Aquatic Herbicide / Algaecide Toxicity

John H. Rodgers, Jr.

2012 MN AIS Symposium March 7-8, 2012

St. Paul, MN

Adaptive Water Resource Management

1. Risk assessment – problem or not?

2. Consider all available options

3. No decision / action vs. decision / action

4. Implement viable option(s)

5. Monitor results modify approach if indicated

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.

Myriophyllum spicatum

Didymosphenia geminata

Cylindrospermopsis raciborskii

Prymnesium parvum

Effects of a P. parvum “Bloom”

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!

Prymnesium parvum

30-mile fish kill in Dunkard Creek

Problem?► Response

• Response “Triggers”

• No Action – Action

Consider all the “competing” water resource uses!

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)

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:FlumioxazinBispyribac Sodium

Herbicides / Algaecides can take advantage of unique physiology

• Plants ≠ Fish, invertebrates, etc.

• Plants have “systems” that animals do not have.

• Unique physiology!

Auxin Mimics

• 2,4-D formulations – auxin-type herbicide (plant hormone)

• Triclopyr – auxin-type herbicide

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

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.

Redox Reactions

• Diquat –redox reactions

• Peroxide – oxidation reactions

• Copper formulations - redox reactions, membrane transport

Light Attenuation

• Dyes – light absorption

Toxicity – Non-target species

• Peroxide – Sodium carbonate peroxyhydrate

• Copper formulation

• Triclopyr (TEA salt)

• Imazapyr

Animal Testing Species for Margins of Safety for Nontarget Species

Sodium Carbonate Peroxyhydrate

Sodium percarbonateIUPAC name : sodium carbonate—hydrogen peroxide (2/3)

other names : PCS, solid hydrogen peroxide, sodium carbonate hydrogen peroxide, sodium carbonate peroxyhydrate

CAS number : 15630-89-4 Properties Molecular formula : Na2CO3·1.5H2O2 Molar mass : 157.01 g/mol Appearance : white solid (granular) Solubility in water : 150 g/L

What is SCP?

• Sodium carbonate peroxyhydrate

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.

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.

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.

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)

Scientific name Algaecide

96 hLOECa

Pimephales promelas

(mg Cu / L)

EC100 b

Prymnesium parvum

(mg Cu / L)

MOS c=

LOEC of Pimephales promelas / [Cu]

required to control Prymnesium parvum

(mg Cu / L)

Pimephales promelas

 

Cutrine®- Plus

 

0.750 0.2 3.75

Margin of Safety (MOS)

a Lowest Observed Effect Concentration (Murray-Gulde et. al, 2002)

b [Cu] used to control Prymnesium parvum (EC100) c Margin of Safety (MOS)

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.

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).

Acute, Chronic Studies

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)

Herbicide / Algaecide Fateand Persistence

• Well Studied

• Laboratory Studies

• Semi-field Studies

• Field Studies

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.

Thank you!