Recovery potential of periphytic biofilms translocated in artificial streams after industrial contamination (Cd and Zn)

Abstract

Metal wastes can significantly disturb aquatic communities, particularly photosynthetic organisms, the main primary producers in freshwater running ecosystems. In this study, biofilms and diatoms were used as bioindicators to characterize the kinetics of biofilm recovery. An experimental decontamination study was conducted under laboratory conditions, after biofilm colonisation at a site subject to discharge of industrial metals (Zn and Cd) and in parallel at an upstream site, metal-free, considered as a control. After 24 days of colonisation, biofilms were translocated and maintained in the laboratory for 56 days under clean conditions (control and decontamination) or metal contamination. Various tests were conducted from the community level--measures of metal bioaccumulation, cell densities and taxonomic investigations, to the individual level--measures of teratological forms. After 56 days of decontamination, Zn and Cd concentrations in decontaminated biofilms showed a sharp decline, respectively ranging from 6.7 ± 2 to 4 ± 2.5 mg Zn g⁻¹ DW and from 207.6 ± 24.5 to 45.4 ± 9.9 μg Cd g⁻¹ DW. However, at the end of the experiment bioaccumulations remained significantly higher than concentrations in control biofilms. Despite a diatom evolution in biofilm assemblages, taxonomic inventories did not demonstrate a complete restoration of diatom communities in biofilms under decontamination conditions compared with controls, since metal-resistant species initially present after colonisation at the contaminated site, such as Eolimna minima, persisted in high abundance in decontaminated biofilms. Biofilms kept under metal pressure showed very high bioaccumulation capacities and a sharp decline of species diversity which allowed identification of some resistant species. Regarding these first results on the behaviour of diatom biofilms under experimental decontamination conditions, improvement of the natural hydrosystem's chemical state appears quickly, but an eventual return to good ecological status appears delayed, with the persistence of metal-tolerant species even after 56 days.

Freshwater Diatoms as Indicators of Combined Long-Term Mining and Urban Stressors in Junction Creek (Ontario, Canada)

“…As suggested by Morin et al [64] and Arini et al [65], deformity frequencies between 0.5 and 1% are considered as naturally occurring. With abnormal valve frequencies of 1-1.2%, it is difficult to confirm a specific response to metal contamination at sites JC1, JC2, JC4, JC5, JC6, JC7, NC1, and NC2, as these values are close to the estimated natural background.…”

Resilience and recovery: The effect of triclosan exposure timing during development, on the structure and function of river biofilm communities

“…In the literature lack of recovery has been linked with retention of contaminants in the biofilm that prevents complete removal of the stress even though it is no longer present in the bulk liquid phase (Ivorra et al, 1999). For example, Arini et al (2012) used artificial streams to assess biofilm recovery following Cd and Zn exposure. After 56 days, full recovery was not observed, and lack of recovery was attributed in part, to retention of the metals in the biofilm matrix.…”

“…While the general biomass measures appeared relatively insensitive measures of effects and recovery, the specific measures related to algal/cyanobacterial and bacterial biomass, were revealing with regard to community response to TCS exposure and recovery. Arini et al (2012) reported that diversity indices and biovolumes measured from biofilms under decontamination conditions did show the beginnings of recovery. Activity measurements include thymidine incorporation and compound-specific estimates based on labeled substrates, as well as commonly-used Biolog Ecoplate.…”

Diatom Deformities and Tolerance to Cadmium Contamination in Four Species

“…The stria density ranges from 32-47/10 µm [14]. N. palea has been described as relatively tolerant to metals [6,15] and to pesticides [16][17][18]. This taxon is considered to be one of the most pollution tolerant species.…”

“…However, diatoms are sensitive to contaminants and have shown their usefulness to assess exposure to toxic agents such as metals. Many studies have investigated the responses of diatom assemblages to metal contamination (e.g., [6][7][8]), and have shown impacts at structural and functional levels. In a review paper on the effects of metals on diatoms, Morin et al [9] presented several diatom-related biological descriptors that can be of interest in monitoring metal contamination.…”