7765 - Laserfiche WebLink

Home Browse Search

~U5 (q1J / J-5'i' (j~K\ Pergamon ~0770) , Environmental Toxicology and Chemistry, Vol..B, No.6, pp. 93~939, 19'Jll Copyright @ 1994 SETAC Printed in the USA 0130-7268/94 $6.00 + .00 0730-7268 (94)E0024-6 ACETYLCHOLINESTERASE INHIBITION IN FEDERALLY ENDANGERED COLORADO SQUAWFISH EXPOSED TO CARBARYL AND MALATHION .... DANIEL W. BEYERS* and PETER ], SIKOSKI Larval Fish Laboratory, Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins, Colorado 80523 .... (Received 21 June 1993; Accepted 2 December 1993) Abstrac~ - ~oxicity. of technical carbaryl and malathion to endangered Colorado squawfish (Ptychocheilus lucius) was estimated by 24-h m VIVO bram acetylcholinesterase-inhibition tests. Effect concentrations were estimated by ANOVA and an alternative procedure utilizing a linear-plateau regression model. NOECs were 29.3 ILg/L carbaryl and 3711Lg/L malathion. Threshold con- centrations estimated by linear-plateau regression were 7.40 ILg/L carbaryl and 150 ILg/L malathion. NOECs showed that car- baryl was approximately 13 times more toxic than malathion. Relative potency of the two toxicants was confirmed by linear-plateau regression analysis: Threshold estimates showed that carbaryl was approximately 20 times more toxic than malathion. NOECs for acetylcholinesterase inhibition were 15 times lower for carbaryl, and four times lower for malathion, than NOECs estimated from growt~ and survival in 32-d early-life-stage tests. The difference between effect concentrations estimated by the two meth- ods was attnbuted to development of tolerance in 32-d early-life-stage tests and greater sensitivity of biochemical processes com- pared to whole-organism responses. Keywords - Carbaryl Threshold concentration Malathion .. INTRODUCTION The insecticides carbaryl and malathion are used to con- trol grasshopper infestations on rangeland and cropland throughout the western United States. Both chemicals exert their toxic effects by inhibiting the enzyme acetylcholinester- ase (AChE), thereby causing disruption of the central ner- vous system [IJ. Insecticides used to control grasshopper infestations pose a hazard to fishes because deposition in aquatic habitats may occur by accidental drift or runoff de- spite no-spray buffer zones [2]. Colorado squawfish (Ptychocheilus lucius) is the largest minnow in North America and historically occurred through- out the Colorado River Basin [3,4]. Colorado squawfish pop- ulations have declined as a result of construction of reservoirs and other management practices [5]. In response to the rapid decline and threat of extinction, the Colorado squaw fish was listed as a federally endangered species in 1967. Although scarcity and federally endangered status have made study of wild Colorado squawfish difficult, information on life history and behavior has been collected [4]. During theJirst several months of life (June-October), larvae of Colorado squawfish occupy shallow, low-velocity, near-shore habitats. Because these habitats have low rates of water exchange, pes- ticides deposited in them may be present in sufficient con- centration and duration for toxic effects to occur. Spatial and temporal overlaps of grasshopper control programs and Col- orado squawfish life history are such that potentially sensi- tive life stages (<30 d old) are at risk of exposure. *To whom correspondence may be addressed. Contribution 68, Larval Fish Laboratory, Colorado State University. Dose-response model End points Toxicity of carbaryl and malathion to fish and aquatic in- vertebrates has been studied [6], but none of the previously tested fishes is closely related to Colorado squawfish. Because of uncertainty of predicting the sensitivity of Colorado squaw- fish to carbaryl and malathion, Beyers et al. [7] estimated toxicity of these chemicals using 4-d renewal-acute and 32-d early-life-stage (ELS) toxicity tests. Although these standard- ized toxicity tests provided quantitative description of toxicant effects, they did not simulate chemical exposure conditions that may result from routine aerial pesticide applications. Therefore, we studied brain AChE inhibition to estimate toxicant effects at a scale consistent with the duration of ex- posure and concentration range that may occur in the field. AChE activity was measured in Colorado squawfish after 24-h in vivo exposure to technical carbaryl or malathion. Data were analyzed using ANOYA and an alternative pro- cedure utilizing a linear-plateau regression model. The ob- jectives were to (a) estimate effect concentrations of AChE inhibition and compare them to those for growth and sur- vival of Colorado squawfish in 32-d ELS toxicity tests, and (b) compare effect-concentration estimates obtained by the two alternative statistical methods. METHODS Experimental animals Colorado squawfish were obtained from Dexter National Fish Hatchery and Technology Center (Dexter, NM), Fish were fed a mixture of live ::524-h-01d brine shrimp nauplii (Aquarium Products, Glen Burnie, MD) and a commercially prepared flake diet (TetraMin@; TetraWerke, Melle, Ger- many) twice daily. 935