Radioactivity in the Exclusive Economic Zone of east coast Peninsular Malaysia: distribution trends of 137 Cs in surface seawater Zaharudin Ahmad • Zal U’yun Wan Mahmood • Hidayah Shahar • Mei Wo Yii • Ahmad Sanadi Abu Bakar Received: 28 June 2010 / Published online: 1 August 2010 Ó Akade ´miai Kiado ´, Budapest, Hungary 2010 Abstract Large volumes of surface seawater samples were collected from thirty locations in the Exclusive Economic Zone (EEZ) of the east coast Peninsular Malaysia on June 2008 to study the activity concentrations of 137 Cs. The results will serve as additional information to the existing baseline data and is very useful for monitoring fresh input of anthropogenic radionuclide into Malaysian marine environment. In this study, the activity concentra- tions of 137 Cs were determined using co-precipitation technique, followed by Gamma Spectrometry measure- ment. The mean activity concentration of 137 Cs ranged between 3.40 and 5.89 Bq/m 3 . Higher activity concentra- tions were observed at the coastal and towards the south of Peninsular Malaysia and were aligned with the high tur- bidity. These may due to the rapid diffusion of 137 Cs from suspended particulates and fine sediments into surface seawater. The activity concentrations of 137 Cs observed in this study were slightly higher than the concentrations reported in seawater at the Straits of Malacca, Vietnam and Philippines. This might be because the study area received more input of 137 Cs that originated from global fallout and then deposited on land which later being transported sub- sequently into the coastal zone due to siltation and erosion processes. It could also be attributed to the intrusion of river waters containing higher concentrations of 137 Cs. Keywords 137 Cs Á Surface seawater Á East coast Peninsular Malaysia Á Gamma spectrometry Introduction Determination of baseline level of pollutants and/or con- taminants in the environment is very important and neces- sary before one attempt to investigate the behavior, monitor and control them. Thus, it is important to determine the baseline level of radionuclides in different environmental compartments before any pollution or contamination event happens [1]. Contamination of radionuclides originating from nuclear weapon tests, releases from nuclear facilities, radioactive waste dumping, Chernobyl accident, and nuclear submarine and aircraft accidents has introduced artificial radionuclides such as 134 Cs, 137 Cs, 239,240 Pu, 238 Pu and 241 Am into the environment, particularly marine environment. These radionuclides can be transported across long distances from their emission sources. It was believed that around 380 and 40 nuclear weapon tests have been carried out in the northern and southern hemisphere, respectively [2]. Even though most of these radionuclides were released and deposited in the northern hemisphere, they could also be partially trans- ported through stratospheric circulation to the southern hemisphere. Amongst these radioisotopes, the long-lived 137 Cs is regarded as an important radioactive pollution indicator in marine environment. This is due to its large produc- tion quantity and longer half-life (30.07 years) as com- pared to other radiocesium isotopes such as 134 Cs (half-life 2.06 years). Anthropogenic radionuclide 137 Cs is the result from nuclear power testing. As soon as the atmospheric fallout deposited onto land, the radioisotope will then attached to fine-grained sediment and trans- ported into marine environment [3]. In coastal area, majory of 137 Cs are originated from atmospheric depo- sition and distribution of 137 Cs in marine environment Z. Ahmad (&) Á Z. U. Wan Mahmood Á H. Shahar Á M. W. Yii Á A. S. Abu Bakar Waste & Environmental Technology Division, Malaysian Nuclear Agency (Nuclear Malaysia), Bangi, 43000 Kajang, Selangor, Malaysia e-mail: zahar@nuclearmalaysia.gov.my 123 J Radioanal Nucl Chem (2011) 287:329–334 DOI 10.1007/s10967-010-0692-4