The present work is aimed at assessing the aftermath effects of the 2014 flood tragedy on the distribution, pollution status and ecological risks of the heavy metals deposited in the surface river sediment. A series of environmental pollution indexes, specifically the enrichment factor, geo-accumulation index, contamination factor, modified degree of contamination, pollution load index, potential ecological risk index and sediment quality guidelines have been adopted. Results revealed that the freshly deposited sediments collected soon after the flood event were dominated by Cu, Fe, Pb, Ni, Zn, Cr and Cd, with the average concentrations of 38.74, 16,892, 17.71, 4.65, 29.22, 42.36 and 0.29 mg/kg, respectively. According to the heavy metal pollution indexes, Pahang River sediments were moderately to severely contaminated with Pb, Ni, Cu, Zn and Cr, while Cd with the highest Efi risk of 91.09 was the predominant element that illustrated an aesthetic ecological risk to the water body after the tragic flood event. The findings highlighted a critical deterioration of the heavy metals content, driven by the catastrophic flood event, which has drastically altered their geochemical cycles, sedimentary pollution status and biochemical balance of the river's environment.
The 2014 flood has been recognized as the most severe tragedy in the history of Malaysia for the past 30 years, which had seriously inundated and devastated 18,000 km2 of the low-lying catchments along Pahang River, signifying 75.9% of the flood-prone areas throughout the country.
The heavy metal pollution loads deposited in the river sediments showed a great amplification after the heavy flood event, with the mean values for Cu, Fe, Pb, Ni, Zn, Cr and Cd of 38.74, 16,892, 17.71, 4.65, 29.22, 43.26 and 0.29 mg/kg, respectively, as compared with 21.13, 14,596, 26.12, 18.65, 59.14, 23.93 and 0.15 mg/kg, respectively, before flooding.
A series of geochemical pollution indexes, including enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), modified degree of contamination (mCd), pollution load index (PLI), potential ecological risk index (PERI) and sediment quality guidelines (SQGs) were thoroughly evaluated.
The qualitative and quantitative analyses of heavy metals in the sediment samples before and after flooding were analysed systematically, and the significant differences between samples before and after flooding were performed using one-way analysis of variance (ANOVA) at p < 0.05.
Cd was the predominant metal that illustrated an aesthetic ecological risk to the water body after the tragic flood event, which have drastically altered the geochemical cycles and biochemical balance, with deleterious implications to the human health and natural ecosystem.