Estimated environmental concentration

Neely, W. B. Mackay, D. "An Evaluative Model for Estimating Environmental Concentrations", in "Modelling the Fate of Chemicals in the Aquatic Environment", editors, Dickson, K.L. Maki, A. W. and Cairns, J., Jr., Ann Arbor Science, Ann Arbor 1982, 127-143. 

Estimating environmental concentrations of chemicals using fate and exposure models. Brussels, European Centre for Ecotoxicology and Toxicology of Chemicals (Technical Report No. 50). 

The risk quotient (RQ) for each combination of contaminant and receptor (plant or animal) of concern is calculated by dividing the estimated environmental concentration (EEC) by the toxicity reference value (TRY) ... 

The methodology of SSD has been used for derivation of environmental quality criteria and for ecological risk assessment. In this chapter, the ecosystem was assumed to be preserved when 95% of species are protected [39], and in this screening-level risk assessment, if the actual or estimated environmental concentration of SCCPs is larger than the HC5 which will protect 95% of species based on the SSD, it is interpreted that it should be assessed further. Risk characterization for birds, the higher predators is also performed because of the high bioconcentration of SCCPs in fish. 

Figure 9.2 Quantification of risk for environmental contaminants using probability density functions. The probability of impacts corresponds to the extent of overlap of the estimated environmental concentration (left curve) and the effective toxic concentration (right curve). The risk can be quantified from the distance between the mean values of the concentrations and the variance in the respective concentrations (due to measurement variability and/or extrapolation errors) represented by the width of the distributions. Reproduced from Nendza, Volmer and Klein (1990) with kind permission from Kluwer Academic Publishers, Dordrecht.

Relating toxicity thresholds (section 9.2) to the estimated environmental concentrations of phenol (section 9.1) makes it possible to determine the likelihood of adverse effects in the target populations, and, thus, to make an ecological risk assessment. For the example of phenol release into the River Rhine, the risk for the most sensitive species was evaluated using the quotient method and the quantitative probabilistic procedure (Table 9.6) for four different communities. 

In 1974, the Harmonized Monitoring Programme was set up by the Department of the Environment (DoE). The objective was to provide a network of sites at the lower end of catchments, where water quality data could be collected and analysed in a nationally consistent manner, allowing the loads of materials carried through river catchments into estuaries to be estimated and long-term trends in river quality to be assessed. The complete list of substances to be monitored is diverse and specifies about 115 substances. The pesticides aldrin, dieldrin, y-HCH, heptachlor, p,p -DDT and p,p -DDE are included. Figures 1 and 2 show the downward trend of y-HCH and dieldrin over the past 20 years at the Harmonized Monitoring Sites. This confirms that reductions in environmental concentrations have been achieved, particularly over the past 10 years. 

Thus, [C] X TEE = TEQ i , i , where [C] = environmental concentration of planar polychlorinated compound. The TEQ is an estimate of the concentration of TCDD that would produce the same effect as the given concentration of the dioxin-like chemical. 

This gives an example of fate modeling in which the risks of an insect growth inhibitor, CGA-72662, in aquatic environments were assessed using a combination of the SWRRB and EXAMS mathematical models.. Runoff of CGA-72662 from agricultural watersheds was estimated using the SWRRB model. The runoff data were then used to estimate the loading of CGA-72662 into the EXAMS model for aquatic environments. EXAMS was used to estimate the maximum concentrations of CGA-72662 that would occur in various compartments of the defined ponds and lakes. The maximum expected environmental concentrations of CGA-72662 in water were then compared with acute and chronic toxicity data for CGA-72662 in fish and aquatic invertebrates in order to establish a safety factor for CGA-72662 in aquatic environments. 

A variety of modeling approaches may be used to estimate pollutant concentrations in exposure media. These range from qualitative estimates extrapolated from case examples or environmental scenarios, simple analytical equilibrium or transport models, to complex multi-media models. In selecting an approach or approaches, it is important that ... 

Exposure estimation is the next logical step in an exposure assessment. In this step, the data and methods developed in the previous steps dre linked together so that the relationship between pollutant sources and human exposure can be examined. Through estimation of the degree of exposure rather than just estimation of concentrations in environmental media, a more detailed analysis of a pollution problem is possible, including ... 

On the other hand, indirect methods should be considered as an alternative when analytical measurements are not feasible. Predicting methods involve extrapolating exposure estimates from existing data, e.g., previous environmental monitoring, data about emissions and chemicals production, and questionnaires. Distribution of chemicals among the different environment compartments is also a key aspect for predicting environmental concentrations. Therefore psysicochemical properties (see Sect. 4) are required inputs in these tools. 

For environmental purposes, different approaches for predicting environmental concentrations have been used. Table 3 gives some representative examples of these studies. The input data required are usually the production or consumption of chemicals in the studied area that allow estimating their emission rates to the environment. Depending on the complexity of the scenario, different number of variables can be used to achieve the prediction. 

To make adequate environmental policies concerning a reduction of the emission of POPs, the risks resulting from the deposition of POPs should be estimated. For that purpose some models to assess the risks of POPs in terrestrial ecosystems have been created (Bakker et al., 1998). The most important step of the approaches is developing models for computation of POP concentrations in soil from the data of their load on the land surface (see section 1). Based on these results, the estimating environmental risk from POPs accumulation in the soil compartment was carried out (Vasilyeva and Shatalov, 2004). 

Jurgens et al. [33] carried out a series of laboratory experiments to study the behavior of estrogens in the aquatic environment and set up a model to estimate their likely environmental concentrations in the water column and bed-sediments. According to this study, between 13 and 92% of the estrogens entering a river system would end up in the bed-sediment compartment with the majority of sorption occurring within the first 24 h of contact. 

The aim of the exposure assessment is to predict the concentration of the substance that is likely to be found in the environment, i.e., the predicted environmental concentration (PEC). Again it may not be possible to establish a PEC, and a qualitative estimation of exposure has to suffice. 

Test methods that analyze individual compounds (e.g., benzene-toluene-ethylbenzene-xylene mixtures and PAHs) are generally applied to detect the presence of an additive or to provide concentration data needed to estimate environmental and health risks that are associated with individual compounds. Common constituent measurement techniques include gas chromatography with second-column confirmation, gas chromatography with multiple selective detectors, and gas chromatography with mass spectrometry detection (GC/MS) (EPA 8240). 

On the basis of the foregoing discussion, it appears that, if traditional criteria for hazard evaluation are applied to the toxicologic data on experimental animals, there is little room for complacency r arding current ambient concentrations of ozone. Functional, biochemical, and structural effects in both pulmonary and extrapulmonary sterns have been reported by numerous investigators at or near concentrations that are at least occasionally achieved in some polluted urban centers. Unfortunately, there are no adequate methods for extrapolating data to obtain reliable quantitative estimates of population risk at environmental concentrations near the standard, and there is no assurance that the risk is zero. 

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