Synergist - September 2009

This generation of data will lead to changes in the hazard profile, and therefore the hazard classification, of many common workplace chemicals.

Some changes will be mere

New and Expanded Hazard
Endpoints

OSHA has clarified that environmental hazards are outside its jurisdiction. In contrast, GHS and REACH address physical, health and environmental hazards. Because of their influence, material safety data sheets (MSDSs) may begin to include significantly more information in section 12 (for ecological information).

GHS includes 16 physical hazards and 10 health hazards. Furthermore, most of these endpoints are divided into multiple categories. While most of these endpoints are consistent with those in the OSHA Hazard Communication Standard, GHS introduces some new endpoints and categories—for example, self-heating substances and substances which, in contact with water, emit flammable gases. New health hazards will include germ cell mutagenicity and effects on or via lactation, as well as the separation of target organ toxicity after single versus repeated exposures.

Existing endpoints with expanded categories include acute toxicity. For example, OSHA has two categories for acute oral toxicity: highly toxic (≤50 mg/kg) and toxic (>50 to 500 mg/kg). Under GHS, there may be as many as five categories for acute oral toxicity: ≤ 5 mg/kg; > 5 to ≤50 mg/kg; >50 to ≤300 mg/kg; >300 to ≤2,000 mg/kg; and >2,000 to ≤ 5,000 mg/kg. As a result of these new and expanded endpoints, both the breadth and depth of the hazard information communicated in the workplace will increase.

semantics, with little impact
on safety and health programs;

others may require changes
in how chemicals are managed
in the workplace.

GHS criteria describe which tests and data should be used for classification as well as the manner in which hazard assessments should be conducted in order to minimize the use of animals in testing. For example, users are directed to classify skin corrosivity and serious eye damage based on pH rather than in vivo tests.

The adoption of GHS in the U.S. will result in significant changes in the classification of untested mixtures. Under the OSHA Hazard Communication Standard, the thresholds for extrapolating the hazards of components to the mixture are 1 percent for non-carcinogens and 0.1 percent for carcinogens. Under GHS, the hazards that need to be extrapolated at 0.1 percent are expanded to include germ cell mutagenicity, and reproductive/developmental toxicity (including effects on or via lactation). The thresholds for some of the other endpoints will be raised to greater than 1 percent.

In addition, GHS will add the European
concepts of “additivity” and “step-down”
of hazards to the mixture rules. Additivity
is the practice of summing the concentra-
tions of components with similar hazards;
if the total exceeds the applicable thresh-
old, the hazard—such as skin corrosion/ir-
ritation or eye damage/irritation—is
extrapolated to the mixture. Step-down
refers to the mitigation of a component’s
hazard at lower concentration in the
mixture as opposed to OSHA’s all-or-
nothing approach.

Prescriptive Classification Criteria and Mixture Rules Appendix A of the Hazard Communication Standard, which is approximately four pages long, defines the OSHA health hazards. Many of the criteria are descriptive rather than prescriptive. In contrast, GHS provides 150 pages of criteria and mixture rules for physical and health hazards, and much of this guidance is prescriptive. These rules will result in changes to the hazard classifications of many common workplace chemicals.

Fraction of Unknown Toxicity While animal rights advocates and even toxicologists have questioned the role of acute toxicity data in health and safety programs, these data are a cornerstone of GHS. All chemicals and mixtures must have either a measured value, a bridged value or a calculated value for acute toxicity. The calculated value for acute toxicity is known as the Acute Toxicity Estimate (ATE); it is derived using acute toxicity data for each component and a formula based on the weighted average approach. An alternate formula can be used if data are not available on all components, but if this data gap is greater than 1 percent of the composition, the communication of the ATE must be accompanied by a statement that indicates which percentage of the mixture is of unknown toxicity. While the concept of “unknown toxicity” is understood by EHS professionals, it will be new to many workers.