Heavy metals | EPFL Graph Search

Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would likely be more concerned with chemical behaviour. More specific definitions have been published, none of which have been widely accepted. The definitions surveyed in this article encompass up to 96 out of the 118 known chemical elements; only mercury, lead and bismuth meet all of them. Despite this lack of agreement, the term (plural or singular) is widely used in science. A density of more than 5 g/cm3 is sometimes quoted as a commonly used criterion and is used in the body of this article. The earliest known metals—common metals such as iron, copper, and tin, and precious metals such as silver,

Substance flow analysis as a tool for urban water management

Nathalie Chèvre Rossi, Luca Rossi

Human activity results in the production of a wide range of pollutants that can enter the water cycle through stormwater or wastewater. Among others, heavy metals are still detected in high concentrations around urban areas and their impact on aquatic organisms is of major concern. In this study, we propose to use a substance flow analysis as a tool for heavy metals management in urban areas. We illustrate the approach with the case of copper in Lausanne, Switzerland. The results show that around 1,500 kg of copper enter the aquatic compartment yearly. This amount contributes to sediment enrichment, which may pose a long-term risk for benthic organisms. The major sources of copper in receiving surface water are roofs and catenaries of trolleybuses. They represent 75% of the total input of copper into the urban water system. Actions to reduce copper pollution should therefore focus on these sources. Substance flow analysis also highlights that copper enters surface water mainly during rain events, i.e., without passing through any treatment procedure. A reduction in pollution could also be achieved by improving stormwater management. In conclusion, the study showed that substance flow analysis is a very effective tool for sustainable urban water management.

IWA Publishing2011

Identifying contaminated sediment problems associated with urban stormwater discharges in lakes

Tom Hugo Antoine Benejam

Urban stormwater discharges during wet weather has always been a sensitive issue to deal with. By inducing combined sewer overflows, substantial impacts on receiving water are commonly feared. Aware of this problematic situation, the VSA already created the STORM guideline to cope with this issue in small rivers. However, such a guideline is still lacking for large rivers and lakes. This project is a first step towards this direction and tries to prospect the necessity of such instructions for lakes. For this purpose, the present master thesis studies the impact of urban stormwater discharged via the Flon river into the Vidy Bay of Lake Geneva, next to the city of Lausanne. A Sediment Quality Triad, meaning a combination of three assessment methods (chemistry, ecotoxicology and in situ benthic communities), was implemented to assess the impact of stormwater discharges on the sediments in this part of the lake. On a large sampling grid composed of 15 sites, heavy metals were measured and ostracod bioassays were performed with the sediment samples collected at these sites. Subsequently, on the five sites located in the central transect of this sampling grid, further experiments were led to understand the incidence of stormwater discharges on sediment quality while moving away from the Flon river’s effluent. In addition to heavy metals, PAHs and PCBs were measured at these sites. A battery of three extra ecotoxicological bioassays was also carried out. These tests were implemented with the following organisms: chironomids, macrophytes and nematodes. Finally, two kind of in situ communities were studied in these five sites: microbial communities in order to perform a pollution-induced community tolerance (PICT) and oligochaete communities in order to implement the oligochaete index of lake bioindication (IOBL). The implementation of these experiments showed that the contamination induced by urban stormwater discharges is limited to the proximity of the combined sewer overflow. A set of pollutants mainly composed of copper, zinc, PCBs and PAHs was identified within this contaminated area. Although no toxicity was observed on the sites affected by this contamination, in situ community studies revealed substantial shifts towards resistant species in both oligochaete and microbial community structures. Another contamination area, observed in remote sites and mainly composed of cobalt, chromium, iron, manganese and nickel, remains not well understood. The laboratory toxicity tests detected some toxicity in benthic invertebrates but the benthic communities studied in situ showed no apparent alteration. Modeling tools are required to get a better understanding of the source of this contamination.

2017

Identifying contaminated sediment problems associated with urban stormwater discharges in lakes

Tom Hugo Antoine Benejam

2017