Cathodic adsorptive stripping voltammetric behaviour of guanine in the presence of copper at the static mercury drop electrode.

The cathodic adsorptive electrochemical behavior of guanine in the presence of some metal ions at the static mercury drop electrode was investigated. A 1.0x10(-3) mol l(-1) NaOH or a 2.0x10(-2) mol l(-1) Hepes buffer at pH 8.0 solutions were used as supporting electrolytes. The reduction peak potential for guanine was found to be around -0.15 V, which is very close to the mercury reduction wave. A new peak appears at -0.60 V in the presence of copper or at -1.05 V in the presence of zinc. A square wave voltammetric procedure for electroanalytical determination of guanine in 2.0x10(-2) mol l(-1) Hepes buffer at pH 8.0 containing 1.6x10(-5) mol l(-1)of copper ions, was developed. An accumulation potential of -0.15 V during 270 s for the prior adsorption of guanine at the electrode surface was used. The response of the system was found to be linear in the range of guanine concentration from 6.62x10(-8) to 1.32x10(-7) mol l(-1) and the detection limit was 7.0x10(-9) mol l(-1). The influence of DNA bases such as adenine, cytosine and thymine was also examined. Cyclic voltammetry was used to characterize the interfacial and redox mechanism.

Occurrence of imposex in Thais haemastoma: possible evidence of environmental contamination derived from organotin compounds in Rio de Janeiro and Fortaleza, Brazil

Existem evidências de que a utilização amplamente disseminada de compostos organoestânicos (TBT e TPT) como antiincrustantes, estabilizadores em plásticos e como pesticidas tenha afetado severamente diversas espécies de organismos marinhos. O mais característico efeito do TBT e do TPT como desreguladores endócrinos é o desenvolvimento de caracteres sexuais masculinos em fêmeas de gastrópodos, conhecido como imposex. Esta síndrome pode levar à esterelização e morte dos organismos afetados. O presente trabalho apresenta uma vista geral ao estado atual do conhecimento sobre a ocorrência do imposex, e reporta os resultados de um estudo conduzido na Baía de Guanabara, Rio de Janeiro, e ao longo da costa de Fortaleza, no Ceará. Diferentes estágios de desenvolvimento do imposex foram verificados neste estudo, os mais proeminentes parecendo associados às fontes pontuais locais conhecidas de TBT e TPT.

On the binding capacity of peat to several metal ions of environmental and economic concern

A series of experiments was performed to characterize the metal binding properties of peat from the Jacarepagu bog and to provide basic knowledge on the sorption process. The kinetics of sorption was fast characterized by relaxation times, on the average, less than 60 min. Erichment factors taken at half saturation level ranged from 400 for zinc and cadmiun to > 2800 for gold. The results indicate that the peat from Jacarepagu can be an interesting option for the expensive conventional materials applied to recover metal ions from waste and poor mining waters.