Pesticides

1. Pesticides Aquatic Ecotoxicology Lecture November 19, 2003 Dr. Matt Moore USDA Agricultural Research Service National Sedimentation Laboratory Oxford, Mississippi

2. Suggested Reading Silent Spring (1962; 1994) Our Stolen Future (1996) Aquatic Dialogue Group: Pesticide Risk Assessment and Mitigation (1994) Principles and Methods of Toxicology (1994) USGS book series on pesticides

3. EVERYTHING IS A STIMULUS – RESPONSE REACTION 3 Types of Stimuli A. Physical B. Biological C. Chemical What is a pesticide? FIFRA definition What are the types of pesticides?

6. Types of pesticides Insecticides 1. Organochlorines 2. Organophosphates 3. Carbamates 4. Biological / botanical / pyrethroids 5. Pyrrole

7. Types of pesticides Herbicides 1. Chlorphenoxy 2. The Quats (para- and di-) 3. Triazine**** 4. Acetamides Fungicides 1. Pentachlorophenol Rodenticides 1. Warfarin 2. Strychnine

8. Types of pesticides Acaracides Molluscicides Etc.

9. What are some important properties of pesticides? Water solubility Photolysis, hydrolysis, volatilization “Table 1”

10. Insecticides -Most work on nervous system -Toxicity mechanism of most insecticides is similar in mammals and insects -Selectivity is primarily in the dose -Dose vs. Exposure

11. Insecticides ORGANOCHLORINES 3 general classes (focus on just 2) DDT and related compounds Chlorinated cyclodienes Aldrin Dieldrin Heptachlor

12. Insecticides ORGANOCHLORINES Limited vapor pressure Very low water solubility High lipophilicity = TROUBLE

13. Insecticides ORGANOCHLORINES Limited vapor pressure Very low water solubility High lipophilicity = TROUBLE

14. Insecticides ORGANOCHLORINES DDT First synthesized in 1874 Insecticidal properties discovered by Paul Mller (Ciba-Geigy) in 1939; Nobel Prize Control animal pests, disease vectors (mosquito), ectoparasites on farm animals Used as emulsifiable concentrate and spray Started noticing problem w/ American robins while spraying for Dutch Elm Disease

15. Insecticides ORGANOCHLORINES DDT MODE OF ACTION --within nerve cell action potential, holds sodium channel open longer than usual --result in delayed repolarization, but still no precise understanding 7. Banned in US – 1972; still in use elsewhere

16. Insecticides ORGANOCHLORINES Chlorinated Cyclodienes (Chlordane, Dieldrin, Aldrin, Endosulfan) As a class, they are significantly more toxic than DDT-type pesticides Endosulfan still has limited registration for use on food

17. Insecticides ORGANOPHOSPHATES Developed in Germany during WWII as a substitute for nicotene to control aphids Inhibit acetylcholinesterase HOW WHERE Example in bird migration Produced for warfare Most OPs are lipophilic

18. Insecticides ORGANOPHOSPHATES Less stable than organochlorines (OCs) Largely short-term (acute) toxicity More polar and water soluble than OCs Largely replaced OCs as pesticides of choice

19. Insecticides ORGANOPHOSPHATES EXAMPLES: Chlorpyrifos – use decreased by 62% in last decade Diazinon (being phased out by EPA); termite & fire ant Parathion - weak inhibitor of cholinesterase; highly toxic in cells due to conversion to paraoxon; promoted by CP450 in endoplasmic reticulum; 9000X more toxic than parathion itself

20. Insecticides ORGANOPHOSPHATES EXAMPLES: Malathion – degrades to non-toxic OP by mammalian carboxyesterases; used in boll weevil eradication Methyl parathion – 50X more toxic to mammals than malathion; use has increased 86% over the last decade

21. Insecticides CARBAMATES Derivatives of carbamic acid Developed more recently than OCs and Ops Acetylcholinesterase inhibitors EXAMPLE: Aldicarb (systemic insecticide)

22. Insecticides BIOLOGICAL / BOTANICAL Nicotine Isolated from leaves of tobacco plant Uses recorded at least 200 years ago Rotenone Derived from roots of Derris, Lonchocarpus, Tephrosia Commercial insecticides in 1930s Flavonoid derivative; strongly inhibits mitochondrial respiration Highly toxic to fish Can be used in smaller amounts to paralyze fish for consumption Relatively non-toxic in humans Exempt from requirement of an EPA tolerance when applied to growing crops

23. Insecticides BIOLOGICAL / BOTANICAL Pyrethroids 1. Originally derived from chrysanthemum plants 2. Significant insecticidal properties 3. Led to derivation of synthetic pyrethroids which have better photostability and are generally more active than their natural counterparts 4. Potential benefits? 5. Potential problems? EXAMPLES: Permethrin, Cypermethrin, Deltamethrin, Fenvalerate, Esfenvalerate, Lambda-cyhalothrin, bifenthrin

24. Insecticides BIOLOGICAL / BOTANICAL Biological Bt (Bacillus thuringiensis) --endotoxin --when ingested by insects, toxin causes paralysis of the gut --or may kill by bacterial growth if endospore germinates

25. Herbicides • Comprise ~ 70% of currently applied pesticides • Many different classes, but we will focus on 5 briefly • Typically characterized as very water soluble, with little – no effects on non-targets (especially vertebrates / invertebrates)

26. CHLORPHENOXY • One of most important groups of herbicides • 2,4-D • Disturb growth processes by interfering with transport of nutrients; similar to natural growth regulator – indole acetic acid • Selectively toxic between monocots and dicots • Mainly used to “weed out” dicots in monocot crops • TCDD (dioxin) – Agent Orange (2,4-D & 2,4,5-T) Herbicides

27. THE QUATS (Bipyridyls) • Formerly most applied herbicide in global market • Primarily two herbicides: Paraquat and Diquat • Diquat registered for aquatic uses • Paraquat (and diquat) are quick acting; widely used • Target anything green (chlorophyll) • Use in cotton for defoliation • Hazardous to humans (lungs) Herbicides

28. ACETAMIDES • Main example: PROPANIL • Formerly most applied rice herbicide; 63% decrease in usage over last decade • Lack of acylamidase enzymes in target plants (e.g. barnyard grass) causes plant death • Fairly low toxicity to non-target organisms (when compared to expected environmental concentrations – EECs) Herbicides

29. GLYPHOSATE • Use increased 93% in last decade • Round-Up • Monsanto; Round-Up ready soybeans; corn • Genetic engineering debate…… Herbicides

30. TRIAZINES • Atrazine is most popular type of triazine applied • Commonly found in Midwest groundwater wells • Relatively non-toxic to MOST non-target vertebrate and invertebrates • Recent arguments….. Herbicides

31. Other Pesticides FUNGICIDES Pentachlorophenol --used as fungicide and wood preservative since the 1930s --35 million lbs / year produced in US (1985) --uncouples oxidative phosphorylation by inhibition of Na+ and K+ ATPase

32. RODENTICIDES 1. Warfarin --Vitamin K antagonist (required for blood clotting) --low water solubility --lipophilic --Second generation of warfarins: “Super Warfarins” are 200x more potent than original warfarin; Half-life is 60x longer Other Pesticides

33. RODENTICIDES 2. Strychnine --kills birds, rodents, moles, predatory animals --human effects similar to animals --blocks neuronal excitability, sensory stimuli produce exaggerated reflex actions --Treatment: DIAZEPAM (anti-depressant) Other Pesticides

34. Pesticide Regulation National pesticide control first attempted by: Insecticide Act of 1910 Targeted more to prevention of fraudulent products rather than misuse of poisons 2 Principle Laws of Pesticides: 1. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) 2. Federal Food Drug and Cosmetic Act (FFDCA)

35. Pesticide Regulation FIFRA --First enacted in 1947; amended in 1959 & 1961 --Emphasized consumer protection & product efficacy --Must be registered before being sold or distributed in interstate commerce --Amended again in 1964 thanks to Silent Spring

36. Pesticide Regulation FIFRA --Prior to 1970, USDA controlled approval under FIFRA --Passed responsibility onto US EPA --Major FIFRA overhaul in 1972 a. Registration was more restrictive b. Burden of proof was on manufacturer

37. Pesticide Regulation FIFRA --1978 further amendments a. Streamline registration w/ generic reregistration reviews b. Added authority to grant conditional registration c. Resolve data issues of propriety and compensation

38. Pesticide Regulation FIFRA --1988 amendments a. Require expedited reregistration of existing pesticides to ensure that registration are supported by adequate data

39. FIFRA Registration --Older pesticides which were registered before the implementation of current regulations and testing guidelines have data base reviewed by EPA --If found unsatisfactory for current requirements, data must be repeated according to current guidelines --After this, EPA issues a “Registration Standard” --If deficiencies exist, manufacturer may repeat studies or must cancel registration Pesticide Regulation

40. Pesticide Regulation FIFRA General ecotoxicology and environmental testing 1. Ecotoxicity tests 2. Environmental fate testing 3. Ecological risk assessments “Tiered ecological testing” ACUTE → CHRONIC →SIMULATED &/OR FIELD STUDY

41. Pesticide Regulation FIFRA Minimum tests to support registration of outdoor-use 1. Avian single-dose oral toxicity test 2. Avian dietary toxicity test w/ upland game bird 3. Avian dietary toxicity test w/ waterfowl species 4. Freshwater fish acute toxicity test w/ warmwater species 5. Freshwater fish acute toxicity test w/ coldwater species 6. Aquatic invertebrate acute toxicity test w/ immature life stage (Other info may be required—estuarine, beneficials, etc.)

42. Pesticide Regulation FIFRA Initial toxicity data used for the following: *Define acute toxicity of a.i. to different aquatic and terrestrial species *Compare initial acute toxicity with actual or EEC to assess potential impact *Provide data to determine whether or not need for precautionary label *Indicate need for further laboratory &/or field studies

43. Pesticide Regulation FIFRA Environmental Fate Testing 1. Significant degradation routes 2. Primary degradates 3. Degradation / metabolic pathway 4. Potential ½ life and persistence in environment 5. Dissipation / mobility of chemical, potential EEC Ecological Risk Assessments

44. Pesticide Regulation FFDCA Food & Drug Administration (FDA) enforces tolerances (residue limits) for pesticides on food crops Delaney Clause (1958) in the Food Additives Amendment states there shall be NO measurable concentration of cancer-causing substance (no matter the true risk) Compare analytical chemistry in 1958 (LOD 20-100 ppm) to analytical chemistry in 2003 (LOD ????)