Toxicants community effects

B. Hunter and co-workers, Coumarin Tumorigenic and Toxic Effects in Prolonged IPietary Administration, Huntingdon Research Centre, personal communication, (1984). 

ECOTOxicoLOGY The study of toxic effects of chemical and physical agents on living organisms as well as human beings, especially on populations and communities within defined ecosystems. 

Mn2+ active transport system in Staphylococcus aureus. These metal-microbe interactions result in decrease microbial growth, abnormal morphological changes, and inhibition of biochemical processes in individual (Akmal et al. 2005a,b). The toxic effects of metals can be seen on a community level as well. In response to metal toxicity, overall community numbers and diversity decrease. Soil is a living system where all biochemical activities proceed through enzymatic processes. Heavy metals have also adverse effects on enzyme activities (Fig. 1). 

Savolainen H. 1979. Toxic effects of peroral o-cresol intake on rat brain. Res Commun Chem Pathol Pharmacol 25(2) 357-364. 

The toxic effects must be seen when normal organisms or communities are exposed to the toxicant under controlled conditions, and any contributory factors should be manifested in the same way during controlled exposures. 

Compared to a number of other metals, vanadium appears to be relatively innocuous when ingested in low concentrations by animals however, it is by no means certain that this will be true for chronic exposure, as toxic effects have been reported [80], The nutrition community treats vanadium as a member of the ultra trace metals, which have a nutritional requirement of less than 1 mg/kg diet and are present in tissues in the range of micrograms per kg [81]. Although evidence suggests that vanadium is beneficial to human health, its mechanism of action remains obscure. No specific dietary recommendations have been made, in part, because there is controversy surrounding whether or not vanadium is an essential element. 

When evaluating the influence of the time of year on responses of aquatic communities to chemical stress, it is convenient to make a distinction in threshold concentrations of direct toxic effects, and in the magnitude of effects that occur above these threshold concentrations. Only a limited number of (model) ecosystem experiments are available that allow a comparison of responses due to treatment with the same chemical in the same type of test system at different periods of the year. These studies indicate that, in freshwater communities, threshold concentrations for direct toxic effects may vary little with the season (within a factor of 2). At higher exposure concentrations, however, the intensity and duration of the responses (direct and indirect effects) may vary considerably between different periods of the year (Section 6.3.2). 

Threshold concentrations for direct toxic effects of the most sensitive endpoints (community metabolism and responses of populations of primary producers) in model ecosystem experiments that studied the ecological impact of long-term exposure to the herbicide atrazine... 

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