Protocol of assessment for species toxity mercury in natural water / Protocolo de avaliação do mercurio potencialmente toxico em aguas naturais

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

A protocol for the assessment of potentially toxic mercury in natural waters has been developed in accordance to the following stages: (i) research for a selective reductant of potentially toxic mercury species present in natural water samples; (ii) method optimization; (iii) experimental calibration carried out with solutions containing 50 mg L of Hg and different organic ligands at different ratios metal:ligand, including humic acid (HA), cysteine (Cys), histidine (Hys) and nitrilotriacetic acid (NTA); (iv) method application in samples from distinct aquatic ecosystems (natural and impacted) were carried out using different concentrations of Hg (5, 10, 25 e 50 mg L) based on titration of water samples with known Hg concentrations and followed by the metal determination using the purposed method; (v) to infer the Hg toxic potential determined with the proposed method, the relationship between analytical results and acute toxicity test with the bacterium Escherichia coli and the microcrustacean Daphnia similis was evaluated. A cold vapor atomic absorption spectrophotometer coupled to flow injection (FIA) system with stop-flow sampling was used. The results showed that the use of ascorbic acid (AA) as a reductant (HgAA), in specifc ratios sample:reductant, at pH 6.4 ± 0.1 (phosphates buffer), with detection after 60 ± 10 min, presented a limit of quantification (LOQ) of 0.5 mg L, with a relative standard deviation (n=6) at 50 mg L of Hg of 4%, linear range of 0.5 – 60.0 mg L and linearity factor of 97.3%. The values of HgAA determinated in the presence of ligands were directly dependent with the ligand nature and concentration, being Cys >Hys >HA >NTA. In natural water samples, HgAA was directly related to particulate matter, total organic and inorganic carbon. A significant correlation (ANOVA, F95% test) was observed between analytical results and bacteria response, being r = 0.97 for the synthetic solutions with ligands and r = 0.94 for natural samples. The correlation with Daphnia results and HgAA in natural samples was r = 0.65, not significance at F95%, but it can be expressive, once accepted the different mechanisms of interaction of this aquatic organism. Considering that the method has adequate sensitivity, analytical repeatability and significant correlation with biological results, this new protocol for the determination of Hg can be useful in generating information concerning the Hg acute toxicity in natural water.

ASSUNTO(S)

mercury aguas naturais toxicidade aguda mercurio vitamina c natural water acute toxicity ascorbic acid

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