Abstract
The SOS/umu genotoxicity assay evaluates the primary DNA damage caused by chemicals from the β-galactosidase activity of S. typhimurium. One of the weaknesses of the common umu test system based on spectrophotometric detection is that it is unable to measure samples containing a high concentration of colored dissolved organic matters, sediment, and suspended solids. However, umu tests with electrochemical detection techniques prove to be a better strategy because it causes less interference, enables the analysis of turbid samples and allows detection even in small volumes without loss of sensitivity. Based on this understanding, we aim to develop a new umu test system with hydrodynamic chronoamperometry using a rotating disk electrode (RDE) in a microliter droplet. PAPG when used as a substrate is not electroactive at the potential at which PAP is oxidized to p-quinone imine (PQI), so the current response of chronoamperometry resulting from the oxidation of PAP to PQI is directly proportional to the enzymatic activity of S. typhimurium. This was achieved by performing genotoxicity tests for 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide (AF-2) and 2-aminoanthracene (2-AA) as model genotoxic compounds. The results obtained in this study indicated that the signal detection in the genotoxicity assay based on hydrodynamic voltammetry was less influenced by the presence of colored components and sediment particles in the samples when compared to the usual colorimetric signal detection. The influence caused by the presence of humic acids (HAs) and artificial sediment on the genotoxic property of selected model compounds such as 4-nitroquinoline-N-oxide (4-NQO), 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), 1,8-dinitropyrene (1,8-DNP) and 1-nitropyrene (1-NP) were also investigated. The results showed that the genotoxicity of 1-NP and MX changed in the presence of 10 mg·L−1 HAs. The genotoxicity of tested chemicals with a high hydrophobicity such as 1,8-DNP and 1-NP were decreased substantially with the presence of 1 g·L−1 sediment. This was not observed in the case of genotoxins with a low log Kow value.
Highlights
The advancement of industrialization, agricultural and urban activities have caused serious concerns about chemical substances that are discharged to the air, soil and water environment
The electrochemical oxidation of PAPG should not influence the oxidation of PAP, because PAPG molecules exist at a much higher concentration compared with PAP molecules which are the enzymatic product
The slope of the relative amperometric respose vs. the relative β-galacotosidase acitivity decreased by the presence of 40 mg·L–1 Wako Pure Chemical Co. (WHA) and 1 g·L–1 artificial sediment. These results indicate that the proposed electrochemical umu test can be applied to samples containing humic acid (HA) and sediment particles, contrary to the common umu test based on optical detection that is strongly interfered by the presence of HA and sediment particles
Summary
The advancement of industrialization, agricultural and urban activities have caused serious concerns about chemical substances that are discharged to the air, soil and water environment. They have a direct impact on the ecosystem and pose a threat to human health. The transformations of chemicals which accumulate in the environment can produce secondary pollutants from reactions with other chemicals. The absolute concentrations of known analytes in the environment can be determined by chemical analysis methods. These kinds of techniques do not provide adequate interpretation of their toxicities to biota. In order to gain a better understanding of the risk posed by various pollutants, there is an inevitable need for an effective analytical approach which is able to access the biological impacts
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