Aquatic invertebrates plants

The major routes of uptake of xenobiotics by animals and plants are discussed in Chapter 4, Section 4.1. With animals, there is an important distinction between terrestrial species, on the one hand, and aquatic invertebrates and fish on the other. The latter readily absorb many xenobiotics directly from ambient water or sediment across permeable respiratory surfaces (e.g., gills). Some amphibia (e.g., frogs) readily absorb such compounds across permeable skin. By contrast, many aquatic vertebrates, such as whales and seabirds, absorb little by this route. In lung-breathing organisms, direct absorption from water across exposed respiratory membranes is not an important route of uptake. 

Mechanistic studies have shown that TBT and certain other forms of trialkyltin have two distinct modes of toxic action in vertebrates. On the one hand they act as inhibitors of oxidative phosphorylation in mitochondria (Aldridge and Street 1964). Inhibition is associated with repression of ATP synthesis, disturbance of ion transport across the mitochondrial membrane, and swelling of the membrane. Oxidative phosphorylation is a vital process in animals and plants, and so trialkyltin compounds act as wide-ranging biocides. Another mode of action involves the inhibition of forms of cytochrome P450, which was referred to earlier in connection with metabolism. This has been demonstrated in mammals, aquatic invertebrates and fish (Morcillo et al. 2004, Oberdorster 2002). TBTO has been shown to inhibit P450 activity in cells from various tissues of mammals, including liver, kidney, and small intestine mucosa, both in vivo and in vitro (Rosenberg and Drummond 1983, Environmental Health Criteria 116). 

Lethality Mammalian systems Aquatic vertebrates and invertebrates Plants Lethal dose5o (LD50) Lethal concentration 50 (LC50) Both LD50/LC50 values greater than a reference compound... 

Acute toxicity In vitro Mammalian systems Aquatic vertebrates and invertebrates Plants IC/EC50 in appropriate test species Use of appropriate indicators of acute toxicity, for example, EPA guidance values, reference doses, and so on... 

Chronic toxicity Mammalian systems Carcinogenicity Neurotoxicity De ve 1 opm e nta l/rep rod u cti ve toxicity Aquatic vertebrates and invertebrates Plants Mutagenicity, increased tumours Reproduction and growth Cancer slope factors Reference doses, and so on IC50, EC50... 

Food Chain Bioaccumulation. Diazinon has an estimated low bioconcentration potential (BCF=77) (Kenaga 1980) in aquatic organisms, which is generally confirmed by measured BCF values obtained from laboratory studies with fish and other aquatic invertebrates (El Arab et al. 1990 Keizer et al. 1991 Sancho et al. 1993 Tsuda et al. 1989, 1995). Further information on measured BCF values for additional edible fish and shellfish would be helpful, as would information on tissue residues of diazinon and its major degradation products in edible species. No information was found on studies associated with plant uptake, but diazinon is rarely detected above EPA tolerance limits (Hundley et al. 1988). Bioaccumulation in aquatic food chains does not appear to be important, and no further information on biomagnification is required. 

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