RESUMEN
The use of a copper solid amalgam electrode (CuSAE) for the analytical determination of triazine herbicides (atrazine and ametryne) instead of the conventional hanging mercury drop electrode (HMDE) is reported. The results obtained using electroanalytical methods utilizing each of these electrodes were also compared with those provided by the HPLC technique. The results indicated that the CuSAE electrode can be used to detect the herbicides studied, since the detection limits reached using the electrode (3.06 microg L-1 and 3.78 microg L-1 for atrazine and ametryne, respectively) are lower than the maximum values permitted by CONAMA (Brazilian National Council for the Environment) for wastewaters (50 microg L-1) and by the US EPA (Environmental Protection Agency of the United States) in natural water samples (10.00 microg L-1). An electroanalytical methodology employing CuSAE and square wave voltammetry (SWV) was successfully applied to the determination of atrazine and ametryne in natural water samples, yielding good recoveries (70.30%-79.40%). This indicates that the CuSAE provides a convenient substitute for the HMDE, particularly since the CuSAE minimizes the toxic waste residues produced by the use of mercury in HDME-based analyses.
Asunto(s)
Aleaciones , Cromatografía Líquida de Alta Presión/métodos , Herbicidas/análisis , Eliminación de Residuos/métodos , Triazinas/análisis , Electrodos , MercurioRESUMEN
This work presents an electrochemical investigation of the benzene oxidation process in aqueous solution on boron-doped diamond (BDD) electrodes. Additionally, in order to determine the main products generated during the oxidation process, electrolysis and high performance liquid chromatography experiments were carried out. The complete degradation of this compound was performed aiming to a further application in waste water treatment. The cyclic voltammetry studies indicate that benzene is irreversibly oxidized in acid medium (H2SO4 0.5 M) on the BDD electrode surface at 2.0 V versus Ag/AgCl in a diffusion controlled process. During the cycling, other products are generated, and a pair of peaks was observed that can be associated with the oxi-reduction of anyone of the following species: hydroquinone, benzoquinone, resorcinol or catechol. The electrolysis experiments were carried out at 2.4 and 2.5 V on the BDD electrode surface in a solution containing 1x10(-2) M of benzene (below the saturation concentration in aqueous solution), for 3 and 5 h, respectively. The main products measured were: hydroquinone, resorcinol, p-benzoquinone, catechol and phenol. The complete electrochemical benzene degradation was performed in the electrolysis experiments using a rotating BDD disc electrode (2.5 V for 5 h) and the main products detected were all measured at concentrations lower than 10(-5) M in this condition. The boron-doped diamond electrode had proved to be a valuable tool for the electrochemical degradation of the benzene, a very stable chemical compound.
Asunto(s)
Benceno/química , Boro/química , Diamante/química , Electrólisis/métodos , Contaminantes Químicos del Agua/química , Contaminación del Agua/prevención & control , Cromatografía Líquida de Alta Presión , Electrodos , Oxidación-ReducciónRESUMEN
Este artigo apresenta breve revisão sobre pesticidas muito utilizados no Brasil em culturas de soja, milho e cana-de-açúcar. Foram abordados o mecanismo de ação, a degradação e a toxidez dos herbicidas glifosato, pendimetalina e atrazina e dos inseticidas fenitrotion e fipronil. Verificou-se que o modo de ação desses pesticidas ocorre por meio da inibição de enzimas específicas como a enolpipuvil shikimato-3-fosfato sintase (glifosato0 e a colinesterase (fenitrotion), de proteínas como as tubulinas (pendimetalina), de receptores do sistema nervoso como o ácido gama aminibutírico (fipronil) e da inibição da fotossíntese (atrazina). Em relação à degradação, a rota mais importante para o desaparecimento dos herbicidas glifosato e atrazina e do inseticida fenitrotion é a biodegradação. Fipronil, moderadamente persistente no ambiente é degradado pela luz (fotodegradação). Para a pendimetalina, tanto os microorganismos quanto a luz são responsáveis pelo desaparecimento desse composto. A toxidez dos pesticidas varia de acordo com o grupo químico em que se enquadram, sendo o efeito tóxico mais agudo para os seres humanos e outros mamíferos apresentado pelo fenitrotion (organofosforado)