New chemical exposure limits

Some of the model 5(e) orders have provisions for new chemical exposure limits, (NCELs) that can be implemented instead of using respirators to limit risks from inhalation of the PMN substance. NCELs are specific numerical limits on the airborne concentrations of the PMN substance. The EPA may develop a maximum concentration for eight hour exposures, a maximum concentration for work shifts that are shorter or longer than eight hours, and a short term exposure limit (STEL) for fifteen minute exposure periods. In order to use NCELs instead of respirators, the signatory must develop a sampling and analytical plan and have it verified by an independent third party laboratory. As of 2002 the EPA had developed thirty four NCELs. ... 

New chemical exposure limits (NCELs) for new chemicals regulated under TSCA are modeled after OSHA s permissible exposure limits (PELs) for workers exposed to a substance by inhalation. NCELs may include an eight-hour time weighted average limit or a short-term exposure limit for a chemical substance. In 1995, the US EPA described the risk basis for determining... 

US EPA. 1995. Response to External Comments on New Chemical Exposure Limits... 

Although there is much controversy over using animals in tests such as these, the information is an essential part of the legal testing required when new chemicals are introduced onto the market in significant quantities. These and other toxicity test results are used to help develop Material Safety Data Sheets, establish Occupational Exposure Limits and guidelines for use of appropriate safety equipment. 

Assessments of these new chemicals are made by teams of multidisciplined scientists, and are based on limited firm data, comparisons to similar chemicals and estimations of exposure to humans and the environment. Generally, these PMNs contain some information on acute health effects but relatively scant information on chronic health and environmental effects. 

Galer, D. M., Leung, H.-W., Sussman, R.G. and Trzos, R.J. (1989). Scientific and practical considerations for developing occupational exposure limits for chemical substances. Presentation to the Second Annual Occupational Toxicology Roundtable, November 21, 1989, Rahway, New Jersey. 

Secondly, firms should cooperate with EPA in spirit and action by moving voluntarily to mitigate risks (when present) from toxic new chemicals. Appropriate actions might include taking precautions and safeguards to limit exposure to humans or the environment in manufacture, use, and disposal. I can cite many examples where chemical companies have faced environmental problems in certain of their activities, and with the... 

Substances not on the Inventory or are not otherwise excluded or exempt are considered new and are subject to a premanufacture notice (PMN). Examples of exclusions would include mixtures, substances subject to another statute, impurities, by-products and nonisolated intermediates. Additional exemptions also include test marketing products, low volume products, polymer exemptions, LoREX (low release and exposure exemption), and R D substances. By statute, chemical manufacturers must notify the Agency at least 90 days before manufacturing a chemical substance that is not listed on the TSCA Chemical Substance Inventory. However, TSCA does not empower the US EPA to require routine testing of new chemicals to permit a valid evaluation of the potential risks. This has been a limitation in the overall effectiveness of the PMN process. Erequently, very little data accompanies the PMN (50% of submissions present no safety data and 90% have only an LD50 and an Ames test) however, the EPA must decide within 90 days if the submitted chemical will pose a health or environmental hazard. 

Conclusions. This section has outlined the problem of uncertainty in preventing risks from chemical exposures and the limitations of current scientific and decision tools based on the concept of risk assessment. It has outlined a new paradigm for decision-making for sustainability embodied in the precautionary principle. This approach has several key aspects ... 

For exposure to multiple chemicals, PBPK modeling is further limited as a predictive tool, as all interactions among the various chemicals within the organism must be known and incorporated into the model. Difficulties in multiple-chemical exposure are clearly illustrated in drug-drug and drug-food interactions, where one substance affects the pharmacokinetics or pharmacodynamics of another. To address the need for predictive capability for individual and mixtures of chemicals, new advances and approaches are required. Biochemical reaction network modeling is one nascent approach, as described in Section 3.4. 

---