Exposure, limiting, mean values

The mean exposure limit value for 3-methyl-1-butanol in the air of workplaces was set at 100 ppm in 1984 by the ACGIH (135). Standards have not been set for the other alcohols (135). 

Binding occupational exposure limit values reflect feasibility factors related to social acceptability. When the results of environmental monitoring have to be compared with OELs, factors that influence exposure and that entail preventive policies are considered. For these values member states shall establish a corresponding national binding occupational exposure limit value based on but not exceeding the community limit value. That is, a binding limit means a minimum requirement. 

The easiest means for assessing occupational exposure hazards associated with materials used in a process is through the use of Permissible or Occupational Exposure Limits (OEL or PEL) which go by a variety of names for example, TLV (U.S. - American Conference of Government Industrial Hygienists), MAK (Germany), or individual company established values. Occupational exposure limits are usually set based on a combination of the inherent toxicological hazard of a chemical and a series of safety factors such as intraspecies variability in test results, nature and severity of the effect, adequacy and quality of... 

There are stringent controls over emissions of particulate matter and solvent vapours—not only must a factory be of standard sufficient to meet the relevant exposure limits (which are controlled under the Health and Safety at Work Act, 1974, and subsequent regulations) but manufacturers have a legal duty to ensure that exposure and emissions are (in the official phrase) as low as is reasonably practicable . Specific values as limits for emissions of particulates and vapours are laid down under the Environmental Protection Act, 1990. In effect this means that there must be continuing attention to the maintenance of operating standards, and to the improvement of formulations—and on the latter, paint technologists are following two main lines of advance ... 

When calculating chronic dietary exposure, the deterministic models use point values for both food consumption and residue concentration, thereby yielding a point estimate of dietary exposure. In the US, the initial chronic dietary exposure estimate is the Theoretical Maximum Residue Contribution (TMRC) and is analogous to the Theoretical Maximum Daily Intake (TMDI) used to estimate chronic dietary exposure in the EU. Both the TMRC and the TMDI are relatively conservative estimates of dietary expostire. The TMRC is calculated as the product of the mean consumption value and the US pesticide tolerance [6]. In the EU, the TMDI is calculated as the product of the mean consumption value and the Maximum Residue Limit (MRL) [7]. The objective of both calculations is essentially identical to calculate an estimate of the central tendency of the dietary exposure. Both calculated values use the central tendency dietary exposure estimate as the estimate of chronic (long-term) dietary exposure and calculate it using mean consumption data and the maximum residue permitted on the commodity. 

When, as is often the case, dietary exposure estimates calculated with tolerances or MRLs exceed acceptable toxicity limits, revised dietary exposure estimates may be calculated using residues derived from field trials. For chronic dietary exposure, the mean field trial residue is used in the US, and the median residue (STMR - Supervised Trials Median Residue) is used in the EU. In addition, as shown m the NESTI calculation, the high residue from field trials can be substituted for the tolerance or MRL value. 

Having obtained a value it is necessary to determine the confidence limits (error bounds) for this estimate. In this way, the impact of any uncertainty surrounding the initial assumptions used can be evaluated. A representation of a mean value for the population and 95% confidence limits for any given percentile is shown in Eig. 6.2. As can be seen, the difference between the upper and lower values of an exposure estimate for a given percentile increases the nearer the selected percentile is to 100%. 

Irritant (Category 2) (applies to all authorities) (1) Mean value of > 2.3 < 4.0 for erythema/eschar or for oedema in at least 2 of 3 tested animals from gradings at 24, 48 and 72 hours after patch removal or, if reactions are delayed, from grades on 3 consecutive days after the onset of skin reactions or (2) Inflammation that persists to the end of the observation period normally 14 days in at least 2 animals, particularly taking into account alopecia (limited area), hyperkeratosis, hyperplasia, and scaling or (3) In some cases where there is pronounced variability of response among animals, with very definite positive effects related to chemical exposure in a single animal but less than the criteria above. 

Within this guidance the term occupational exposure limit(s) refers to limits in the air of the workplace or biological limit values. In addition, for the purposes of this document exposure control means the full range of specific protection and prevention measures to be taken during use in order to minimize worker and environmental exposure. Engineering control measures that are needed to minimize exposure to, and risks associated with the hazards of, the substance or mixture should be included in this section. 

Seven male volunteers were exposed to 2-butoxyethanol for 2 hours at the Swedish occupational exposure limit (20 ppm or 0.85 mmol/m ) during light physical exercise on a bicycle ergometer (Johanson et al. 1986a). Expired air was collected at regular time intervals for estimation of the respiratory uptake of the solvent. Capillary blood and urine were sampled, during and after the exposure period, and analyzed for 2-butoxyethanol and its metabolite, free 2-butoxyacetic acid. 2-Butoxyethanol was no longer detectable in the blood 2-4 hours after the end of exposure. The apparent values of elimination half-time, mean residence time, total blood clearance, and steady-state volume of distribution were 40 minutes, 42 minutes, 1.2 E/minute, and 54 L, respectively, for 2-butoxyethanol. The half-life for 2-butoxyethanol in urine was 1.36 hours. The amount of 2-butoxyethanol excreted in urine was less than... 

Occupational exposure limit value means the limit of the time-weigjited average of the concentration of a chemical agent in the air within the breathing zone of a worker in relation to a specified refer ce period . 

---