Risk assessment reference concentration

The oral reference dose (RfD) for trichloroethylene is currently imder review by an EPA workgroup (IRIS 1996). No inhalation reference concentration (RfC) has been derived (IRIS 1996). The National Center for Environmental Assessment, EPA has begun an effort to reassess the health risks associated with trichloroethylene. 

The outputs provided by the model can be used to perform a risk assessment if they are compared with reference limit values and literature data in order to determine whether the situation is risky or not. The values obtained by USEtox and used for the characterization of the risk in China are presented in the following tables. Table 4 presents the values for the concentration into the environmental compartments of the concerning additives (Pb and DeBDE). 

In order to assess the risk for the population living in Guiyu, the daily intake was compared with the oral reference value for DeBDE. According to EPA (US EPA [30]), the DeBDE daily oral reference and oral slope factor are 7.0E-03 mg (kg day)-1 and 7.0 x 10-4 mg-1 kg day. Inhalatory reference concentration and inhalatory unit risk have not been established. 

It is interesting to mention that USEtox is mainly a tool for LCIA studies where characterization factors are obtained for a wide list of substances. However, the model also provides intermediate output parameters (e.g., intake doses, concentrations in environmental compartments, substance exposure) that can be used for risk assessment studies. This was the case in the present study comparing the values from USEtox with reference limit values. 

At present, the calculation and mapping of critical loads for heavy metals is only at the beginning and in Europe there are only a few examples of application of methods described in Section 3.2. We will refer to case studies from Germany and Russia as the most characteristic research in this direction. The typical endpoints in these calculations refer to critical concentrations of different heavy metals in the ecosystems. The determination of the given critical concentrations is still uncertain and the relevant risk assessment calculated as an exceedance of critical loads should be based on selecting values of critical concentrations (see 3.2.2). 

US-EPA. 2002. A review of the reference dose and reference concentration processes. EPA/630/P-02/002F, December 2002, Final Report. Washington, DC Risk Assessment Forum, U.S. Environmental Protection Agency. http jjwww.epa.gov/rris/RFD FINAL[ 1 ]. pdf... 

The approaches described previously can be used to relate biomonitoring results to a reference population or to workplace exposures, but they do not evaluate the risk associated with the amount of a chemical found in the body. To do that, one needs to develop a relationship between biomarker concentration and toxic response, a relationship that is not commonly derived in standard toxicologic practice. The following sections outline methods for deriving such a relationship. The approaches include the ideal case of existing risk assessments based on biomarker-response relationships established in epidemiologic research. Lead and mercury are used as examples of cases in which exposure was quantified according to hair or blood biomarkers and dose-response associations were developed on this basis. 

Geographic Information System (GIS) A system that allows for the interrelation of quality data (as well as other information) from a diversity of sources based on multilayered geographical information-processing techniques, hazard (toxic) The set of inherent properties of a stressor or mixture of stressors that makes it capable of causing adverse effects in humans or the environment when a particular intensity of exposure occurs. See also risk, hazard assessment (HA) Comparison of the intrinsic ability to cause harm with expected environmental concentration. In Europe, it is typically a comparison of predicted environmental concentration (PEC) with predicted no-effect concentration (PNEC). It is normally based on a single value for effects and exposure. It is sometimes incorrectly referred to as risk assessment. 

Figure 5.4 Flowchart showing various human risk assessment options for a chemical mixture based on whole mixture data. RfD = reference dose RfC = reference concentration.

Hazard assessment Comparison of the intrinsic ability to cause harm with expected environmental concentration. In Europe it is typically a comparison of PEC with PNEC. It is sometimes loosely referred to as risk assessment. 

To ensure that chemical contamination is rednced to safe concentrations at stockpile and NSCM sites before they are used for residential, occupational, or wildlife purposes, the U.S. Army requested that health-based exposure limits for GA, GB, GD, VX, sulfur mustard, and lewisite be developed to protect the pnblic and the environment. Oak Ridge National Laboratory (ORNL) was asked to conduct the health risk assessments and propose chronic oral reference doses (RfDs) and, where... 

Interspecies and intraspecies UFs have been used in the development of safe or threshold exposure levels for chronic, noncancer toxicity by health organizations throughout the world. Examples include the acceptable daily intake (ADI) (Lu 1988 Truhaut 1991 Lu and Sielken 1991), the tolerable daily intake (TDI) or tolerable concentration (TC) (Meek et al. 1994 IPCS 1994), the minimal risk level (MRL) (Pohl and Abadin 1995), the reference dose (RfD) (Barnes and Dourson 1988 Dourson 1996), and the reference concentration (RfC) (EPA 1994 Jarabek et al. 1990). The importance of using distribution-based analyses to assess the degree of variability and uncertainty in risk assessments has been emphasized in recent trends in risk analysis. This will enable risk managers to make more informed decisions and... 

For MTBE, ERA has not formally established health effects and reference dose. A preliminary estimate of the threshold reference concentration was developed for this risk assessment. Estimated concentrations for the MEI location were 10-15% of the reference concentration. No further evaluation was done for MTBE. 

See also Benchmark Dose Exposure Assessment Exposure Criteria Hazard Identification Hormesis, LD50/ LC50 (Lethai Dosage 50/Lethai Concentration 50) Levels of Effect in Toxicoiogicai Assessment Maximum Allowable Concentration (MAC) Maximum Tolerated Dose (MTD) Pharmacokinetics/Toxicokinetics Reference Concentration (RfC) Reference Dose (RfD) Risk Assessment, Ecological Risk Assessment, Human Health Risk Characterization Toxicity, Acute. 

See also Reference Concentration (RfC) Risk Assessment, Human Heaith Uncertainty Factors. 

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