Geochemical and Ecological Risk Assessment of Heavy Metals and Hydrocarbons in Sediments of the Coastal and Four Rivers Estuary of Kuching Division of Sarawak, Malaysia

Ebenezer Aquisman, Asare (2023) Geochemical and Ecological Risk Assessment of Heavy Metals and Hydrocarbons in Sediments of the Coastal and Four Rivers Estuary of Kuching Division of Sarawak, Malaysia. PhD thesis, Universiti Malaysia Sarawak.

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Abstract

Contamination of heavy metals and hydrocarbons in the coastal and estuarine sediment could harm water quality and aquatic organisms, leading to potential long-term health risks to the environment and humans. Thus, this study was carried out to determine the concentration of heavy metals, aliphatic hydrocarbons (AHs), and polycyclic aromatic hydrocarbons (PAHs) distribution in surface sediments and to establish baseline concentrations of heavy metals using core sediments from the coastal and four rivers estuary of the Kuching Division of Sarawak, Malaysia. Validated inductively coupled optical emission spectroscopy (ICP-OES) was used to determine heavy metals and their distribution in surface sediments was evaluated for eco-toxicological impacts. Source appointment of the heavy metals within the catchment area was determined using geochemical indices. The ICP-OES technique validated was appropriate and less laborious for determining the 12 metals of interest (i.e., Al, Mn, Ca, Cd, Cu, Fe, Cr, Ni, Co, Zn, and Pb) in the sediments. Heavy metal concentrations were recorded based on dry weight (d.w). The concentrations of heavy metals in core sediments varied in the range: Pb(8.9 – 188.9 mg/kg), Zn(19.4 – 431.8 mg/kg), Cd(0.014 – 0.061 mg/kg), Ni(6.6 – 33.4 mg/kg), Mn(2.4 – 16.8 mg/kg), Cu(9.4 – 133.3 mg/kg), Ba(1.3 – 9.9 mg/kg), As(0.4 – 7.9 mg/kg), Co(0.9 – 5.1 mg/kg), Cr(1.4 – 7.8 mg/kg), Mg(68.8 – 499.3 mg/kg), Ca(11.3 – 64.9 mg/kg), Al(24.7 – 141.7 mg/kg), Na(8.8 – 29.4 mg/kg), and Fe (12011 – 35124.6 mg/kg). The enrichment factor assessment suggested enrichment of Pb, Zn, Cu, As, Co, and Mg occurred at the top layer of the core sediments. Continuous accumulation of Pb and Cu metals over time can be detrimental to living organisms and the ecology. The pollution load index values indicated that the study area is unpolluted. Sediment quality guidelines (SQGs) compared to the detected heavy metals suggested no likely deleterious impact on bottom-dwelling living things. The risk index estimation in each study site showed a low ecological risk impact on the environment. The statistical analysis suggested that the deposition of As, Cd, Pb, Cu, Mn, and Zn in the study sites is due to anthropogenic inputs from the adjacent land-based sources while Fe, Al, Mg, Na, Ni, and Ba are from lithogenic origin. This study further explains the monitoring, sources, and risk assessment of hydrocarbons in surface sediments. Validation of the performance of gas chromatography flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS)showed that these techniques are in an excellent position to quantify aliphatic and polycyclic aromatic hydrocarbons, respectively. Total n-alkanes (C10 – C33) concentrations varied from 96.63 – 367.28 ng/g. The lowest and highest n-alkane content was observed at Santubong estuary (CZ10) and offshore of Batang Rambungan opposite small Satang Island (CZ2), respectively. The contents of PAHs varied from 12.54 – 21.20 ng/g. The highest PAH content was detected in the sediments of coastal site CZ8 (21.20 ng/g), whereas; the lowest content was recorded in the sediments of coastal site CZ3 (12.54 ng/g). The aliphatic diagnostic indices values showed hydrocarbon input from biogenic and petrogenic sources. The isomeric ratios values also indicated that PAHs in sediments are from a mixture of petrogenic and pyrogenic origins. The carcinogenic PAHs risk assessment suggested no risk impacts of carcinogenic PAHs in the study area. The findings of this study can be used to understand the sources and possible risks of hydrocarbons and provide information for safeguarding human health and aquatic bodies in coastal and estuary settings.

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