Progress 09/15/03 to 09/14/06
Outputs
The overall objective of this research was to further develop an understanding of the mechanisms responsible for the synergistic toxicity noted between atrazine and various organophosphate (OP) insecticides. We found that atrazine alone did not affect organisms at concentrations up to 5000 μg/L; however, the presence of atrazine at 1000 μg/L did result in a significant increase in the acute toxicity of chlorpyrifos in the African clawed frog and fathead minnows. No effect of atrazine on chlorpyrifos toxicity was observed for bluegill sunfish and green frogs. Experiments with midges and amphipods found that the triazine herbicides tested (atrazine, simazine, cyanazine and hexazinone) were capable of potentiating the toxicity of the OPs, whereas the degradation products had less effect. Based on the results of the toxicity testing study, it does not appear that mixture toxicity of atrazine and chlorpyrifos at environmentally relevant concentrations (<1000
μg/L) presents a risk to the vertebrate organisms examined in this study, but these mixtures have significant impacts on aquatic invertebrates at environmentally relevant concentrations. Results from our molecular research have identified a CYP4 gene that was amplified by RACE PCR and sequenced from midges. Northern blot analysis, using the CYP4 gene as a probe, confirmed over-expression in midges exposed to atrazine (10 mg/L). Two-dimensional gel electrophoresis and MALDI-TOF mass spectroscopy were used to identify a set of fourteen proteins from midges exposed to atrazine that exhibited differences in expression. These proteins corresponded to both mitochondrial and membrane proteins. The effect of atrazine exposure on cytochrome P450-dependent monooxygenase activity was also measured in adult fathead minnow and increased activity was found in males exposed to atrazine (2000 μg/L). Finally, molecular results suggest that atrazine appears to enhance respiration of midges
leading to increased oxygen consumption. Increased oxygen consumption can rapidly cause hypoxic stress for the midges. Such an atrazine-induced hypoxic stress in turn results in reduced hemoglobin biosynthesis and down regulation of hemoglobin genes as a feedback mechanism, probably due to the unavailability of oxygen molecules for hemoglobin to bind in the water. Our study also suggests that hemoglobin in midges may play an important role in oxygen conservation. When oxygen is abundant in water, midges may synthesize a large amount of hemoglobin proteins to bind oxygen molecules that can be saved for later use, especially when oxygen depletion occurs. However, when oxygen is not abundant in water, the biosynthesis of hemoglobins can be rapidly shut down as an adaptive mechanism in response to their environmental changes. This is the first report on atrazine-induced hypoxic stress in an ecologically important non-target organism. Fourteen peer-reviewed papers, 39 presentations (10
invited talks), four DNA/amino acid sequences, and five graduate student thesis/dissertations have originated from this funded research.
Impacts
Our research has generated a great deal of new information on effects of some representative pesticides on non-target aquatic organisms. Such information will be very useful for developing and implementing knowledge-based strategies to realistically assess environmental risks of pesticides and to reduce the number of incidence of synergistic interactions of pesticide mixtures. Toxicity testing has shown that triazine herbicides (atrazine, simazine, cyanazine and hexazinone) are capable of potentiating the effects of OP insecticides in aquatic invertebrates, and that it does not appear that mixture toxicity of atrazine and chlorpyrifos at environmentally relevant concentrations (<1000 μg/L) presents a risk to the vertebrate organisms examined in this study. Toxicogenomic analysis of atrazine has demonstrated the effect of pesticide exposures on the expression of a number of different genes in aquatic midges. Identifications of pesticide-specific genes could help us
readily evaluate toxicological effects of specific pesticides and develop pesticide-specific biomarkers that permit extrapolation from the aquatic midge to other non-target organisms. It is expected that many environmental biologists, environmentalists, pesticide companies and regulatory agencies will be interested in our findings. Finally, the results from this NRI project have been helpful in obtaining additional federal funding for pesticide mixture research from the U.S. Geological Survey.
Publications
- Le Goff, G., F. Hilliou, B.D. Siegfried, S. Boundy, E. Wajnberg, L. Sofer, P. Audant, R. H. French-Constant, & R. Feyereisen. 2006. Xenobiotic response in Drosophila melanogaster: Sex dependence of P450 and GST gene induction. Insect Biochem. Mol. Biol. 36: 674-682.
- Rakotondravelo M., Anderson T. D., Charlton R. E. & Zhu K. Y. 2006. Sublethal effects of three pesticides on larval survivorship, growth and macromolecule production in the aquatic midge, Chironomus tentans (Diptera: Chironomidae). Arch. Environ. Contam. Toxicol. 51: 352-359.
- Rakotondravelo M., Anderson T. D., Charlton R. E. & Zhu K. Y. 2006. Sublethal effects of three pesticides on activities of selected target and detoxification enzymes in the aquatic midge, Chironomus tentans (Diptera: Chironomidae). Arch. Environ. Contam. Toxicol. 51: 360-366.
- Trimble, A.J. & M.J. Lydy. 2006. Effects of triazine herbicides on organophosphate insecticide toxicity in Hyalella azetca. Arch. Environ. Contam. Toxicol. 51: 29-34.
- Belden, J.B. & M.J. Lydy. 2006. Joint toxicity of chlorpyrifos and esfenvalerate to fathead minnows and midge larvae. Envion. Toxicol. & Chem. 25(2):623-629.
- Wacksman, M.N., J.D. Maul & M.J. Lydy. 2006. Impact of atrazine on chloropyrifos toxicity in four aquatic vertebrates. Arch. Environ. Contam. Toxicol. 51: 681-689.
- Anderson T. D. & K.Y. Zhu. 2004. Synergistic and antagonistic effects of atrazine on the toxicity of organophosphorodithioate- and organophosphorothioate-insecticides to Chironomus tentans (Diptera: Chironomidae). Pestic. Biochem. Physiol. 80: 54-64. (TOP25 Most Downloaded Article 2004-2005)
- Zhu K. Y. 2004. Insecticide bioassay, pp. 1180-1182. In: Capinera, J. L. [ed.], Encyclopedia of Entomology. Kluwer Academic Publishers, Dordrecht, The Netherlands.
- Zhu K. Y. 2004. Insecticide formulation, pp. 1182-1184. In: Capinera, J. L. [ed.], Encyclopedia of Entomology. Kluwer Academic Publishers, Dordrecht, The Netherlands.
- Zhu K. Y. 2004. Insecticide resistance, pp. 1184-1186. In: Capinera, J. L. [ed.], Encyclopedia of Entomology, Kluwer Academic Publishers, Dordrecht, The Netherlands.
- Zhu K. Y. 2004. Insecticide toxicity, pp. 1186-1188. In: Capinera, J. L. [ed.], Encyclopedia of Entomology. Kluwer Academic Publishers, Dordrecht, The Netherlands.
- Zhu K. Y. 2004. Synergism, pp. 2171-2173. In: Capinera, J. L. [ed.], Encyclopedia of Entomology. Kluwer Academic Publishers, Dordrecht, The Netherlands.
- Londono, D.K., B.D. Siegfried, and M.J. Lydy. 2004. Atrazine induction of a family 4 cytochrome P450 gene in Chironomus tentans (Diptera: Chironomidae). Chemosphere 56: 701-706.
- Schuler, L.J., A.J. Trimble, J.B. Belden & M.J. Lydy. 2005 Joint toxicity of triazine herbicides and organophosphate insecticides to the midge, Chironomus tentans. Arch. Environ. Contam. Toxicol. 49:173-177.
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Progress 10/01/03 to 09/30/04
Outputs
A fundamental goal in the study of ecotoxicology of surface waters in the Great Plains is to predict the effects of pesticide stressors. Our lack of knowledge concerning the impacts of pesticides on mid-western aquatic communities is at least partially attributable to a general lack of understanding of the potential interactions of multiple contaminants on aquatic biota. Although both atrazine and organophosphate insecticides may be relatively innocuous at environmentally relevant concentrations when tested individually, little information exists on the potential synergistic effects when they co-occur in the same environment. The purpose of this study is to investigate both the potential synergistic effects between atrazine and organophosphate insecticides and the underlying mechanisms of the synergism in instances where it has been previously documented. We will examine these effects in various non-target species that would potentially be exposed to these mixtures in
aquatic ecosystems including the aquatic amphipod, Hyalella azteca, fathead minnow, Pimephales promelas and leopard frog, Rana pipens.
Impacts
The purpose of this study is to investigate the potential synergistic effects between atrazine and organophosphate insecticides and the underlying mechanisms of the synergism. To date, we have found synergistic responses of atrazine in pulsed exposures with organophosphate insecticides in aquatic invertebrates and frogs. We have also found 120 up- and down-regulated putative genes in atrazine-treated organisms that should allow us to identify atrazine-specific marker genes that can be potentially used to evaluate non-target effects of atrazine and aquatic environmental health. Overall, this study will help improve risk assessments by providing water managers responsible for policy decisions with important information on acceptable levels of pesticide contaminants and will facilitate interpretation of the ecological significance of existing mixture toxicity data. Finally, the results from this NRI project have been helpful in obtaining additional funding for pesticide
mixture research from the US Geological Survey.
Publications
- Anderson, T D and Zhu KY (2004) Synergistic and antagonistic effects of atrazine on the toxicity of organophosphorodithioate- and organophosphorothioate-insecticides to Chironomus tentans (Diptera: Chironomidae). Pestic. Biochem. Physiol. 80: 54-64.
- Belden, JB and Lydy MJ (2006) Framework for evaluation of the toxicity of pesticide mixtures using conceptually useful models. Environmental Toxicology and Chemistry in press
- Schuler LJ, Trimble AJ, Belden JB, and Lydy MJ (2005) Joint toxicity of triazine herbicides and organophosphorous insecticides to the midge, Chironomus tentans. Arch Environ Contam Toxicol 49: 173-177
- Trimble AT, and Lydy MJ (2005) Effects of triazine herbicides on organophosphate insecticide toxicity in Hyalella azteca. Arch Environ Toxicol Chem in press
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