Spatial extent and ecotoxicological risk assessment of a micropollutant-contaminated wastewater plume in Lake Geneva

In this study, the spatial extent of a wastewater-influenced water mass originating from a wastewater treatment plant outlet in Vidy Bay (Lake Geneva) was monitored by two manned submersibles from June to August 2011. The main goal was to assess whether micropollutants in the wastewater mass cause an ecotoxicological risk to the aquatic environment, and to determine how far the zone of risk extends beyond the wastewater outlet. Real-time measurements of elevated electrical conductivity were used as a proxy to indicate the presence of wastewater-influenced water. Conductivity was highest in immediate proximity to the wastewater outlet, though if all measurements obtained over the duration of the sampling campaign were integrated, elevated conductivity extended over an area of at least 1 km2 surrounding the outlet. Additionally, water samples were collected within and outside the Vidy Bay, and were analyzed for 39 micropollutants (pharmaceuticals, pesticides, and corrosion inhibitors). Micropollutant concentrations were generally in the low ng/L range, though for some substances > 100 ng/L was measured. The concentrations of most pharmaceuticals, which are primarily wastewater-derived, decreased with decreasing conductivity and with increasing distance from the wastewater outlet. Pesticide concentrations, in contrast, were homogeneous throughout the Vidy Bay and the lake. An ecotoxicological risk assessment based on the cumulative risk exerted by all measured substances indicated that the wastewater caused a zone of potential ecotoxicological risk that extended well into the deep lake and in the direction of a downstream drinking water intake.

Sources, Spreading and Fate of Antibiotic Resistance Genes and Resistant Bacteria in Vidy Bay, Lake Geneva, Switzerland

Nadine Czekalski

Increasing numbers of multiresistant bacterial pathogens cause severe health problems on a global scale. Large quantities of bacteria and their resistance genes are discharged into natural environments via human and animal waste. Not much is known so far about the fate and further spread of resistance determinants in the environment. There is evidence that aquatic environments may function as important compartments for preserving and exchanging antibiotic resistance genes (ARG) from sewage and drinking water. Lake Geneva is the largest fresh water reservoir of Western Europe and supplies the surrounding cities. At the same time these cities discharge sewage into the lake. Lausanne is the largest city in the lake’s catchment and discharges the highest amount of treated, as well as in case of heavy rain events, partly untreated waste waters. Also two rivers, Chambering and Flown, transport untreated sewage (bypass), in case of storm events. Only 3.4 km from the sewage discharge point lake water is pumped for drinking water preparation for Lausanne. Many studies have reported on contamination of the bay with heavy metals, inorganic nutrients, organic carbon and fecal indicator bacteria due to the sewage discharge. The present thesis aimed on investigating the sources, spreading and fate of antibiotic resistant bacteria and antibiotic resistance genes in the Vida bay, Lake Geneva. In the first part of this dissertation, a screening for antibiotic- and specifically multi-resistant bacteria was carried out as one of the first studies in a Swiss waste water stream and the receiving fresh water lake. For this purpose, a combined set of culture based (viable bacterial counts on nutrient media supplemented with antibiotics) and molecular tools (detection and quantitation of antibiotic resistance genes from environmental DNA-extracts using quantitative real-time PCR) was applied. Raw hospital and communal sewage, as well as partly treated/mixed sewage, which is discharged into the lake via an effluent pipe 700 m off shore, were taken into account. Furthermore lake water samples nearby the end of the waste water discharge pipe and the drinking water pump as well as close to the two river mouths were analyzed. Finally, the role of Lausannes WTP was evaluated for its potential to remove resistant and multiresistant bacteria, as well ARG. Results show highest levels of multiresistant bacteria and ARG in both hospital and communal sewage. Incidence was found that the WTP is a selective environment for multiresistant bacteria and resistance genes. Moreover, lake water and sediments nearby the end of the WTP discharge pipe and the two river mouths exhibited significantly higher levels of resistant determinants as compared to samples from the drinking water uptake. If the level of antibiotic resistance close to the drinking water uptake represents the natural background level of the lake or whether it is impacted by the WTP plume remained open during this first survey. The spatial distribution and persistence of ARG discharged via waste water into lake systems has been evaluated for the first time in the second part of this thesis. 22 sediment cores were sampled along two major transects (leading either into the deep lake or along the south-western shore line to the drinking water uptake) and in the vicinity of the WTP discharge pipe in the Vidy bay. A subset of samples was also analyzed for contamination with a “conventional” pollutant of sewage (mercury), for which a similar transport behavior (particle bound) as for bacteria and their resistance genes is assumed. The microbial community composition in all sediment as well as in waste water samples was analyzed using ARISA. Strong pollution with both ARG and mercury was detected in close proximity of the WTP discharge pipe and both contaminants significantly decreased along the transect into the deep lake. In general however, the spatial contamination of mercury and ARG was only moderately correlated. While the mercury contaminated sediment surface area tended to have a pollution tail in south eastern direction, ARG showed only a slow decrease along the south western transect. These findings imply differences in transport and fate of mercury and ARG in the bay, or additional sources of ARG contamination. Analysis of the microbial diversity in the samples support these hypotheses. This study revealed feasibility of qPCR as a tool to semi-quantitatively track spatial ARG contamination in fresh water lake sediments. Not much is known yet on the antibiotic resistance background level of fresh water lakes and how this may be influenced by anthropogenic activities in the surrounding catchment. Water samples from 21 Swiss lakes have been collected and were analyzed for the prevalence of different ARG (2 sulfonamide resistance genes sul1 & sul2, 3 tetracycline resistance genes tetB, tetM, tetW and one plasmid mediated fluoroquinolone resistance gene qnrA). In order to document the abundance of these genes in the bacterial populations, they were normalized to bacterial 16S rRNA gene copy numbers. The lakes differ in size, geographical position, land use pattern, and trophical status. The composition of the microbial community of all lakes was analyzed using ARISA. Sulfonamide resistance genes were detected in all investigated lakes (0.2-4%, sul1 and 0.01-0.3%, sul2), with highest levels in Lake Baldegger (21%). Lake Baldegger also contained all of the three tetracycline resistance genes, which were found in only 4 other lakes. None of the lakes was positive for qnrA. Important anthropogenic catchment activities linked to sul gene prevalence could not be identified based on our data and may require further analysis and an additional variables to complete our data set. However, our study demonstrates contamination of Swiss lakes with sulfonamide resistance genes and the potential of fresh water lakes preserve these genes, even remote from direct sources of pollution.

EPFL2013

Pesticides drive risk of micropollutants in wastewater-impacted streams during low flow conditions

Juliane Hollender

Micropollutants enter surface waters through various pathways, of which wastewater treatment plants (WWTPs) are a major source. The large diversity of micropollutants and their many modes of toxic action pose a challenge for assessing environmental risks. In this study, we investigated the potential impact of WWTPs on receiving ecosystems by describing concentration patterns of micropollutants, predicting acute risks for aquatic organisms and validating these results with macroinvertebrate biomonitoring data. Grab samples were taken upstream, downstream and at the effluent of 24 Swiss WWTPs during low flow conditions across independent catchments with different land uses. Using liquid chromatography high resolution tandem mass spectrometry, a comprehensive target screening of almost 400 organic substances, focusing mainly on pesticides and pharmaceuticals, was conducted at two time points, and complemented with the analysis of a priority mixture of 57 substances over eight time points. Acute toxic pressure was predicted using the risk assessment approach of the multi-substance potentially affected fraction, first applying concentration addition for substances with the same toxic mode of action and subsequently response addition for the calculation of the risk of the total mixture. This toxic pressure was compared to macroinvertebrate sensitivity to pesticides (SPEAR index) upstream and downstream of the WWTPs. The concentrations were, as expected, especially for pharmaceuticals and other household chemicals higher downstream than upstream, with the detection frequency of plant protection products upstream correlating with the fraction of arable land in the catchments. While the concentration sums downstream were clearly dominated by pharmaceuticals or other household chemicals, the acute toxic pressure was mainly driven by pesticides, often caused by the episodic occurrence of these compounds even during low flow conditions. In general, five single substances explained much of the total risk, with diclofenac, diazinon and clothianidin as the main drivers. Despite the low predicted acute risk of 0%-2.1% for affected species, a significant positive correlation with macroinvertebrate sensitivity to pesticides was observed. However, more effect data for pharmaceuticals and a better quantification of episodic pesticide pollution events are needed for a more comprehensive risk assessment. (C) 2016 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2017

Micropollutants in Large Lakes: From Potential Pollution to Risk Assessments

David Andrew Barry, Florence Bonvin, Neil Graham, Luca Rossi

This book is divided into six additional chapters: Chapter 2 deals with the agricultural source of micropollutants; Chapter 3 with the urban source of micropollutants; Chapter 4 with lake circulation; Chapter 5 with the influence of a wastewater treatment plant on a bay; Chapter 6 with the input of sediments and their transport in a bay; and Chapter 7 with the risk assessment of the mixture of the compounds present in lake water. A last chapter (8) synthesizes the main findings and presents perspectives for future studies. More specifically: Chapter 2 is dedicated to the micropollutants that enter lakes through agriculture. These are mainly pesticides. After a review of the different types of compounds, the authors will put forth the main pathways these compounds follow to enter lakes. The case of glyphosate, an herbicide used worldwide, will be discussed. Chapter 3 illustrates the urban sources of pollutants with pharmaceuticals and biocides. Two models will be covered that allow estimating the load and dynamics of these chemicals that may exit from an urban catchment and therefore reach lakes. Special attention will be paid to the “end of pipe” removal of these compounds at a WWTP. Chapter 4 is dedicated to lake circulation. The aim of this chapter is to present an overall description of lake hydrodynamics, which is driven by three factors: wind, temperature and Coriolis forces. The main inflow to Lake Geneva is provided by the Rhône River. In addition, the topography surrounding the lake varies rapidly, for example, with mountains in the eastern part. As a consequence, the lake’s currents can vary markedly. To achieve our objective, we will utilise hydrodynamic modelling. A model will be proposed that permits describing the behavior of the top layer of the lake based on wind direction. The importance of stable hydrogen and oxygen isotopes for characterising the sources of water and mixing processes in the lake will be described and illustrated with the example of the Rhône river interflow to it. The measured variations of the isotopic compositions within the lake can serve as verification of the lake hydrodynamic models. However, the emphasis of the chapter will be on explaining the major current features and how they relate to wind forcing, which is one of the main drivers. Chapter 5 and 6 are devoted to the Vidy Bay in the Lausanne area of Lake Geneva. This bay receives the treated effluents of the largest wastewater treatment plant of the lake catchment. The latter represents therefore one of the major point sources of contaminants for the lake. These two chapters will focus on the various processes that control the transfer of contaminants (associated with particles or in a dissolved state) discharged into the bay and transported to the lake’s main water body. More specifically, Chapter 5 describes the WWTP plume dynamics. In relation to hydrodynamics (Chapter 4), specifically the behaviour of the plume formed through the treatment plant effluent release, field measurements are utilised to attempt to determine the plume behavior under various lake conditions. Furthermore, it investigates the degradation of organic pollutants. Photodegradation and other degradation processes are studied with theoretical, experimental and modelling approaches. Chapter 6 focuses on sediment path tracing. The pollutants associated with particles (trace metals, hydrophobic components, etc.) settle to the lakebed, but can be remobilized and transported to deeper parts of the lake. Bottom currents, and other physical forces, can cause resuspension and advection. Tracers used to identify this advection comprise natural and anthropogenic radioisotopes along with mercury as a major toxic trace element. Chapter 7 concentrates on one major issue of micropollutants in aquatic systems, like lakes, i.e., the risk of the mixture. The evaluation of the risk of mixture of micropollutants is not trivial and we will first present critically the models that allow doing so. We will also demonstrate their validity as predictive tools with the example of herbicide mixtures in Lake Geneva. Finally, we will map the risk of micropollutants around the lake. Finally in Chapter 8, we synthesize the main findings of all chapters and discuss recommendations for the management of mid-sized lakes regarding micropollution.

CRC Press & EPFL Press2018