, the health effects due to natural radioactivity levels have not been completely understood, it is a general internationally accepted principle that additional exposures to ionizing radiations should be kept to as low as reasonably achievable (ALARA), recommended by ICRP. Therefore, determination of background radiation dose rate is important in the process of assessing risks to the environment. This helps in deriving the incremental dose rate and as a point of reference for evaluating the significance of the exposure level.

Based on the international and national scenario, we quantified the level of ²¹⁰Po in two common species of marine bivalves. The study mainly focused on the quantification of polonium in soft tissue and its relationship with the mussels' allometric parameters. The radiation dose naturally received by the molluscs was calculated using the ERICA assessment tool. The committed effective dose to the adults consuming the mussels was also estimated.