Exposure concentration distributions

The likely range of the intersex indicator (ISI) for L. littorea was also calculated based on the dose-response relationship for L. littorea as published by Oehlmann (2002) and the spatial distribution of water concentrations. The range of possible ISI values from the 5 and 95 percentile of the exposure concentration distributions were calculated applying Formula 1. 

Dedicated exposure concentration distributions were derived for all areas and locations (open waters and harbours), representing the spatial distribution of water concentrations for each area. In Table 2 the 5 and 95 percentile of the distribution represent the range of water concentrations for each area. 

To check the correspondence between the maximum ISI levels that can be expected in a harbour and the ecological risk, PAF values have been plotted against the calculated ISI value corresponding to the 95 percentile of the exposure concentration distribution (Figure 3). The 95 percentile was chosen because this value corresponds to the most polluted part of the harbour or water body corresponding to a maximum ISI value that might be encountered during... 

Besides meeting its assumptions, other problems in the application of SSD in risk assessment to extrapolate from the population level to the community level also exist. First, when use is made of databases (such as ECOTOX USEPA 2001) from which it is difficult to check the validity of the data, one does not know what is modeled. In practice, a combination of differences between laboratories, between endpoints, between test durations, between test conditions, between genotypes, between phenotypes, and eventually between species is modeled. Another issue is the ambiguous integration of SSD with exposure distribution to calculate risk (Verdonck et al. 2003). They showed that, in order to be able to set threshold levels using probabilistic risk assessment and interpret the risk associated with a given exposure concentration distribution and SSD, the spatial and temporal interpretations of the exposure concentration distribution must be known. 

From these data, aquatic fate models construct outputs delineating exposure, fate, and persistence of the compound. In general, exposure can be determined as a time-course of chemical concentrations, as ultimate (steady-state) concentration distributions, or as statistical summaries of computed time-series. Fate of chemicals may mean either the distribution of the chemical among subsystems (e.g., fraction captured by benthic sediments), or a fractionation among transformation processes. The latter data can be used in sensitivity analyses to determine relative needs for accuracy and precision in chemical measurements. Persistence of the compound can be estimated from the time constants of the response of the system to chemical loadings. 

Antibodies to hydroxymethyl uracil, an oxdized DNA base, were determined in workers exposed to nickel and cadmium, and in welders (Frenkel et al. 1994). Compared to controls, a significant increase in these antibodies was noted in the most highly exposed workers. Personal monitoring of 12 workers exposed to nickel and cadmium showed correlation coefficients between exposure concentrations and the antibodies of 0.4699 for cadmium and 0.7225 for nickel. Antibodies to hydroxymethyl uracil were not increased among welders. The levels of antibodies in the control populations for the nickel cadmium workers and for the welders were different indicating the importance of determining the distribution of a new biomarker in controls for each population that is studied. This preliminary study suggests that antibodies to oxidized DNA products may be useful biomarkers for nickel and other metals that induce oxidative stress. 

Trichloroethane inhaled by animals distributes primarily into fat, liver and, to a lesser extent, kidney and brain, and is rapidly cleared after cessation of exposure (Holmberg etal., 9Tl-, Savolainen etal., 911-, Schumann etal., 1982a Takahara, 1986). A linear relationship between exposure concentration and tissue concentration was found (Holmberg et al., 1977). 

Laws regulating toxic substances in various countries are designed to assess and control risk of chemicals to man and his environment. Science can contribute in two areas to this assessment firstly in the area of toxicology and secondly in the area of chemical exposure. The available concentration ( environmental exposure concentration ) depends on the fate of chemical compounds in the environment and thus their distribution and reaction behaviour in the environment. One very important contribution of Environmental Chemistry to... 

It may be possible to use Geographic Information Systems (GIS) to map biomonitoring results to determine whether there is a spatial pattern in exposure concentrations. This could be overlaid with GIS maps of environmental data (for example, air or water pollution or distribution of waste sites) to determine whether biomonitoring results correspond to specific environmental sources. However, mapping techniques are generally not useful for sporadic, localized sources such as food or consumer products. In such cases, survey questionnaires and sampling of the home environment are of more direct use in understanding exposure sources. 

Tier 2 PRA process involved developing environmental exposure data and chronic toxicity data distributions for individual POPs. The mean concentrations of POPs in local marine water measured at various locations were used as exposure data in the construction of the exposure distribution. The chronic toxicity data distribution was established based on published international acute toxicity data (LC50, EC50) on a variety of aquatic organisms tested in many jurisdictions, drawn primarily from the USEPA ECOTOX database (2002) (available at http //www.epa.gov/ ecotox). If the upper 5th centile of the measured chemical exposure data distribution did not exceed the lower 5th centile of its estimated chronic toxicity distribution, the potential ecological risk posed by the chemical was judged to be tolerable (Hall and Giddings, 2000). 

SimpleBox was created as a research tool in environmental risk assessment. Simple-Box (Brandes et al. 1996) is implemented in the regulatory European Union System for the Evaluation of Substances (EUSES) models (Vermeire et al. 1997) that are used for risk assessment of new and existing chemicals. Dedicated SimpleBox 1.0 applications have been used for integrating environmental quality criteria for air, water, and soil in The Netherlands. Spreadsheet versions of SimpleBox 2.0 are used for multi-media chemical fate modeling by scientists at universities and research institutes in various countries. SimpleBox models exposure concentrations in the environmental media. In addition to exposure concentrations, SimpleBox provides output at the level of toxic pressure on ecosystems by calculating potentially affected fractions (PAF) on the basis of species sensitivity distribution (SSD) calculus (see Chapter 4). 

The toxic pressure of each of the compounds in a mixture is calculated using the species sensitivity distribution (SSD) concept. In this concept, laboratory toxicity data for various species are collected from a database, for example, the USEPA s Ecotox database (USEPA 2005) or the RIVM e-toxBase (Wintersen et al. 2004), and compiled for each compound. A statistical distribution of these data, called the SSD, is derived. Each SSD describes the relationship between exposure concentration (X) and toxic pressure (Y), whereby the latter is expressed as the probably affected fraction (PAF, %) per compound (Posthuma et al. 2002). Depending on the test endpoint chosen for deriving SSDs, there is the option to derive chronic and acute toxic pressures, based on SSDN0ECs and SSDEC50s, respectively. 

Fig. 6.5 Simplified scatter plot between the average exposure of BADGE with the sampled values used for the mean of the beverage concentration distribution (Holmes et al. 2005).

In animals, uranium that has been absorbed from the lungs leaves the blood very quickly for distribution to body tissues. The insoluble compounds (uranium tetrafluoride, uranium dioxide) were found to accumulate in the lungs and lymph nodes with the amount retained dependent on the exposure concentration and duration. In a continuous exposure study, more than 90% of the uranium retained at the end of the first year of exposure to a uranium dioxide aerosol was cleared by the end of the second year despite continued inhalation of uranyl nitrate. All of the uranium retained following one year of inhalation of uranyl hexafluoride was cleared by the end of the second year. For uranyl nitrate inhalation, no retention was found in the soft tissues. Uranium has also been shown to accumulate in the tracheobronchial lymph nodes, lungs, bones, and kidneys of rats, dogs, and monkeys exposed to uranium... 

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