Effect of dissolved oxygen deficiency on 210Pb content in mussel's tissues at the Johor strait, Malaysia

Abstract

Aim: To investigate the effect of dissolved oxygen deficiency on the level of 210Pb in mussel's tissues, Perna viridis which has been reported to be highly tolerant to hypoxia. Methodology: Mussels (Perna viridis), seawater and sediment samples were collected from nine stations along the Johor Straits during North-east monsoon (November 2017), inter-monsoon (March 2018), and South-west monsoon (August 2018). The 210Pb contents were extracted and estimated by Gross Alpha-beta Counter. Results: The lowest dissolved oxygen was recorded at Station 4 which decreased from 2.14 mg l-1 to 2.10 mg l-1 and subsequently to 1.63 mg l-1 during first to third samplings. In sediment, 210Pb activities increased with the increase in organic matter. Meanwhile, in mussels, the 210Pb activities showed almost similar trend with sediment where 210Pb activities were much higher adjacent to the causeway structure, especially at the East part of Johor Strait. The level of 210Pb in mussel's tissue and sediment also increased with decreasing level of dissolved oxygen. Interpretation: A causeway structure disrupted the water quality of Johor Straits and caused almost hypoxic conditions nearby. The coverage of oxygen depletion expanded during inter-monsoon. An inverse relationship between 210Pb activities and dissolved oxygen prove that deficiency of dissolved oxygen potentially influenced the bioaccumulation of 210Pb in mussels to correspond to the build-up of concentration factor in their tissues which exceeded the recommended value.