Lecture
In the Russian Federation there are three methods for establishing the MAC of harmful substances in the air of the working zone:
1. preliminary toxicological assessment;
2. full toxicological assessment;
3. clinical-statistical method
On the basis of physico-chemical properties, as well as the structural formula of the new substances under study, toxicological indicators and approximate MAC values are calculated. Approximate regulation is also carried out by analogy with a substance of similar chemical structure, by extrapolation and interpolation of compounds within series of the same class. More reliable results for calculating approximate MAC values for the air of the working zone can be obtained on the basis of experimental determination of the lethal concentration and dose in experiments on small animals.
Preliminary toxicological assessment of a substance contains the following quantitative characteristics: information on physico-chemical properties (saturation concentration, water/air and oil/water distribution coefficients), on median lethal doses, the KVIO (coefficient of possible inhalation poisoning), which gives an idea of the real hazard of acute poisoning, and practical recommendations.
Full toxicological assessment of a substance includes acute and chronic experiments on animals, toxicological studies of technological samples, the study of long-term effects, and the examination of workers at pilot-plant and laboratory installations.
The clinical-statistical method is carried out during the first three years of operation of a new technological installation, but it can continue longer in order to study the long-term effects of exposure to substances on workers. The clinical-statistical method is not independent, but only supplements the full and preliminary toxicological assessment of substances.
On the basis of the physico-chemical properties of harmful substances, and from indicators of the acute toxicity of a substance, it is possible to determine their MAC by a calculation method. A relationship has been established between MAC and molar mass, density, refractive index, and melting and boiling temperature. The derived equations for calculating MAC express average values of the compared quantities, and therefore a correction for their chemical structure is necessary.
Calculations using the formulas can be carried out only for those substances whose physico-chemical
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constants have the following defined limits: |
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- molar mass M, kg/mol |
from 3 |
to 300; |
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- density , kg/m3 |
0C |
from 0,6 to 2,0; |
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- boiling temperature tbp. |
from – 100 to + 300; |
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-melting temperature tmp. |
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from – 190 to + 180; |
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- refractive index nD |
from 1,3 to 1,6 |
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The maximum allowable concentration of the working zone is calculated as the average value from |
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the following equations: |
lgMACw.z. = 14,2 – 10 nD + lg M; |
(14) |
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lgMACw.z. =lgM |
- 0,012tmp |
- 1,2; |
(15) |
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lgMACw.z. = 0,4 – 0,01M + lgM; |
(16) |
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lgMACw.z. = 0,6 – 0,01tbp + |
lgM; |
(17) |
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lgMACw.z. = 1,6 – 2,2 + |
lgM |
(18) |
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For the final calculation of the MACw.z. of harmful substances, corrections are taken into account for various |
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chemical compounds (Table 7). |
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Table 7. |
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Correction when calculating the MAC of the working zone for certain compounds |
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Compounds |
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Correction to |
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the calculated |
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lg MAC |
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Saturated aromatic hydrocarbons |
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+ 0,5 |
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Saturated ketones, alcohols, ethers and esters |
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+ 0,5 |
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Cyclic saturated hydrocarbons with a benzene ring |
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+0,5 |
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Compounds with a triple bond in a straight chain |
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- 0,5 |
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Fatty (aliphatic) amines |
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- 1,0 |
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Aniline and its derivatives |
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- 1,0 |
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Acid anhydrides |
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- 1,0 |
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Cyclic compounds containing an NO2 group in the side chain |
- 1,0 |
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Compounds with a double or triple bond, together with active |
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- 1,0 |
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elements or a group (Cl, Br, F, NO2, OH) in a straight chain |
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- 1,5
Compounds containing an epoxy group
- 1,5
Organophosphorus compounds
- 1,5
Aldehydes
- 2,0
Compounds splitting off a CN group
Correlations between various toxicity indicators, the molar masses of substances, and MAC values are of great importance.
For calculating the MACw.z. of gases, inorganic and organic substances, aerosols and their oxides
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the following formulas are applied. |
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For calculating gases and vapors of organic substances: |
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lgMACw.z. = 0,91 · lgLC50 |
+ 0,1 + lgM; |
(19) |
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lgMACw.z. = lgLD50 – 2,0 |
+ lgM; |
(20) |
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For calculating aerosols of non-volatile, low-volatility, and organoelement substances (in particular |
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pesticides): |
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lgMACw.z. = lgLD50 – 3,1 + lgM |
(21) |
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For calculating inorganic gases and vapors: |
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lgMACw.z.= lgLC50 + 0,4 + lgM |
(22) |
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For calculating metals and their oxides: |
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lgMACw.z. = 0,85 · lgLD50 – 3 + lgM – lgN (23)
where N is the number of metal atoms in the molecule of the substance
Appendix 1 provides examples of calculating the MACw.z based on physico-chemical and toxicological characteristics.
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