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Open-File Report 2012–1213

Toxicity, Sublethal Effects, and Potential Modes of Action of Select Fungicides on Freshwater Fish and Invertebrates

By Adria A. Elskus

Thumbnail of and link to report PDF (832 KB)Abstract

Despite decades of agricultural and urban use of fungicides and widespread detection of these pesticides in surface waters, relatively few data are available on the effects of fungicides on fish and invertebrates in the aquatic environment. Nine fungicides are reviewed in this report: azoxystrobin, boscalid, chlorothalonil, fludioxonil, myclobutanil, fenarimol, pyraclostrobin, pyrimethanil, and zoxamide. These fungicides were identified as emerging chemicals of concern because of their high or increasing global use rates, detection frequency in surface waters, or likely persistence in the environment. A review of the literature revealed significant sublethal effects of fungicides on fish, aquatic invertebrates, and ecosystems, including zooplankton and fish reproduction, fish immune function, zooplankton community composition, metabolic enzymes, and ecosystem processes, such as leaf decomposition in streams, among other biological effects. Some of these effects can occur at fungicide concentrations well below single-species acute lethality values (48- or 96-hour concentration that effects a response in 50 percent of the organisms, that is, effective concentration killing 50 percent of the organisms in 48 or 96 hours) and chronic sublethal values (for example, 21-day no observed adverse effects concentration), indicating that single-species toxicity values may dramatically underestimate the toxic potency of some fungicides. Fungicide modes of toxic action in fungi can sometimes reflect the biochemical and (or) physiological effects of fungicides observed in vertebrates and invertebrates; however, far more studies are needed to explore the potential to predict effects in nontarget organisms based on specific fungicide modes of toxic action. Fungicides can also have additive and (or) synergistic effects when used with other fungicides and insecticides, highlighting the need to study pesticide mixtures that occur in surface waters. For fungicides that partition to organic matter in sediment and soils, it is particularly important to determine their effects on freshwater mussels and other freshwater benthic invertebrates in contact with sediments, as available toxicity studies with pelagic species, mainly Daphnia magna, may not be representative of these benthic organisms. Finally, there is a critical need for studies of the chronic effects of fungicides on reproduction, immunocompetence, and ecosystem function; sublethal endpoints with population and community-level relevance.

First posted September 27, 2012

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Suggested citation:

Elskus, A.A., 2012, Toxicity, sublethal effects, and potential modes of action of select fungicides on freshwater fish and invertebrates: U.S. Geological Survey Open-File Report 2012–1213, 44 p., at http://pubs.usgs.gov/of/2012/1213/.



Contents

Acknowledgments

Abstract

Introduction

Purpose and Scope

Overview of Fungicides

Fungicide Resistance Action Committee

Fungicide Modes of Action

Are Modes of Fungicide Action Related to Biochemical and Toxicological Effects in Fish and Invertebrates?

Which Organisms, Life Stages, and Endpoints Are Most Sensitive?

Organisms and Life Stages

Ecosystem Effects

Immune Function

Oxidative Stress

Endocrine Effects

Mixtures

Detailed Summaries for Select Fungicides by Fungicide Resistance Action Committee Mode of Action

Fungicide Resistance Action Committee Mode of Action B: Mitosis and Cell Division

Zoxamide

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Relationship Between Zoxamide Fungal MOA and Effects in Nonfungal Organisms

Fungicide Resistance Action Committee Mode of Action C: Respiration

Boscalid

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Data Gaps

Relationship Between Boscalid Fungal MOA and Effects in Nonfungal Organisms

Azoxystrobin

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Data Gaps

Relationship Between Azoxystrobin Fungal MOA and Effects in Nonfungal Organisms

Pyraclostrobin

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Data Gaps

Relationship Between Fungicide MOA and Effects in Nonfungal Organisms

Fungicide Resistance Action Committee Mode of Action D. Amino Acids and Protein Synthesis

Pyrimethanil

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

iochemical Effects in Mammals

TBoxic Effects in Freshwater Organisms

Data Gaps

Relationship Between Fungicide MOA and Effects in Nonfungal Organisms

Fungicide Resistance Action Committee Mode of Action E: Signal Transduction

Fludioxonil

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Data Gaps

Relationship Between Fungicide MOA and Effects in Nonfungal Organisms

Fungicide Resistance Action Committee Mode of Action G: Sterol Biosynthesis in Membranes

Myclobutanil

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Data Gaps

Relationship Between Fungicide MOA and Effects in Nonfungal Organisms

Fenarimol

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Relationship Between Fenarimol Fungal MOA and Effects in Nonfungal Organisms

Fungicide Resistance Action Committee Mode of Action: Multisite Contact Activity

Chlorothalonil

Environmental Fate in Aquatic Systems

Mode of Toxic Action in Fungi

Biochemical Effects in Mammals

Toxic Effects in Freshwater Organisms

Relationship Between Chlorothalonil MOA and Effects in Nonfungal Organisms

Summary and Conclusions

References Cited

Appendix 1. Qualitative Toxicity Categories

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