Trophic-level specificity

Of the 188 studies reported in Tables 1, 2 and 3, more than half (n = 101) were conducted with two or more tests representing at least two biotic levels (i.e., test battery approach or TBA), as opposed to those performed with a single biotic level (n = 87). While test and biotic level selection may be based on a variety of reasons and study objectives (e.g., practicality, cost, personnel availability), preference for TBAs can also be influenced by the need to assess hazard at different levels so as not to underestimate toxicity. Indeed, contaminants can demonstrate trophic-level specificity (e.g., phytototoxic effects of herbicides) or they can exert adverse effects at multiple levels (e.g., particular sensitivity of cladocerans toward heavy metals in contrast to bacteria). When TBAs are used, they are mostly conducted with two, three or four trophic levels (Tab. 4). 

The bulk hydrogen isotopic composition of amino acids has been shown to depend on animal trophic level (Birchall et al. 2005). Furthermore, compound-specific hydrogen isotopic analyses of amino acids may help elucidate the mechanism behind this enrichment, by determining the differences in 8D value between essential and non-essential amino acids, and may also provide a further palaeodietary indicator (e.g. Corr et al. 2005). However, amino acids are highly functional, with both amino and carboxyl extremely... 

Viruses Shunt that prevents transfer of organic carbon and nutrients to higher trophic levels Infects prokaryotes and eukaryotes sometimes very specific to host. Thought to be responsible for lateral gene transfer... 

The ethylene-insensitive plants also showed reduced defense protein synthesis and were susceptible to soil pathogens to which they were normally fully resistant. In connection with the third trophic level, Kahl et al. (2000) found that attack by Manduca caterpillars on wild tobacco plants causes an ethylene burst that suppressed induced nicotine production but stimulated volatile emissions. They argued that the plant chooses to employ an indirect defense (the attraction of natural enemies) rather than a direct defense to which the attacker could adapt (Kahl et al, 2000 Winz and Baldwin, 2001). This implies that the plant is capable of identifying its attacker. We discuss this possibility in more detail in the discussion of specificity. 

Several authors have shown that concentrations of total toxaphene (lipid-adjusted) increases significantly with trophic and specifically with S15N in Great Lakes food webs [5,74,138,139]. The <51SN values are known to increase by about 3.5%o from prey to predator. Thus trophic levels can be assigned... 

Radium may be transported in the atmosphere in association with particulate matter. It exists primarily as a divalent ion in water, and its concentration is usually controlled by adsorption-desorption mechanisms at solid-liquid interfaces and by the solubility of radium-containing minerals. Radium does not degrade in water other than by radioactive decay at rates that are specific to each isotope. Radium may be readily adsorbed by earth materials consequently, it is usually not a mobile constituent in the environment. It may be bioconcentrated and bioaccumulated by plants and animals, and it is transferred in food chains from lower trophic levels to humans. 

Inclusion of a test representative of the fish level of organization in future PEEP bioassay batteries is nevertheless highly advisable owing to the specific adverse effects that liquid wastes can manifest on this trophic level. To offset the constraints mentioned above, appropriate surrogates can now be found with tests conducted with fish cells. Indeed, fish cell bioassays such as those reported in this book (see Chapters 14 and 15, volume 1 of this book) offer reliable and relevant alternatives to whole organism testing that alleviate sample volume and budgetary considerations. 

Thus far, quality objectives for chemical substances are derived from the most sensitive organisms in acute and chronic toxicity test batteries that determine NOEC values for different trophic levels. The pT-method similarly determines specific sample dilution levels that are devoid of adverse effects toward (micro)organisms of a standardized test battery. Common to both approaches is the more frequent use of water-column test organisms as opposed to benthic-dwelling organism that reflect more intimate contact with sediment. This practice is primarily based on the fact that standardized bioassays capable of appraising sediment porewaters and elutriates are presently more numerous than solid-phase tests for whole-sediment assessment. As more of these latter tests become developed and standardized (see Chapters 12 and 13, volume 1 of this book on amphipod and chironomid tests), their more frequent use will contribute to a better understand of the toxic effects of sediment-bound contaminants. 

Indirect effects.—Indirect effects are those that do not require a direct interaction between the herbicide and an organism. As an example, herbicides, because they directly influence plant cover, result in modification of animal habitat (food, cover, microclimate) which, in turn, influences carrying capacity for specific wildlife species. As a result of the interrelations within food chains, direct effects on relatively minor species can be transferred indirectly to organisms at higher trophic levels. Other examples of indirect effects are those that result from the alteration of vegetation density and species composition. For instance, severe and prolonged... 

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