Temporal trends and compartment-specific behaviour of ¹³⁷Cs across five decades of environmental monitoring in tropical Malaysia.

Authors

M S M Sanusi, K Y H Gin, S Hashim, H N Idris, R M Taha

Published in

Journal of environmental radioactivity. Volume 300. Pages 108204. Oct 25, 2026. Epub Oct 25, 2026.

Abstract

Long-term environmental surveillance of radiocesium (¹³⁷Cs) in tropical regions provides important baseline data for assessing radionuclide behaviour under low-background conditions, yet multi-compartment synthesis studies from Southeast Asia remain scarce. This study presents a retrospective analysis of ¹³⁷Cs activity concentrations across five environmental compartments: seawater (n = 609), soil (n = 483), sediment (n = 474), biota (n = 114), and airborne particulates (n = 20 seasonal records), in Malaysian environments spanning 1972-2024. Censored observations below analytical detection limits were treated using Regression on Order Statistics (ROS), with Limit of Detection (LOD) substitution sensitivity assessed under three scenarios (X_i = 0, LOD/2, LOD). A complementary statistical framework combining Mann-Kendall (MK) trend analysis, Pettitt change-point detection, cumulative sum (CUSUM) diagnostics, relative detectability metrics (SNR), and segmented regression was applied to characterise temporal structure and compartment-specific behaviour. A statistically significant monotonic decline was identified in seawater only (τ = -0.547, p = 0.002), however, a candidate change-point at 1995 (p = 0.026) was excluded from primary inference owing to a 9-year sampling gap (1987-1994; Table S3). Soil and biota exhibited declining tendencies (τ = -0.167 and -0.500, respectively) that did not reach statistical significance (p > 0.05). Sediment results were excluded from trend inference as the direction of the apparent trend reversed between LOD substitution scenarios, indicating that the result is driven by the high proportion of censored values (74.7%) rather than the quantified data. Airborne observations (85% non-detect) were reported descriptively only. Indicative effective half-lives of ¹³⁷Cs were estimated across all four compartments under a sensitivity analysis spanning five historically motivated starting years (Table S2). Seawater yields T_½ (eff) = 27.7-30.8 yr across the primary fits, bracketing the physical half-life (30.17 yr), while biota yields T_½ (eff) ≈ 12-19 yr, consistent with biological turnover superimposed on radioactive decay. Soil and sediment estimates are sensitive to starting year and are considered indicative only. Signal-to-noise ratios (SNR) were below 1 for soil (0.455), sediment (0.060), and biota (0.260); seawater showed marginal detectability (SNR = 1.35, consistent across all LOD substitution scenarios), reflecting the long-term declining trend rather than a post-2011 enrichment signal. Statistical inference is subject to inherent limitations of the analytical framework: the MK test has reduced power for episodic signals and censored-data-rich series; the Pettitt test assumes a single dominant change-point; and CUSUM results are treated as exploratory given irregular sampling intervals and high censoring rates in several compartments. The results document baseline temporal trajectories of ¹³⁷Cs in a tropical low-background environment and highlight compartment-specific differences in temporal sensitivity, data sufficiency, and inferential reliability as central challenges for long-term radionuclide surveillance in tropical radioecology.

PMID:
42927706
Bibliographic data and abstract were imported from PubMed on 26 Oct 2026.

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