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lO4 RESULTS D.W. BEYERS ET AL. Four-day renewal-acute tests Median lethal concentrations and 95070 confidence limits (in parentheses) for Colorado squawfish and bonytail exposed to carbaryl were 1.31 (1.23, 1.40) and 2.02 mg/L (1.78, 2.25), respectively. Median lethal concentrations for Colorado squaw fish and bony tail exposed to Sevin-4-0il were 3.18 (2.87,3,52) and 3.31 mg/L (3.06,3.55), respectively. Toxicity of Sevin-4-0il (49% carbaryl) was approximately one-half that of carbaryl. The ratio of median lethal concentrations of carbaryl to Sevin-4-0il was 0.840 and 1.24 for Colorado squawfish and bonytail, respectively. Ratios between 0.5 and 1.5 are considered within the range of normal experimental variation [6]; therefore, no synergistic or antagonistic toxic effects due to formulation of carbaryl as Sevin-4-0il were ob- served. Median lethal concentrations for Colorado squaw- fish and bonytail exposed to malathion were 9.14 (8.36, 10.0) and 15.3 mg/L (14.4, 16.4), respectively. Malathion was ap- proximately seven times less toxic to Colorado squawfish and bony tail than carbaryl. Carbaryl and malathion concentrations declined during the 24 h between renewals. Initial concentrations of carba- ryl and malathion in test solutions nearest the median lethal concentrations were 1.95 and 14.5 mg/L; final concentra- tions were 0.817 and 9.20 mg/L, respectively. Dilution wa- ter had a pH of 8.2, and temperature was 220C. ELS tests As in 4-d renewal-acute studies, carbaryl was consistently more toxic than malathion (Table 1). Estimates of effect con- centrations for survival were identical, regardless of whether the angular or logistic transformation was used. For hypoth- esis tests, growth was as sensitive or more sensitive than sur- vival as a measure of toxic effects; therefore, only NOECs for growth are presented: 445 JLg/L carbaryl and 1,680 JLg/L malathion for Colorado squawfish; and 650 ILg/L carbaryl and 990 ILg/L malathion for bony tail. Threshold concentra- tions as estimated by linear-plateau regression were 364lLg/L carbaryl and 455 ILg/L malathion for Colorado squawfish; and 217 ILg/L carbaryl and 5211Lg/L malathion for bony tail (see Beyers [21] for summaries of measured toxicant concen- trations, survival, and weight). For each toxicant and endpoint, the distribution of data as a function of concentration was such that a linear-plateau regression model was appropriate. In all cases, the regression accounted for a significant amount of total experimental variation (p = 0.001). Regression analyses permitted com- pilation of a family of linear-plateau functions for each test species and toxicant (Fig. I). Typically, growth was as sen- sitive or more sensitive than survival as a measure of toxic effects. The one exception to this pattern was the exposure of Colorado squawfish to malathion, in which growth was least sensitive. DISCUSSION Four-day renewal-acute tests A concern responsible for initiation of our toxicological studies was that Colorado squawfish or bonytail might be su- persensitive to carbaryl or malathion. To evaluate the rela- tive sensitivity of Colorado squawfish and bony tail, we compared median lethal concentrations estimated in our study to those summarized by Mayer and Ellersieck [6]. Compared to other commonly studied fishes, Colorado squawfish and bony tail were approximately as sensitive to carbaryl as cutthroat trout (Oncorhynchus clarki), rainbow Table I. Threshold and effect concentrations estimated from exposure of Colorado squawfish (CS) and bony tail (BT) to technical carbaryl and technical malathion Threshold" NOEC LOEC Measure Plateau Slope Intercept (/lg/L) (/lg/L) (/lg/L) Survival b.c Carbaryl 445 866 CS 2.76 -1.88 18.8 364 (203, 653) BT 3.57 -6.73 65.6 593 (566, 621) 650 1,240 Malathion 3,5lO CS 3.18 -0.833 lO.5 455 (236, 786) 1,680 BT 3.39 -3.20 36.9 1,420 (936,2,160) 2,000 4,060 Weightb.d Carbaryl 364 (30 I, 440) 445 866 CS 62.6 -18.9 224 BT 66.3 -6.95 120 217 (180, 262) 650 1,240 Malathion 3,5lO CS 46.0 -21.7 275 1,470 (l,4lO, 1,520) 1,680 BT 64.0 -18.9 234 521 (487, 557) 990 2,000 Plateau, slope, and intercept estimates are for the linear-plateau regression equation y = intercept + slope (Iogz concentration). "Threshold values and their 95070 confidence limits (in parentheses) were derived from regression and back-transformed for comparison to NOECs and LOECs. b32-d exposure period. cUnits of dependent variable = logits. dUnits of dependent variable = milligrams. ,.