Modulation of the genotoxicity of pesticides reacted with redox‐modified smectite clay

Abstract

Pesticides are toxic agents intentionally released into the environment; their use raises public health and environmental concerns. In recent years there has been much attention to the biotic degradation of pesticides. Abiotic mechanisms in the soil can contribute to pesticide degradation yet the toxicological impact of such degradation is unclear. This study combines for the first time an investigation into abiotic mechanisms of degradation coupled with toxicological endpoints in mammalian cells. The genotoxicity of three commonly used agricultural pesticides was assessed before and after exposure to redox-modified clay minerals. The objectives of the study were to determine the genotoxicity of 2,4-dichlorophenoxy acetic acid (2,4-D), dicamba, and oxamyl, using single cell gel electrophoresis with Chinese hamster ovary (CHO) cells, and to determine the effect of the iron oxidation state in clay minerals (ferruginous smectite SWa-1) on the genotoxic potency of the pesticides. 2,4-D alone or following reaction with redox-modified clays did not induce DNA damage in CHO cells. Oxamyl alone induced a concentration-dependent increase in genomic DNA damage; however, its genotoxicity declined after reaction with reduced clay minerals. Dicamba was not genotoxic when directly analyzed. When dicamba was reacted with reduced clay, a concentration-dependent increase in genomic DNA damage was observed. This is the first reported case of a pesticide being converted into a genotoxin after exposure to redox-modified smectites. These data introduce a new paradigm on the interaction between redox-modified clays and pesticide-related environmental genotoxicity.

Herbicides in Argentina. Comparative Evaluation of the Genotoxic and Cytotoxic Effects on Mammalian Cells Exerted by Auxinic Members

“…González et al (2007) demonstrated an increase in the frequency of DNA lesions in this cell line. Similar observations were reported by Sorensen et al (2004Sorensen et al ( , 2005 on Dicamba-treated CHO cells cultured in the presence of reduced-clay smectites but not when the clay system was not included within the culture protocol. Both González et al (2006González et al ( , 2007González et al ( , 2009) and Perocco et al (1990) demonstrated the ability of the herbicide to induce SCEs in CHO cells and human lymphocytes with and without S9 fraction treated in vitro, respectively.…”

“…Induction of DNA single-strand breaks estimated by the alkaline comet assay was evaluated in normal and transformed cells exposed in vitro to 2,4-D. González et al (2005), Maire et al (2007), and Sandal and Yilmaz (2010) observed an increased frequency of DNA primary lesions in CHO and SHE cells as well as in human lymphocytes. On the other hand, negative results were also revealed when this end-point was assayed on the same cell type by others researchers (Sorensen et al, 2005;Sandal & Yilmaz, 2010). However, Maire and co-workers (2007) showed that 2,4-D was unable to induce DNA fragmentation in SHE cells.…”

Microbial reduction of iron(III)-rich nontronite and uranium(VI)

“…Experiments have demonstrated that U(VI) can be reduced by Fe(II) sorbed to a variety of iron oxides (Liger et al, 1999;Fredrickson et al, 2000;Jeon et al, 2004b;Jang et al, 2008), Fe(II)-containing natural sediments (Behrends and Van Cappellen, 2005;Jeon et al, 2005), Fe(II)-containing carboxyl-functionalized microspheres (Boyanov et al, 2007), structural Fe(II) in green rust (O'Loughlin et al, 2003), and structural Fe(II) in magnetite (Missana et al, 2003). Experiments have also demonstrated that structural Fe(II) in specimen and natural smectites can reduce nitroaromatic compounds (Hofstetter et al, 2003(Hofstetter et al, , 2006, chlorinated aliphatics (Sorensen et al, 2005), pesticides (Elsner et al, 2004), Cr(VI) (Gan et al, 1996;Taylor et al, 2000), and Tc(VII) (Peretyazhko et al, 2008).…”

Geosmin induces genomic instability in the mammalian cell microplate-based comet assay

“…In addition, using mammalian cells that attach as a monolayer to the bottom of a 96-well microplate ensures uniform exposure to the test compound (Wagner and Plewa 2009). The mammalian cell microplate-based comet assay requires a very small volume of test agent solution per experiment, and this methodology has been used to investigate the genotoxicity of environmental chemical agents and complex mixtures (Sorensen et al 2005;Muellner et al 2007). …”