Indicator species population effects

The relationship between biomarker responses and effects at the population level can be tested in both field experiments and more controlled experiments in mesocosms. It may be possible to define thresholds for biomarker assays performed on indicator species, above which population effects have been shown to occur. Indicator species may be either free living or deployed. The advantage of the latter is... 

Apart from the use of this approach to study the ecotoxicology of neurotoxic pollutants in the field, it also has potential for use during the course of environmental risk assessment. An understanding of the relationship between biomarker responses to neurotoxic compounds and effects at the population level can be gained from both field studies and the use of mesocosms and other model systems. From these it may be possible to define critical thresholds in biomarker responses of indicator species above which population effects begin to appear. In the longer term, this approach... 

A very cogent example is provided by the pair of ions Fe(CN) and Fe(CN) . The formal oxidation states or the iron atom are obviously +3 and +2, respectively, but detailed studies of Mossbauer and esr spectra, coupled with an MO treatment of the bonding,1 indicate that the effective charge residing on the metal atom is practically the same in the two cases. In other words, the conventional practice of attributing the difference of one in the electron populations of the two species to the metal atoms is not... 

These comments deal with environmental levels likely to produce toxic responses at the indicated species level. The focus has been on the probability of risk groups undergoing ecotoxic responses, mainly for comparative purposes. We do not deal with complex effects that may be expressed at low lead exposures in systems and populations, or interplays between relatively larger groupings that occur or may occur because certain populations are reduced, directly or indirectly, by changes in environmental compartment levels of lead. Lead readily accumulates in sediments so that there may be different sedimentary populations that relate to that lead accumulation more detrimentally than others. This topic of subtle, large-scale ecotoxic effects as an aspect of concern largely unknown in the lead literature is presented in WHO s 1989 report on the ecotoxicity of lead (WHO, 1989) and sections of the current EPA Pb criteria document (U.S. EPA, 2006). 

Dose—response relationships are useful for many purposes in particular, the following if a positive dose—response relationship exists, then this is good evidence that exposure to the material under test is causally related to the response the quantitative information obtained gives an indication of the spread of sensitivity of the population at risk, and hence influences ha2ard evaluation the data may allow assessments of no effects and minimum effects doses, and hence may be valuable in assessing ha2ard and by appropriate considerations of the dose—response data, it is possible to make quantitative comparisons and contrasts between materials or between species. 

In risk characterization, step four, the human exposure situation is compared to the toxicity data from animal studies, and often a safety -margin approach is utilized. The safety margin is based on a knowledge of uncertainties and individual variation in sensitivity of animals and humans to the effects of chemical compounds. Usually one assumes that humans are more sensitive than experimental animals to the effects of chemicals. For this reason, a safety margin is often used. This margin contains two factors, differences in biotransformation within a species (human), usually 10, and differences in the sensitivity between species (e.g., rat vs. human), usually also 10. The safety factor which takes into consideration interindividual differences within the human population predominately indicates differences in biotransformation, but sensitivity to effects of chemicals is also taken into consideration (e.g., safety faaor of 4 for biotransformation and 2.5 for sensitivity 4 x 2.5 = 10). For example, if the lowest dose that does not cause any toxicity to rodents, rats, or mice, i.e., the no-ob-servable-adverse-effect level (NOAEL) is 100 mg/kg, this dose is divided by the safety factor of 100. The safe dose level for humans would be then 1 mg/kg. Occasionally, a NOAEL is not found, and one has to use the lowest-observable-adverse-effect level (LOAEL) in safety assessment. In this situation, often an additional un-... 

A risk estimate indicates Uie likelihood of occurrence of the different types of health or enviroinnental effects in exposed populations. Risk assessment should include both liuimn health and environmental evaluations (i.c., impacts on ecosystems). Ecological impacts include actual or potential effects on plants and animals (other than domesticated species). The number produced from the risk characleriznlion, representing the probability of adi crse... 

More controversially, endocrine disruption as a consequence of exposure to the herbicide atrazine (2-chloro-4-ethylamine-6-isopropylamine-s-triazine), one of the most widely used herbicides in the world, has also been hypothesized to explain various adverse biological effects in frog populations in the United States. Exposure to atrazine in the laboratory at high concentrations, far exceeding those found in the natural environment, has been reported to induce external deformities in the anuran species Rana pipiens, Rana sylvatica, and Bufo americanus (Allran and Karasov 2001). Studies by Hayes et al. have suggested that atrazine can induce hermaphroditism in amphibians at environmentally relevant concentrations (Hayes et al. 2002 Hayes et al. 2003). Laboratory studies with atrazine also indicated the herbicide... 

Data for lead effects on mammalian wildlife are scarce. Shore (1995) indicates that lead residues in soils could successfully predict lead concentrations in kidneys and livers of wood mice and field voles however, this could not be demonstrated for shrews. In view of the large interspecies differences in lead responses reported for domestic livestock and laboratory populations of small animals (Table 4.9), more research is needed to determine if lead criteria for these groups are applicable to sensitive species of mammalian wildlife. 

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