Risk assessment surface area

Almost all common metals and structural steels are liable to corrode in seawater. Regulations have to be followed in the proper choice of materials [16], In addition, there is a greater risk of corrosion in mixed constructions consisting of different metals on account of the good conductivity of seawater. The electrochemical series in seawater (see Table 2-4), the surface area rule [Eq. (2-44)] and the geometrical arrangement of the structural components serve to assess the possibility of bimetallic corrosion (see Section 2.2.4.2 and Ref. 17). Moreover the polarization resistances have considerable influence [see Eq. (2-43)]. The standards on bimetallic corrosion provide a survey [16,17]. 

The effects of size surface area, shape, purity method of synthesis, charge, surface coating, functionalized groups, and aggregation need to be carefully considered when assessing potential risks of CNT toxicity. Toxicology studies on CNTs should be accompanied by improved control in manufacturing and improved analysis before CNTs can be successfully used for pharmaceutical applications. 

And there are significant questions (as yet unanswered) regarding methods for assessing risks. Perhaps, for example, traditional notions of dose-response relationships are inapplicable when the particle size, or perhaps the surface area (huge relative to mass) is the real risk determinant. There is much to be done, and those promoting these exciting new products should no doubt be equally determined to promote the development of the information needed for reliably assessing their health and environmental risks. 

Gronlund (1992) has investigated methods used for quantitative risk assessment of non-genotoxic substances, with special regard to the selection of assessment factors. Gronlund found that humans, in most cases, seem to be more sensitive to the toxic effects of chemicals than experimental animals, and that the traditional 10-fold factor for interspecies differences apparently is too small in order to cover the real variation. It was also noted that a general interspecies factor to cover all types of chemicals and all types of experimental animals cannot be expected. It was concluded that a 10-fold factor for interspecies variability probably protects a majority, but not all of the population, provided that the dose correction for differences in body size between experimental animals and humans is performed by the body surface area approach (Section 5.3.2.2). If the dose correction is based on the body weight approach (Section 5.3.2.1), the 10-fold factor was considered to be too small in most cases. 

The National Research Council (NRC) published a report, Science and Judgment in Risk Assessment, that critiqued the current approaches to characterizing human cancer risks from exposure to chemicals. One issue raised in the report relates to the use of default options for assessing of cancer risks. These general guidelines can be used for risk assessment when specific information about a chemical is absent. Research on 1,3-butadiene indicates that two default options may no longer be tenable Humans are as sensitive as the most sensitive animal species and the rate of metabolism is a function of body surface area rather than inherent species differences in metabolic capacity. 

Like HD, the subject of PD adequacy has received considerable attention. The K/DOQI recommends the use of two criteria to assess the dose of dialysis delivered during PD total weekly ff/Purea and total weekly CLj (in liters per week) normalized to 1.73 m body surface area. Although K/DOQI recommends target values for these adequacy indices, which are discussed below, the optimal dose of PD remains undefined, and the lower threshold of dialysis dose that constitutes an acceptable risk for patient outcome has been termed adequate dialysis. ... 

Hoffman and Hammonds 1994). In addition, standard data distributions have been proposed for a variety of exposure variables, such as age-specific distributions for soil ingestion rates, inhalation rates, body weights, skin surface area, tap water and fish consumption, residential occupancy and occupational tenure, and soil-on-skin adherence (Finley et al. 1994). It should also be pointed out that these techniques can be combined with other advanced risk assessment methods (i.e., PBPK modeling) to further reduce uncertainty in exposure estimates (Cronin et al. 1995 Simon 1997 Nestorov 1999, 2003). 

The development of an ADI is essentially the same in the NAS procedures, the EPA Food Tolerance procedures, and the NACA proposal for groundwater. An ADI is determined by dividing the NOEL in the most sensitive species by a suitable Safety Factor (SF). Safety Factors for subchronic or repeat administration are usually 1,000 for chronic or lifetime studies, 100 is used. Species conversions can be based upon mg/kg, ppm in the food, or body surface area conversion [29]. Currently, non-oncogenic effects are considered on an mg/kg basis without attempts to correct for species differences. Risk assessment procedures for oncogenic risk employed by the EPA are based upon surface area extrapolations in an attempt to relate to man [30]. 

In summary, the CDC assessment proposed a site-specific recommendation, not a universal standard for clean-up. CDC s analysis assumed a uniform contamination of the entire soil surface in residential neighborhoods, a situation not known to exist in Missouri or elsewhere in the United States. Further, the CDC 1 ppb guideline and risk assessment methodology were intended for application only to residential sites -not to industrial sites or other areas where the exposure to children would not occur. The present assessment indicates that, depending on the site characteristics and the use patterns, a soil concentration of TCDD considerably in excess of 1 ppb is acceptable for residential areas. Soil concentrations greater than 100 ppb in non-residential areas should amply protect the environment and public health. 

Nanoproducts can be used at exceedingly low volumes. This mitigates potential risk to some extent. Their small size and extremely high surface area leads to exposures and interactions not previously examined. Risk assessment is driven by data and, for technical and economic reasons, it may be impractical to conduct many common types of animal toxicity tests. 

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