Impacts of the Samarco tailing dam collapse on metals and arsenic concentration in freshwater fish muscle from Doce River, southeastern Brazil

On November 2015, Samarco tailings dam in Mariana MG, Brazil, collapsed, releasing 62 million tons of tailings that advanced through 668 km of the Doce River and adjacent floodplain. Although being the worst environmental disaster in Brazil, little is known about consequences to aquatic biota. Here we evaluate the effects of the tailings mudflow on metal and arsenic concentration in fish and how concentration correlates with water and fish characteristics. We quantified semitotal amounts of Ag, Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in fish muscle tissue using ICP-MS in 255 individuals (34 species) sampled in unaffected and affected along the Doce River basin. Arsenic and Hg were higher in fish from affected sites, likely due to turbulent mixing of previously sedimented material by the giant tailings wave. Silver and Zn concentrations were higher in unaffected sites. Arsenic concentration in Geophagus brasiliensis decreased with increasing fish weight. Copper and Zn decreased with increasing fish weight considering the whole assembly of fish. The tailings mudflow increased water conductivity and conductivity increased Al concentration in fish, so we expected a larger Al concentration in fishes from affected sites. However, the observed Al concentration in fishes from affected sites was lower than expected by water conductivity. Thus, the tailings mudflow reduced Al uptake or accumulation in fishes. Mercury decreased with increasing water conductivity in both unaffected and affected sites considering all species and in G. brasiliensis alone. Despite the relatively low concentration range of metals and As found in fish, fishes from sites affected by the iron ore tailings mudflow showed higher As and Hg concentration, compared to fishes from unaffected sites. The higher As and Hg in affected sites require further detailed monitoring to ensure safeguards of human health by fishing activity along the Doce River.

Aluminium–silicon interactions in higher plants: an update

Aluminium (Al) and silicon (Si) are abundant in soils, but their availability for plant uptake is limited by low solubility. However, Al toxicity is a major problem in naturally occurring acid soils and in soils affected by acidic precipitation. When, in 1995, we reviewed this topic for the Journal of Experimental Botany, it was clear that under certain circumstances soluble Si could ameliorate the toxic effects of Al, an effect mirrored in organisms beyond the plant kingdom. In the 25 years since our review, it has become evident that the amelioration phenomenon occurs in the root apoplast, with the formation of hydroxyaluminosilicates being part of the mechanism. A much better knowledge of the molecular basis for Si and Al uptake by plants and of Al toxicity mechanisms has been developed. However, relating this work to amelioration by Si is at an early stage. It is now clear that co-deposition of Al and Si in phytoliths is a fairly common phenomenon in the plant kingdom, and this may be important in detoxification of Al. Relatively little work on Al–Si interactions in field situations has been done in the last 25 years, and this is a key area for future development.

Performance of Crambe Submitted to Aluminum Stress: An Important Oilseed Plant

Crambe is a potential oilseed plant, which has been suggested for cultivation as a cover crop in the Brazilian Savanna where acidic soils predominate. Understanding of its performance in those conditions is essential. Thus, the objective of this study was to characterize the morphological and physiological changes in crambe plants when subjected to Al exposure at different dose levels. Plants were allocated to a nutrient solution with Al treatments at concentrations of 0.0, 0.1, 0.2, 0.3 and 0.4 mmol L-1. The following parameters were determined: length of root (LR) and shoot (LS), dry mass of roots (RDM) and shoots (SDM), Al uptake in plant tissues, leaf area (LA), absolute growth rate (AGR), grain yield (GY), net CO2 assimilation rate (A), stomatal conductance (gs), transpiration rate (E) and chlorophyll α fluorescence. The experimental design was completely randomized, consisting of five treatments with four replications. Regression analyses of growth parameters and mean comparative tests of physiological traits were performed. Roots concentrated approximately 40-fold more Al than shoots. There was a linear reduction in LS and LR with increasing doses of Al. For RDM, SDM, LA, AGR and GY, the reductions were similar and were better explained by quadratic models. Al damaged the photosynthetic apparatus of crambe plants, demonstrated by a significant reduction in the values of Fv/Fm (estimation of photosynthetic efficiency), A, gs and E, compared to the control. Al negatively affected growth parameters as well as the photosynthetic response of crambe plants, resulting in a substantial decrease in its grain yield.

Soil Metals and Ectomycorrhizal Fungi Associated with American Chestnut Hybrids as Reclamation Trees on Formerly Coal Mined Land

Hybrid chestnut(Castanea dentata×C. mollissima)has the potential to provide a valuable agroforestry crop on formerly coal mined landscapes. However, the soil interactions of mycorrhizal fungi and buried metals associated with mining are not known. This study examined soil, plant tissue, and ectomycorrhizal (ECM) root colonization on eight-year-old hybrid (BC1F3and BC2F3) and American chestnuts on a reclaimed coal mine in Ohio, USA. Chestnut trees were measured and ECM colonization on roots was quantified. Leaves, flowers, and soil were analyzed for heavy metals. Differences were not detected among tree types regarding metal accumulation in plant tissue or ECM colonization. BC2F3hybrids had greater survival and less cankers than American chestnuts (P= 0.006 and <0.0001). Taller trees were associated with greater ECM root colonization and correlated with an increase in Al uptake (P= 0.02 and 0.01). When comparing tissue, manganese and aluminum were in higher concentrations in leaves than flowers, where copper and selenium were significantly higher in floral tissue (P< 0.05). All trees were flowering at this time meriting further examination in nut tissue. Block effects for selenium and zinc indicate the variability in reclaimed soils requiring further monitoring for possible elemental transfer to nut and wood tissue.

Mutational loss of Arabidopsis SLOW WALKER2 results in reduced endogenous spermine concomitant with increased aluminum sensitivity

A previously-identified Arabidopsis mutant with hypersensitivity to aluminum, als7–1 was studied further to determine the nature of the mutation and subsequently establish the biochemical basis of the increase in Al sensitivity. Physiological analysis revealed that the Al hypersensitivity phenotype is correlated with increased Al uptake and Al-dependent gene expression, indicating that als7–1 has a defect in an Al-exclusion mechanism. Cloning of the als7–1 mutation showed that it negatively affects the gene encoding the putative nucleolar localised ribosomal biogenesis factor SLOW WALKER2, which is required for normal gametogenesis and mitotic progression. Molecular analysis indicated that Al hypersensitivity in als7–1 is correlated with loss of expression of a factor required for S-adenosylmethionine recycling and reduced levels of endogenous polyamines in the mutant. Further analysis shows that Al-dependent root growth inhibition is reversed by addition of exogenous spermine, which is correlated with a significant reduction in Al uptake by spermine treated roots. Endogenous spermine likely functions to compete with Al3+ for binding to extra- and intracellular anionic sites, which suggests that increased spermine levels may be an effective means to improve root growth in Al toxic acid soil environments.

Long-term Aluminum Exposure Effects on Physiological and Biochemical Features of Highbush Blueberry Cultivars

We compared the aluminum tolerance of two highbush blueberry (Vaccinium corymbosum) cultivars, Legacy and Bluegold, grown in a greenhouse in Hoagland's solution with increasing concentrations of Al (0, 25, 50, 100, and 200 μm) for 7 to 20 days, using root lipid peroxidation (LP), radical scavenging activity (RSA), Al uptake by roots, and relative growth rate (RGR) as criteria. Leaf physiological [photochemical and non-photochemical parameters of photosystem II (PSII)] and biochemical (pigments, LP, RSA, and total soluble carbohydrates) responses to Al stress were also analyzed and then a principal component analysis (PCA) was performed. The results indicated that ‘Bluegold’ showed the highest Al uptake and LP in roots and a lower RGR in contrast to ‘Legacy’. The photochemical parameters were more affected in ‘Bluegold’ than in ‘Legacy’, particularly at the beginning of the experiment. At this point, a sharp increase in RSA was found in ‘Legacy’. According to these parameters, ‘Legacy’ was more Al tolerant than ‘Bluegold’. PCA revealed that among the underlying processes affected by Al toxicity in the highbush blueberry, the photochemical efficiency of PSII followed by modifications of photosynthetic pigment contents are of greatest significance after long-term Al stress. Additionally, RSA plays an important role in the long-term acclimation response mechanisms to Al stress in highbush blueberry leaves.