Using accelerated life testing procedures to compare the relative sensitivity of rainbow trout and the federally listed threatened bull trout to three commonly used rangeland herbicides (picloram, 2,4-D, and clopyralid).
We conducted 96-h static acute toxicity studies to evaluate the relative sensitivity of juveniles of the threatened bull trout (Salvelinus confluentus) and the standard cold-water surrogate rainbow trout (Onchorhyncus mykiss) to three rangeland herbicides commonly used for controlling invasive weeds in the northwestern United States. Relative species sensitivity was compared using three procedures: standard acute toxicity testing, fractional estimates of lethal concentrations, and accelerated life testing chronic estimation procedures. The acutely lethal concentrations (ALC) resulting in 50% mortality at 96 h (96-h ALC50s) were determined using linear regression and indicated that the three herbicides were toxic in the order of picloram acid > 2,4-D acid > clopyralid acid. The 96-h ALC50 values for rainbow trout were as follows: picloram, 41 mg/L; 2.4-D, 707 mg/L; and clopyralid, 700 mg/L. The 96-h ALC50 values for bull trout were as follows: picloram, 24 mg/L; 2.4-D, 398 mg/L; and clopyralid, 802 mg/L. Fractional estimates of safe concentrations, based on 5% of the 96-h ALC50, were conservative (overestimated toxicity) of regression-derived 96-h ALC5 values by an order of magnitude. Accelerated life testing procedures were used to estimate chronic lethal concentrations (CLC) resulting in 1% mortality at 30 d (30-d CLC1) for the three herbicides: picloram (1 mg/L rainbow trout, 5 mg/L bull trout), 2,4-D (56 mg/L rainbow trout, 84 mg/L bull trout), and clopyralid (477 mg/L rainbow trout; 552 mg/L bull trout). Collectively, the results indicated that the standard surrogate rainbow trout is similar in sensitivity to bull trout. Accelerated life testing procedures provided cost-effective, statistically defensible methods for estimating safe chronic concentrations (30-d CLC1s) of herbicides from acute toxicity data because they use statistical models based on the entire mortality:concentration:time data matrix.
Fairchild
James F
JF
US. Geological Survey, Columbia, Missouri 65201, USA. jfairchild@usgs.gov
Allert
Ann
A
Sappington
Linda S
LS
Nelson
Karen J
KJ
Valle
Janet
J
D015084:2,4-Dichlorophenoxyacetic Acid / Q000633:toxicity*; D000818:Animals; D003247:Conservation of Natural Resources; D006540:Herbicides / Q000633:toxicity*; D010846:Picloram / Q000633:toxicity*; D010848:Picolinic Acids / Q000633:toxicity*; D012680:Sensitivity and Specificity; D013045:Species Specificity; D014337:Trout; D014874:Water Pollutants, Chemical / Q000633:toxicity
D006540:Herbicides; D010848:Picolinic Acids; D014874:Water Pollutants, Chemical; C011767:clopyralid; D015084:2,4-Dichlorophenoxyacetic Acid; D010846:Picloram