Human health risk estimates

Let us consider the methods used to estimate the health impacts of particulate air pollution, followed by those used to perform economic valuation of changes in illness and premature mortality, and discusses the appropriateness of transferring health benefit estimates from studies in other regions to developing countries. 

Epidemiological studies can be grouped according to how exposure is measured (acute exposure studies and chronic exposure studies) and how health effects are measured (individual-based panel or cohort studies and population-based or ecological studies). Most studies in the scientific literature have examined acute, not chronic, health consequences. 

Human Health Impacts of Chronic Exposure to Particulate Air Pollution Chronic exposure studies examine the impact of long-term exposure to PM air pollution as well as the cumulative effects of short-term elevated PM levels. These studies 

City and season Diesel Gasoline Road dust Coal Biomass Secondary sulfates Secondary nitrates Secondary ammonium Total 

Note Insufficient sample was collected in summer in Mumbai to carry out hydrocarbon speciation. 

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Accurate assessment of human health risks associated with oral exposure to metals requires knowledge of the fraction of the dose absorbed into the blood. This information is important for As-contaminated environmental media, such as soil and mine waste, because metal contaminants exist in a variety of soluble and insoluble forms and may be contained within particles of inert matrix, such as rock or slag. Physicochemical properties such as these influence the enteric absorption fraction (bioavailability) of ingested metals. Therefore, site-speciflc data on metal bioavailability in the environmental media of concern will increase the accuracy and decrease the uncertainty in human health risk estimates. 

Human health risk assessment estimates the likelihood of health problems occurring if no cleanup action were ttikcn at the site. To cstiimite the baseline risk at a site, the following four-step process should be taken to detennine Uie possible human risk which will then detennine what sort of corrective action should be employed ... 

The dangerous properties of acute toxicity, irritation, corrosivity, sensitisation, repeated-dose toxicity and CMR are evaluated in terms of their potential toxic effects to workers, consumers and man exposed indirectly via the environment, based on the use for each stage in the lifecycle of the substance from which exposure can occur. Risk assessment is also required if there are reasonable grounds for concern for potential hazardous properties, e.g., from positive in vitro mutagenicity tests or structural alerts. The risk assessment involves comparing the estimated occupational or consumer exposure levels with the exposure levels at which no adverse effects are anticipated. This may be a quantitative risk assessment, based on the ratio between the two values, or a qualitative evaluation. The principles of human health risk assessment are covered in detail by Illing (a.30) and more briefly in Chapter 7 of (73). 

The adequacy of experimental data for identifying potential human health risks and, in particular, for estimating their probable magnitude has been the subject of scientific question and debate. Laboratory animals can and do differ from humans in a number of respects that may affect responses to hazardous exposures.. . . Nevertheless, experimental evidence to date certainly suggests that there are more similarities between laboratory animals and humans than there are differences. These similarities increase the probability that results observed in a laboratory setting will predict similar results in humans. 

The TOCDF QRA estimates the risk to the public and workers from accidental releases of chemical agent associated with all activities during storage at DCD and throughout the disposal process at the TOCDF. The HRA, which was conducted by the Utah Division of Solid and Hazardous Waste (Department of Environmental Quality), is a screening analysis to estimate possible off-site human health risks associated with exposure to airborne emissions from the TOCDF under normal and upset conditions. The HRA also estimates risks to wildlife and the environment. 

Whichever method of presentation is chosen, it is critical that the numerical estimates not be separated from the various assumptions upon which they are based and their uncertainties. The dose-response characterization should contain a discussion and interpretation of the numerical estimates so that the risk manager gains significant insight into the extent to which the quantitative estimate reflects the true magnitude of potential human responses. The risk manager needs to understand that the true human health risk cannot be known with the degree of accuracy reflected in the numerical estimates. 

The human health risk assessment was conducted based on exposure estimates from two most relevant exposure pathways, namely dietary intake of POPs from food consumption and inhalation intake of airborne POPs contaminants. The potential intake of POPs from drinking water (considered to be a relatively minor exposure pathway) was not taken into account due to lack of relevant local data necessary for their estimation. 

Total intakes of OCPs from the Australian diet and environment have been estimated from the 1970s to the 1990s and used to evaluate human health risks for the Australian population. The Hazard Index (HI) was estimated for the general Australian population for the OCPs for 1996 at <1.0 in all cases. In addition, the USA-EPA model for occurrence of cancer has been applied to some of the persistent OCPs and found to be in the range of >1 x 10-6 to 4 x 10-5. The level of health risk for the general Australian population was considered to be acceptable in 1996. 

Ebert E, Price P, Keenan R. 1996. Estimating exposures to dioxin-like compounds for subsistence anglers in North American. In Human exposure, human health risk assessment, and organohalogen compounds, 16th Symposium on Chlorinated Dioxins and Related Compounds, Amsterdam Holland, volume 30, 66-69. 

In human health risk assessment, direct and indirect methods of exposure assessment are distinguished. The direct method involves measurements of exposure at the point of contact or uptake, for instance, by monitoring chemical concentrations in humans or the environments they are exposed to (food, air, water). The indirect methods use modeling and extrapolation techniques to estimate exposure levels (Fryer et al. 2006). Also in environmental exposure assessment, these 2 ways to assess exposure may be applied. 

The human health risk characterization is typically carried out by comparing the No-Observed-Adverse-Effect-Level (NOAEL) to the human exposure level. The ratio is called Margin of Safety. If human exposure is estimated to exceed the NOAEL, the substance is considered to be of concern . If the exposure estimate is less than the NOAEL, the appropriate margin of safety is assessed case-by-case (European Commission 2003a). 

Human health risk assessment has often been dominated by the use of default assumptions and worst-case analyses based on the use of upper bounds on the dose estimated from the exposure instead of distributional characterizations of the dose. There are severe limitations associated with the use of default assumptions and upper bounds instead of distributions when detailed exposme and/or dose-response data are available. The US National Academy of Sciences, the USEPA and many others have recognized the need for new risk assessment methodology (NRC, 1983, 1993, 1994 USEPA, 1992 CRARM 1997 van Hemmen and van der Jagt, 2001). This need has promoted the development of quantitative risk assessment methods that use probabilistic techniques such as Monte Carlo simulations for distributional characterizations of exposme, the... 

TERA created and manages the International Toxicity Estimates for Risk (ITER) database, a comparative database of human health risk values and cancer classifications from leading government... 

Chemical Dosimetry bv TSP LC/MS. One of our long-term objectives in studying TSP LC/MS is the development of chemical dosimetry based on direct determination of polar metabolites in biological fluids. Most toxic substance exposure scenarios (i.e., near hazardous waste sites) involve complex and variable mixtures of substances. Biological monitoring, where human fluids, tissues and excreta are analyzed, measures actual exposure, whereas analysis of soil, air or water can only provide an estimate of potential exposure. Exposure data forms the basis of human health risk assessment, and ultimately defines cleanup requirements at contaminated sites. 

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