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Too much of a good thing?

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By Michael L. Dourson, PhD., DABT, FATS, FSRA

We have all likely heard someone say something is “too much of a good thing.” This applies to foods, like ice cream, drinks, like wine, and many kinds of activities, like watching movies. However, this also applies to chemicals to which we are exposed every day, or about which we often read in our daily news. 

In fact, all chemicals are toxic at some level – some can cause harm at very small concentrations, while others need a large amount before there is a danger to our health. For example, ingesting large amounts of dihydrogen monoxide can cause low blood sodium concentrations leading to nausea, fatigue, confusion and seizures, and even death, but few people would want to ban di-hydrogen (H2) mono-oxide (O)—also known as “water”— from public sale and or other uses, since water is safe and necessary when we drink a normal amount.

For many chemicals, however, it’s difficult to know what level causes or does not cause harm. For example, most people know arsenic as a poison, but may not know that many foods contain small amounts of arsenic, since it is a part of our environment. How much arsenic can people eat and not be harmed? 

You might remember the scare a while back about too much arsenic in apple juice. The U.S. Food and Drug Administration analyzed a large number of apple juice samples for arsenic and compared them with their estimate of its safe dose, the level at which no harm was expected. The FDA concluded that the very low levels of naturally occurring arsenic in apply juice were not a public health risk and the juice was safe for consumption. Eventually FDA developed guidance for manufacturers.

Because of this difficulty, toxicologists have been trained to make a determination of levels where a chemical causes harm and where it does not, generally in experimental animals. These determinations are then evaluated by scientists who specialize in risk assessment to make a judgment about the safe dose or safe level of the chemical to humans. These risk scientists work in governments, industries, consultancies, and, to a less extent, universities and non-governmental organizations (NGOs).

These safe levels go by different names, a common one in the US is the reference dose (RfD). But despite different names and slightly different approaches, risk scientists all follow three basic steps:

Toxicity data are reviewed from laboratory studies generally on animals to confirm the levels of exposure that show harm and those which do not. Sometimes important information is found from unintended human exposures.

Uncertainties in the data and analyses are then considered, particularly when using animal studies, and a judgment is made of a chemical exposure that would be safe, even for sensitive groups of people (like children or the elderly).

New research may be requested of toxicologists to resolve uncertainties or unclear data or analysis.

If you want to learn more about safe levels of chemicals, or how they are developed, many agencies provide a wealth of information. For example:

U.S. National Library of Medicine, has useful toxicity information about chemicals on its websites (see http://toxnet.nlm.nih.gov);

U.S. Environmental Protection Agency also has a wealth of information on many of its websites (http://epa.gov; 

Society of Toxicology has its annual meeting in March (see https://www.toxicology.org/index.asp).

Toxicology Excellence for Risk Assessment assesses the risk to chemicals and shares this information (see https://tera.org); 

Toxicology Education Foundation has produced an excellent 15-minute video called “Is It Safe?” (http://toxedfoundation.org/is-it-safe-video-english-with-japanese-subtitles/) that provides information for the general public about chemicals and risk so that you can make good decisions associated with everyday products (see also other topics at: http://toxedfoundation.org).

American Council on Science and Health at https://www.acsh.org has essays on numerous topics many of them associated with chemicals and their safety.

These are only six examples of many groups that work on behalf of the public to keep us s.afe

WEEL OEL

Occupational Exposure Limits (OELs) are designed to safeguard the health of healthy workers during their careers. These limits are based on the assumption of repeated daily exposure throughout a working lifetime, typically averaged over an 8-hour workday. Their purpose is to prevent both immediate (acute) and long-term (chronic) health issues arising from workplace exposures. It’s important to note that OELs are not intended for the general public, which includes vulnerable groups like infants, the elderly, and those with pre-existing health conditions.

Workplace Environmental Exposure Levels (WEELs) are health-based guidelines for chemical hazards in the workplace. These values represent air concentrations believed to protect the majority of workers from negative health effects resulting from occupational chemical exposure.

The WEEL Process
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The development of new or revision of existing WEELs is typically assigned to voluntarily designated subcommittees. A subcommittee usually comprises 3 – 4 members from the WEEL Committee. New WEELs are developed using the OARS-WEEL administrative standard operating procedure (SOP), while existing WEELs are usually revised every 10 years, unless the availability of significant new data which may impact the existing WEEL value compels the committee to make a revision sooner. The OARS-WEEL SOP contains procedures and guidelines governing conflicts of interest, draft document preparation, literature searches, draft document review, balloting process, post-ballot WEEL documentation quality assurance scientific review, and publication.

Once a subcommittee has prepared a draft WEEL document, a review of the draft is scheduled for the next available Committee meeting. The WEEL Committee members are expected to have reviewed all such drafts prior to the meeting. If no major changes are necessary to a draft, the attending Committee membership may, by a simple majority, approve the WEEL for balloting. Alternatively, the Committee may direct the subcommittee to revise the WEEL and present it for further discussion at a future meeting. If a ballot is not approved by a two-thirds majority of non-abstaining Committee members, it is discussed at the next Committee meeting to determine the appropriate course of action. Once the WEEL is approved by a two-thirds majority of non-abstaining Committee members, copies of ballot comments are forwarded to the designated subcommittee and all substantive comments must be addressed in the final draft. If resolution of a substantive comment results in a change to the WEEL value or a change in the basis for the value, the draft must be re-balloted.

Once all comments have been addressed on a successfully balloted draft, document formatting and editorial review are performed by TERA, before the draft WEEL document is made available for public comment (usually for a period of 30 days but may be extended if the need arises). After the public comment period has elapsed, comments are addressed by the subcommittee responsible for that specific draft, after which the WEEL documentation is submitted to Toxicology and Industrial Health (TIH), a peer-reviewed medical journal that covers research in the fields of occupational health and toxicology, for publication. A thorough review of the galley proof by the scientific content quality coordinator at TERA, and proofreaders and editors at TIH is the penultimate step before eventual publication of the WEEL documentation.

The WEEL Committee

The OARS-WEEL Committee is composed of volunteer experts specializing in the scientific determination of occupational exposure levels. This committee actively seeks a balanced representation of professionals from toxicology and industrial hygiene, drawing upon a diverse range of experience from industry, government, academia, and consulting. Importantly, each member contributes to the Committee based on their individual expertise and not as an official representative of their respective employer, organization, or agency.