Prevalent Exposures

Trudel and his co-workers also observed that product-related exposure tends to be more important for PFOA than for PFOS, most likely because PFOS is no longer used in consumer products. It is, therefore, apparent that the paucity of indoor source and exposure data contributes to the significant uncertainty and differences of opinion about the most prevalent exposure routes for these compounds. 

Reviews on the occurrence, biochemical basis, and treatment of lead toxicity in children (11) and workers (3,12,13) have been pubhshed. Approximately 17% of all preschool children in the United States have blood lead levels >10 //g/dL. In inner city, low income minority children the prevalence of blood lead levels >10 //g/dL is 68%. It has been estimated that over two million American workers are at risk of exposure to lead as a result of their work. PubHc health surveillance data document that each year thousands of American workers occupationally exposed to lead develop signs and symptoms indicative of... 

In a cross-sectional study, exposure and effect are studied simultaneously. This approach contains an inherent problem because exposure must precede the effect. However, it can he used to investigate acute effects and also mild chronic effects (which do not force people to leave their jobs) if exposure has remained rather stable for a long time. When the prevalence of the effects studied are compared with the prevalence in other worker groups (controls or references) which correspond otherwise with the study group but are not exposed to the agent investigated, indicative evidence of possible causality may be obtained. For example, cross-sectional studies have been applied successfully to reveal the associations between mild neurotoxic effects and exposure to organic solvents. ... 

A vast cascade of cytokines appear to be induced by the presence of this polysaccharide, and immunopoiesis- and hemopoiesis-inhibition are probably the most prevalent during the first two weeks of daily exposure [61]. Studies relating structure to the biological activity have not been performed. 

Additional studies of the Woburn population have been completed (MDPH 1994). The final report indicated that there was an increased prevalence in choanal atresia, a rare respiratory effect, and hypospadias/congenital chordee. A small increase in eye defects was observed, but there was no association between TCE exposure and heart defects. There was no statistically significant associations between exposure concentrations and birth defects, although analyses was limited by the small number of cases observed. Based on four cases in the Woburn population, a rate of 0.88 was observed in the exposed population, compared to rates of 0.11 and 0.13 in the Atlanta and California comparison populations, respectively. In a prospective study completed after well closure, the rate of choanal atresia was 0.88 (based on 1 case) in Woburn, 0.11 in the surrounding communities, and 0.2 and 0.13 in Atlanta and California, respectively. The study authors cautioned that their study did not rule out moderate increases in rates of the less common adverse reproductive outcomes. For these outcomes only large increases would have been detected. 

Kilbum KH, Warshaw RH. 1992. Prevalence of symptoms of systemic lupus erythematosus (SLE) and of fluorescent antinuclear antibodies associated with chronic exposure to trichloroethylene and other chemicals in well water. Environ Res 57 1-9. 

Figure 4.10 With increasing oxygen exposure at 295 K, the Mg(0001) surface consists of both hexagonal and square lattice structures the line profiles indicate repeat distances of 0.321 and 0.56 nm in the atom resolved hexagonal and square structures, respectively, the former being the most prevalent structure present. (Reproduced from Ref. 41).

Genetic factors cannot explain the recent rapid rise in asthma prevalence. Asthma appears to require both genetic predisposition and environmental exposure. Many patients with occupational asthma develop the disease late in life upon exposure to specific allergens in the workplace. Environmental influences in utero or in infancy may contribute to the development of asthma. Maternal smoking during pregnancy or exposure to secondhand smoke after birth increases the risk of childhood asthma.3 Adult-onset asthma is not uncommon and may be related to atopy, nasal polyps, aspirin sensitivity, occupational exposure, or a recurrence of childhood asthma. 

Risk factors for the development of AML include exposure to environmental toxins, Hispanic ethnicity, and genetics.6 Of greater concern is the increased prevalence of AML as a secondary malignancy, resulting from chemotherapy and radiation treatment for other cancers. Alkylating agents, such as ifosfamide and cyclophosphamide, and topoisomerase inhibitors, such as etoposide, are linked to an increased risk of myelodysplastic syndrome (MDS) and AML.8... 

Exposure Levels in Environmental Media. Monitoring data were not located for diisopropyl methylphosphonate in ambient air. This chemical has been detected in surface and groundwater receiving effluent from the RMA (ATSDR 1996). It has also been detected in soil at the RMA. Since this chemical is not expected to be prevalent in the environment and exposure of the general population is not expected to be of concern, monitoring of ambient environmental media does not appear to be required. However, monitoring of environmental media such as groundwater and soil in the vicinity of the RMA has been conducted to help determine the potential for exposure. 

In the U.S., the central nervous system syndrome is usually more common among children, and the gastrointestinal syndrome is more prevalent in adults. Exposure to lead is also linked to decreased fertility in men. Lead is a probable human carcinogen, based on sufficient animal evidence. Populations at increased risk of toxicity from exposure to lead include developing fetuses and young children, individuals with decreased kidney function, and children with sickle-cell anemia. 

Chia et al. 1995a). Another index of exposure examined was the number of times the PbB level was above critical values (e.g., 40, 50, 60 ig/dL). Serum P2 X -globulin was the only marker showing a significantly higher prevalence rate ratio of abnormalities (increase) among lead-exposed workers. 

A number of methods and models have been used at sites to estimate potential risks from exposure to lead. One method is the use of prevalence data for estimating PbB levels. In this case, PbB measurements can be made at a site and extrapolated to other sites with similar environmental and demographic data. Limitations of this method include site-to-site variability with respect to, among other things, children s behavioral patterns, age, and bioavailability issues. Estimation of past exposures can be problematic because of redistribution of Pb out of the blood compartment since PbB is only an indicator of recent exposure (<90 days). 

Exposure (= prevalence) in controls assuming a diallelic locus with a dominant or recessive allele at Hardy-Weinberg equilibrium. 

Power calculations assumed that there are two controls for each case and a SNP that operates as if it was a simple binary factor to which a proportion of the population are exposed in a manner directly related to the genotypic frequency (e.g., for 19% exposure, equivalent to a dominant allele at Hardy-Weinberg equilibrium with a prevalence of 10%). 

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