Substance-Specific Issues

Silica, crystalline, non respirable; classification of

Substances:

Silica, crystalline - quartz; CAS No. 14808-60-7
Silica, crystalline - cristobalite; CAS No. 14464-46-1

Issue:

What [WHMIS] requirements do the Hazardous Products Act (HPA) and Controlled Products Regulations (CPR) place on a supplier of products containing greater than 0.1% w/w non respirable crystalline silica?

Background:

As opposed to referencing tests, the criteria for carcinogenicity specified in section 54 of the CPR for pure substances and tested mixtures refer to lists by ACGIH and IARC. The criteria for untested mixtures in section 58 of the CPR cross-reference section 54.

Concerning the different forms of crystalline silica, IARC's monograph states:

"Possible differences in carcinogenic potential among polymorphs of crystalline silica were considered. Some studies were of populations exposed principally to quartz. In only one study (that of United States diatomaceous earth workers) was the exposure predominantly cristobalite. Studies of mixed environments (i.e. ceramics, pottery, refractory brick) could not delineate exposures specifically to quartz or cristobalite. Although there were some indications that cancer risks varied by type of industry and process in a manner suggestive of polymorph-specific hazards, the Working Group could only reach a single evaluation for quartz and cristobalite. Nonetheless, the Working Group did note a reasonable degree of consistency across studies of workers exposed to one or both polymorphs."

IARC's "overall evaluation" states:

• "In making the overall evaluation, the Working Group noted that carcinogenicity in humans was not detected in all industrial circumstances studied. Carcinogenicity may be dependent on inherent characteristics of the crystalline silica or on external factors affecting its biological activity or distribution of its polymorphs.
• Crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (Group 1).
• Amorphous silica is not classifiable as to its carcinogenicity to humans (Group 3)."

Appendix A, "Clarifications and Interpretations of the Hazard Communication Standard" to U.S.

OSHA Directive CPL 2-2.38D, states:

"Any substance which is inextricably bound in a product is not covered under the HCS. For example, a hazard determination for a product containing crystalline silica may reveal that it is bound in a rubber elastomer and under normal conditions of use or during foreseeable emergencies cannot become airborne and, therefore, cannot present an inhalation hazard. In such a situation, the crystalline silica need not be indicated as a hazardous ingredient since it cannot result in employee exposure."

Additional background information has been incorporated into the "rationale" section below.

Conclusions:

(1) If scientific testing demonstrates that the carcinogenic effects associated with crystalline silica are not applicable to the products being sold, then these products would not fall within the criteria described in section 58 of the CPR with respect to the cross reference to section 54 as it pertains to crystalline silica. Encapsulated crystalline silica has not been assessed by either ACGIH or IARC. The assessments made in relation to crystalline silica can not be extrapolated to draw definitive conclusions in relation to encapsulated crystalline silica. Therefore, encapsulated crystalline silica is not considered to fall within the criteria specified in section 54 of the CPR. Therefore, unless the product falls within other CPR criteria, the [WHMIS] supplier label and MSDS requirements of the HPA would not apply to the sale nor importation of this product.

(2) If, for example, polyethylene resins containing crystalline silica do fall within other CPR criteria, (i.e., the product is a [WHMIS] "controlled"product), neither the MSDS nor label need disclose information related to the carcinogenicity of respirable crystalline silica if, as per subsection 12(2) of the CPR, this information is not applicable to the controlled product nor, as per subparagraph 19(1)(e)(i), "appropriate to the controlled product". The MSDS must disclose, however, that silica is an ingredient if present at or above the applicable cut-off concentration.

Rationale:

The term "untested mixture" as used in section 58 of the CPR is not defined in the regulations. Therefore, the wording of section 58 implies that an "untested mixture" means "a mixture that has not been tested by any of the tests listed in sections 52 to 57". Problems arise, however, because section 54, which deals with carcinogenicity, specifies no tests. Rather, section 54 refers to literature that provides information on what "pure substances" and "tested mixtures" have been tested.

Therefore, the combined effect of section 54 and section 58 implies that an "untested mixture" in section 58 is a "mixture that has not been tested by any of the tests referred to in sections 52, 53, and 55 to 57 or a mixture that has not been tested for carcinogenicity as determined from the documents listed in section 54."

The absence of specified test methods in regulations does not have the effect of prohibiting testing or requiring that any particular test be used. Rather, the absence of a specified test leaves the

selection of the test method open to the tester so that any scientifically valid test method may be used. Similarly, the incorporation by reference of a series of test results such as the IARC list in paragraph 54(b) does not have the effect of limiting the available test methods to those used to achieve the incorporated test results. A mixture is "tested"whenever a scientifically valid test method is used to answer a testing hypothesis:

Section 58 of the CPR conveys the "hypothesis" that, under reasonable foreseeable use, an untested mixture containing an ingredient (at 0.1% or greater) listed in the referenced ACGIH and/or IARC documents will present carcinogenic risks analogous to that of the ingredient in pure form as a direct consequence of including the carcinogenic substance as an ingredient in the untested mixture.

In the present case, the hypothesis is that, under reasonable foreseeable use, polyethylene resins containing crystalline silica will present the same carcinogenic risks as pure crystalline silica as a direct consequence of the inclusion of crystalline silica as an ingredient in the product.

Scientifically valid testing entails sample preparation. Professional judgement must be used to prepare the sample, particularly if such directions are not included in the studies on which the IARC assessment is based. If a supplier attempted to produce respirable crystalline silica from, for example, polyethylene pellets in accordance with generally accepted standards of good scientific practice, this would be considered to be part of the scientific testing procedure. If respirable silica cannot be generated, the CPR does not impose a requirement to test the resulting substance. In the case of polyethylene encapsulated silica, with respect to testing for toxicological (and physical) endpoints, this is a different substance which is not included in the documents referenced in section 54 of the CPR.

References:

Canadian Centre for Occupational Health and Safety, "WHMIS Classification Workshop [February 22, 1988]", pages 110-112.

IARC Monographs on the Evaluation of Carcinogenic Risks to Humans; Volume 68, "Silica, Some Silicates, Coal Dust and para-Aramid Fibrils"; Silica [14808-60-7], crystalline (inhaled in the form of quartz or cristobalite from occupational sources) (Vol. 68; 1997).

U.S. Dept. of Labor; OSHA Directives, CPL 2-2.38D - Inspection Procedures for the Hazard Communication Standard, 29 CFR 1910.1200, 1915.99, 1917.28, 1918.90, 1926.59, 1928.21; March 20, 1998; http://www.osha.gov/pls/oshaweb/owadisp.show_document? p_table=DIRECTIVES&p_id=1551 &p_text_version=FALSE

U.S. Dept. of Labor; OSHA Standard Interpretation and Compliance Letters; "Applicability of the HCS to crystalline silica when bound in a polymeric compound and silicone rubber elastomers"; February 8, 1989 letter from Thomas J. Shepich, Director, Directorate of Compliance Programs; http://www.osha.gov/pls/oshaweb/owadisp.show_document? p_table=INTERPRETATIONS&p_id=19746&p_text_version=FALSEx