The Role of Manganese in Toxicity Assays Using Algae in Environmental Samples
DOI:
https://doi.org/10.5132/jbse.2006.01.002Keywords:
Selenastrum capricornutum, biomonitoring, ground water, manganeseAbstract
Studies using ecotoxicological assays have been employed in the evaluation of the quality of ground water. In these studies, several authors suggested that bioassays using algae are more sensitive for this kind of environment. To have a better knowledge on the applicability of bioassays utilizing algae as test organism in the monitoring of ground water, we analyzed 75 samples from a total of 19 monitoring wells from an industrial area in the Metropolitan region of Porto Alegre, RS, Brazil. The toxicity of these samples was evaluated using Selenastrum capricornutum (USEPA, 1994) as test organism. In addition, pH, electrical conductivity, chlorides, total hydrocarbons, phenols, ammoniacal nitrogen, total dissolved solid and metals (Cd, Pb, Cu, Cr, Mn, Zn, Hg, Ni) were also analyzed. Samples were collected twice a year between 2001 and 2003. Results demonstrated a high frequency of samples with inhibitory effect on S. capricornutum (72%), and statistical analyses showed a statistically significant correlation (α = 0.05) between manganese concentrations and the observed toxicity for S. capricornutum (r = 0.298). Considering: (1) the low availability of manganese to organisms as a result of its natural precipitation as manganese oxides; (2) the efficiency of manganese in sequestering metals from the aquatic environments by adsorption, ionic exchange, or co-precipitation; (3) the occurrence, for some micro algae species, of competitive interactions between nutrients and inhibitory metals; (4) the fact that manganese could sequester metals like Zn, Co, Ni e Cu (used as micro-nutrients) through the formation of stable co-precipitates of manganese oxides; and (5) the constant input of oxygen in the samples during the running time of the bioassays with algae, due to the orbital agitation of the experimental flasks, it is concluded that the interference of manganese on the bio-availability of the micronutrients added to the samples during the experiment may have occurred.
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