What is a B chromosome? Early definitions revisited.

Since the discovery of B chromosomes, multiple different definitions of these selfish genetic elements have been put forth. We reconsidered early definitions in light of recently published studies. While there are many characteristics that vary among different B chromosomes, such as their evolutionary origins, size, segregation behaviors, gene content, and function, there is one defining trait of all B chromosomes: they are nonessential for the organism. The points raised here may be useful for framing future B chromosome studies and help guide the categorization of new chromosomal elements that are uncovered in genomic studies.

Transcribing the enigma: the B chromosome as a territory of uncharted RNAs.

B chromosomes are supernumerary elements found in several groups of eukaryotes, including fungi, plants, and animals. Typically, these chromosomes either originate from their hosts through errors in meiosis or interspecifically through horizontal transfer. While many B chromosomes are primarily heterochromatic and possess a low number of coding genes, these additional elements are still capable of transcribing sequences and exerting influence on the expression of host genes. How B chromosomes escape elimination and which impacts can be promoted in the cell always intrigued the cytogeneticists. In pursuit of understanding the behavior and functional impacts of these extra elements, cytogenetic studies meet the advances of molecular biology, incorporating various techniques into investigating B chromosomes from a functional perspective. In this review, we present a timeline of studies investigating B chromosomes and RNAs, highlighting the advances and key findings throughout their history. Additionally, we identified which RNA classes are reported in the B chromosomes and emphasized the necessity for further investigation into new perspectives on the B chromosome functions. In this context, we present a phylogenetic tree that illustrates which branches either report B chromosome presence or have functional RNA studies related to B chromosomes. We propose investigating other unexplored RNA classes and conducting functional analysis in conjunction with cytogenetic studies to enhance our understanding of the B chromosome from an RNA perspective.

Establishment and Characterization of a Primary Fibroblast Cell Culture from the Amazonian Manatee (Trichechus inunguis).

The vulnerable status of the Amazon manatee, Trichechus inunguis, indicates the need to seek measures to guarantee its conservation. In this context, the cultivation of cells in vitro is a strategy that should at least guarantee the preservation of their genetic material. Thus, we established for the first time a primary culture of Amazonian manatee fibroblasts (TINsf) from a skin biopsy of a young male. Karyotypic analysis of the 3rd, 7th, and 12th passages confirmed the taxonomic identity of the species T. inunguis (2n = 56/NF = 92) and indicated that this culture presents genomic stability. Gene and protein expression of vimentin at the 13th passage show the predominant presence of fibroblasts in TINsf. To test the cell line's responsiveness to materials and demonstrate a possible application of this culture, it was exposed to andiroba seed oil (ASO), and its viability and proliferative capacity were evaluated. ASO demonstrated toxic effects at the highest concentrations and longest exposure times tested, reproducing results observed in human cultures, indicating the applicability of TINsf in toxicological and biotechnological studies. After cryopreservation, the TINsf line maintained its proliferative potential, indicating the establishment of a new culture available for future studies.

Pollutant bioaccumulation in sentinel fish chronically exposed in Iguaçu river reservoirs (Southern Brazil) and human health risk of fish consumption.

Bioaccumulation studies in fish mark the initial phase of assessing the risk of chemical exposure to biota and human populations. The Iguaçu River boasting a diverse endemic ichthyofauna, is grappling with the repercussions of human activities. This study delved into the bioaccumulation of micropollutants, the early-warning effects on Rhamdia quelen and Oreochomis niloticus in the Segredo Reservoir (HRS) and the potential risk of human exposure. Two groups of caged fish in three sites of the reservoir were exposed during the autumn-winter and spring-summer, while a third group (O. niloticus) underwent a twelve-month exposure, and inorganic and organic chemicals analysis in water, sediment, and biota. Additionally, metallothionein expression and genotoxicity were employed as biomarkers. PAHs, PCBs, Al, Cu, Fe, and As in water and DDTs, Cu, Zn, and As in sediment surpassed the thresholds set by Brazilian regulations, where DDT exhibited bioaccumulation in muscle, alongside metals in liver, kidney, gills, and muscle tissues. R. quelen showed metallothionein expression whereas DNA damage and NMA frequencies were elevated in target organs and in brain and erythrocytes of O. niloticus during summer. In this species the DNA damage in liver was remarkable after twelve months. Target Hazard Quotients and Cancer Risk values shedding light on the vulnerability of both children and adults. The reservoir's conditions led to heightened sensitivity to micropollutants for R. quelen species. The data presented herein provides decision-makers with pertinent insights to facilitate effective management and conservation initiatives within the Iguaçu Basin.

Chromosomal organization of multigene families and meiotic analysis in species of Loricariidae (Siluriformes) from Brazilian Amazon, with description of a new cytotype for genus Spatuloricaria.

In the Amazon, some species of Loricariidae are at risk of extinction due to habitat loss and overexploitation by the ornamental fish market. Cytogenetic data related to the karyotype and meiotic cycle can contribute to understanding the reproductive biology and help management and conservation programs of these fish. Additionally, chromosomal mapping of repetitive DNA in Loricariidae may aid comparative genomic studies in this family. However, cytogenetics analysis is limited in Amazonian locariids. In this study, chromosomal mapping of multigenic families was performed in Scobinancistrus aureatus, Scobinancistrus pariolispos and Spatuloricaria sp. Meiotic analyzes were performed in Hypancistrus zebra and Hypancistrus sp. "pão". Results showed new karyotype for Spatuloricaria sp. (2n=66, NF=82, 50m-10sm-6m). Distinct patterns of chromosomal organization of histone H1, histone H3 and snDNA U2 genes were registered in the karyotypes of the studied species, proving to be an excellent cytotaxonomic tool. Hypotheses to explain the evolutionary dynamics of these sequences in studied Loricariidae were proposed. Regarding H. zebra and H. sp. "pão", we describe the events related to synapse and transcriptional activity during the meiotic cycle, which in both species showed 26 fully synapsed bivalents, with high gene expression only during zygotene and pachytene. Both Hypancistrus species could be used may be models for evaluating changes in spermatogenesis of Loricariidae.

Unraveling sources of hydrocarbons in subtropical estuaries with distinct degrees of protection in the Southwestern Atlantic Ocean, Brazil.

Sedimentary aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were studied in subtropical estuaries with distinct degrees of legal protection, located in the Southwestern Atlantic Ocean, São Paulo State, Brazil. A multivariate approach was adopted, using the Hierarchical cluster analysis followed by the Principal Matrix Factorization analysis to support the hydrocarbons sources findings using diagnostic ratios. In general, the sites with the highest values of hydrocarbons were in the vicinity of well-urbanized cities, where sewage discharge, harbor and industrial activities take place. Pyrolitic PAHs were the predominant source of PAHs in the sites. The region can be considered not highly contaminated by hydrocarbons; however, specific sites under local anthropogenic impact from sewage and/or urban drainage, presented relatively high hydrocarbons levels. These findings highlight the importance of sources identification as reliable approach to be included in the management plan of protected areas under the inputs of several vectors of contamination.

How did a tailings spill change the distribution of legacy organochlorine compounds in a Southeast Atlantic inner shelf area: Is a hidden danger being transferred to the ocean?

Polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT) were evaluated in water and sediments from the Espírito Santo Inner Shelf (ESIS), Brazil, three years after the Fundão dam failure (FDF). We discuss the levels, sources, fate, and current environmental risks of these contaminants on temporal and spatial scales. In addition, the associated coastal dispersion patterns, water-sediment exchange trends, and environmental alterations were also discussed. Low contributions and no environmental risks were verified for PCBs after FDF. However, the low concentrations and frequency of occurrence in the samples did not allow for further reliable conclusions regarding the source of this contaminant. In contrast, hazard risk has been detected for DDTs in water and sediments. In sediments, there were a significant increase in level (up to 13.42 ng g-1; outlier = 369.6 ng g-1), inventory (maximum = 35.98 ng cm-2) and mean total mass (21.1 ± 39.4 kg) of DDTs after FDF. The integrated assessment of the spatial distribution in water and sediment suggests that DDTs was released from the Doce River, travelled south by the water column, and returned to the mouth region by northward sediment transport, where it accumulated. However, intense rainfall increased the input of DDTs to the ESIS and may have also altered its spatial distribution. Fugacity fraction analysis (ƒƒ) indicated a net flux of DDTs from water to sediment, suggesting that vertical sinking was an important transport process in this area. Finally, the findings indicate that FDF contributed to DDTs input on ESIS by remobilizing contaminated past sediments and soils from the Doce River drainage basin. This contribution is expected to continue since a large amount of tailings is still stored in the river basin and estuary. These results highlight the importance of assessing the indirect impacts of large-scale land disasters on marine environments, and may be helpful in future interpretations of additional local trends and global inventories of legacy pollutants.

Exploratory evaluation of iron and its speciation in surface waters of Admiralty Bay, King George Island, Antarctica.

The determination of dissolved iron concentrations and speciation was conducted for the first time in surface seawater coastline samples collected during the austral summer of 2020 in Admiralty Bay, King George Island, Antarctica. The technique of competitive ligand exchange/adsorptive cathodic stripping voltammetry with 2,3-dihydroxynaphthalene as the competing ligand was evaluated, showing a sensitivity between 14.25 and 21.05 nA nmol L-1 min-1, with an LOD of 14 pmol L-1 and a mean blank contribution of 0.248 nmol L-1. Physicochemical parameters such as pH (7.85 ± 0.2), salinity (32.7 ± 0.8) and dissolved oxygen (51.3 ± 26.6%) were compatible with those of the literature; however, the average temperature (4.2 ± 0.8 °C) was higher, possibly as a reflection of global warming. The dissolved iron mean value was 18.9 ± 6.1 nmol L-1, with a total ligand concentration of 23.6 ± 12.2 nmol L-1 and a conditional stability complex constant of 12.2 ± 0.2, indicating humic substances as possible ligands. On average, the calculated free iron concentrations were 0.7 ± 0.3 pmol L-1. Relatively high concentrations of iron indicate a possible local source of Fe, likely predominantly from upwelling sediments and secondarily from ice-melting waters, which does not limit the growth of the phytoplankton.

Performance analysis of innovative cleaning and soiling mitigation solutions in the semi-arid climate of Benguerir Morocco.

The objective of this paper is to evaluate the performance of the hydrophobic coatings and detergent cleaning & antistatic protection for photovoltaic solar panels in semi-arid weather conditions in Benguerir Morocco. Various coating and cleaning strategies were tested on five photovoltaic (PV) systems with the same PV panels and electrical configurations. The first PV system (uncleaned) was not subject to any coatings or cleaning solutions. The second PV system (Water Cleaned) was periodically cleaned with raw water. The third PV system: solar wash protects (SWP) made use of a cleaning solution. The fourth:D solar defender (DSS) and fifth: industrial glass protect (IGP) PV systems each had a unique combination of the two hydrophobic coatings. The results demonstrated that after 9 months of operation, in the first 3 months (cleaning period) the average efficiency gain of the coated PV panels is around 10% compared to the reference system. Whereas in the non-cleaning period after 6 months of exposure, the efficiency gain is around 5%. After the outdoor exposure period, the cumulative energy gain of the coated systems compared to the water-cleaned reference reaches an average of 3%. It has been found that the SWP used 50% less water to clean the PV panels than the system cleaned without a cleaning solution, which made the panels harder to clean. The SWP is more successful at dust removal during the dry season (August-February) with low rain rates. However, during the rainy season (March-April), IGP outperformed SWP and DSD, with a small difference in PV performance. This study demonstrates the significance of using new cleaning strategies such as anti-soling coatings in dry areas to enhance the performance of photovoltaic systems, which may be useful for investors, researchers, and engineers interested in grid-connected photovoltaic and self-cleaning technology.

Characterization of repetitive DNA on the genome of the marsh rat Holochilus nanus (Cricetidae: Sigmodontinae).

Repetitive DNA are sequences repeated hundreds or thousands of times and an abundant part of eukaryotic genomes. SatDNA represents the majority of the repetitive sequences, followed by transposable elements. The species Holochilus nanus (HNA) belongs to the rodent tribe Oryzomyini, the most taxonomically diverse of Sigmodontinae subfamily. Cytogenetic studies on Oryzomyini reflect such diversity by revealing an exceptional range of karyotype variability. However, little is known about the repetitive DNA content and its involvement in chromosomal diversification of these species. In the search for a more detailed understanding about the composition of repetitive DNA on the genome of HNA and other species of Oryzomyini, we employed a combination of bioinformatic, cytogenetic and molecular techniques to characterize the repetitive DNA content of these species. RepeatExplorer analysis showed that almost half of repetitive content of HNA genome are composed by Long Terminal Repeats and a less significant portion are composed by Short Interspersed Nuclear Elements and Long Interspersed Nuclear Elements. RepeatMasker showed that more than 30% of HNA genome are composed by repetitive sequences, with two main waves of repetitive element insertion. It was also possible to identify a satellite DNA sequence present in the centromeric region of Oryzomyini species, and a repetitive sequence enriched on the long arm of HNA X chromosome. Also, comparative analysis between HNA genome with and without B chromosome did not evidence any repeat element enriched on the supernumerary, suggesting that B chromosome of HNA is composed by a fraction of repeats from all the genome.

Integrative Analysis of the Ethanol Tolerance of Saccharomyces cerevisiae.

Ethanol (EtOH) alters many cellular processes in yeast. An integrated view of different EtOH-tolerant phenotypes and their long noncoding RNAs (lncRNAs) is not yet available. Here, large-scale data integration showed the core EtOH-responsive pathways, lncRNAs, and triggers of higher (HT) and lower (LT) EtOH-tolerant phenotypes. LncRNAs act in a strain-specific manner in the EtOH stress response. Network and omics analyses revealed that cells prepare for stress relief by favoring activation of life-essential systems. Therefore, longevity, peroxisomal, energy, lipid, and RNA/protein metabolisms are the core processes that drive EtOH tolerance. By integrating omics, network analysis, and several other experiments, we showed how the HT and LT phenotypes may arise: (1) the divergence occurs after cell signaling reaches the longevity and peroxisomal pathways, with CTA1 and ROS playing key roles; (2) signals reaching essential ribosomal and RNA pathways via SUI2 enhance the divergence; (3) specific lipid metabolism pathways also act on phenotype-specific profiles; (4) HTs take greater advantage of degradation and membraneless structures to cope with EtOH stress; and (5) our EtOH stress-buffering model suggests that diauxic shift drives EtOH buffering through an energy burst, mainly in HTs. Finally, critical genes, pathways, and the first models including lncRNAs to describe nuances of EtOH tolerance are reported here.

Earthquake, floods and changing land use history: A 200-year overview of environmental changes in Selenga River basin as indicated by n-alkanes and related proxies in sediments from shallow lakes.

The Selenga River basin, located in southern Siberia, is an important component of the Lake Baikal ecosystem, and comprises approximately 80 % of the Baikal watershed. Within the Selenga River basin, two localized study regions were chosen. The first, the Selenga Delta, is one of the largest inland freshwater floodplains in the world and plays an important role in the ecosystem functioning of Baikal. It purifies the river waters before they enter the lake and acts as a refuge for many of Baikal's endemic species. The second location, the Gusinoozersk region, is southwest of Lake Baikal and the Selenga Delta, and was chosen as a more heavily industrialized region within the Selenga River basin. Anthropogenic activities, including industry, urban settlements, aquaculture and agriculture, have historically increased ecological damage within this area. We assessed possible drivers of changes in sedimentary organic matter (OM) composition within two shallow lakes (SLNG04 and Black Lake), located in the Selenga Delta and the Selenga watershed, respectively. We focused on individual n-alkanes, one of the most abundant and common lipids used to provide information on past vegetation and used multivariate statistics to disentangle changes in the sources of sedimentary OM over time. The depositional OM history of SLNG04B core can be divided in four zones: (i) major influence of non-emergent vascular plants, typically found in transitional environments (ca. 1835 to ca. 1875); (ii) increased influence of grasses/herbs (ca. 1880 to ca. 1910); (iii) transition from non-emergent vascular plants and grasses/herbs to submerged and floating macrophytes and phytoplankton (ca. 1915 to ca. 1945); (iv) maintenance of autochthonous OM from submerged and floating macrophytes and phytoplankton (ca. 1945 to ca. 2014). The depositional OM history of the Black Lake core can be divided in two main zones: (i) major influence of non-emergent vascular plants and submerged and floating macrophytes (ca. 1915 to ca. 1980); (ii) increased influence of grasses/herbs and phytoplankton (ca. 1980 to ca. 2010). Natural events (e.g., an earthquake in 1862 caused flooding and subsidence of much of the land surrounding SLNG04 lake and a further catastrophic flood event in 1897) and anthropogenic activities (e.g., nutrient pollution from expansion of agricultural and livestock population) changed the composition of sedimentary OM resulting in ecological shifts across trophic levels in the Selenga River basin.

Polycyclic aromatic hydrocarbons in a Natural Heritage Estuary influenced by anthropogenic activities in the South Atlantic: Integrating multiple source apportionment approaches.

Polycyclic aromatic hydrocarbons (PAHs) were analysed in the sediments of one of the most well-preserved estuaries in South Brazil, the Paranaguá Estuarine System (PES), using several source apportionment tools. The ∑PAH ranged from < DL to 125.6 ng g-1 dw (dry weight) (average 29.9 ± 26.1 ng g-1 dw), and the lowest levels detected were similar to those found in other protected areas of the world. In general, the PAH concentrations indicated excellent environmental quality for the entire estuary. Principal component analysis indicated that fine sediments and total organic carbon were the main factors controlling PAH concentrations in the PES. Multiple PAH sources were identified in the study area; biomass burning and fossil fuel combustion predominated but considerable amounts of petrogenic residues were also observed. We identified evidence of a contribution from an adjacent watershed resulting from the construction of interconnections between large rivers and from years of intense deforestation in the local Atlantic Forest.

First characterization of PIWI-interacting RNA clusters in a cichlid fish with a B chromosome.

BACKGROUND: B chromosomes are extra elements found in several eukaryote species. Usually, they do not express a phenotype in the host. However, advances in bioinformatics over the last decades have allowed us to describe several genes and molecular functions related to B chromosomes. These advances enable investigations of the relationship between the B chromosome and the host to understand how this element has been preserved in genomes. However, considering that transposable elements (TEs) are highly abundant in this supernumerary chromosome, there is a lack of knowledge concerning the dynamics of TE control in B-carrying cells. Thus, the present study characterized PIWI-interacting RNA (piRNA) clusters and pathways responsible for silencing the mobilization of TEs in gonads of the cichlid fish Astatotilapia latifasciata carrying the B chromosome. RESULTS: Through small RNA-seq and genome assembly, we predicted and annotated piRNA clusters in the A. latifasciata genome for the first time. We observed that these clusters had biased expression related to sex and the presence of the B chromosome. Furthermore, three piRNA clusters, named curupira, were identified in the B chromosome. Two of them were expressed exclusively in gonads of samples with the B chromosome. The composition of these curupira sequences was derived from LTR, LINE, and DNA elements, representing old and recent transposition events in the A. latifasciata genome and the B chromosome. The presence of the B chromosome also affected the expression of piRNA pathway genes. The mitochondrial cardiolipin hydrolase-like (pld6) gene is present in the B chromosome, as previously reported, and an increase in its expression was detected in gonads with the B chromosome. CONCLUSIONS: Due to the high abundance of TEs in the B chromosome, it was possible to investigate the origin of piRNA from these jumping genes. We hypothesize that the B chromosome has evolved its own genomic guardians to prevent uncontrolled TE mobilization. Furthermore, we also detected an expression bias in the presence of the B chromosome over A. latifasciata piRNA clusters and pathway genes.

Kinetic Activity of Chromosomes and Expression of Recombination Genes in Achiasmatic Meiosis of Tityus (Archaeotityus) Scorpions.

Several species of Tityus (Scorpiones, Buthidae) present multi-chromosomal meiotic associations and failures in the synaptic process, originated from reciprocal translocations. Holocentric chromosomes and achiasmatic meiosis in males are present in all members of this genus. In the present study, we investigated synapse dynamics, transcriptional silencing by γH2AX, and meiotic microtubule association in bivalents and a quadrivalent of the scorpion Tityus maranhensis. Additionally, we performed RT-PCR to verify the expression of mismatch repair enzymes involved in crossing-over formation in Tityus silvestris gonads. The quadrivalent association in T. maranhensis showed delay in the synaptic process and long asynaptic regions during pachytene. In this species, γH2AX was recorded only at the chromosome ends during early stages of prophase I; in metaphase I, bivalents and quadrivalents of T. maranhensis exhibited binding to microtubules along their entire length, while in metaphase II/anaphase II transition, spindle fibers interacted only with telomeric regions. Regarding T. silvestris, genes involved in the recombination process were transcribed in ovaries, testes and embryos, without significant difference between these tissues. The expression of these genes during T. silvestris achiasmatic meiosis is discussed in the present study. The absence of meiotic inactivation by γH2AX and holo/telokinetic behavior of the chromosomes are important factors for the maintenance of the quadrivalent in T. maranhensis and the normal continuation of the meiotic cycle in this species.

Karyotypes of Manatees: New Insights into Hybrid Formation (Trichechus inunguis × Trichechus m. manatus) in the Amazon Estuary.

Great efforts have been made to preserve manatees. Recently, a hybrid zone was described between Trichechus inunguis (TIN) and the Trichechus manatus manatus (TMM) in the Amazon estuary. Cytogenetic data on these sirenians are limited, despite being fundamental to understanding the hybridization/introgression dynamics and genomic organization in Trichechus. We analyzed the karyotype of TMM, TIN, and two hybrid specimens ("Poque" and "Vitor") by classical and molecular cytogenetics. G-band analysis revealed that TMM (2n = 48) and TIN (2n = 56) diverge by at least six Robertsonian translocations and a pericentric inversion. Hybrids had 2n = 50, however, with Autosomal Fundamental Number (FNA) = 88 in "Poque" and FNA = 74 in "Vitor", and chromosomal distinct pairs in heterozygous; additionally, "Vitor" exhibited heteromorphisms and chromosomes whose pairs could not be determined. The U2 snDNA and Histone H3 multi genes are distributed in small clusters along TIN and TMM chromosomes and have transposable Keno and Helitron elements (TEs) in their sequences. The different karyotypes observed among manatee hybrids may indicate that they represent different generations formed by crossing between fertile hybrids and TIN. On the other hand, it is also possible that all hybrids recorded represent F1 and the observed karyotype differences must result from mechanisms of elimination.

Meiotic behavior, transmission and active genes of B chromosomes in the cichlid Astatotilapia latifasciata: new clues about nature, evolution and maintenance of accessory elements.

Supernumerary B chromosomes (Bs) are dispensable genetic elements widespread in eukaryotes and are poorly understood mainly in relation to mechanisms of maintenance and transmission. The cichlid Astatotilapia latifasciata can harbor Bs in a range of 0 (named B -) and 1-2 (named B +). The B in A. latifasciata is rich in several classes of repetitive DNA sequences, contains protein coding genes, and affects hosts in diverse ways, including sex-biased effects. To advance in the knowledge about the mechanisms of maintenance and transmission of B chromosomes in A. latifasciata, here, we studied the meiotic behavior in males and transmission rates of A. latifasciata B chromosome. We also analyzed structurally and functionally the predicted B chromosome copies of the cell cycle genes separin-like, tubb1-like and kif11-like. We identified in the meiotic structure relative to the B chromosome the presence of proteins associated with Synaptonemal Complex organization (SMC3, SYCP1 and SYCP3) and found that the B performs self-pairing. These data suggest that isochromosome formation was a step during B chromosome evolution and this element is in a stage of diversification of the two arms keeping the self-pairing behavior to protect the A chromosome complement of negative effects of recombination. Moreover, we observed no occurrence of B-drive and confirmed the presence of cell cycle genes copies in the B chromosome and their transcription in encephalon, muscle and gonads, which can indicates beneficial effects to hosts and contribute to B maintenance.

The Fundão dam failure: Iron ore tailing impact on marine benthic macrofauna.

The Fundão dam failure, the worst environmental disaster in Brazilian history, launched 50 million m3 of iron ore tailings mud through the Doce River, reaching the Atlantic Ocean. Generally, mine tailings increase the sediment inflow, leading to mud burial of epibenthic macrofauna, and the raise of metal(oid)s concentration causing macrofauna long-term changes. After almost four years, tailings mud was still spreading on the Doce River Shelf, while impacts on marine macrofauna were still unknown. Herein, the IMS index (a tracer of Fundão dam tailings mud), sediment variables, organic pollutants, and metal(oid)s were integrated to uncover the drives of macrofauna structure from Costas da Algas to Abrolhos bank MPAs. Tailings mud was present only in Doce River Mouth and Degredo, organic pollutants and metal(oid)s above safety levels were concentrated in those same areas. Tailings mud (IMS index) drastically reduced species richness and diversity, favoring the abundance of opportunistic species. Mud, IMS index and Al, Ba, and V, metal(oid)s linked to dam failure, structured macrofauna composition in this impacted area, dominated by resistant groups as Nuculidae, Spionidae, and Magelonidae. Conversely, an opposite pattern was found for further and deeper sites with high CaCO3 content and total nitrogen that also showed large grain size, in areas known to harbour biogenic structures, sustaining a macrofauna composition distinct from the impacted areas, dominated by Syllidae and Crassatellidae, sensitives to impacts. Macrofauna composition was most structured by sediment variables, followed by the intersection between metal(oid)s-IMS and Mud, both gradients acting almost entirely on a broad spatial scale. Benthic macrofauna at the Doce River Shelf is still impacted by Fundão dam tailings mud, even after almost four years of the disaster, and may continue to, since the influx of tailings does not stop, and sediment resuspension is a recurrent source for those impacts.

Organic and inorganic pollutants in Jordão and Iguaçu rivers southern Brazil impact early phases of Rhamdia quelen and represent a risk for population.

The Iguaçu River basin presents high ecological importance due to its expressive endemic ichthyofauna rate, but chemical pollution may threat this biodiversity. Jordão River is one of the main tributaries of Iguaçu River and contribute to this pollution status, since it drains large agricultural areas receiving domestic and industrial effluents before flowing into the Iguaçu River. The objective of the current study was to evaluate the toxic effects of the Iguaçu, Jordão, and the combination of their waters to the embryo-larval phase of R. quelen, investigating the consequences to the population by means of mathematical modelling. R. quelen fertilized eggs were exposed for 96 h to water samples from Iguaçu River upstream (IR), Jordão River (JR), and downstream of both rivers (MR). The analysis of micropollutants in the water showed that JR presented the most complex mixture of substances and elements, followed by IR, while MR showed the lower number of micropollutants detected. Survival rate was not a sensitive endpoint, while the deformity indices were higher in individuals exposed to water from the three studied sites. Superoxide dismutase activity was increased in MR, while non-protein thiol levels were reduced in MR and JR showing the antioxidant mechanism activation. The mathematical modelling revealed that fish exposed to JR would lead to the greater population reduction (46.19%), followed by IR (40.48%) and MR (33.33%). Although the results showed toxicity in all studied sites, the JR site is the most impacted by micropollutants but decrease its toxicity after dilution with Iguaçu River.