Chromophoric Dissolved Organic Matter as a Tracer of Fecal Contamination for Bathing Water Quality Monitoring in the Northern Tyrrhenian Sea (Latium, Italy)

Viviana Piermattei,Alice Madonia,Marco Marcelli,Giuseppe Zappalà,Daniele Piazzolla,Gabriella Caruso,Simone Bonamano

doi:10.3390/jmse8060430

Abstract

Dissolved organic matter present in natural aquatic environments is a heterogeneous mixture of allochthonous and autochthonous materials. In coastal areas vulnerable to sewage waste, its biologically active component, the chromophoric dissolved organic matter (CDOM), is expected to change its composition and distribution in relation to anthropogenic activities, suggesting the possible use of CDOM as a proxy of fecal contamination. This study aimed at testing such hypothesis by investigating and relating the optical properties of CDOM with Escherichia coli abundance, physiological state, and enzymatic activities in a bathing area of the Northern Tyrrhenian Sea (Latium, Italy) affected by urban wastewaters. The parallel factor analysis (PARAFAC) applied to the excitation–emission matrices (EEMs) of CDOM allowed us to distinguish three main components: C1 (λEx/λEm = 342 nm/435 nm), C2 (λEx/λEm = 281–373 nm/460 nm), and C3 (λEx/λEm = 286 nm/360 nm). C1 and C2 corresponded to humic acids of terrestrial origin, while C3 to tryptophan, whose fluorescence peak was detected close to sewage sites, strongly related to active E. coli cells. The comparison between spectral and microbiological methods is suggested as a suitable approach to monitor bathing water quality for the implementation of coastal observing system capability.

Highlights

Coastal marine environments are known to be highly susceptible to pollution as they are characterized by the coexistence of multiple human activities as well as high population densities
The Analysis of variance (ANOVA) results showed the presence of statistically significant differences between the SC0, SC1, and SC2–SC6 sites considering the chromophoric dissolved organic matter (CDOM) absorption coefficients at 280 and 355 nm (p < 0.01)
This study showed that, during the 2015–2017 bathing seasons, coastal marine areas of the Northern Latium experienced fecal contamination

Summary

Introduction

Coastal marine environments are known to be highly susceptible to pollution as they are characterized by the coexistence of multiple human activities (e.g., aquaculture, industries, maritime transport, and tourism) as well as high population densities. During the tourist season or under intense rainfall, sewage networks can overload, spreading untreated sewage waste directly into the sea Such episodes are the main cause of the occurrence of fecal contamination events on coastal bathing areas limiting their recreational uses and increasing possible risks for public health [6]. Laboratory analysis based on culture methods is time and labor-consuming, making their use in environmental monitoring largely inadequate [9,10]. To this end, rapid microscopic analytical protocols such as those based on labeled immune sera, applied in immunofluorescence, provide an estimate of fecal contamination by E. coli more accurately than conventional plate methods. Fluorescent antibody methods allow for the detection of target bacteria, regardless of their physiological status, including moribund or stressed cells that have lost their ability to grow on conventional culture media [11,12,13]

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