TSCA and Exposure Assessment: Risk Evaluation

This post is a continuation of the series on TSCA and exposure assessment. Today’s topic is risk evaluation, including the prioritization process for EPA.

15 CFR 53 Part 2605 explains how, once the U.S. Environmental Protection Agency (EPA) Administrator determines that a chemical substance or mixture presents a risk, the Administrator can apply one or more requirements to the substance.

The requirements can include:

• A prohibition or limitation restriction on manufacturing, processing, or distribution of the substance
• A prohibition or limitation on manufacturing, processing, or distribution of a substance for a particular use or concentration in excess of a level set by the Administrator
• A requirement for the substance or mixture to be marked with warnings and instructions with respect to use, distribution, and/or disposal – the form and content of these warnings is prescribed by the Administrator
• A requirement to maintain records associated with the manufacturing process and tests used to assure compliance with TSCA
• A requirement prohibiting or regulating any commercial use of a substance
• A requirement prohibiting or regulating any manner or method of disposal of a substance, or of any article containing the substance (applies to manufacturers, processors, and commercial use)

The EPA has released a risk-based screening process which will be explained in detail in a later post, but basically delineates chemical substances and mixtures as high-priority or low-priority. Only high-priority substances undergo risk evaluation at this time, and this is anticipated to a be a 3- to 3.5-year process. EPA must consider the hazard and exposure potential of the substance, including persistence and bioaccumulation, susceptible subpopulations, storage near drinking water sources, and whether there are conditions of use or volumes that are of concern.

A chemical substance submitted to EPA should have prioritization conducted within 9 months to 1 year. EPA will start with the chemical substances previously identified in the TSCA chemical work plan and then move on to other chemicals. EPA has 3.5 years to start conducting risk evaluations on 20 other high-priority substances, with preference given to chemicals on the 2014 update of the TSCA chemical work plan that are persistent, bioaccumulative, carcinogenic, or toxic (acute or chronic effects).

An interesting quote from 15 CFR 53 Part 2605 (b)(2)(c): “The Administrator shall continue to designate priority substances and conduct risk evaluations […] at a pace consistent with the Administrator to complete risk evaluations […]” (emphasis added). So, basically, EPA gets to set its own pace on this. 

Another interesting requirement is that risk evaluations of metals and metal compounds must use the Framework for Metals Risk Assessment of the EPA’s Office of the Science Advisor (2007) or its successor document.

The requirements for a risk evaluation are identified as:

• Integrate and assess available information on hazards and exposures for the conditions of use of the substance (considering risk of injury to health or the environment and susceptible subpopulations)
• Describe whether aggregate or sentinel exposures to a chemical substance under the conditions of use were considered, and the basis for that consideration
• Not consider costs or other non-risk factors
• Take into account the anticipated duration, intensity, frequency, and number of exposures under the conditions of use
• Describe the weight of scientific evidence for the identified hazard(s) and exposure(s)

“Aggregate” and “sentinel” exposures are not defined in the regulation. EPA further complicates this by using “aggregate” and “cumulative” in their website about exposure assessment tools being used.

• Aggregate = considers combined exposures to a single stressor across multiple routes and multiple pathways
• Cumulative = evaluates combined exposure to multiple stressors via multiple exposure pathways

The American Chemistry Council (ACC) had these same concerns in their response letter to EPA, recommending that EPA consider including “definitions of both aggregate and sentinel exposures in the proposed regulation so the regulated community will understand how EPA intends to apply the terms, and to ensure consistency and regularity in application.” ACC provided the following definitions for clarification:

• Aggregate = combined exposure for one substance over multiple exposure pathways from multiple difference sources (similar to definition given above)
• Sentinel = the exposure that is judged to cause the plausible upper-bound individual human exposure to a substance of interest within a broad category

When the EPA completes a risk evaluation, the Administrator should consider and publish a statement based on “reasonably available information” with respect to:

• Effects of the chemical substance on health and magnitude of exposure of human beings
• Effects of the chemical substance on the environment and magnitude of exposure of the environment
• Benefits of chemical substance (for various conditions of use)
• Reasonably ascertainable economic consequences of the rule, including the effect on the national economy, small business, technological innovation, the environment, and public health, as well as the costs/benefits of the regulatory action and the cost effectiveness of the regulatory action

This is seemingly contradictory, since the risk evaluation is supposed to be conducted without consideration of costs, but the final risk evaluation must consider costs and other economic consequences…it also requires the Administrator to consider if there are technically and economically feasible alternatives available before releasing a final rule on a substance.

In my next post, I’ll explain the risk evaluation process for TSCA. Future posts will include the following topics:

• Imminent hazards in TSCA
• Reporting requirements of TSCA
• Research aspects of TSCA
• How TSCA handles confidential information
• Citizen’s civil actions and petitions in TSCA
• Employee protection and TSCA effects on employment
• How test methods will be developed and evaluated for TSCA
• ReachScan: the exposure assessment model
• Using predictive methods to assess exposure 
• New chemical exposure limits under TSCA