Buhl, K.J. Faerber, N.L.



Acute Toxicity of Selected Herbicides and Surfactants to Larvae of the Midge 
Chironomus riparius.



National Fisheries Contaminant Research Center



Archives of Environmental Contamination and Toxicology AECTCV, Vol. 18, No. 4, 
p 530-536, July/August 1989. 4 tab, 24 ref.



 The acute toxicities of eight commercial herbicides and two surfactants to 
early fourth instar larvae of the midge surfactants to early fourth instar 
larvae of the midge Chironomus riparius were determined under static 
conditions. The formulated herbicides tested were Eradicane (EPTC), Fargo 
(triallate),Lasso (alachlor), ME4 Brominal (bromoxynil), Ramrod 
(propachlor), Rodeo (glyphosate), Sencor (metribuzin), and Sutan (+) 
(butylate); the two surfactants were Activator N.F. and Ortho X-77. In 
addition, technical grade alachlor, metribuzin, propachlor, and triallate were 
tested for comparison with the formulated herbicides. The relative toxicity of 
the commercial formulations, based on percent active ingredient, varied 
considerably. The EC50 values ranged from 1.23 mg/L for Fargo to 5600 mg/L for 
Rodeo. Fargo, ME4 Brominal, and Ramrod were moderately toxic to midge 
larvae; Lasso, Sutan (+), and Eradicane were slightly toxic; and Sencor and 
Rodeo were practically non-toxic. The 48-hour EC50 values of the two 
surfactants were nearly identical and were considered moderately toxic to 
midges. For two of the herbicides, in which the technical grade material was 
tested, the inert ingredients in the formulations had a significant effect 
on the toxicity of the active ingredients. Fargo was twice as toxic as 
technical grade triallate, whereas Sencor was considerably less toxic than 
technical grade metribuzin. A comparison of the slope function values 
indicated that the toxic action of all compounds occurred within a 
relatively narrow range. In general. the relative order of toxicity to 
Chironomus riparius was similar to those for other freshwater invertebrates. 
Maximum concentrations of each herbicide in bulk runoff during a projected 
critical runoff event were calculated as a percentage of the application 
rate lost in a given volume of runoff. A comparison between estimated 
maximum herbicide concentrations in runoff and results of acute tests 
indicated that Ramrod, ME4 Brominal, and Lasso pose the greatest direct risk 
to midge larva during a storm event.



Aquatic insects Bioassay Herbicides Midges Surfactants Toxicity Water 
pollution effects Alachlor Bromoxynil Butylate Insect larvae Lethal limit 
Metribuzin Storms Triallate