Lipid Biomarker Analysis of Suspended Particulate Matter from the Great Kwa River, SE Nigeria: Origins and Environmental Implications of Biogenic and Anthropogenic Organic Compounds

Abstract

Biomarkers found in natural waters, sediments, soils, fossils, crude oil, and coal can be unambiguously linked to specific precursors biosynthesized by biota. Petroleum and its refinery products carry their biomarker information into the environment when they are released by pollution. Lipid biomarkers can be used to assess the environmental status of an ecosystem and the degree to which it has been influenced by biogenic and anthropogenic inputs. The marine ecosystem of the southeastern Niger Delta of Nigeria is receiving new attention due to increased human and industrial development and the consequent potential health effects. Suspended particulate matter (SPM) from the Great Kwa River was characterized using biomarkers to assess such pollution. The total organic carbon contents of SPM from the river at low and high tide was 12–50% (avg 34.75%) and 16–28% (avg 24.25%), respectively. The lipid biomarkers identified using gas chromatography–mass spectrometry were mainly n-alkanes, n-alkan-2-ones, triterpenoids and minor amounts of aromatic compounds. The n-alkanes ranged from C ₁₇ to C ₃₅, with an odd/even predominance and C _max > 27, indicating a mixed origin from higher plant wax, biodegraded detritus, and petroleum. The n-alkan-2-ones in most samples ranged from C ₁₆ to C ₃₃, with C _max = 31, also supporting an input from vascular plants dominating the riparian zone along the river. The triterpenoids, mainly taraxerone, taraxerol, α- and β-amyrins, and friedelin, also derived from higher plants (angiosperms). Minor amounts of aromatic hydrocarbon derivatives from α- and β-amyrins were present and are likely the result of different diagenetic processes. The presence of trace fossil fuel-derived hopanes with an unresolved complex mixture of branched and cyclic hydrocarbons supported a minor petroleum product input to the SPM of the Great Kwa River.