Two environmental disasters of large proportions involving mining dams occurred in Brazil in less than four years. Iron ore tailings released by the ruptures of both the Fundão and Brumadinho Dams have similar features, such as fine particulate material, with a majority of silt-clay particles and a predominance of Al, Fe, and Mn9,12,13. The major components of the Brumadinho tailings were also observed by the Brazilian Geological Service14. The similarity of the tailings released by the Brumadinho and Fundão Dams occurred because both mine complexes are located in the Quadrilátero Ferrífero region in southeast Brazil, which is rich in iron deposits15.
Immediate consequences of the tailings dam rupture along the Paraopeba River
The turbidity levels reached 3000 NTU and achieved the highest levels of SPM (516.14 mg/L) at the sampling site immediate from the dam rupture (Brumadinho – 5.2 km from the rupture area). According to the Brazilian Geological Service, the turbidity levels in the Paraopeba River reached even higher values from 11 to 22.000 NTU after the dam rupture6, with values above 1.100 NTU and incompatible with the historical series from 2002 to 20186 and with the limit of Brazilian legislation (100 NTU) for class 2 and 3 waters (for human supply after conventional or advanced treatment)16. For comparison, after the Fundão Dam rupture, the turbidity reached the order of hundreds of thousands of NTU at the Doce River2,17, with SPM reaching 33.000 mg/L7 in the first days of monitoring, closest to the break site.
After the Brumadinho (S3) sampling site, the turbidity and SPM levels decreased to historic values. This decrease was observed because the sampling campaign occurred only 5 days after the rupture, and the dense released material moved very little within the Paraopeba River. These results are in accordance with the information regarding the plume movement along the Paraopeba River18,19. The estimated velocity of the plume was approximately 0.55 km/h on the sampling day, and the visual aspect of the intense color of the tailings was observed in the municipality of Pará de Minas (42 km)18,19. The lowest turbidity values at Juatuba (S4–48 km downstream from the rupture area) indicated that this sampling site was still not affected by the mud. In fact, the conservation of other physical and chemical parameters, such as SPM, conductivity, pH, OD and temperature, from Juatuba (48 km) to Retiro Baixo (S7) also indicated that these sampling sites were not yet affected by the tailings dam rupture (Supplementary Table S2).
Total and dissolved elements in the water
In relation to the metal concentrations in the water, the dissolved Al, Ba, Fe and Pb levels (Al: 5×, Ba: 5×, Fe: 2x and Pb: 4×) were higher than the historic means for the Paraopeba basin20. According to CPRM20, only the dissolved Al and Fe presented levels above the legal limit established by Brazilian law (CONAMA 357/2005) in a sampling that occurred during the same period. However, the present results indicated that the concentrations of total Cd, Mn, Pb, Zn, and U and dissolved Al and Fe presented values higher than the levels allowed by Brazilian law for class I water (for human supply after simplified treatment), raising concern about the possible effects on biota and human health.
These differences may be due to methodological issues. In the present study, the Al, Fe and Cu concentrations were compared to the dissolved fraction in the Brazilian legislation, while the total levels were used for the other elements, according to the recommendations of Brazilian and international protocols. The analysis of all elements performed by the Brazilian Geological Service in the water samples involved a filtration process, and the results were representative of the dissolved fraction of metals in the water.
According to the historical series between 2000 and 2018, the incidence of levels above those in Brazilian law (CONAMA 357/2005) was already demonstrated along the Paraopeba basin for dissolved Fe (35%), total Mn (90% upstream and 50% downstream from the dam rupture area), dissolved Al (30%), Pb (10%), As, Cr, Ni, Zn, dissolved Cu and Cd (less than 5%)21. These variations may be natural due to the high background contents of the elements in rocks and soils or due to iron and gold deposits, together with the pollution caused by intense human activity in the region15. However, the potential impact of tailings dam rupture can worsen this situation and cannot be ignored because some elements, such as Al, Ba, Cd, Ce, Co, Er, Fe, Gd, Hg, In, La, Li, Lu, Mn, Ni, P, Pb, Sc, Ti, U, V, Y, and Zn, increased their levels in the water downstream of the dam rupture area in relation to upstream levels as a direct influence of the tailings passage (Supplementary Table S4).
Most of the water parameters analyzed (SPM, turbidity, conductivity, and total Al, Ba, Cr, Cu, Fe, Hg, Li, Mn, Nd, Pb, Rb and Ti concentrations and dissolved Ba, Cu, Fe, Mg, Mn, Pb, Sr, and Zn concentrations) presented concentration peaks at the Brumadinho sampling site (S3–5.2 km), followed by decreases in their levels with increasing distance from the dam (Fig. 2a). This result occurred because during the sampling period, the plume had extended 42 km18,19. Therefore, the effect of the tailings on the increases in metal concentrations in Juatuba water (S4–48 km) was not as evident at this moment. Beyond these facts, the Dam B1 rupture led to the deposition of tailings at the confluence, partially blocking the Paraopeba River6, which might shave lowed the velocity of mud transport along the course and consequently affected the metal concentrations in the water. The DOC (Fig. 2b), pH, DO, TDN, total Ca, K, S, Na and Zn and dissolved Ca, K, S, Na and Ti (Fig. 2c) showed less influence associated with the dam rupture.
The higher levels of total Sr and dissolved Al, Hg and Nd (Fig. 2d) upstream of the dam rupture area might reflect the impacts that already existed in the region, such as those from other mining areas (see the mining areas in Fig. 1), plantations, livestock, and urbanization, which influence concentrations for certain elements20. Other parameters, such as SPM, turbidity, conductivity, and total Al, Ba, Cr, Cu, Fe, Hg, Li, Mn, Nd, Pb, Rb and Ti concentrations and dissolved Ba, Cu, Fe, Mg, Mn, Pb, Sr, and Zn concentrations, also showed elevated levels upstream from the dam rupture area. Higher levels upstream of the dam (-10 km) had already been observed for some elements, especially dissolved Fe and total Mn21. Previous data from the region show a deeply impacted basin with high levels of Hg, Mn, Fe and Al in the soil, sediments and water20. However, the mud release along the Paraopeba River accentuated these problems along the basin.
Association between the elements in the muscle of D. rerio fishes exposed to the water (blue) or sediment (brown) of the Paraopeba River five after days of the Brumadinho mine tailings dam rupture. The values of the observations were transformed to a z-scale to make the variables comparable. (a) Al and Fe in muscle of the fishes exposed to the water. (b) Mn in muscle of the fishes exposed to the water. (c) Al in muscle of the fishes exposed to the sediment. (d) Fe and Mn in muscle of the fishes exposed to the sediment. The light blue shading identifies the standard error of the regression model. The dashed lines represent two water dams along the river.
Elements in the sediments
Many elements (Ag, Bi, Cd, Cu, Dy, Eu, Fe, Ga, Gd, Hg, In, La, Lu, Mn, P, Pb, Sn, Sr, Tb, U, Pr, Y, Yb and Zn) showed peak levels at Brumadinho (S3–5.2 km), the sampling site immediately downstream from the dam rupture area, followed by decreases in concentrations beyond S4. The behavior of these elements indicates that the mud from Dam B1 still had not reached Juatuba (S4–48 km). The same pattern of higher Fe, Mn, Pb, Hg, Cu, Ni, and Zn levels in the sediments after the dam rupture (between distances of 20 and 42 km from the dam) followed by decreases between 59 and 318 km has been observed by other monitoring programs22. The present data corroborate the information that during the sampling period, the mud traveled approximately 42 km along the Paraopeba River18,19.
Another group of metals in the sediments (Al, As, Ba, Be, Ca, Ce, Cr, K, Li, Mg, Na, Nd, Ni, Rb, S, Sb, Sc, Ti, and V) showed less oscillation in their levels between the upstream and downstream sides of the dam. These metals showed less influence from the passage of tailings and might reflect high natural levels from rocks and soils with deposits of iron and gold and the presence of other mining areas (see Fig. 1), plantations, livestock and urbanization along the basin that contribute to the metal concentrations in the sediments.
The present study and other data from the same period showed As, Cu, Cr, Hg, Pb, and Ni levels above the TEL. Our data also show Cd levels even above the PEL for almost all sampling sites downstream of the dam22. These levels emphasize the possibility of inducing adverse effects in organisms because the elements deposited in the bottom sediments can eventually be remobilized to the water column, available for biotic accumulation and incorporation of metals in the trophic chain. Cu and Cr values above the levels set by Brazilian legislation for drainage sediment (CONAMA 454/2012 resolution) were also observed in Brazilian Geological Service monitoring20.
Enrichment factor
The correlations made with the elements present in the tailings and those present in the sediments are important to determine one or a set of marker elements for the presence of the tailings. The enrichments observed for Ag, Cd, Cu, Fe, Hg, La, Li, Mn, P, Pb, Y and Zn might be used as indicators of mud presence along the Paraopeba River after the dam rupture because higher values were observed only in the tailings and at Brumadinho (S3–5.2 km), immediately downstream of the dam area (Fig. 4). Ag, Fe, La, Mn, P, and Y also showed enrichments in comparison with 2011 levels20. Meanwhile, As, Cd, Co, K, Na and S showed high enrichment levels since upstream the dam rupture area, which might be used to show the influence of natural and/or anthropogenic activities in the upper part of the basin.
In particular, for Al, despite the enrichment observed downstream from the dam rupture, this element is not a good marker for the observation of the movement of tailings along the Paraopeba River. Al in the sediments was observed throughout the river, even in sections that had not yet been impacted by the tailings in both the present study and data from other monitoring programs during the same sampling period22.
Biological effects of the tailings dam rupture
Including various organisms in toxicity evaluations ensures a better integrated response because the test organisms show different sensitivities to the contaminants, which in turn maximizes the chance to detect a response after exposure to a sample with unknown chemical composition10. The toxicological tests demonstrated that the water and sediments with mine ores from the Brumadinho Dam rupture were toxic to different trophic levels. The unicellular algae were more sensitive because growth inhibition was observed at all sampled sites, especially beyond Brumadinho (S3), where water rich in tailings induced complete inhibition of algae growth. The oscillations in algal growth after the dam failure was a likely result of both eutrophication and the existence of secondary pollution in a deeply impacted region23, with large areas of mining, plantations, livestock and the proximity of urban centers20. The incidences of immobilization in microcrustaceans and fish deaths also demonstrate the toxicity of the Paraopeba River water and sediments. These data strongly support the susceptibility of the natural biota in the Paraopeba River and reinforce the need for long-term monitoring, considering not only the metal levels in abiotic matrices but also the biological effects in the local trophic chain, through toxicological evaluations and field studies. The sediments showed a higher toxic potential than the water due to the 20% mortality occurrence in the fish exposed to S1 (Moeda: − 61.3 km) to S5 (São José da Varginha: 111 km) sediment samples.
Accumulation of metals in fish
The fish exposed to water and sediments containing mine ore from the Brumadinho Dam rupture accumulated metals in their muscle tissue. The metal accumulation in the muscular tissue of fish exposed to water and sediments shows that these elements are available for accumulation in the biota, suggesting a possible incorporation into the trophic chain and eventual risk of human contamination through the consumption of contaminated fish. The metal accumulation in fish can be related to the oscillation of metal levels in the water and sediments between the sampling sites, which demonstrates the importance of biomonitoring considering the whole path of the tailings along the Paraopeba River.
Future consequences of the tailings dam rupture along the Paraopeba River
The tailings composition with large amounts of Fe, Al, Mn, and Ti, together with the high concentrations of toxic metals such as U, Cd, Pb, As and Hg and rare earth metals such as In and Ga, among others, has aroused great concern. The Paraopeba River is responsible for at least 4% of the water flow and at least 11% of the suspended sediment flow to the São Francisco River21. The initial data from the present study and the official governmental information indicate no evidence that the mining tailings from Dam B1 exceeded the limits of the Retiro Baixo reservoir (more than 302 km from the dam) and the São Francisco River24. However, with time, much of the SPM will undergo transport, dilution and sedimentation processes, and some will reach the São Francisco River, overspreading the effects of the tailings release. These metals will consolidate in the bottom sediments of the Paraopeba River and may eventually be released into the water, leading to biotic accumulation and the possibility of immediate and long-term effects, such as mortality or decreases in reproduction. Particularly in relation to rare earth metals, many of their toxicological effects are unknown. In addition, due to the different uses of the water from the Paraopeba River, there is a risk of human contamination. Therefore, the present study provides the first insight into the water and sediment quality of the Paraopeba River and provides evidence for the influence of tailings as a source of metals at the sampling sites along the Paraopeba River. This initial evaluation (only five days after the rupture) demonstrated that the tailings transported along the Paraopeba River still had not reached the farther sampling sites (beyond 48 km from the dam). However, the composition of the tailings with large amounts of Fe, Al, Mn, and Ti, toxic metals such as U, Cd, Pb, As and Hg and rare earth metals such as In and Ga was toxic to different trophic levels, from primary producers such as algae to primary and secondary consumers such as microcrustaceans and fish species. Therefore, the long-term biomonitoring of the metal concentrations in abiotic matrices together with biological evaluations involving toxicological assays and field studies are necessary for the region.
Source: Ecology - nature.com
