Fish toxicity Subject

The biological test result reflects a systematic error. This can be a difference between a nominal and an actual test concentration as a result of loss of the chemical through volatilization during the test. Fish toxicity test results performed on volatile chemicals are subject to this type of problem. 

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. 

This chapter presents a summary of the available information regarding the toxicity of surfactants in the aquatic environment and also the new data with special emphasis on the marine environment, the use of microalgae and early life-stages of fish in toxicity assays. In the last few years, one aspect related to the impact of biodegradation products of surfactants in the environment has acquired a significant relevance—the estrogenic effect—and this subject is treated in depth in Chapter 7.3 of this book. 

The particular form of mercury that accumulates in fish or shellfish, methylmercury, has been the subject of extensive investigations in recent years, and results from these studies tell us much about the potential some chemicals have for interfering with the highly sensitive processes that are at work to build the nervous system during the developmental period of life. We shall come back to this subject later, when the subject of developmental toxicity is covered. 

York and New England are devoid of fish due to the effects of acid rain. Indirect effects of the low pH values associated with acid rain also affect organisms. As noted in Table 13.1, one of the properties of an acid is the ability to dissolve certain metals. This has a profound effect on soil subjected to acid rain. Acid rain can mobilize metal ions such as aluminum, iron, and manganese in the basin surrounding a lake. This not only depletes the soil of these cations disrupting nutrient uptake in plants, but also introduces toxic metals into the aquatic system. 

Bromate has been classified as a human carcinogen by both the I/VRC (International Agency for the Research on Cancer) and the USEPA (United States Environmental Protection Agency) and is known to be toxic to fish and other aquatic life [11, 12]. Bromate could be produced in aquatic systems upon the oxidation of aqueous bromide. Controlled ozonation has been considered as an effective disinfectant tool in aquatic systems [13] but when sea water is subjected to ozonation, oxy-bromide ozonation by-products (OBP) are produced and these are important both in terms of their disinfection ability and also in relation to their potential toxicity. When seawater is oxidized, aqueous bromide (Br-) is initially converted to hypobro-mite (OBr ) which can then either be reduced back to bromide or oxidized further to bromate (Br03-) which is known to be toxic to fish and other aquatic life and classified as a human carcinogen. There has been thus a considerable interest in bromate analysis so that trace analysis of bromate in water has received considerable attention in recent years. 

The retinoid toxicology of fish is a new subject, with only a decade s worth of research. The reduction of retinoid stores with toxicant exposure has been well documented however, the mechanism of this reduction and the implications on RA and fish physiology and health have not been determined. This is partially due to the lack of technology that would allow the easy measurement of RA in fish tissues (required in some remarkably small tissue samples compared to mammals ). It is very important for future studies to establish whether reductions of stored retinoids alter RA levels and whether changes in RA are responsible for the effects of a toxicant observed in fish. However, this may be a challenge in that long-term studies (months to years) may be required to induce retinoid deficiency in fish. 

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