Herbicide Toxicity to Lemna:  Test Results.

Comparative toxicity of 16 herbicides to Lemna minor

Toxicity is based on counting the fronds in the cultures each day.  The EC₅₀ is the concentration of the dissolved test substance that gives a 50% inhibition of growth rate.
 

Chemical Class Herbicide 96-h EC50 (g/L) 95% C.I. (g/L) Acetanilide Alachlor 198 80-316 Acetanilide Metolachlor 343 187-872 Triazine Atrazine 153 89-217 Triazine Cyanazine 705 577-834 Triazine Metribuzin 37 22-47 Triazine Simazine 166 102-230 Sulfonylurea Chlorsulfuron 0.7 0.5-0.9 Sulfonylurea Metsulfuron 0.4 0.3-0.5 Pyridine Diquat 18 37-99 Pyridine Paraquat 51 25-77 Thiocarbamate EPTC 7512 1736-13288 Thiocarbamate Triallate >10000  ---- Benzonitrile Bromoxynil 8065 3783-12348 Benzoic acid Dicamba >100000  ---- Dinitroaniline Trifluralin 170 10-330 Phenoxy 2,4-D >100000 ----

Data from Fairchild et al. 1997 (see below), cited in Appendix 5: from Michael Davy, Richard Petrie, and Jerry Smrchek, EPA; Ted Kuchnicki and Derek Francois, PMRA,  USEPA Scientific Advisory Panel Briefing "Proposal to update non-target plant toxicity testing under NAFTA."  June 27-29, 2001 http://www.epa.gov/scipoly/sap/2001/june/sap14.pdf

Fairchild, J.F., D.S. Ruessler, P.S. Heverland and A.R. Carlson. 1997. "Comparative Sensitivity of Selenastrum capricornutum and Lemna minor to Sixteen Herbicides." Arch. Environ. Contam. Toxicol., 32: 353-357.

Phytotoxicity Research

Lemna growth assays are intended to determine if and how toxic a chemical is to green plants.  Duckweeds are also used in research to understand why a chemical is toxic.  Many classes of toxins have been studied, ranging from toxic elements (e.g. selenium and heavy metals) to fungal toxins, pesticides and industrial chemicals.
 
• Lemna test abstracts from the Annual Meetings of the Society for Environmental Toxicology and Chemistry (SETAC).  These abstracts provide the results from a wide variety of chemicals tested.

[ 2001 US Meeting ] [ 2002 US Meeting ] [ 2002 SETAC Europe ]
 
• Photooxidation products of environmental contaminants.  Lemna was used to show that ultraviolet light enhances the oxidation of certain aromatic substances to more toxic products.  Research from the laboratory of B.M. Greenberg, University of Waterloo, Ontario:

Mallakin A et al. (1999) "Impacts of structural photomodification on the toxicity of environmental contaminants: anthracene photooxidation products."  Ecotoxicol Environ Safety 43(2):204-12.
 
• Water leaching from smelters and mine tailings often contains heavy metals not recovered in processing:

T.L. Williams,  M.J. Lydy, and A.L. Youngman (Wichita State University, KS) Utilization of a duckweed bioassay to evaluate leaching of heavy metals in smelter-contaminated soils.  12th Annual Conference on Hazardous Waste Research, Kansas City, MO, 1997.
[ Link to abstract ]

Fungi produce some of the most toxic substances known. Lemna bioassays are useful in discovering and studying these (often) food-borne toxins:

Vesonder, Ronald F. and Weisleder, David (USDA, Peoria, IL) Metabolites from Fusarium spp. inhibitory to growth of Lemna minor L. TEKTRAN, United States Department of Agriculture, Agricultural Research Service, 1998.

"Corn containing toxins produced by fungi when used as farm animal food can make the animal sick.  In this report, the usefulness of a bioassay using a water plant called duckweed is demonstrated for finding toxins in corn harmful to animals."
[ Link to abstract ]

Abbas, Hamed K., Duke, Stephen O., Merrill, A.H., Wang, E. and Shier, W.T. (USDA/ARS Southern Weed Science Lab., Stoneville, MS) "Phytotoxicity of australifungin produced by Sporomiella australis AAL toxin and fumonisin B1 to duckweed (Lemna pausicostata L.)" TEKTRAN, United States Department of Agriculture, Agricultural Research Service, 1998.

"This paper describes the effects of australifungin which is a newly discovered ceramide synthase inhibitor.  The compounds that affect this enzyme, especially fumonisin B1, are toxic to animals.  It is our goal to find a safe and effective weed control agent that works at this molecular site.  We demonstrate in this study that australifungin is phytotoxic to duckweed."
 

• Ethylene glycol is the main component of automotive antifreeze:

Barber, John T., Thomas, Dana A., Ensley, Harry E., Yatsu, Lawrence Y. (Tulane University), Duckweed, diols and death. American Society of Plant Physiologists Annual Meeting, 1997.
[ Link to abstract ]

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Revised:  April 25, 2003