Controlled exposure studies

In humans, metabolites of acrylonitrile have been identified in urine following occupational exposure (assumed to be by the inhalation route), and also in controlled exposure studies. Metabolites identified in humans were the same as those in animals (Jakubowski et al. 1987 Sakurai et al. 

Controlled Exposure Study in Human Volunteers Wearing 900 cm2 patch for 2 Hours (adapted from Newton and Norris, l i). 

There have been limited field and controlled exposure studies that evaluated human reactions to carpet emissions. Winfield (1987) described a USA primary school where odor, headache, nausea, fatigue and mucosal irritation were reported by a high proportion of the students. Elevated indoor air concentrations of styrene (900-4000 xg m 3) were found, which were believed to be due to a SB R latex-backed carpet which had been installed several years previously. The carpet was removed and the ill-effects were reported to abate. Johnsen et al. (1990) exposed asthma sufferers to a foam rubber-backed carpet in a room chamber. While no clinical effects on lung function were observed, objective eye measurements found that there was a change in tear film quality. This was proposed to result from a degreasing effect of lipophilic VOCs, identified as toluene and acetone (Wolkoff, Nielsen and Hansen, 1990). 

Controlled exposure studies of volunteers in stainless steel chambers have been performed. Most have involved exposure to one specific mixture of VOCs for example, the work of Molhave and Nielsen in 1992. These studies consistently document relationships between symptoms and increasing exposure levels. Office workers who perceived themselves as susceptible to the effects of usual levels of VOCs indoors demonstrated some impairment on standard tests of neuropsychological performance. Healthy volunteers, on the other hand, demonstrated mucous membrane irritation and headaches at exposures in the range of 10-25mgm but no changes on neuropsychological performance. Recently, office workers demonstrated similar symptoms after simulated work in environments where pollutants were... 

Formaldehyde-induced effects on human pulmonary function variables including forced vital capacity (FVC), forced expiratory volume in 1.0 seconds (FEV, q), peak expiratory flow rate (PEFR), and forced expiratory flowrate between 25 and 75% FVC (FEFRoj,, ), have not been found as consistently as symptoms of eye and nose irritation at acute exposure levels in the range of 0.4-3 ppm. In controlled exposure studies, no statistically significant exposure-related effects on lung function measurements were found in 10 healthy subjects exposed to up to 2 ppm for 3 hours (Kulle et al. 1987 Kulle 1993),... 

A few controlled exposure studies have found only subtle or infrequent effects of acute exposure to low concentrations of formaldehyde on pulmonary flinction variables (Green et al. 1987 Nordman et al. 

Ocular Effects. As discussed in Section 2.2.1.2 (in the Respiratory Effects and Ocular Effects sections), health surveys of occupationally-exposed workers and acute controlled exposure studies with volunteers have demonstrated that exposure to formaldehyde air concentrations in the range of 0.4-3.0 ppm and above can cause eye irritation. 

A few controlled exposure studies have found only subtle or infrequent effects of formaldehyde on lower respiratory tract function in this concentration range, supporting the hypotheses that the upper respiratory tract is a more likely target of formaldehyde toxicity than the lower respiratory tract and that pulmonary hypersensitivity to formaldehyde is rare (Green et al. 1987 Nordman et al. 1985 Sauder et al. 1986). 

Data from acute controlled-exposure studies, supported by data from animal studies, generally indicate that formaldehyde does not induce airway hyper-reactivity at concentrations 3 ppm, but further studies with asthmatics may be required because of somewhat conflicting data in this potentially sensitive population. Other persons with demial sensitization to fonnaldehyde are not likely to develop signs of respiratory insufficiency. Persons with multiple chemical sensitivities may represent a third potentially sensitive population, but studies linking this syndrome with exposure to formaldehyde were not located. 

Three well-conducted, controlled exposure studies have investigated the effect of pure MTBE on symptoms and objective measures of irritation and performance amongst healthy subjects, hi addition, there has been one similar study of effects of MTBE in gasoline on subjects that have reported themselves as being particularly sensitive to MTBE. There has also been one study of ETBE. 

Research into mechanisms of the adverse health effects of PMio mass concentrations observed in recent epidemiological studies needs to be undertaken in controlled exposure studies of humans and animals. It is only through integration of the complementary evidence from laboratory animal and controlled human exposure studies with the results from epidemiological studies that the risk of particle exposures can be fully evaluated. Nevertheless, these recent epidemiological studies implicate particulate air pollution as contributing to respiratory morbidity and mortality, even at exposure levels below the current ambient air quality standards in the United States and in Europe. 

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