Pre-exposure levels

Short-term inhalation studies (<2 min) in human volunteers have demonstrated that ammonia is almost completely retained (83-92%) in the nasal mucosa (Landahl and Herrmann 1950). With longer exposures (500 ppm for 30 min), retention of ammonia in the nasal mucosa decreases progressively until reaching equilibrium at 23% (range 4-30%) after 10-27 min of exposure (Silverman et al. 1949). The authors reported that the concentration of ammonia in exhaled air remained stable after this period and returned to pre-exposure levels within 3-8 min after the exposure. Localized irritation in the nose and pharynx was further... 

Seven men who were exposed for 6 hours/day for 5 days to 616 mg/m of vaporized white spirits (with a composition of 99% alkanes, as compared to 30-50% alkanes in Stoddard solvent) had a decrease (p<0.05) in serum follicle-stimulating hormone levels at 24 and 96 hours after the initiation of exposure as compared to pre-exposure levels (Pedersen and Cohr 1984b). This change did not correspond to blood or adipose levels of white spirits. No tests of reproductive function were performed. In another study, 11 men in a printing factory were occupationally exposed to a wide variety of solvents, including 294 mg/m of white spirits for 1-17 years. Sperm counts, motility, and morphology were monitored for 2 months, and all values were normal (Tuohimaa and Wichmann 1981). 

Because of the physiological variations of RBC-ACHE and PCHE levels, the sensitivity of these tests to detect low-level inhibitions can be increased by comparison with individual pre-exposure values, adopted as a reference. The World Health Organization (WHO, 1982) recommends calculating individual pre-exposure values as the average of three samples cholinesterase activities after exposure should be expressed as percentage change with... 

Low levels of 3,5,6-TCP were also observed in pre-exposure urine from most of the field workers. These 3,5,6-TCP levels were subtracted from urine field recovery samples and were used to correct levels of 3,5,6-TCP found in the post-exposure urine samples from these same workers. This procedure was necessary to calculate the amount of 3,5,6-TCP in the urine that was attributable to the exposure period. 

Exposure of animals to therapeutic levels of antibiotics will markedly raise the level of resistance and a long period of time is required for the resistance levels to return to the pre-treatment level In an experiment replicated five times (Lang lo is et al ifi.) we found that exposure of animals to subtherapeutic levels of gram-positive spectrum antibiotics also resulted in increased levels of tetracycline resistance During the course of our study we have sampled pigs on two separate occasions (1974 and 1985) from another research herd in which antibiotics have never been used as feed additives but only for therapeutic purposes Of the 100 pigs sampled in 1974 only one had been... 

Other Systemic Effects. In rabbits exposed dermally to isophorone at doses up to 3160 mg/kg, no systemic pathological effects were found by gross necropsy (Hazleton Labs 1964), but histological examinations were not performed. In this study, the site of application was occluded for 24 hours to prevent evaporation of isophorone from the skin. No significant differences between pre-exposure and post-exposure levels of serum electrolytes, blood glucose and sulfhydride radicals, SGOT,... 

Anesthetized rabbits were burned on intact skin with 5,700 mg/kg white phosphoms (Bowen et al. 1971). Those that died after white phosphoms bums showed significant (p<0.001) increases in serum phosphate levels over pre-bum levels. The pre-bum levels ranged between 4.5 and 5.5 mg/100 mL, and post-exposure levels measured at 12 hours to 3 days ranged between 6.5 and 10.5 mg/100 mL. Phosphate levels in phosphoms-bumed animals that survived remained normal throughout the study. 

Inadequate pre-exposure information. Although workers fill out questionaires indicating that they have not used phenoxy herbicides during the previous two weeks, sometimes these workers come into the study with positive background levels of phenoxy in their urine. 

In residents of Seveso, Italy, a significant rise in the incidence of birth defects, as compared to pre-accident levels, was observed the year after the accident (Bisanti et al. 1980). A variety of birth defects were observed, but the incidence for any particular defect was not elevated. The authors suggest that the rise in birth defects may not be related to 2,3,7,8-TCDD exposure. Prior to 1976, birth defects in Italy were usually under reported the authors note that the reported incidences of birth defects after the accident (23 per 1,000 births) were similar to incidences reported in other western countries. Thus, the increased incidence may be reflective of the increased reporting rather than an increased number of birth defects. In a study which assessed the risk of birth defects for the 6-year period after the Seveso accident, no increases were observed for the risk of total defects (RR of 1.2, 90% Cl of 0.88-1.64 for zones A and B and RR of 0.97, 90% 0=0.83-1.13 for zones A, B, and R), major defects RR of 1.02, 90% 0=0.64-1.61 for zones A and B and RR of 0.83, 90% 0=0.67-1.04 for zones A, B and R), and minor defects RR of 1.44 90% 0=0.92-2.24 for zones A and B and RR of 1.14, 90% 0=0.92-1.42 for zones A, B and R) (Mastroiacovo et al. 1988). The small number of observed birth defects limits the statistical power of this study to detect significant increases in a specific defect. 

Exposure to organophosphate pesticides is often measured by determination of alkyl phosphate or phenol metabolites in the urine. Determination of blood cholinesterase activity can be a valuable indicator of exposure if pre-exposure cholinesterase activity is known (3, 5). Since normal cholinesterase levels... 

Relationship Between Water-Soluble Chromium(VI) Concentration in Workroom Air (CrA) and Daily Increase in Urinary Chromium Levels (CrU) (Pre-exposure Values were Subtracted from End-of-Shift Values)... 

Examination of end-of-shift chromium levels indicated a correlation between urinary chromium levels and exposure to soluble chromium(VI) compounds, but not to insoluble chromates or chromium(III) compounds (Minoia and Cavalleri 1988 Mutti et al. 1985b). The relationship between workroom air concentrations of water soluble chromium(VI) compounds and daily increases in urinary chromium (preexposure values subtracted from end-of-shift values) are shown in Figure 2-6. An increase in urinary chromium of 12.2 pg/g creatinine above pre-exposure values or a total concentration of 29.8 pg/g creatinine (end-of-shift values) corresponded to an air concentration of 50 pg chromium(VI)/m3 from welding fumes (Mutti et al. 1985b). 

The data on which the estimated levels of exposure are based vary greatly. Some of the differences in these calculated exposure levels might be explained by the nse of different statistics, differences between pre-registration studies (UK model, German model and PHED) and surveillance (post-registration studies), but it is likely that some other (local) factors contribute substantially to the variance. 

Changes in plasma-ChE activity in dosed and control animals are shown in Table 4. Over the course of the study, plasma-ChE activity levels in dosed and control animals appear to be more stable than RBC-AChE activity. It was reported that plasma-ChE activity was decreased by about 55% in dosed females at week 7, and by 37.5% in dosed males at week 3. Mean plasma-ChE activity in the female controls exhibited a slow increase over the 13-week test period (from 1743 lU/L at week -1 to 2891 lU/L at week 13). A similar response was seen in the two lowest dose groups of females. In males, mean plasma-ChE activity in controls was lower than preexposure levels (401 lU/L at week -1) at all weeks except week 3 (413 lU/L). In the dosed groups of males, mean plasma-ChE levels were lower than pre-exposure values at all sampling times. Statistical analysis of the plasma-ChE activity indicated that mean values were significantly lower than controls in the mid- and high-dose females at weeks -1, 1, 3, and 7 but not at week 13, and in the high-dose males at weeks 3 and 7. 

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