Effects on invertebrates

The invertebrate phyla are often neglected in ecotoxicological testing protocols. A token invertebrate species such as the copepod Daphnia may be used to evaluate the effects on extremely diverse phyla. This neglects the diversity of biochemical and physiological functions that may render different phyla vulnerable to different classes of compound at different stages of their life cycles. 

Pyrethroids show very marked selective toxicity (Table 12.2). They are highly toxic to terrestrial and aquatic arthropods and to fish, but only moderately toxic to rodents, and less toxic still to birds. The selectivity ratio between bees and rodents is 10,000- to 100,000-fold with topical application of the insecticides. They therefore appear to be environmentally safe so far as terrestrial vertebrates are concerned. There are, inevitably, concerns about their possible side effects in aquatic systems, especially on invertebrates. 

Among pharmacenticals, EE2 has been the snbject of particular recent attention becanse of its ability to canse endocrine disrnption in fish, as has been described in Chapter 15. Low levels of mixtnres of beta blockers, such as propranolol, metoprol, and nadolol have been detected in snrface waters, and there have been investigations of their possible effects on aqnatic invertebrates (Huggett et al. 2002). Veterinary medicines, too, have come nnder scrntiny for example, the dramatic effects of diclofenac on vnltnres, which will be discnssed shortly. Many questions remain to be answered abont the possible ecological effects of complex mixtures of pharmaceuticals and veterinary medicines. 

Tyramine is produced by decarboxylation of tyrosine and is present in the CNS in higher (threefold) concentrations than m-tyramine, the hydroxylated derivative of phenylethylamine. In the periphery / -tyramine is easily hydroxylated to octopamine, which has some direct effects on ai adrenoceptors, unlike tyramine which functions by releasing NA. When tested on central neurons tyramine always produces the same effects as NA but they are slower and less marked, implying an indirect action. By contrast octopamine often produces the opposite effect to NA and it is probable that octopamine may have a functional role in the invertebrate CNS where it is found in higher concentrations (5pg/g) than in the mammalian brain (0.5ng/g). Neither tyramine nor octopamine have distinct behavioural effects, unlike phenylethylamine,... 

Intracellular symbiosis is extremely widespread in invertebrates. For example, mutualistic symbioses with intracellular bacteria can be found in almost all animal phyla, including sponges, cnidaria, nematodes, anellids, mollusca and arthropoda. Buchner (1965) thoroughly reviews most information published on bacterial symbiosis in animals up to 1964. After this monumental work, various reviews on more specific subjects have been published (e.g. Baumann, 1998, and references therein) including some recent reviews on Wolbachia (O Neill et al., 1997 Werren, 1997). In most of these papers, the term symbiosis is apparently used with a broad meaning the intracellular bacterium is usually referred to as an endosymbiont even in the absence of data on effects on host fitness. Here only key points on intracellular symbiosis and Wolbachia will be summarized, so as to put the information available on symbiosis in filarial nematodes into a broader context. 

Warbrick, E., Barker, G., Rees, H. and Howells, R. (1993) The effect of invertebrate hormones and potential hormone inhibitors on the third larval moult of the filarial nematode, Dirofilaria immitis, in vitro. Parasitology 107, 459-463. 

The effects of Flix sediment pollution on invertebrates were examined at two levels. Local populations of zebra mussels and crayfish (P. clarkii) were sampled right over the Flix residue sediment, across the reservoir, in a meander immediately downstream the dam and in Asco, in addition to the Riba-roja reference site (Fig. 5a, b). Results from a battery of biochemical biomarkers (Fig. 5c) were similar... 

Copper is toxic to sensitive species of terrestrial vegetation at >40 pg/L nutrient solution (seedlings of pines, Pirns spp.), at >10 mg/kg DW leaves (cucumber, Cucumis sativus), and >60 mg extractable Cu/kg DW soil (sweet orange, Citrus sinensis Table 3.4). Among sensitive species of terrestrial invertebrates, adverse effects on survival, growth, or reproduction occur at 2 pg Cu/cm2 on paper discs (earthworms), >50 mg Cu/kg diet (larvae of gypsy moth, Lymantria dispar), and 53 to 70 mg Cu/kg DW soil (earthworms and soil nematodes Table 3.4). 

Numerous and disparate copper criteria are proposed for protecting the health of agricultural crops, aquatic life, terrestrial invertebrates, poultry, laboratory white rats, and humans (Table 3.8) however, no copper criteria are now available for protection of avian and mammalian wildlife, and this needs to be rectified. Several of the proposed criteria do not adequately protect sensitive species of plants and animals and need to be reexamined. Other research areas that merit additional effort include biomarkers of early copper stress copper interactions with interrelated trace elements in cases of deficiency and excess copper status effects on disease resistance, cancer, mutagenicity, and birth defects mechanisms of copper tolerance or acclimatization and chemical speciation of copper, including measurement of flux rates of ionic copper from metallic copper. 

Woodward, D.F., W.G. Brumbaugh, A.J. Deloney, E.E. Little, and C.E. Smith. 1994. Effects on rainbow trout fry of a metals-contaminated diet of benthic invertebrates from the Clark Fork River, Montana. Trans. Amer. Fish. Soc. 123 51-62. 

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