Ecotoxicity assessment of boreal lake sediments affected by metal mining: Sediment quality triad approach complemented with metal bioavailability and body residue studies

Metal bioaccumulation in fish from the Araguari River (Amazon biome) and human health risks from fish consumption

Recently, high concentrations of metals have been found in the waters from sampling sites located in the Araguari River lower section. These metals can be bioaccumulated by fish, but also biomagnified, representing a potential risk through human consumption. Here, we aimed to (1) determine the metal concentrations in muscle samples from fish; (2) evaluate bioaccumulation of metals in muscle tissue of fish species with different feeding behaviors; and (3) investigate the risks of single metals, as well as mixture of metals, to human fish consumption. Eleven fish species were sampled (3 carnivorous, 5 omnivorous, and 3 detritivorous). In four fish species, Cd and Pb concentrations exceeded the Brazilian maximum limits (MLs) for human consumption. Individually, Pb and Cd concentrations in the muscle of these fish indicate risks to human health. When considering the mixture of metals, the consumption of all fish species represents risks. The highest risks implicate detritivorous species. For all fish species evaluated, the estimated daily intake (EDI) of Hg shows values above its reference dose (RfD). Our results suggest the need to establish an environmental monitoring program that aims to preserve environmental quality, biodiversity, and human health. It is also necessary to develop actions that aim to educate Amazonian populations on safe fish preparation and consumption.

Do sediment-bound nickel and lead affect chironomids life-history? Toxicity assessment under environmentally relevant conditions

Metal pollution in aquatic ecosystems translates into increased concentrations of sediment-bound metals, representing a risk for benthic species. This risk might be enhanced in soft and moderately hard waters, world widely distributed, due to the protective role of hardness against metal toxicity. As lead (Pb) and nickel (Ni) are amongst the more abundant metals in aquatic systems, and since their combined effects to benthic species have been overlooked, in this study we aimed to investigate the life-cycle toxicity of Pb and Ni (using spiked sediment) to the benthic species Chironomus riparius, considering both single and mixture exposures, in moderately hard water. Environmentally relevant concentrations of each metal were used (25 and 75 mg kg^-1, based on a scenario of pollution by runoff waters from burnt forests), following a full factorial design. Effects of the mixture with the highest metal concentrations (Pb 75 mg kg^-1 dw + Ni 75 mg kg^-1 dw) were also assessed in the second generation. In the first generation, exposure to Pb increased emergence and the weight of males, and decreased time to emergence of both males and females. Conversely, exposure to Ni delayed female emergence and decreased the weight of imagoes. Summarizing, Pb affected more endpoints but showed an apparent positive effect, whereas Ni affected less endpoints but exhibited adverse effects. Reproduction was not affected by these metals. In the second generation, the mixture Pb 75 mg kg^-1 + Ni 75 mg kg^-1 dw delayed emergence and reduced the emerged female fraction and their weight. These results highlight that Pb and Ni can alter the structure of C. riparius populations at environmentally relevant concentrations, which signals potential repercussions in the dynamics and functioning of freshwater ecosystems under these contamination scenarios. The findings of the present study are relevant not only for metal-polluted environments, in general, but also for fire-affected ecosystems.

Metal contamination in alkaline Phantom Lake (Flin Flon, Manitoba, Canada) generates strong responses in multiple paleolimnological proxies

The copper-zinc smelter at Flin Flon (Manitoba) operated between 1930 and 2010 and emitted large amounts of metal(loid)s and sulphur dioxide into the atmosphere, damaging the surrounding terrestrial landscapes and depositing airborne industrial pollutants into aquatic ecosystems. However, the extent of biological impairment in regional lakes is largely unknown. Here, we analysed biological and geochemical proxies preserved in a dated sediment core from Phantom Lake, collected seven years after the smelter closed in 2010. Our objectives were to determine how smelting history affected long-term trends in (1) sedimentary elements, (2) biota across multiple trophic levels, and (3) spectrally-inferred chlorophyll a and lake-water total organic carbon. The effects of smelting activities were clearest in the diatom record, in concordance with modest responses in chironomid and cladoceran assemblages. Several metal(loid)s were naturally high and exceeded sediment quality guidelines during the pre-smelting era. With the opening of the smelter, metal(loid) concentrations in sediments increased through the 1930s, peaked in the 1960s, and declined thereafter with technological improvements but remained above background to this day. Although modest declines in inferred lake-water total organic carbon indicate reduced terrestrial carbon supply following sulphate deposition in the catchment, the diatom record showed no evidence of acidification as the lake was and remained well-buffered. Pre-smelting diatom and invertebrate assemblages were diverse and indicated oligo-mesotrophic conditions. Smelting was associated with the loss of metal-sensitive biological indicators and the emergence of assemblages dominated by metal-tolerant, generalist taxa. Diatoms tracked substantial reductions in aerial emissions since the 1990s, particularly after the smelter closed, but also indicated that the biological effects of metal pollution persist in Phantom Lake. Examining the effects of a base metal smelter on a well-buffered lake offered insights into multi-trophic level responses to severe metal contamination and potential recovery without the confounding effects of concurrent changes in lake acidity.

Transfer of elements relevant to radioactive waste into chironomids and fish in boreal freshwater bodies

Information on transfer of elements and their radionuclides is essential for radioecological modeling. In the present study, we investigated the transfer of Cl, Co, Mo, Ni, Se, Sr, U and Zn in a boreal freshwater food chain. These elements were selected on the basis that they have important radionuclides that might be released into the biosphere from various stages of the nuclear fuel cycle. Water, sediment, chironomid larvae (Chironomus sp.), roach (Rutilus rutilus) and perch (Perca fluviatilis) were sampled from two ponds near a former uranium mine and one reference pond located further away from the mining area. Concentrations measured in water, sediment and the three animal species indicated the importance of sediment as a source of uptake for most of the elements (but not Cl). This should be considered in radioecological models, which conventionally predict concentration in aquatic organisms from concentration in water. The results also show that the assumption of linear transfer (constant concentration ratio) may not be valid for elements into fish. The results of this study show that further basic research is needed to understand the fundamental processes involved in transfer of elements into freshwater organisms in order to develop radioecological models.

M-Triad: An improvement of the sediment quality triad

The traditional sediment quality triad generally uses three lines of evidence (LOE) in the assessment, integrating environmental chemistry, ecology and ecotoxicology. However the assessment is performed without considering the multivariate structure within LOE. In order to improve the sediment quality assessment, the M-Triad is proposed. Instead of averaging the values within a LOE, the new approach is based on the Euclidean distance between each sampling station and the reference station (s) for each LOE. These distances are then plotted in a radar-chart to obtain the area of the triangle and the quality assessment is subsequently obtained from the difference between the triangle areas of the impacted and the reference station. Three studies were selected to test the applicability of the M-Triad. In two cases, the M-Triad returned a more realistic ranking of the stations as observed in the principal component analysis (PCA) from each LOE By including the Euclidean distance, the use of M-Triad is advantageous when multiple variables with negative or uncorrelated patterns within a LOE are analyzed simultaneously. The combination of the M-Triad and the results of the PCA allows one to identify multiple contamination gradients and how biota and bioassays respond to each of these gradients. In comparison to the traditional method, the M-Triad reduces the uncertainty of the final analysis, permitting a more comprehensive ecological assessment.

Contaminated aquatic sediments

The remediation of contaminated aquatic sediments requires a range of expertise from assessment (investigation, risk evaluations, modeling, and remedy selection) to design and construction. Research in 2019 has added to knowledge on optimizing the use of passive samplers for assessing chemical concentrations in sediment porewater. The porewater and black carbon appear to be better predictors of contaminant bioaccumulation than total organic carbon alone. This has led to better characterization of potential risk at sediment sites. Tools to identify and model sources of chemicals have been developed and used particularly for some metals, polynuclear aromatic hydrocarbons and polychlorinated biphenyls. There is great emphasis on beneficially using dredged sediment, treating it as a resource rather than a waste. Amendments used in sediment caps continue to be refined including the use of activated carbon within the caps and by itself. A technique involving 16S rRNA has been established as a means of identifying microbiological composition that naturally degrade contaminants. © 2020 Water Environment Federation PRACTITIONER POINTS: Sediment capping technology continues to advance Sampling and testing methods continue to be refined Natural processes such as biodegradation are being better understood Beneficial use of dredged sediment continue to be emphasized.

Is the Doce River elutriate or its water toxic to Astyanax lacustris (Teleostei: Characidae) three years after the Samarco mining dam collapse?

In 2015, after the Fundão dam failure, in Minas Gerais State, Brazil, around 50 million cubic meters of sludge from iron mining tailings were discharged into the Doce River. After the dam collapse, surpassing concentrations of metals were observed in the river sediment, which could be harmful to aquatic organisms, including the fishes. The present study aimed to evaluate the toxic effects of both elutriate and water, collected from the Doce River, on Astyanax lacustris three years after the dam failure. A bioassay was carried out through subchronic exposure to Doce River water (E0) and three elutriate concentrations (10, 50 and 100%). Biochemical analyses (CAT, GST, AChE), metal bioaccumulation assays and calculation of the integrated biomarker response index, version 2 (IBRv2) were performed. The outcomes uncovered deleterious consequences on organisms exposed to E0, with AChE inhibition and bioaccumulation of Fe and Mn in both liver and gills. IBRv2 values were more elevated in fishes exposed to E0 for all tissues. Thus, the elutriate was not harmful for the assessed fishes, since complexing agents presented in the sediment, such as goethite and hematite, may have triggered metals' chelation. In this scenario, the elutriate may have acted as a protective agent for the subjected organisms, unlike the Doce River waters, in which contaminants were proven to be hazardous for the aquatic biota.

Is developmental instability in chironomids a sensitive endpoint for testing uranium mine-affected sediments?

There is increasing interest in effects of radionuclides on non-human species, but methods for studying such effects are not well developed. The aims of the current study were to investigate the effects of uranium mine-affected sediments on non-biting midge Chironomus riparius and to compare sensitivity of different endpoints. The midge larvae were exposed in controlled laboratory conditions to sediments from two ponds downstream from an abandoned uranium mine and a reference pond not receiving water from the mining site. Quartz sand was used as an additional control. Developmental effects were assessed by evaluating emergence of adult midges, body mass, and fluctuating asymmetry (FA) in the length of wing upper vein. FA has been suggested to be a sensitive indicator of developmental instability, but the results of previous studies are inconsistent. In the present study, no difference in FA was observed between the treatment groups, but time to emergence was significantly delayed in the contaminated sediments. The approach used in this study (laboratory experiments with sediments from a contaminated site) avoids confounding due to uncontrolled environmental variables and adaptation to long-term contamination, which may mask effects on natural populations. Using this approach, we found no effects on FA of wing length. Time to emergence, in contrast, was found to be a more sensitive endpoint.

Evaluation of the hazard of irregularly-shaped co-polyamide microplastics on the freshwater non-biting midge Chironomus riparius through its life cycle

Plastics pollution is increasingly attracting societal and political attention. However, despite extensive research effort recently dedicated to the hazard of plastics in the environment, the data obtained are often redundant and essential knowledge gaps exist: available freshwater ecotoxicity data mostly concern Daphnia magna and are derived from acute exposure to spherical particles. In this paper, we address this gap by exploring the biological effects of irregularly-shaped co-polyamide (PA, 10-180 μm) on Chironomus riparius - a very versatile organism that during its life-stages inhabits both sediment and water column - relevant compartments for microplastics (MP) pollution. C. riparius represents an important part of the freshwater food chain and is also a standard OECD test organism. Different toxicity endpoints along the life cycle of C. riparius (28 days) were used as described in OECD 218: emergence, time to emergence, sex ratio of imagoes and the number of egg clutches per female. Chironomid larvae were exposed to 100 mg PA kg^-1 (i.e., 10,100 particles kg^-1) sediment throughout. Soluble Zn-salt (1 mg Zn L^-1) was used as a positive control and as a co-pollutant in combination with PA. We demonstrated that the tested concentrations of PA and Zn alone as well in combination showed no adverse effects for C. riparius in chronic exposures. 100 mg PA kg^-1 also did not affect the life cycle traits of the offspring of PA-exposed parent Chironomids. The data obtained will be useful for environmental risk assessment of PA when actual environmental concentrations of PA will be available.