Aggregate and Cumulative Exposures

An understanding of the various routes of exposure for chemicals in products, as well as their interaction with similar chemicals, are an important element of REACH and will likewise be central to a reformed TSCA. In combination with data on health effects, this information will allow authorities to make required safety determinations. Reliable modeling of exposure scenarios will also equip companies to persuasively defend their products against unfounded accusations in the media, the internet and the courts.

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An influential 1994 National Academy of Sciences report called Science and Judgment in Risk Assessment was one of the first voices citing aggregate and cumulative chemical exposures as critical to understanding real-world risk. Aggregate and cumulative exposures are related concepts concerning the potential impact of a given chemical through multiple routes of exposure, as well as the possibility that multiple chemicals might interact to produce additive or synergistic effects. For example, a person might be exposed to mercury from a smelting plant, but also in the fish he consumers. The same person might be exposed to different substances that share mercury’s neurotoxic effects, for example in pesticides he uses in the garden.

The Lautenberg bill directs EPA to “consider” the work of the Academy in this area. H.R. 5820 goes further, directing EPA to incorporate aggregate exposures in its determination of “reasonable certainty of no harm” (RCNH) for a particular chemical. At the July 29 hearing, there was some disagreement among witnesses and subcommittee members whether EPA or the chemical manufacturer or processor bore the ultimate responsibility for examining and making judgments on these complex issues.

Several lawmakers, including Rep. Diana DeGette (D-CO) noted that a recent modification to the bill agreed to by its drafters would make the company responsible only for providing information on exposure related to the chemical’s “intended use.” The agency would then amalgamate company submissions on various uses and exposures and incorporate these into its safety determination. However, other sections of the bill make clear that the agency’s failure to make timely determinations can have the effect of keeping a chemical out of the marketplace. Consequently, if EPA is thwarted in its efforts by the complexity of the analysis, by resource constraints or other factors, producers, formulators and commercial users may well have to undertake this effort themselves in order to keep the substance in use.

Regardless of what TSCA eventually requires, we believe there are compelling reasons for companies involved in the production and use of chemicals to take a proactive approach to exposure modeling and life-cycle analysis. Exposure data is a necessary complement to data on human and ecological toxicity in the realm of product stewardship and defense. Given the ready access to information from a variety of media sources and the ease with which this information can be distorted or misunderstood, a company’s ability to substantiate its exposure, hazard and disposal findings will prove critical in defending a product, company or industry. The groundswell of toxic torts cases, along with state-initiatives to restrict or eliminate chemicals based on inaccurate data, further support the wisdom of building a baseline understanding of exposure. We believe there’s no need to wait for legislation, news coverage or litigation to begin assembling one's product defense arsenal.

Regulating Wood Dust - Is There A Better Way?

California OSHA is in the process of updating permissible exposure limits (PELs) for a number of airborne substances found in the state’s workplaces. Currently under review is wood dust, a byproduct of wood milling, sanding and routing in businesses ranging from small custom cabinetry shops to the largest sawmills and flooring producers. The history of wood dust regulation provides an interesting window into the interaction between researchers, federal and state safety agencies, courts and non-governmental standard setting bodies.

Wood dust first came to the attention of health researchers in connection with nasal adenocarcinoma. In the 1960's, English scientists observed a much higher than expected incidence of tumors in High Wycombe, an area northwest of London that was then a center of the furniture and cabinet industry. Adenocarcinoma cases were several hundred times more common among this group than among comparable industrial workers. When U.S. researchers attempted to replicate these findings, however, they found much lower relative risks associated with occupational wood exposure. In fact, pooled analysis of 220,000 woodworkers studied in North Carolina and Virginia identified only three cases, about what would be expected among the general public.

In light of this ambiguous evidence, U.S. OSHA proposed a fairly reasonable 5 mg /m3 standard for total dust as a time-weighted average (TWA) in 1989. This level, which was supported by key woodworking industry organizations, essentially required older plants to adopt the dust-control technologies such as cyclones and baghouses already being implemented by newer facilities. Unfortunately, OSHA compiled the wood dust standard with proposed PELs for hundreds of unrelated airborne substances. In 1992, a federal court found that not all of these standards were supported by good science and invalidated all of them.

Technically, that left wood dust regulated as a “nuisance dust” at 15 mg/m3. However, state occupational agencies (including Cal OSHA) adopted the 5 mg standard for total dust, and federal OSHA retained the power to cite dusty workplaces under its General Duty Clause. Recent workplace monitoring shows that the vast majority of work stations in woodworking facilities meet the 5 mg level. For example, Glindmeyer (2008) found inhalable dust samples ranging from 0.82 to 2.51 mg/m3 across a group of ten plants, which included furniture, kitchen cabinet, and flooring facilities as well as a sawmill. Geometric standard deviations ranged from 2.1-2.8 mg/m3.

About 15 years ago, researchers began focusing on non-cancer effects of wood dust. The concern was that long-term occupational exposure could compromise pulmonary function. This placed renewed focus on the smallest “respirable” dust particles most likely to reach the lungs. Generally, these measure 2.5 microns or less, the same size as the PM 2.5 particulate matter that have been the subject of ambient air regulation over the last decade.

A concern about the respirable fraction of dust and its impact on pulmonary health has informed analysis and standard setting in recent years. The American Conference of Governmental Industrial Hygienists (ACGIH) has set a recommended threshold limit value (TLV) of 1 mg/m3 for inhalable dust of most wood species. Cal OSHA is evaluating a mandatory PEL of 1 mg/m3 total dust. The agency’s health effects advisory committee wrote earlier this year that “the history of lung disease findings at higher wood dust exposure levels, with recent lower wood dust dose studies showing no or little adverse effect, and the … carcinogenicity of wood dust vis. a vis. sino-nasal cancer [supports] lowering the PEL to 1 mg/m3.” A committee charged with evaluating the technical and economic feasibility of this standard meets this October 6 in Oakland.

Deliberations over wood dust spotlight a complex interaction between researchers, state and federal regulators, industry, and the courts. This is probably not a decision-making apparatus that any of us would design from scratch. However, it has arguably responded effectively to emerging research and technological innovation. Is there a better, time and cost-effective approach?

We welcome your comments.