Section I: Overview and Fundamentals

"j Total Exposure Health

Total Exposure Health: An Exposure Science Framework for the Fourth Industrial Age

Kirk A. Phillips

LJB, Inc. Engineering

Origins of Total Exposure Health

Total Exposure Health (TEH) provides today’s industrial hygienists (IHs), environmental health specialists (EHS), and safety professionals a framework to more effectively respond to the changing nature of the industrial work environment, the increased availability of technology to obtain exposure monitoring, and the ability of the human body to respond to internal and external exposures at the genetic and molecular biological response levels. TEH can, therefore, be thought of as the way for the exposure scientist to respond in a more effective way to society’s desire for healthier life choices.

The Steadfast Practice of Industrial Hygiene

A review of the Text-Book of Hygiene, 3rd Ed (Rohe 1898), is an amazing trip through time from an occupational exposure standpoint. It is interesting to note that many of the tables and knowledge in the early edition were pre-American Civil War. So much was learned during the war because Sanitary Engineers, the term for IHs of the day, were embedded with the fighting forces, and revised editions were needed to incorporate significant increases in preventive health knowledge. What makes this textbook amazing today is that much of what is understood about exposures to workers and communities was also understood to some extent back then in each of the primary categories of chemical, physical, and biological agents (Rohe 1898). Chapter 5 of this volume by Yamamoto provides additional historical perspective on the development of the practice of IH.

Due to the limits of science in 1898, Rohe’s work was qualitative not quantitative measurements. For example, coal miner’s lung was described, and the essential elements of an exposure assessment (anticipation, recognition, evaluation, and control) were used. This early text concluded that the causes of the lung disease were the contaminants in the air along with increased time of exposure. It also carefully tabulated the life expectancy of each job type in the industry. Disease-causing organisms, such as bacteria, were just being understood, and their causes and effects were being debated in scientific communities. Nevertheless, the handbook described the symptoms of cholera, its connection to water, the need to observe spread in a population, and the need to change the water source. Similar descriptions of exposures to arsenic, noise, acids, ammonia, chlorine, mercury, lead, carbon monoxide, carbon disulfide, mineral wools, cotton dust, phosphorous, illness from heat, sedentary lifestyle, mechanical violence, and many more were all covered and applied to populations of people or essentially similar exposure groups (SEGs). Today, the application of IH and environmental health (EH) is significantly enhanced as scientists better understand the functions of organs and systems in the body, develop ways to quantitatively match exposures to observed effect levels, and then establish criteria to reduce or limit the negative effects. What has not changed is the use of population studies to determine the exposure level of concern. This stable application of IH and EH practices through many years led to the realization that TEH could be used to refine the science of IH and EH.

Exposures and Exposed Populations Are Decreasing

The second indicator that a new application of exposure science was needed was the changing nature of exposure from a quantification standpoint both in the levels of exposure and in the number of people being exposed. The nature of work in societies across the industrial world is changing rapidly as the industrial nature of work decreases for many workers (Sterling 2019). The reduction of exposures across the industrial workforce utilizes the full spectrum of the hierarchy of controls. Many manufacturing and heavy industry positions have been modified to decrease exposure to the worker using engineering controls, material substitutions, roboticiza- tion, and personal protective equipment (PPE). The result of these efforts is that the occupational and environmental health communities have been successful in identifying, measuring, and reducing exposures for significant portions of the workforce. Although it is true that significant numbers of workers are still being exposed to chemical, physical, and biological agents, the exposures have been reduced. Despite these reductions, IHs still desire to make a difference in the healthfulness of workers and to be able to demonstrate that they are being successful.

The challenge today is that many exposed populations under an IH’s or EH’s management have few exposures that exceed exposure limits; when exposures do exceed limits, there are controls that place the exposures within acceptable levels. Success, as defined today, is protecting a statistically significant portion of the population by using a standard established to protect the majority of the population. Those individuals who manifest a disease are often thought to be outside of the ability to be protected, or their disease is not considered to have been significantly caused by their exposures.

Over time, the trend will be for exposures of individuals to go lower and for the number of workers in jobs with exposure to continue to decrease (Postelnicu and CSlea 2019). Relevancy of the IH is bound to be questioned by many business owners and workplace supervisors. There will still be disease and the exposures will still have an impact on workers, but the overall cost to the business will decrease and make the job of the IH seem irrelevant.

Sensors Are (Almost) Ubiquitous

IHs, by definition, take care of exposures in the workplace, but to effectively protect workers, they must consider the environment outside of the workplace. A worker who plays in a rock band as a hobby or for a secondary income is not likely to have the requisite hours of quiet needed for recovery if he or she is exposed to noise at work, and alternative allowable exposure levels and intervals should be considered in determining his or her overall health. Other examples of outside of the w'ork environment issues w'ould be workers with hobbies like small engine repair or artists w'ho use spray can paints or those whose hobbies use significant amounts of volatile organic chemicals. Such environments must have their exposures considered so that the combination of all exposures does not exceed a unity calculation for chemicals with similar metabolic mechanisms or organ targets. In these situations, IHs should inquire about these outside exposures, but many do not; if they do, they rely on generalized estimations of exposures of concern based on a narrative given by the worker.

A concerned person might ask, “Why not just send a sensor home wdth the worker to collect data on these exposures?” Often, the answer is that IHs w'ho desire to collect data outside of the workplace have concerns with the legal implications of sampling outside the workplace and/or the instrumentation is too expensive and in limited quantities and there simply are not enough resources to gather data for periods of non-work. However, sensors are becoming smaller and cheaper to the point that individuals are buying them and using them in their everyday lives.

The fact that sensors are becoming cheaper and more available gives the IHs new tools that can be incorporated into their practices and obtained from the EH community to ensure exposures to individuals are accounted for regardless of location and time exposed. For a more in-depth discussion of this new possibility, refer to the chapters in the “Advances in Exposure Sciences” and “Bioethics” sections in this volume. The important aspects that led to the creation of TEH are the availability of the data under the IHs control and the data being collected through sensors owned by others.

Expanded Knowledge of Disease, Mechanisms of Disease, and Genetics

Historically, exposure limits have been derived occasionally from actual human exposures when significant numbers of humans were being exposed to sufficient toxic levels. These exposures were not intentionally given in order to develop an exposure limit; they just occurred, and occupational health benefitted. Disease-producing agents, noise, asbestos, and lead are commonly understood to be in this category. However, it is difficult to get the exact data needed through human exposure due to the ethics of intentionally exposing a human.

The animal study has been the gold standard for exposure-based science, and toxicologists apply the science of exposure to these populations and then apply the observed exposure effects from an animal model to a human model. These studies look for significant changes that can alter cell viability or organ performance. This approach has been effective in the past and is the present source of many exposure limits. However, these studies document numerous limitations and introduce some fairly significant and potentially large safety factors. They all additionally have the limitation of applying to a population which cannot account for outlier members of the populations but instead provides protection for the majority.

Three professions are diligently working on a better understanding of the human body at the cellular level: computational toxicologists, molecular biologists, and geneticists. More will be discussed in this text, but for now, it is sufficient to understand that IHs and EHS have not, as a community, necessarily begun to see these science disciplines as partners in the exposure science community and valuable team members to achieve the goal of disease prevention among workers and non-workers.