Poster
# 46
Poster |
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6th Internet World Congress for Biomedical Sciences |
Mariarosa Re(1)
(1)Dipart. Medicina Preventiva, Occupazionale e di Comunità. University of Pavia - Pavia. Italy
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[Hygiene, Public Health & Preventive Medicine] |
[Occupational Health] |
Procedures for assessment of occupational exposure to hazardous chemicals through correlation-based methods may be applied to several working situations, such as: (a) mapping of concentrations around the emitting source of a chemical agent, as a function of distance from source; (b) classification of levels of exposure for different operations of the same job, involving use of the same chemicals; (c) evaluation of multiple exposure, resulting from use of mixtures of chemicals, so that the concentration in air of each substance is more or less significantly correlated with concentrations of all the other substances in the mixture.
Since interest in multiple exposure assessment has been increasing in recent years, this paper will analyse and discuss correlation-based procedures applicable to multiple exposure.
Epidemiological studies have shown that in many cases occupational risk cannot be ascribed to a single chemical hazard, but to simultaneous exposure to more or less complex mixtures of several chemicals (e.g. rubber production). Therefore, several studies have been reported (1-4) concerning multiple occupational exposure and its adverse effects on health as a result of toxicokinetic and toxicodynamic interactions of chemicals in the mixture. The following types of effects have been identified ( 3):
(a) additivity, i.e. the resulting effect is the sum of effects of individual hazards;
(b) potentiation, i.e. the effect of one chemical is increased by exposure to other chemicals that are only slightly active when alone;
(c) synergism, i.e. the effect of interactions is greater than that resulting purely from additivity;
(d) antagonism, i.e. interactions result in a decrease of toxicity, owing to interference of chemicals with each other.
Another important question to be considered (2,4) is possible potentiation of carcinogenic or allergic effects (for instance in occupational exposure to metals) that may be expected even at very low concentrations.
It has been reported (3) that potentiation effects are found more frequently than the other effects, and are worth being considered, in presence of mixtures, as capable of modifying the expected action of a single substance.
Additive effects are considered as criteria for establishing occupational exposure limits for mixtures by the American Conference of Governmental Industrial Hygienists (ACGIH) (5). ACGIH recommends that, in presence of two or more hazardous substances acting upon the same organ system, their combined effect should be considered, rather than the individual effects; these should be considered additive unless it is reasonable to believe that they are in reality independent. ACGIH also recommends that cases of synergistic or potentiating action must be considered singularly. Moreover, when multiple exposure is evaluated by measuring a single substance, its limit should be reduced by a suitable factor, as a function of number, toxicity and quantity of the other substances.
As already reported (2-4,6) the ideally correct procedure for multiple exposure assessment involves complete identification and quantification of each hazardous chemical. However, such a procedure is not easily applicable to workplaces and working situations for reasons of technical and economic feasibility. So, the traditional approach to multiple exposure assessment is to quantify only one component of the mixture. As an alternative to the traditional approach, a more accurate and reliable estimate of multiple exposure may be obtained through correlation-based procedures, described in the following section.
Software Statistical calculations for correlation-based procedures may be performed by SPSS or any other easily available statistical package (e.g. SYSTAT etc.)
Procedures The strategy for applying correlation methods to multiple exposure evaluation consists of the following steps:
(a) Use of simple correlation techniques for testing correlation of measurements of individual substances with each other and with total quantity of all contaminants. Data required at this step need be collected through a preliminary survey. As concentrations of contaminants in air follow a lognormal statistical distribution (7), the parametric (Pearson) correlation test (8) is applied to logarithms of concentrations. If a significant correlation is found at this stage, an index or predictor substance can be singled out: for instance the one that is most abundant in the mixture, or the one that most correlates with total quantity of contaminants, or the one that is most easily analysed, or the one that is most toxic. The sum of concentrations of all components can itself be a predictor for exposure evaluation. This choice is particularly convenient when the correlation with individual substances is high and the total quantity can be determined by a simpler or less expensive analytical technique than required for specific determination of single substances.
(b) Routine monitoring of multiple exposure can be performed by direct measurement of the index substance and prediction of concentrations for each unmeasured component of the mixture and for total quantity of contaminants by statistical regression.
(c) An alternative technique to step (b), that is more reliable but less practical as it requires not only measuring the index component, but also a small random sample of concentration values for each component to be estimated, involves using the concentration of the index component as auxiliary variable and ratio or regression estimators (9).
Examples of working activities where it is expected that correlation-based methods may be advantageously applied for multiple exposure monitoring are reported in the following section.
As demonstrated by a literature search through recent years on MEDLINE, a great number of scientific reports deal with multiple exposure. However, many studies concern cases of multiple exposure where concentrations of chemical agents are not likely to be correlated. Such cases occur when multiple exposure is not due to use of mixtures of chemicals, but to simultaneous presence in workplaces of contaminants originating from different sources. As a consequence, concentrations of chemicals are expected not to be correlated, but to vary independently from each other, as a function of individual emitting sources or working operations.
A series of working activities where correlated concentrations are very likely to be found is grouped in Table 1 with the following specifications: (a) type of working activity, with bibliographic references; (b) chemical agents responsible of multiple exposure; (c) monitoring method (E.C.: by determination of each component; I.S.: by determination of an index substance; A.I.S.: by determination of an added index substance; T.A.: by determination of total amount; P.M.: by predictive model).
It is remarkable that use of correlation-based methods for multiple exposure monitoring is reported just in two studies (10,13), although from the point of view of feasibility it is likely to be more advantageous than the adopted methods , at least for routine exposure monitoring. Of course determination of each component of the mixture is the ideally correct technique , but it is not easily applicable for routine exposure monitoring.
Table 1 - Multiple occupational exposure with expected correlated concentrations.
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Type of working activity (references) |
Chemical agents |
Monitoring methods (E.C., I.S., A.I.S., T.A., P.M.) |
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Art Glass Manufacturing (2) Welding (4) Painting, paint removing Aluminum smelter (13)
Aluminum smelter (14) Coking plant (6) Coke oven (15) Forestry-logging (16) Electric utility industry (17) Insecticides application (18) |
Chemical elements
Metals
Solvents (ketones, ethylacetate, toluene) PAH (Polycyclic Aromatic Hydrocarbons) PAH
PAH
PAH
Chain saw exhaust
Diesel exhaust
Pesticides |
E.C.
E.C.
E.C.
E.C., I.S.
E.C.
E.C.
T.A.
I.S.
I.S.
A.I.S. |
In occupational hygiene surveys and occupational epidemiology studies correlation-based techniques may be a helpful tool for assessment of exposure to chemical hazards. Working situations where concentrations of contaminants are expected to be highly correlated with each other are frequent: among them use of mixtures of chemical substances or elements. Whenever correlation of concentrations is statistically significant (for instance between individual contaminants in case of use of mixtures) occupational exposure may be monitored by measurement of just one chemical, as concentrations of the other contaminants can be estimated through statistical correlation and regression.
The drawback to applying these methods is the need for a preliminary survey to collect data for statistical correlation testing. However, it is compensated for by a consistent decrease in number of required measurements for routine exposure monitoring, as recommended in compliance control programs for certain chemical hazards and in occupational epidemiology studies.
1.- Alessio L, Apostoli P, Crippa M (1994). Esposizioni lavorative multiple a solventi.G. Ital. Med. Lav., 16, 37-42.
2.- Apostoli P, Giusti S, Bartoli D, Perico A, Bavazzano P, Alessio L (1998).Multiple Exposure to Arsenic, Antimony and Other Elements in Art Glass Manufacturing.Am. J. Ind. Med., 34, 65-72.
3.- Alessio L. (1996). Multiple Exposure to Solvents in the Workplace. Int. Arch. Occup. Environ. Health, 69, 1-4.
4.- Apostoli P, Porru S, Brunelli E, Alessio L (1997). Multiple exposure to metals in eight types of welding.G. Ital. Med. Lav. Erg., 19, 8-14.
5.- ACGIH (1999). 1999 TLVs and BEIs - Threshold Limit Values for Chemical Substances and Physical Agents - Biological Exposure Indices.
6.- Yrjanheikki E, Pyy L, Hakala E, Lapinlampi T, Lisko A, Vahakangas K (1995). Exposure to Polycyclic Aromatic Hydrocarbons in a New Coking Plant. Am. Ind. Hyg. Assoc. J., 56, 782-787.
7.- Leidel NA, Busch KA, Lynch JR (1977).Occupational Exposure Sampling Strategy Manual. DHEW (NIOSH) Publication No. 77-173.
8.- Armitage P, Berry G (1994). Statistical Methods in Medical Research. Blackwell Scientific Publication, Oxford.
9.- Thompson SK (1992). Sampling. John Wiley and Sons, New York.
10.- Kumagai S, Matsunaga I (1992). Fluctuations of occupational exposure indices to mixtures. Ann. Occup. Hyg. 36, 131-143.
11.- Kumagai S, Matsunaga I (1995). Models describing variation of short-term exposure levels of two chemicals. Ann. Occup. Hyg. 39, 7-20.
12.- Re M (1992). Occupational exposure to chemicals with additive effects: a statistical procedure for evaluation. In Clean Air at Work. Brown RH, Curtis M, Saunders KJ, Vandendriessche S eds. The Royal Society of Chemistry, Cambridge U.K., 112-114.
13.- Farant JP, Gariépy M. (1998). Relationship between Benzo[a]pyrene and Individual Polycyclic Aromatic Hydrocarbons in a Soederberg Primary Aluminum Smelter. Am. Ind. Hyg. Assoc. J. 54, 758-765.
14.- Ny FT, Heederick D, Kromhout H, Jongeneelen F (1993). The Relationship between Polycyclic Aromatic Hydrocarbons in Air and in Urine of Workers in a Soederberg Potroom. Am. Ind. Hyg. Assoc. J. 54, 277-284.
15.- Chen M, Mao I, Wu M, Chen J, Ho C, Smith T, Wypij D, Christiani D (1999). Assessment of Coke Oven Emissions Exposure among Coking Workers. Am. Ind. Hyg. Assoc. J. 60, 105-110.
16.- Buenger J, Bombosch F, Mesecke U, Hallier E (1997). Monitoring and Analysis of Occupational Exposure to Chain Saw Exhaust. Am. Ind. Hyg. Assoc. J. 60, 635-640.
17.- Whittaker LS, MacIntosh DL, Williams PL (1999). Employee Exposure to Diesel Exhaust in the Electric Utility Industry. Am. Ind. Hyg. Assoc. J. 60, 635-640.
18.- Stewart P, Frears T, Nicholson H, Kross BC, Ogilvie LK, Zahm SH, Ward MH, Blair AA (1999). Exposure received from Application of Animal Insecticides. Am. Ind. Hyg. Assoc. J. 60, 208-212.
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[Hygiene, Public Health & Preventive Medicine] |
[Occupational Health] |
