Envvonmenral zyxwvutsrqponmlkji Toxicology zyxwvutsrqponmlk ond Chemistry, zyxwvutsrqpon Vol. 10, zyxwvutsrqpon pp. 365-374, 1991 Printed in the USA. Pergamon Press plc 0730-7268/91 $3.00 zyxw + .OO Copyright zyxwv 0 1991 SETAC EXPOSURE-RELATED PATTERNS OF BIOCHEMICAL INDICATORS IN RAINBOW TROUT EXPOSED TO NO. 2 FUEL OIL B.L. STEADMAN," A.M. FARAG and H.L. BERGMAN Fish Physiology and Toxicology Laboratory, Department of Zoology and Physiology, University of Wyoming, University Station, Box 3166, Laramie, Wyoming 82071 (Received 12 July 1989; Accepted 23 June 1990) Abstract - Several biochemical indicators were evaluated as monitoring techniques in rainbow trout (Oncorhynchusmykiss) exposed to No. 2 fuel oil (2FO) for their ability to predict the exposure con- centration. The principal factor affecting the response of the ratio of liver weight to body weight, microsomal and cytosolic protein, reduced glutathione (GSH), 7-ethoxyresorufin 0-deethylation (EROD) and metallothionein (MTN) was the length of exposure, not the exposure concentration. Two patterns of response were observed, depending on the length of exposure. In rainbow trout ex- posed for 3 d to 12 to 100 mg/L 2F0, cytoplasmic protein and EROD activity were elevated and GSH was depleted; in fish exposed for 21 d, liver size, microsomal and cytoplasmic protein, EROD activity, GSH and MTN were all increased. The appearance of an MTN response due to 2 F 0 ex- posure causes us to question the use of this protein as a metal bioindicator. Furthermore, we did not observe a dose-dependent response in any of the biochemical responses and suggest that tox- icity was responsible for the lack of concentration dependence. This lack of a concentration-depen- dent response will complicate the use of these biochemical indicators in a biomonitoring program. Keywords-Biomonitoring Mixed-functionoxidase Glutathione Metallothionein INTRODUCTION The use of biochemical end points to monitor for the presence of contaminants in the environ- ment has been suggested by numerous authors [l- 31. Biochemical tests are frequently suggested for use as indicators of environmental contamination because they have three advantages: the capability to detect effects before the appearance of gross le- sions, reproductive impairment or mortality; the potential of indicating the type or types of contam- inants causing environmental damage; and the ca- pacity to be applied to diverse life stages of both vertebrate and invertebrate organisms. The characteristics of ideal biochemical indica- tors have been summarized [l], and techniques have been proposed that meet many of those criteria. However, routine use of bioindicator techniques has been limited for several reasons: difficulties in relating changes in biochemical measures to tradi- tional toxicity end points (pathology, growth, re- production, mortality, etc.); insufficient knowledge concerning exposure concentration (dose) and time response of the indicator; and high variability in field-collected specimens due to factors such as age, sex, diet and species of organisms tested. In spite of the limitations, mixed-function oxi- dase (MFO) activity and metallothionein (MTN) levels have been used to document the presence or bioavailability of contaminants in the field (e.g., [4-71). A logical extension of the use of biochem- ical indicators for the detection of chemical contam- inants is their use to predict exposure concentration or contaminant type. If biological indicator tech- niques can quantify contaminant gradients or rank contaminated sites, the relationship between expo- sure concentration and bioindicator response must be defined. Some bioindicator responses are corre- lated to tissue concentration (e.g., [8]), not expo- sure concentration. Thus, the duration of exposure to a contaminant and the subsequent disposition in the test organism could also affect bioindicator responses. carbon exposure. As it was unlikely that a single 365