Bioaccumulation kinetics and effects of sediment-bound contaminants on chironomids in deep waters: new insights using a low-disturbance in situ system

Testing the Use of Standardized Laboratory Tests to Infer Hg Bioaccumulation in Indigenous Benthic Organisms of Lake Maggiore (NW Italy)

The chronic toxicity of mercury essentially derives from its strong tendency to biomagnify along food webs. For this reason, the European regulatory framework establishes an environmental quality standard for Hg based on the total Hg concentration in prey fish to protect top predators. A considerable part of the Hg burden of prey fish can come from the ingestion of benthic organisms that, in the presence of contaminated sediments, may remobilize substantial amounts of Hg towards the pelagic food webs. The present study evaluated whether Hg accumulation in assemblages of indigenous chironomids and oligochaetes could be predicted using standardized laboratory bioaccumulation tests with Chironomus riparius and Lumbriculus variegatus. Indigenous chironomids and oligochaetes were recovered at different sites in a lake suffering from legacy Hg pollution and analyzed for total Hg content. Sediment aliquots from the same sites were used to assess Hg bioaccumulation using laboratory-reared C. riparius and L. variegatus. Mercury concentrations in indigenous versus laboratory organisms showed a good correlation (p < 0.05; Spearman correlation test) only in the case of C. riparius versus indigenous chironomids, suggesting the possibility of using linear regressions to predict Hg accumulation by these benthic invertebrates. Further research needs and caveats as to the applicability of the present results to other aquatic systems are identified and discussed.

Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 2: New insights from laboratory and in situ testing with Chironomus riparius Meigen (Diptera, Chironomidae)

Chromium is widely used as a tanning agent and can become a contaminant of concern in aquatic ecosystems receiving discharges from industrial or artisanal tanning activities. In a companion study, we showed that Cr discharged by tanneries was bioavailable to indigenous chironomids with accumulation via sediment ingestion likely to represent the predominant exposure route. However, Cr accumulation by chironomids did not directly reflect the degree of sediment contamination and the potential adverse effects of Cr accumulation on chironomids were not evaluated. In the present study, chironomids were exposed to homogenised, field-collected sediments in the laboratory and to intact sediments in situ using a customized caging system. Chromium concentrations were assessed in sediments, exposed larvae of laboratory-reared Chironomus riparius and overlying waters of in situ cages. Experimental results of Cr bioaccumulation were compared with expected Cr body burden in chironomids calculated using biodynamic modelling. Our data provided strong support to the hypothesis that Cr bioaccumulation in the field is specifically controlled by the deposition of contaminated suspended particulate matter (SPM) containing a pool of Cr readily bioavailable to surface deposit feeders. Considering freshly deposited SPM as an additional route of exposure for surface deposit feeders leads to a good agreement between the modelling and experimental results. Additionally, a Cr body burden of about 77 μg g^-1 d.w. was identified as a tentative threshold above which effects on the growth of C. riparius may appear. While both laboratory and in situ experiments provide evidence for the availability of Cr in aquatic system impacted by tannery wastewaters, standard laboratory exposure conditions may miss additional exposure routes in the field and underestimate possible adverse effects on benthic organisms.

Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 1: Understanding chromium accumulation by indigenous chironomids

The tanning industry uses large quantities of Cr whose contribution to the contaminant burden of aquatic organisms is not yet fully understood. The present study investigated Cr bioaccumulation by indigenous chironomids in a freshwater ecosystem impacted by tannery effluents. Total Cr content in sediments and in chironomids was determined on several occasions. Chromium distribution among sediments and pore waters, and Cr speciation in overlying and pore waters were studied in detail to understand possible factors controlling Cr bioavailability to chironomids. Total chromium concentration ranged from 69 to over 3000 μg g^-1 dry weight in sediments and from negligible to over 300 μg g^-1 dry weight in chironomids (values corrected for sediment gut content). Filterable (<0.45 μm) Cr concentration in overlying waters and pore waters from the surface sediment layers (upper 2 cm) ranged from 3 to 120 μg L^-1, with Cr(VI) representing 0.5-28% of the total filterable Cr. Chromium profiles in pore waters as determined by diffusive equilibration in thin films (DET) and diffusive gradient in thin films (DGT) were comparable. DGT-labile Cr accounted for <2% of the total Cr measured by DET. Although Cr concentrations in sedimentary and aqueous matrices were not directly proportional to Cr levels measured in chironomids, the available findings suggested that Cr inputs from tanneries were bioavailable to resident chironomids. These observations are of particular importance considering that Cr(III), putatively of limited bioavailability and ecotoxicological concern, is the predominant redox form of Cr in bed sediments impacted by tannery discharges. The companion paper provides further insight into Cr bioavailability and effects in tannery impacted ecosystems using a combination of in situ and laboratory approaches.

Encaged Chironomus riparius larvae in assessment of trace metal bioavailability and transfer in a landfill leachate collection pond

Household wastes may constitute a vector of environmental contamination when buried, in particular through degradation and production of leachates containing significant trace metal (TM) concentrations that may constitute a serious risk to biota. The objectives of this study were to assess the bioavailability and transfer potential of various TMs present in water and sediments in a reservoir receiving landfill leachates. An active biomonitoring approach was adopted consisting of exposing naive laboratory organisms in cages deployed in the field. Aquatic insects such as Chironomus riparius larvae are good candidates since they represent key organisms in the trophic functioning of aquatic ecosystems. The results show that water, suspended particles, and sediments were significantly contaminated by various TMs (As, Cd, Cu, Ni, Pb, and Zn). Their contribution to the transfer of TMs depends, however, on the specific element considered, e.g., Cd in sediments or Pb in both suspended particles and sediments. The internal fate of TMs was investigated according to their fractionation between an insoluble and a cytosolic fraction. This approach revealed different detoxification strategies capable of preventing the induction of deleterious effects at the individual scale. However, the accumulation of several TMs in C. riparius larvae tissues may also represent a significant load potentially transferable to higher trophic levels.

Refining uptake and depuration constants for fluoroalkyl chemicals in Chironomus riparius larvae on the basis of experimental results and modelling

The aims of this study were to determine depuration rates for a range of per- and polyfluoroalkyl substances (PFASs) using Chironomus riparius, and to test a concentration-dependency hypothesis for the long-chain perfluorotridecanoic acid (PFTrDA) for this species. Midge larvae were exposed to field sediments collected downstream of a fluorotelomer plant, and to the same sediment spiked with PFTrDA. Elimination kinetics results indicated complete elimination of all PFASs by chironomids after 42h. These data were used to develop two PFTrDA bioaccumulation models accounting for chironomid growth and for compound concentration dependency or not. There was much better agreement between observed and simulated data under the concentration-dependency hypothesis than under the alternative one (passive diffusion). The PFTrDA uptake rate derived from the concentration-dependency model equaled 0.013 ± 0.008g_ocg_wwh^-1, and the depuration rate 0.032 ± 0.009h^-1.

Field assessment of reproduction-related traits of chironomids using a newly developed emergence platform (E-Board)

Further progress in the development of reliable biomonitoring strategies requires to better link effects in aquatic ecological systems to ambient concentrations of chemical contaminants. Among existing tools, in situ bioassays using caging method represent an interesting way to achieve this challenge. However, elaboration of adapted exposure chambers and suitable operating procedures is still required, particularly to assess ecological relevant traits such as those related to the reproduction. In such context, we developed a new device (Emergence board - E-Board) which allows assessing in rivers the development of the Chironomus riparius species from the early fourth instar larvae to the adult stage. The system acts as a suspended matter trap floating in the subsurface of the water equipped of an emergence trap for catching adults. The system was tested in actual field conditions. Its easy handling allowed obtaining data which demonstrated its applicability for assessing the development of the chironomids. Moreover, by adapting energy-based models (DEB) specifically developed in the laboratory for the species C. riparius, we were able to predict the growth pattern and the emergence of chironomids in real environmental conditions. The E-Board represents thus a promising new in situ tool in perspective of evaluation of the quality of the ecosystems.

Active biomonitoring for assessing effects of metal polluted sediment resuspension on gammarid amphipods during fluvial traffic

The resuspension of polluted sediments by boat traffic could release substantial amounts of metals to the water column, affecting at the same time their bioavailability. In order to characterize the impact of sediment resuspensions on biota, caged amphipods have been deployed on three different channelized watercourses in Northern France. Firstly, the biological responses of transplanted freshwater gammarid amphipods, Gammarus fossarum, described by trace metal accumulation, feeding and reproduction activities were quite similar for the three water courses despite the differences of metal contamination and navigability. Secondly, the concentrations of metals accumulated in gammarids never exceeded the contamination thresholds previously defined for Co, Cu, Cr and Zn. Values were in the same order of magnitude whatever the studied site despite: (i) large differences noticed in the sediment quality and (ii) some concentrations in the overlying waters exceeding the Environmental Quality Standards (EQS) defined by the Water Framework Directive. Conversely, Pb was highly bioaccumulated with values systematically exceeding the threshold value whatever the site. Therefore, the impact of navigation cannot be proved and the difference between the 3 monitoring periods is rather attributed to environmental variability, probably linked to the seasonality. Moreover, this study also confirms that organisms sampled from a local population in the vicinity of the three studied watercourses could be used as test organisms, leading to similar results than the ones obtained with reference gammarids initially used for developing all the biological responses. This would simplify and then promote the development of studies based on gammarid amphipod, G. fossarum, as bioindicators.

On the bioavailability of trace metals in surface sediments: a combined geochemical and biological approach

The bioavailability of metals was estimated in three river sediments (Sensée, Scarpe, and Deûle Rivers) impacted by different levels of Cu, Cd, Pb, and Zn (Northern France). For that, a combination of geochemistry and biological responses (bacteria and chironomids) was used. The results obtained illustrate the complexity of the notion of "bioavailability." Indeed, geochemical indexes suggested a low toxicity, even in surface sediments with high concentrations of total metals and a predicted severe effect levels for the organisms. This was also suggested by the abundance of total bacteria as determined by DAPI counts, with high bacterial cell numbers even in contaminated areas. However, a fraction of metals may be bioavailable as it was shown for chironomid larvae which were able to accumulate an important quantity of metals in surface sediments within just a few days.We concluded that (1) the best approach to estimate bioavailability in the selected sediments is a combination of geochemical and biological approaches and that (2) the sediments in the Deûle and Scarpe Rivers are highly contaminated and may impact bacterial populations but also benthic invertebrates.