Contemporary Contamination of Urban Floodplains in Chennai (India)

Abstract

Fast growing coastal population centers face an increasing vulnerability to several emission sources of anthropogenic and industrial pollutants. The ongoing industrialization in emerging countries increases the environmental and human risk for people living in coastal megacities, especially in the global south of Asia. Extreme weather events, such as heavy rainfalls and resulting flood events, are projected to increase in frequency in the foreseen future, facing an increasing vulnerability to monsoon-induced floods and the release and distribution of xenobiotics causing harm to communities and the environment along a river’s pathway. To endeavor the unknown risks posed by these toxic floods and to assess the associated contamination distribution, the preserved organic geochemical signature from floodplain sediments is studied.This investigation evaluates the inorganic and organic pollutant assemblage in ten surface sediments along the Adyar and Cooum river in the urban areas of Chennai (southern India). Potentially toxic elements (Cr, Ni, Cu, Zn, Pb) show a continuous concentration decrease downstream. Four main groups of persistent organic pollutants have been detected: petrogenic pollutants (hopanes, PAHs), urban wastewater pollutants (LABs, DEHA, methyl-triclosan, octocrylene), technical compounds (Mesamoll®, DPE, NBFA), and pesticides (DDX). While most organic compounds show source specific properties, the definite sources for others remain vague based on the multitude of potential sources and diffusiveness of anthropogenic emissions. The chosen approaches have shown that urban wastewater pollutants and several technical compounds are suitable to assess the anthropogenic-induced contamination in floodplain sediments. However, sedimentary archives in fast-growing, urbanized environments are influenced and superimposed by anthropogenic alterations.

Inventory of aqueous and sediment-associated organic pollutants released by the 2021 flood in the Vicht–Inde catchment, Germany

“…In fraction F2 the phthalates dimethyl phthalate dimethyl phthalate (DMP), diisobutyl phthalate (DIBP), dioctyl isophthalate (DOIP) were identified. In both fraction the degradation product phthalic acid ester (PAE) was found synthesis and have been documented in urban effluents (e.g., [7]). The drug-related compounds are caffeine and myosmine (closely related to nicotine).…”

“…6C) have been identified in the sediments. Through the past two decades, few studies provided evidence for the widespread distribution of Mesamoll ® in the environment, as well as the ability to adsorb and accumulate in sediments (e.g., [7,34,36,83,94]). Mesamoll ® pollution in the Rur catchment, to which the Vicht-Inde catchment contributes, has previously been documented by Schwanen et al [92].…”

“…In contrast to the pollution hotspots, it is imperative to acknowledge that a significant proportion of the flood-associated pollution has likely been transported downstream along the Rur (as documented by Schwanen et al [92]) and Meuse rivers. The phenomenon of washing-out is often overlooked in flood analyses (e.g., [7,66]).…”

“…The 2021 flood event, for instance, witnessed the occurrence of at least 2-3 distinct flood pulses recorded by gauges in Mulatshütte (Vicht), Kornelimünster, and Eschweiler (Inde), further complicating the dynamics of sediment-associated pollution transport and deposition. Collectively, these mechanisms give rise to a pollution wash-out phenomenon in unconfined river sections, notably floodplains (e.g., [7]). This occurrence presents a potential concern, particularly given that numerous post-flood investigations commonly focus on surveying "unaltered" floodplains, viewing them as archives for flood-induced pollution.…”

“…Major river systems are known to be highways for pollutants with various residence times either within their water phase or associated with sediments transported in the river or archived with high-stand deposits on floodplains (e.g., [7,103]). In particular, river floods are the main drivers for the release, remobilization, and distribution of organic and inorganic contaminants in the aqueous and sediment phase ( [19], and references therein).…”