1. Aquatic Herbicide / Algaecide Toxicity
John H. Rodgers, Jr MN AIS Symposium March 7-8, 2012 St. Paul, MN

2. Adaptive Water Resource Management
Risk assessment – problem or not?
Consider all available options
No decision / action vs. decision / action
Implement viable option(s)
Monitor results modify approach if indicated

3. Why use herbicides or algaecides?
Invasive and exotic species move at unprecedented rates.
We have changed the landscape – e.g. canals, reservoirs, stormwater detention basins, etc.
Human population increase – plant / people interface.
Changing climate – globally
Pressure on water resources.

4. Myriophyllum spicatum

5. Didymosphenia geminata

6. Cylindrospermopsis raciborskii

7. Prymnesium parvum

8. Effects of a P. parvum “Bloom”

9. Problems Caused by Vascular and Nonvascular (Algae) Plants
Aesthetics
Devalue property
Disrupt transportation
Taste and odor problems/ Toxin production
Impact fisheries and endangered species
Impede irrigation
Human health
Interfere with water resource uses!

10. Prymnesium parvum

11. 30-mile fish kill in Dunkard Creek

13. Problem?► Response Response “Triggers” No Action – Action
Consider all the “competing” water resource uses!

15. Factors influencing herbicide selection
Target plant species (strain)
Water resource usages
Water body and water characteristics
Efficacy
Costs
Margin of safety for non-target species
Social acceptance (Regulatory approval)

16. Chemical Control Options for Aquatic Vascular Plants and Algae
Carfentrazone ethyl
Copper formulations
Diquat
2,4-D formulations
Dyes
Endothall formulations
Fluridone
Glyphosate
Imazamox
Imazapyr
Penoxsulam
Peroxide formulations
Triclopyr formulations
Conditional registration:
Flumioxazin
Bispyribac Sodium

17. Herbicides / Algaecides can take advantage of unique physiology
Plants ≠ Fish, invertebrates, etc.
Plants have “systems” that animals do not have.
Unique physiology!

18. Auxin Mimics 2,4-D formulations – auxin-type herbicide (plant hormone)
Triclopyr – auxin-type herbicide

19. ALS Inhibitors Imazapyr – inhibits ALS Penoxsulam – inhibits ALS
Bispyribac Sodium – inhibits ALS
Imazamox – inhibits the enzyme acetohydroxyacid synthase (AHAS) in plant species, which is involved in the synthesis of three branched-chain aliphatic amino acids: isoleucine, leucine and valine

20. Enzyme or Biochemical Inhibitors
Carfentrazone ethyl - protoporhyrinogen oxidase inhibitor or 'protox' inhibitor
Fluridone – inhibits phytoene dismutase, blocks carotenoid biosynthesis
Glyphosate – inhibits ESPS synthesis
Endothall – inhibits lipid and protein synthesis
Flumioxazin - inhibition of protoporphyrinogen oxidase, an enzyme important in the synthesis of chlorophyll.

21. Redox Reactions Diquat –redox reactions Peroxide – oxidation reactions
Copper formulations - redox reactions, membrane transport

22. Light Attenuation
Dyes – light absorption

23. Toxicity – Non-target species
Peroxide – Sodium carbonate peroxyhydrate
Copper formulation
Triclopyr (TEA salt)
Imazapyr

24. Animal Testing Species for Margins of Safety for Nontarget Species

25. Sodium Carbonate Peroxyhydrate
Sodium percarbonate
IUPAC name : sodium carbonate—hydrogen peroxide (2/3)
other names : PCS, solid hydrogen peroxide, sodium carbonate hydrogen peroxide, sodium carbonate peroxyhydrate CAS number : Properties Molecular formula : Na2CO3·1.5H2O2 Molar mass : g/mol Appearance : white solid (granular) Solubility in water : 150 g/L

26. What is SCP?
Sodium carbonate peroxyhydrate

27. SCP Algaecide
Made by combining 2 molecules of sodium carbonate with 3 molecules of hydrogen peroxide.
Free-flowing granular.
Stable source of alkaline hydrogen peroxide.
In water, produces hydrogen peroxide and sodium carbonate.

28. SCP Algae Treatments 0.3 mg/L – 10.2 mg/L H2O2
3.0 – 100 pounds / acre-foot
48 hours between applications
Large lake or heavy infestation (bloom) – treat 1/3 – 1/2 of the area and wait 2-3 days before treating the remaining water.

29. SCP Algaecide Algaecide – SCP concentration = 85%
= 27.6 % hydrogen peroxide
Registered by US EPA as algaecide for use in ponds, lakes, reservoirs and drinking water.

30. SCP Toxicity Pimephales promelas 96-h LC50 = 70.7 mg/L
Pimephales promelas 96-h NOEC = 1 mg/L
Daphnia pulex 48-h EC50 = 4.9 mg/L
Daphnia pulex 48-h NOEC = 1 mg/L
No bioconcentration, bioaccumulation
Abiotic degradation
Low toxicity of ultimate degradation products (H2O, O2)

31. Margin of Safety (MOS)
Scientific
name
Algaecide
96 h
LOECa
Pimephales promelas
(mg Cu / L)
EC100 b
Prymnesium parvum
MOS c=
LOEC of Pimephales promelas / [Cu] required to control Prymnesium parvum
Cutrine®- Plus
0.750
0.2
3.75
Algae in a two site waters were evaluated. The pH ranged from 7.8 to The hardness ranged from 312 to 427 mg/L as calcium carbonate.
Alkalinity ranged from 130 to 335mg/L and conductivity ranged from 1604 to 2700.
The fathead minnow is about the size of a 12 point font comma (,).
a Lowest Observed Effect Concentration
(Murray-Gulde et. al, 2002)
b [Cu] used to control Prymnesium parvum (EC100)
c Margin of Safety (MOS)
Table 1. Water Characteristics of Lake Whitney, Clemson University Culture, Unnamed Area (MI), and Sandy Hills Nursery
Table 1. Water Characteristics of Lake Whitney, Clemson University Culture, Unnamed Area (MI), and Sandy Hills Nursery

32. Triclopyr Toxicity
The TEA salt is "slightly toxic" to fish with 96h LC50 values of 552 and 891 ppm for rainbow trout and bluegill sunfish respectively.
The corresponding values for the unformulated triclopyr are 117 ppm for rainbow trout and 148 for bluegill sunfish.
Both species were less sensitive to the TEA salt than to the active ingredient.

33. Imazapyr Toxicity
The 48- and 96-h LC50s for rainbow trout, bluegill sunfish, channel catfish, and the water flea (Daphnia magna) are all >100 mg/L (WSSA 1994).
Concentrations up to 1,600 mg/L did not affect the osmoregulatory capacity of Chinook salmon smolts (Patten 2003).
The 96-h LC50 for rainbow trout fry is 77,716 mg/L (ppm) ( ~22,305 ppm of the active ingredient).

34. Acute, Chronic Studies

35. Herbicides / Algaecides can take advantage of differences in responses to exposures
Fish may detect and avoid herbicide or algaecide.
Pattern and timing of application.
Pulse or episodic exposure vs. continuous exposure.
Formulation (e.g. granular vs. liquid)

36. Herbicide / Algaecide Fate and Persistence
Well Studied
Laboratory Studies
Semi-field Studies
Field Studies

38. Conclusions – Aquatic Herbicides and Algaecides
Effective for target algal species.
MOS (margin-of-safety) for non-target species varies.
Research ongoing to improve and expand data, uses and effectiveness.
Development of new chemistries and formulations underway.

39. Thank you!