Time Course Transformations and Fate of Mercury in Aquatic Model Ecosystems

Abstract

Model aquatic ecosystems have been used to study the natural mechanisms involved in the distribution and transformation of inorganic mercury (IHg) in the different compartments and its interactions with the biota. Laboratory incubations in indoor freshwater microcosms, presenting a simple biological organization, were carried out at various spiked concentrations (3, 25 and 257 nmol l −1 of IHg, as mercuric chloride) and from a single initial contamination of the water column. The different compartments of the model ecosystems (water, sediment, macrophytes Elodea canadensis and snails Lymnaea stagnalis) were investigated for mercury distribution and speciation during a 2-month experimental period.The principal results obtained have evidenced different Hg biogeochemical pathways including biotic IHg methylation and reduction and transfer to the biota. A fast transfer of IHg from the water to the aquatic organisms and to the sediment was first observed with IHg half-lives of 24 h and 8 days, respectively. IHg methylation, clearly related to biogenic processes, was also demonstrated in all contaminated microcosms after 1 week of exposure. Finally, gaseous mercury species were determined in the different microcosms and significant biological induced production of elemental Hg (Hg°) and dimethyl Hg (DMHg) was observed. This overall investigation, based on the time courses evolution of IHg and in situ produced monomethylmercury (MMHg) concentrations allows to determine uptake and elimination rate constants for IHg as well as the bioaccumulation kinetics of MMHg in macrophytes and snails. The applicability of these aquatic model ecosystems to provide real insights for pollution impact and ecotoxicological risk assessments has been demonstrated.

Mercury distribution, methylation and volatilization in microcosms with and without the sea anemone Bunodosoma caissarum

“…So there were higher levels of total Me 203 Hg in the microcosms without B. caissarum. In an incubation experiment, with sediment, freshwater, waterweeds and snails, Tessier et al (2007) also recorded higher MeHg concentrations in the water column of the control microcosms. The same authors observed a higher content of inorganic Hg in water available for methylation in the control systems when compared to the treatments, suggesting this as a possible reason for the increased MeHg concentration in the controls.…”

“…Several authors have observed the production of MeHg in the water column of freshwater systems (Ribeiro Guevara et al, 2008Guevara et al, , 2007Tessier et al, 2007), although Hg methylation is considered to occur predominantly in sediment , periphyton (Correia et al, 2012b;Mauro et al, 2002) and epilithon (Desrosiers et al, 2006). Koron et al (2012) detected Me 197 Hg production in seawater of incubation experiments with the radiotracer 197 Hg in different incubation periods.…”

“…Depending on the environmental conditions, inorganic Hg can be converted to more toxic methylated forms, such as MeHg (Correia et al, 2012b;Driscoll et al, 2012;Guimarães et al, 2000a;Ribeiro Guevara et al, 2008;Ullrich et al, 2001). In spite of the extensive literature concerning the behavior of Hg in aquatic environments, including the transformation and distribution mechanisms, there are still knowledge gaps in this area (Ribeiro Guevara et al, 2008Guevara et al, , 2007Tessier et al, 2007;Ullrich et al, 2001;Žagar et al, 2007).…”

“…Model ecosystems can be a useful tool for assessing the fate and the implications of mercury contamination in aquatic environments (Correia et al, 2012a;Tessier et al, 2007). Incubation experiments using isotope tracers allow modeling environments and processes that occur in nature.…”

“…Incubation experiments using isotope tracers allow modeling environments and processes that occur in nature. From these types of experiments, it is possible to investigate the distribution and the behavior of mercury in different environmental compartments by the construction of an indoor microcosm (Correia et al, 2012a;Ribeiro Guevara et al, 2008Tessier et al, 2007). Microcosm experiments simulate natural environments and can be developed and later validated in real aquatic ecosystems (Mason et al, 1996;Tseng et al, 2001), supporting ecotoxicological risk assessments .…”