Introduction

During the past three years we have been studying the rates of uptake by fishes of selected synthetic organic chemicals, foreign to natural systems, known as xenobiotics. We have conducted several tests using an automated respirometer in which we have exposed fish to 1, 2, 4, 5-tetrachlorobenzene (TCB). Our principal test animal has been the rainbow trout (Oncorhynchus mykiss), although we have also tested other fish species to compare results. One of our long-range objectives is to determine to what extent uptake and depuration rates of xenobiotics by fishes may be related to their respiration rates. Using that information, we are working toward developing a simple predictive model to describe the rates of uptake and depuration of xenobiotics as a function of the oxygen uptake rate and chemical properties of the chemical in question. Some of our laboratory research, and our progress to date on developing the predictive model, are reported in Chapter 1, Randall et al. (1995). In the present paper, we will provide details of the methods used while conducting our respirometry experiments, and also provide results of some of the other experiments conducted during early stages of our study.

Methods

Test conditions

Many of our preliminary tests were conducted at Fisheries Bioassay Laboratory, Montana State University (MSU), and most of our respirometry experiments were conducted in a modified Brett-type respirometer at the Zoology Department, University of British Columbia (UBC). All fish tissue and water analyses were conducted at MSU. The UBC respirometer was designed and built specifically for our studies, and has been described in some detail by Gehrke et al. (1990).

Introduction

There is a massive production of chemicals synthesized to meet the demands of industry. Most of these chemicals are foreign to the body (xenobiotics). They enter the environment where they are available for uptake by organisms. Most animals possess enzymes (multi-function oxidases) which reduce the toxicity of the xenobiotics and facilitate their excretion. Many xenobiotics, however, are resistant to metabolic degradation, are accumulated in the body and can be extremely toxic.

Most organic chemicals must enter the body before they can exert their toxic effect(s). Uptake can occur through the food chain or by direct uptake from the environment across the respiratory surface and skin. The uptake of xenobiotics from water by fish is determined by numerous factors, the most important of which are the transfer capacity of the gills and the physio-chemical properties of the compound.

Exchange at the gills

In adult fish, the gills comprise the major surface area of the body, and constitute a thin but continuous barrier between the environment and the blood. Water flows over the gills counter to blood flow ensuring a constant partial pressure gradient of O2 and CO2 over the duration of blood transit through the gills. Conditions for diffusion of O2 are further maximized by the presence of haemoglobin which binds molecular oxygen keeping the PO2 in the blood low. The gills in fish are hyperventilated with water relative to blood to ensure adequate rates of oxygen uptake from the environment.