Abstract
We have studied the isolated and combined effects of metals (Fe and Mn) and NaCl the on growth, physiology, and metal-uptake capacity of two photosynthetic periphytic species—Synechococcus elongatus (Cyanobacteria) and Chlorococcum infusionum (Chlorophyta)—isolated from an impacted area of the Rio Doce River (Brazil) after the Fundão dam collapse. The effective concentrations found to reduce 10 and 50% growth were 15.2 and 31.6 mg Fe L−1, and 2.5 and 7.9 mg Mn L−1 for S. elongatus and 53.9 and 61.6 mg Fe L−1, and 53.2 and 60.9 mg Mn L−1 for C. infusionum. Although the metal toxicity was related to oxidative stress, both species showed activation of antioxidant systems under phytotoxic concentrations of Fe and Mn. By binding large concentrations of metals on its cell surface and thus avoiding their entrance into the cells, C. infusionum presents greater resistance to Fe and Mn than S. elongatus. Under environmental realistic concentrations of Fe and Mn in river water from the Rio Doce Basin, S. elongatus and C. infusionum showed a metal removal efficiency of 42 and 65% and 53 and 79%, respectively after 96 h. These species were insensitive to increased NaCl concentrations which, in addition, did not disrupt the metal removal capacity of the species. Due to their salt and metal tolerance, S. elongatus and C. infusionum can be used for the remediation of waters contaminated with Fe and Mn.
Highlights
On 5 November 2015, the Fundão dam operated by the company Samarco collapsed in the municipality of Mariana, Minas Gerais (Brazil), releasing about 50 million m3 of tailings in the Rio Doce Basin
After 96 h of exposure, the S. elongatus cell density was increased by 3 mg Fe L−1 treatment and decreased by Fe concentrations > 30 mg L−1 and Mn concentrations ≥ 10 mg L−1 in relation to the control (F = 22.79; p < 0.01; Figure 1)
S. elongatus and C. infusionum are periphytic algal and cyanobacterial species showing great tolerance to metal (Fe and Mn) as well as salinity (NaCl) stress. These species employed different strategies to accumulate Fe and Mn which were reflected in their metal tolerances: while C. infusionum restrained the transport of metals to internal compartments of cells, S. elongatus were less selective allowing greater entrance of Fe and Mn, which resulted in oxidative damage and related decreases on photosynthesis and growth
Summary
On 5 November 2015, the Fundão dam operated by the company Samarco collapsed in the municipality of Mariana, Minas Gerais (Brazil), releasing about 50 million m3 of tailings in the Rio Doce Basin. High concentrations of sodium (Na) were detected in sediments of areas affected by the mud from the Fundão dam, and Na was proposed as one of the main candidates responsible for the mud’s environmental toxicity [8] In this context, due to its mining-activity influence as well as the disposal of iron tailing in its water, Rio Doce is prone to salinization; the combined contamination of metals and NaCl must be expected. Due to its mining-activity influence as well as the disposal of iron tailing in its water, Rio Doce is prone to salinization; the combined contamination of metals and NaCl must be expected This is a worldwide problem since several bodies of water around the world are threatened by similar conditions [9], which may alter their ecosystem services
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