A high-resolution historical record of nutrients, trace elements and organochlorines (DDT and PCB) deposition in a drinking water reservoir (Lake Brêt, Switzerland) points at local and regional pollutant sources

The 137Cs and 210Pb dating of a 61-cm long sediment core retrieved from a drinking water reservoir (Lake Bret) located in Switzerland revealed a linear and relatively high sedimentation rate (∼1 cm/year) over the last decades. The continuous centimeter scale measurements of physical (porewater and granulometry), organic (Corg, P, N, HI and OI index) and mineral (Cmin and lithogenic trace elements) parameters therefore enables reconstructing the environmental history of the lake and anthropogenic pollutant input (trace metals, DDT and PCBs) at high resolution. A major change in the physical properties of the lowermost sediments occured following the artificial rise of the dam in 1922. After ca. 1940, there was a long-term up-core increase in organic matter deposition attributed to enhance primary production and anoxic bottom water conditions, due to excessive nutrient input from a watershed predominantly used for agriculture that also received domestic effluents from two wastewater-treatment plants. This pattern contrasts with the terrigenius element input (Eu, Sc, Mg, Ti, Al, and Fe) which doubled after the rising of the dam but continuously decreased during the last 60 years. By comparison, the trace metals (Cu, Pb and Hg) present a slight enrichment factor (EF) only during the second part of the 20th century. Although maximum EF Pb (>2) occurred synchronously with the use of leaded gasoline in Switzerland (between ca. 1947 and 1985) the Hg and Cu profiles exhibited a relatively similar trend than Pb during the 20th century, therefore excluding the alkyl-lead added to petrol as the dominant (atmospheric) source of lead input to Lake Brêt. Conversely, the Cu profile that did not follow the decrease registered in Pb and Hg, suggesting an additional source of Cu probably linked to the impact of agricultural activities in the area. In absence of heavy industries in the catchment, the atmospheric deposition of DDT and PCBs via surface runoff follows the historical emissions of POPs in Switzerland. Such result highlights the regional contamination of freshwater resources by the large-scale emission of toxic industrial chemicals in the 1960s and 1970s as well as the efficiency of the regulatory measures subsequently taken.

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

Development of a hyphenated analytical methodology for the fractionation and characterization of environmental colloids

Enrica Alasonati

Natural colloids are defined as macromolecules and nanoparticles with sizes ranging between 1 nm and 1 µm. Colloidal pool is complex "ill-defined" mixture of humic substances, exopolymeric substances (EPS), inorganic oxides, clays, etc. Aquatic colloids have been recognized as key mediators in the removal of trace elements, facilitating contaminant transport, organic carbon cycling and micronutrient bioavailability. The residence times of the colloidal pool (and associate contaminants) can be order of magnitude different from those of the particulate fraction, but unlike the "truly" dissolved fraction, can be subjected to different coagulation and sedimentation processes. Colloids may also influence metal bioavailability by affecting free metal ion concentrations, constraining diffusion and affecting the dissociation kinetics of biological processes. The important environmental role of natural colloids is largely influenced by their surface area and closely related colloidal size. Nonetheless, it is currently unclear to what extend colloidal size can influence their behaviour and contaminant (e.g. toxic metals) binding properties. In our view this is partially related to the difficulties in determination of the colloidal size distributions and their impact in metal behaviour, mainly due to the inherent heterogeneity of the environmental colloids and their low concentrations in the environment. Furthermore, in addition to average parameters, there is a lack of appropriate sample collection and processing procedures, as well as analytical techniques to measure simultaneously the size (or related parameter) distributions of the colloid associated metal. The objective of the present work was therefore to develop sensitive analytical procedures for the fractionation of natural colloids and to apply them to improve the current understanding on the fate of the colloids and associated toxic metals in the freshwaters. To achieve these goals, the capabilities of asymmetric flow-field flow fractionation (aFlFFF) coupled to several detectors was explored. aFlFFF is a versatile technique separating colloids according to their diffusion coefficient. The system was hyphenated with multi-angle laser light scattering (MALS), differential refractive index (DRI), UV detector and, when necessary, high resolution inductively coupled plasma mass spectrometry (ICP-MS). Correct interpretation of the experimental results and extrapolation of meaningful molecular parameters by using an analytical tool with such a level of complexity requires improvement of the knowledge of colloids behaviour in the aFlFFF channel and careful optimization of the separation conditions. Given the very complex and dynamic nature of environmental colloids, different experimental procedures was first optimized and validate under lab conditions by using "standardized" colloids (e.g. alginate and EPS isolate from lab bacterial cultures), then applied to characterize colloidal organic matter (COM) isolated from natural water systems. The influence of critical operating parameters, such as crossflow rate, carrier composition and concentration, and sample load, on the alginate retention was carefully evaluated. Combined information obtained simultaneously by DRI and MALS detectors, allowed to set the appropriate combination of optimal parameters for the characterization of alginate, as a model COM. The metal distributions of metal-alginate complexes were probed by aFlFFF - ICP-MS: average values and continuous distributions of molar masses, radius of gyration and hydrodynamic radius, critical for understanding their role as carriers of metal pollutants, were evaluated in presence of lead or cadmium and compared to those in metal-free solutions of alginate. Furthermore, the molecular characteristic of exopolymeric substances (EPS) secreted by bacterium Sinorhizobium meliloti wild type and exoY strains, which is deficient in the production of the succinoglycan, were studied. EPS were collected in the extracellular environment or desorbed from the cell surface using different extraction protocols. EPS fractions with different chemical characteristic and molar mass were found, depending on the strain and extraction protocol. Molecular parameters as the distributions and average values of molar mass and gyration radius, and the polydispersity index have been measured and compared with data obtained by the chemical characterization. Size exclusion chromatography coupled to UV detection was also employed to provide additional information on the small class of size. Moreover, the effect of the cadmium, lead and calcium addition to exopolymeric substances excreted in the extracellular environment was investigated, with the aim to study how does EPS composition, size and mass distributions, can affect the trace metal binding properties of EPS and how the metal addition affects the EPS conformation. Obtained results revealed that cadmium and calcium bound preferentially on the low-size species population and the amount of the bound metal increased with the increasing of the concentration of added metal. In contrast, lead bound on preferentially larger classes of EPS size. The aFlFFF separation parameters were also optimized for the fractionation and characterization of humic substances, as other COM component, and applied to probe the temporal and spatial variability in the size and mass characteristics of COM samples collected in the Amazon River basin. COM characterization demonstrated the existence of a clear decrease of size of the colloidal material when passing from small to large watercourses (spatial variation). No significant changes were found in size distributions of samples collected in different period of the year, during the low and high flow, respectively (temporal variation). The analytical methodology, adapted to determine not only mean characteristics, but the population distributions, developed in the present work, allowed to obtain new information about the colloidal organic matter size distribution, which play utmost role in colloids behaviour and fate in the environment, in particular as toxic metal carriers.

EPFL2009

Assessment of the effects of wastewater treatment plant effluents on receiving streams using oligochaete communities of the porous matrix

Régis Lionel Vivien

Human activities can disturb the natural dynamics of exchanges between surface water and groundwater in rivers. Such exchanges contribute to the self-purification of the environment and an excess of infiltration can lead to contamination of groundwater. In addition, the porous matrix (coarse surface sediments and hyporheic zone), through which water exchanges occur, is a sink for pollutants. For environmental monitoring programs, it is therefore essential to take into account both the dynamics of vertical hydrological exchanges and the biological quality of this matrix. The Functional Trait (FTR) method, which is based on the study of oligochaete communities in coarse surface sediments and the hyporheic zone, was proposed as a tool to simultaneously assess the dynamics of vertical hydrological exchanges and the effects of pollutants present in the porous matrix. Here, we applied this method during two different periods (in March and September 2016), upstream and downstream of locations affected by discharges from wastewater treatment plants (WWTP) located in Switzerland. The biological quality of surface sediments and the hyporheic zone was shown to be better upstream of the WWTP in both campaigns. In addition, results suggested that the capacity for self-purification was lower downstream of the WWTP, and that groundwater at these locations was vulnerable to pollution by surface water. The FTR method proved valuable as a field method for detecting the effects of point source contamination on receiving streams. In the near future, this community-based approach will benefit from advances in the use of DNA barcodes for oligochaete species identification.