A literature review of metal mixture interaction analyses identified that there was not a consistent method to determine the impact of metal mixtures on an aquatic organism. The review also revealed that a majority of the research on mixtures made use of water concentrations only. Therefore research was conducted to determine the relationship between exposure, bioaccumulation and chronic effects of the four elements As, Co, Cr and Mn individually. Mechanistically based saturation models of bioaccumulation and toxicity were determined for the benthic invertebrate Hyalella azteca, from which lethal water concentrations and body concentrations were also determined. These models were then combined with those previously done for the metals Cd, Cu, Ni, Pb, Tl and Zn to model the impact of 10 metal mixtures on bioaccumulation in short term (1-week) exposures and on bioaccumulation and toxicity in chronic (4-week) exposures at “equi-toxic” concentrations. Interactions between the metals were identified in which; Cd, Co and Ni bioaccumulations were significantly inhibited, Tl and Zn bioaccumulations were marginally inhibited, there was no impact on Cr, Cu or Mn bioaccumulation, and both As and Pb bioaccumulation were enhanced by some mixtures of metals. It was determined that strict competitive inhibition may be a plausible mechanism of interaction affecting Co, Cd and Ni bioaccumulation but not for any of the other metals. However, it is possible that other interactions such as non-competitive or anti-competitive inhibition may have been responsible. A metal effects addition model (MEAM) was developed for Hyalella azteca based on both the bioaccumulation (body concentrations) to effects and the exposure (water concentration) to effects relationships developed from the single metal only studies The MEAM was used to predict the impact of metal mixture exposures on mortality. Toxicity was under-estimated when based on measured water or body concentrations, however, its best prediction was based on body concentrations. The MEAM, when based on measured body concentrations, takes bioavailability into account, which is important since the chemical characteristics of water can greatly alter the bioavailability and therefore toxicity of metals. The MEAM was compared to the traditional Concentration Addition Model (CAM), which calculates toxic units based on water concentrations and LC50s or body concentrations and LBC50s. The CAM overestimated toxicity, but had its best prediction when based on water concentrations. Over all, the best fit to observed mortality was the prediction by the MEAM, based on body concentrations. The measurement of bioaccumulated metals and the use of the MEAM could be important in field site assessments since it takes into account changes in bioavailability due to different site water chemistries whereas the traditional CAM based on water concentration does not.

L’eutrophisation et la contamination des sédiments (ex : métaux, nutriments, etc.) sont des problèmes majeurs pour la protection des écosystèmes aquatiques et la protection des ressources d’eau douce. Le lac Saint-Augustin (Québec, Canada) est aux prises avec ces deux problèmes. Depuis 2001, plusieurs épisodes de fleurs d’eau de cyanobactéries sont rapportés durant la saison estivale (P > 70 µg/L). Galvez et collaborateurs ont proposé une méthode de restauration pour ce lac consistant : (I) à réduire la teneur en phosphore de l’eau du lac par coagulation/floculation avec du sulfate d’aluminium et (II) à effectuer un recouvrement actif de roche calcaire et de sable afin d’isoler le floc d’Al, le P et les autres contaminants (ex., métaux) et permettre la recolonisation par le benthos. L’objectif des présents travaux était d’évaluer l’écocompatibilité de cette méthode. Deux approches écotoxicologiques ont été employées : (I) essais de toxicité monospécifiques (croissance de l’algue Pseudokirchneriella subcapitata et de la lentille d’eau Lemna minor; survie et reproduction de la daphnie Daphnia magna et de l’amphipode Hyalella azteca, survie, croissance et émergence de l’invertébré Chironomus riparius ainsi que survie des larves de tête-de-boule Pimephales promelas et des alevins de truites arc-en-ciel Oncorhynchus mykiss) et (II) essai en microcosmes de 2 litres tel qu’adapté par Triffault-Bouchet. La toxicité de l’aluminium et l’impact de la roche calcaire ont été étudiés séparément : d’abord avec eau et sédiments artificiels et ensuite avec eau et sédiments du lac Saint-Augustin. Les résultats démontrent que les algues et les daphnies sont affectées par l’application d’alun. Aucun effet n’a été observé chez les autres organismes. Ceux-ci ont eu la capacité de recoloniser les milieux traités avec l’alun ou avec la technique complète. Ces résultats tendent à démontrer que la méthode de restauration est prometteuse. L’écocompatibilité de la technique ne pourra cependant être démontrée que par des essais in situ et après un suivi étroit du phytoplancton et du zooplancton dans le lac. Toutefois, dans le cadre des présents travaux, l’efficacité des traitements (en terme de déphosphatation) n’a pas permis d’atteindre le critère de qualité du MDDEP (20 µg/L). Ces paramètres devront être étroitement suivis lors des essais in situ. Mots clés : Eutrophisation, sédiments contaminés, restauration de lac, aluminium, recouvrement actif, évaluation écotoxicologique, bioessais monospécifique, microcosmes. / Eutrophication and contaminated sediments (e.g.: nutrients, metals, etc.) are preoccupying issues in aquatic ecosystems and water resource protection. Saint-Augustin Lake (Quebec, Canada) is affected by both problems in addition to the presence of de-icing salts. This small shallow lake has low renewal time and receives an intensive phosphorus transfer from bottom sediments to the water column. Since 2001, the lake presents cyanobacteria blooms every summer (P > 70 μg/L). Galvez and collaborators has proposed a remediation method for this lake that consists of (i) the precipitation of phosphorus present in the water column by the addition of alum, in association with the deposition of (ii) an active capping layer (limestone + sand) to isolated P, Al and other contaminants (e.g., metals) within bottom sediments and allow recolonisation by benthos. The objective of this study is to assess the ecotoxicological impact of that remediation method. Two ecotoxicological approaches are used to assess the impact of this method: (I) single-species bioassays (algae Pseudokirchneriella subcapitata and duckweed Lemna minor growth; daphnid Daphnia magna and amphipod Hyalella azteca survival and reproduction, invertebrate Chironomes riparius survival, growth and emergence, fathead minnow P. promelas and rainbow trouts O. mykiss survival) and (II) a 2-L microcosm as adapted by Triffault-Bouchet. Alum toxicity and limestone impact were studied separately in laboratory: first with artificial water and sediments and then using actual lake overlying water and sediments. The results show that algae and daphnids are sensitive to alum treatment. No significant effects were observed on the other organisms. These organisms had the ability to recolonize the treated media either with alum treatment or with complete treatment. These results suggest that the restoration method is promising. The environmental compatibility of the technique, would be demonstrated after testing in situ with a close monitoring of phytoplankton and zooplankton in the lake. However, the results of this study showed that the treatments dephosphatation efficacity was not enought to reach the MDDEP quality criteria (20 µg/L). Also, the concentration of residual aluminum after treatments was still over the MDDEP quality criteria after treatments. Keywords : Eutrophication, contaminated sédiments, lake restauration, aluminum, active capping, écotoxicological évaluation, monospécific bioessais, microcosms.