Experimental database on water equivalent factor (WEQp) and organically bound tritium activity for tropical monsoonal climate region of South West Coast of India

Nayak S Rashmi; Renita Shiny D'Souza; Srinivas S Kamath; M P Mohan; S Bharath; B Narayana; P M Ravi; N Karunakara

doi:10.1016/j.apradiso.2020.109390

Experimental database on water equivalent factor (WEQ_p) and organically bound tritium activity for tropical monsoonal climate region of South West Coast of India

Appl Radiat Isot. 2020 Dec:166:109390. doi: 10.1016/j.apradiso.2020.109390. Epub 2020 Sep 12.

Authors

Nayak S Rashmi¹, Renita Shiny D'Souza¹, Srinivas S Kamath¹, M P Mohan¹, S Bharath¹, B Narayana¹, P M Ravi¹, N Karunakara²

Affiliations

¹ Centre for Advanced Research in Environmental Radioactivity (CARER), Mangalore University, Mangalagangothri, 574199, India.
² Centre for Advanced Research in Environmental Radioactivity (CARER), Mangalore University, Mangalagangothri, 574199, India. Electronic address: drkarunakara@gmail.com.

PMID: 33091858
DOI: 10.1016/j.apradiso.2020.109390

Abstract

Tritium in the form of tritiated water is easily incorporated into terrestrial biota as tissue free water tritium (TFWT). A part of TFWT is converted into organically bound tritium (OBT) through metabolic processes. For the computation of NE-OBT activity (expressed as Bq L^-1 of combustion water) in terrestrial plants, knowledge on 'water equivalent factor (WEQ_p)', defined as the volume of water produced from the combustion of 1 kg of the dry sample, is essential. On a global scenario, experimental data are not available on this parameter. This paper presents (i) a method for determination of WEQ_p by combustion method using a tube furnace system, (ii) a large database (N = 294) on WEQ_p parameter for samples of tropical monsoonal climate region of the Indian subcontinent, and (iii) NE-OBT activity in terrestrial biota samples (N = 186) collected from the vicinity of a PHWR nuclear power plant of India. The data generated in this study on WEQ_p serves for the validation of the data compiled in IAEA (2009 and 2010), which are estimated based on the hydrogen content of protein, fat and carbohydrates, and the fractions of protein, fat and carbohydrates. The WEQ_p varied in the ranges of 0.492-0.678 L kg^-1 (GM = 0.569 Bq L^-1, GSD = 1.06), 0.520-0.630 L kg^-1 (GM = 0.557 Bq L^-1, GSD = 1.02) 0.473-0.633 L kg^-1 (GM = 0.562 Bq L^-1, GSD = 1.02) for non-leafy vegetables, leafy vegetables, and fruits, respectively. A comparison between the experimental WEQ_p data with those compiled in the IAEA report revealed that the maximum deviation between the two data sets is <10%. The NE-OBT activity in the food samples collected from 2.3 to 20 km zone around NPP had a geometric mean (GM) value of 25.4 Bq L^-1 (GSD = 1.6, N = 186). Variations in NE-OBT activity with different seasons of the year are discussed.

Keywords: Organically bound tritium; RADDEC Pyrolyser; Water equivalent factor (WEQ(p)).