Flood events with increasing frequency and magnitude as the result of climate change cause severe harm to local populations especially in fast-growing urban centers, such as Chennai (India). These large coastal population centers face an increasing vulnerability to frequently reoccurring monsoon-induced floods (e.g., Chennai flood 2015), intensified by the advancing urbanization along the urban landscape crossing river systems. Accompanied with these extreme floods are the increased release, re-localization and distribution of pollutants (e.g., PAHs, LABs, DEHA, Mesamoll®, NBFA, and pesticides) causing harm to adjacent communities and the environment along the river’s pathway. In order to endeavor the unknown risk posed by toxic river floods, to assess the flood and associated pollution history the preserved pollution signature from sedimentary records needs to be considered. This investigation evaluates the inorganic and organic pollutant assemblage in 9 sediment profiles along the Adyar and Cooum rivers (Chennai, India). Thereby heavy metals (Cr, Ni, Cu, Zn, Pb) showed a continuous concentration decrease towards the coast with their specific sources remaining unsolved. Four main groups of organic contaminats have been identified: petrogenic pollutants (hopanes, PAHs), urban wastewater constituents (LABs, DEHA, methyl-triclosan, octocrylene), technical compounds (Mesamoll®, DPE, NBFA, PCBs) and pesticides (DDX). Organic compounds show a distinctly differing distribution pattern compared to the heavy metals. Some compounds (e.g., PAHs, LABs, DEHA, NBFA, Mesamoll®) were detected in high concentrations deriving from nearby point sources. Pollutants from urban wastewater and several technical compounds has been identified to be suitable markers to assess the anthropogenic induced pollution and event history in sedimentary archives. However, the given sedimentary archives in these fast-growing and urbanized areas might not always allow a full reconstruction of past events, as anthropogenic alterations on the rivers course and floodplains effect the archive’s preservation potential. For Chennai, advantages and disadvantages regarding the chemostratigraphic preservation are delicately balanced. However, increasing urbanization and anthropogenic overprinting causes the disruption of sedimentary archives and redistribution of contaminated material (e.g., through dredging), this favors remobilization and relocation of hazardous contaminants.

Harmful contaminants in flood affected sediment deposits of an urban (sub-) tropical river system (Chennai, India)

ACS Spring Meeting 2021

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