Xenobiotics in fish

Kleinow, K.M. Melancon, M.J. Lech, J.J., Biotransformation and induction Implications for toxicity, bioaccumulation, and monitoring of environmental xenobiotics in fish Environ. Health Perspect. 1987, 71, 105-119. 

It should be noted that the BCF can also be determined solely from the uptake curve of the chemical in the organisms. The method and equations for calculating the BCF values in this way were recently published by Wang et al. [23]. An important paper on different compartment models and the mathematical descriptions of uptake, elimination and bioconcentration of xenobiotics in fish and other aquatic gill-breathing organisms was given by Butte [24]. 

Law F, A PBPK model for predicting the withdrawal period of oxytetracycline in cultured Chinook salmon, in Smith DJ, Gingerich WH, Beconi-Barker MG, eds., Xenobiotics in Fish, Kluwer Academic, New York, 1999, pp. 105-121. 

Measurement of contaminants in fish has concentrated on muscle tissue since the aim has generally been to protect the health of the consumer rather than that of the fish. Endocrine tissue such as the gonads has been much more rarely examined, while data for adrenal, thyroid and pituitary levels are virtually non-existent. More data are available for the liver, as a lipid rich tissue and the major site of xenobiotic catabolism, but the concentrations have rarely been related to its capacity to produce vitellogenin or metabolise endogenous hormones. Tissue concentrations of a wide range of chemicals, are at a level which suggests that, either alone or in combination, they will cause significant endocrine disruption in fish in many polluted habitats. 

Egaas, E., J.U. Skaare, N.O. Svendsen, M. Sandvik, J.G. Falls, W.C. Dautennan, T.K. Collier, and J. Netland. 1993. A comparative study of effects of atrazine on xenobiotic metabolizing enzymes in fish and insect, and of the in vitro phase II atrazine metabolism in some fish, insects, mammals and one plant species. Comp. Biochem. Physiol. 106C 141-149. 

Keizer, J., G. D Agostino, and L. Vittozzi. 1991. The importance of biotransformation in the toxicity of xenobiotics to fish. I. Toxicity and bioaccumulation of diazinon in guppy (Poecilia reticulata) and zebra fish (Brachydanio rerio). Aquat. Toxicol. 21 239-254. 

Britvic, S., D. Lucic, and B. Kurelec. 1993. Bile fluorescence and some early biological effects in fish as indicators of pollution by xenobiotics. Environ. Toxicol. Chem. 12 765-773. 

As observed in mammalian models, the immune system of fishes is a sensitive target organ system to evaluate toxicity. For a more thorough review of environmental immunotoxicology in fishes, with reference to specific classes of xenobiotics, readers are referred to several reviews that deal with the subject over a span of nearly three decades [45-47, 54-57], While fish in the environment may be exposed to a variety of xenobiotics, the most frequently investigated xenobiotics are the polycyclic aromatic hydrocarbons (PAHs) and halogenated aromatic hydrocarbons (HAHs) due to the presence and activation of the aryl hydrocarbon receptor (AhR) in fish, and heavy metals due to their ubiquitous environmental distribution. 

Many investigations of relevant enzymes in transformation of xenobiotics by aquatic species have shown that the similar enzymes observed in metabolism in soil, plant, and mammals play a role, such as esterases and oxidases [10, 159, 160]. Metabolism of pyrethroids has been most extensively studied in fish for cypermethrin (5) and permethrin (15). Aromatic hydroxylation at the 4 -position of the 3-phenoxybenzyl moiety followed by conjugation with glucuronic acid... 

The measurement of the ethoxyresorufin-O-deethylase (EROD) activity is another sensitive parameter to detect the effects of paper mill industrial effluents on living organisms in the receiving waters. The EROD activity is a measure of the activity of the cytochrome P-450 enzyme system, which plays a central role in the transformation and elimination of xenobiotics. Increased EROD activity has been shown as far as 40 km from pulp mills, and EROD induction in fish caused by pulp mill effluents remains after biological treatment [60]. It is specified that EROD activity and erythrocytic nuclear abnormalities are induced by abietic and dehydroabietic acid [60]. 

Butte, W. (1991) Mathematical Description of Uptake, Accumulation and Elimination of Xenobiotics in a Fish/Water System, In Bioaccumulation in Aquatic Systems Contributions to the Assessment (eds. Nagel, R. and Loskill, R.), VCH, Weinheim. 

Despite all the problems attendant on studies of aquatic animals, however, great strides have been made in the past 10 years in defining biochemical pathways used by fishes to biotransform and eliminate xenobiotics (2, 3, 4, 5). Many of the earlier studies, especially the extensive work of DeWaide (6), defined various biochemical transformations which xenobiotics may undergo in vitro. Only in the past 10 years have in vivo studies been undertaken to define the routes and rates of elimination of xenobiotics by fishes (7, 8, 9, 10, ll). 

Chambers, J. E., Yarbrough, J. D. Xenobiotic biotransformation systems in fishes. Comp. Bioahem. Physiol. (1976)... 

Our questions broadened to consider how the transport and metabolic capabilities of these aquatic species compare with those of mammalian species. One reason for asking such a question is to assess whether the presence or absence of these capabilities alters the ability of fish to survive in toxic environments. Survival mechanisms fall into two catagories - behavioral and physiologic. An example of a behavioral mechanism could be as simple as a fish avoiding that area of a stream which contains toxic quantitites of phenol. When external perturbations caused by pollutants are small, homeostatic mechanisms such as those of the liver and kidney, allow fish to adapt to the body of water in which they exist. The problem then is related to defining the limits to which homeostatic phenomena can be stressed in aquatic species. An important reason to establish such information in fish is that bodies of water are the "ultimate sink" for a number of pollutants (12). Thus, while a behavioral response such as removing itself from a toxic environment is invariably available to a mammalian species, this type of response is impossible for a fish if a toxic xenobiotic occurs uniformly throughout an entire body of water. 

What are some of the general modes by which terrestrial animals can diminish toxic effects of xenobiotics and how do these compare in fish ... 

Routes of entry - fish and mammals share two potential routes of entry, namely oral and percutaneous. Mammals also absorb xenobiotics via the lungs while gill absorption is possible in fish. 

Metabolism - a final factor in need of comparative studies is the metabolism of xenobiotics. One obvious difference between mammalian and fish species is that their bodies usually function at temperatures at least 10°C different. This fact undoubtedly explains some differences in metabolic rate but even when in vitro incubations are run at optimal temperatures there is a 10 - 100 fold higher rate of mammalian vs. fish metabolism (14, 15). In other words, the level of the xenobiotic-metabolizing capacity, especially for oxidative pathways, of the poikilothermic animals is considerably lower than that of the homeothermic species. Elsewhere in this volume Dr. Bend has focused on this aspect of the handling of xenobiotics by fish (16). 

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