Chemical Hazards

After reading this chapter, you will be able to:

• ➤ Define chemical hazards and explain how they affect workers.
• ➤ Interpret toxicity data to prioritize chemical hazards.
• ➤ Explain how occupational exposure limits were set and assess the validity of these limits.

In the spring of 2024, Allan Adam, the chief of the Athabasca Chipewyan First Nation, served a statement of claim on the Alberta Energy Regulator. The lawsuit, which has not yet been proven in court, seeks damages because of multiple tailing pond leaks at Imperial Oil’s Kearl facility between May 2022 and February 2023. Imperial Oil initially reported to the energy regulator in May 2022 that it had found the leak outside the boundaries of the company’s site on Treaty 8 territory. However, it was not until early 2023 that the public, and members of the Athabasca Chipewyan First Nation, became aware that 5.3 million litres of toxic chemicals had leaked from four tailings ponds.1 Over the 9-month period, the energy regulator took no steps to notify the First Nation of the leaks.

The occupational and environmental risks associated with oil and gas can be significant and complicated. Tailings ponds result from oil sands mining and are used to store waste. Tailings contain increased concentrations of substances such as mercury, lead, ammonia, naphthenic acid, and cadmium. Currently, there are no effective and cost-efficient methods for dealing with tailing ponds by-products. Although researchers try to come up with treatment technology, workers and the public are left with the accumulating tailings ponds and the associated chemical hazards.

Oil sands workers, particularly those involved in maintaining tailings ponds, are exposed to these hazards. The chemical hazards can also affect the general public. The ponds can leak because of improper design, aging, or natural events such as floods. Chemicals from tailings ponds can seep into the local water table, which often serves as the source of local drinking water for people and wildlife, posing a significant health risk.

Back in 2006, Dr. John O’Connor raised concerns about elevated cancer rates in the Fort Chipewyan community, home to the Athabasca Chipewyan First Nation, suspecting a link to nearby oil sands development. As a result of raising concerns, Dr. O’Connor was accused of causing “undue alarm” and investigated by the Alberta College of Physicians and Surgeons. Subsequently, a 2009 study by the Alberta Cancer Board confirmed higher rates of cancer in the community but offered a number of alternative reasons, such as chance and increased health risks taken by community members. In 2009, the Alberta College of Physicians and Surgeons found that Dr. O’Connor had committed no wrongdoing in raising the alarm.2

Tailings ponds are but one example of the growing threat that chemical hazards pose to the health of workers. It also demonstrates that there is no clear division between a workplace hazard and an environmental hazard. There is no comprehensive list of chemical substances that workers may be exposed to in the workplace, but the number is suspected to be at more than 194,000. As we will see below, there is toxicological data available for fewer than 1% of these chemicals, and the data that is available is highly suspect. The essentially unregulated nature of chemical exposures in the workplace is an important argument for adopting the precautionary principle in occupational health and safety.

Chemicals are everywhere in the modern workplace, from printer toner to engine exhaust to sink cleaners. While most chemical exposures do not cause ill effects, some certainly do. As we saw in Chapter 3, chemical hazards cause harm to human tissue or interfere with normal physiological functioning when they enter our bodies. Some chemicals irritate our tissue while others poison our systems or organs. Chemicals can asphyxiate us or negatively affect the functioning of our central nervous systems. Chemicals can also cause our immune systems to overreact, change our DNA, cause cancer, or damage a fetus.

The impacts of chemicals on people’s bodies can be understood with the acronym ADME, which stands for absorption, distribution, metabolism, and elimination.3Absorption refers to the four routes of entry by which chemicals can get into a worker’s body, the most common being through respiration (i.e., breathing in contaminated air, fumes, or gases) and absorption through the skin or eyes. Chemicals can also enter our bodies through ingestion (i.e., we can eat or drink them—usually accidentally) and through injection or breaking through the skin. Different chemicals are absorbed at varying rates in the body, and, though some effects might be localized to the absorption site, absorption is often just the initial step. It is important to consider how a chemical enters the body since it has impacts for the next steps. For example, if a chemical enters a person’s blood plasma, then it will move much faster since blood moves through the body rapidly compared with interstitial fluid (the fluid surrounding cells), which is slower.

Distribution is how and where the chemical moves in a body. A chemical’s ability to move throughout the body is often linked to its water or fat solubility (i.e., its ability to form a solution in water or fat) and its size or molecular weight. Not all chemicals move easily through the body, and in many cases the exact mechanism of distribution might not be known. Instead, a chemical’s toxicity is often assessed based on characteristics such as molecular weight and water solubility. Understanding how a chemical is likely to be distributed is critical for understanding the impact of the chemical on a body. A chemical that can quickly dissolve in water and has a smaller molecular weight will have less difficulty getting through cell membranes. Similarly, if a chemical can enter the bloodstream, as mentioned above, then it can distribute much faster into the rest of the body.

Metabolism refers to how the chemical breaks down in a person’s body. Specific organs, such as the liver, are responsible for metabolizing substances that enter the body, and thus these organs can be at risk when exposed to certain chemicals. Also, our bodies metabolize some chemicals into other substances, which can be more or less toxic than the original substance. For example, carbon tetrachloride, a solvent commonly used in dry cleaning, becomes more toxic when metabolized and can cause liver cancer.

Elimination is how the chemical is expelled from the body or, in some cases, how it accumulates in the body. Our bodies excrete some chemicals in our sweat, exhaled breath, urine, and feces while retaining other substances. If a chemical is not excreted, then it can accumulate in the body, or, if our bodies break down a chemical, then the components can bioaccumulate and cause disease or ill health. For example, graphite or silica dust inhaled into the lungs can remain in them forever and lead to chronic diseases such as graphite pneumoconiosis and lung cancer.

Chemical hazards have varying levels of toxicity (i.e., ability to cause injury). Toxicity can be local or systemic. Local toxicity is a reaction at the point of contact. For example, you might experience a burn on the skin of your fingers after handling spicy peppers in a restaurant kitchen. Systemic toxicity occurs at a point in the body other than the point of contact. Allergic reactions after prolonged exposure to latex would be an example of systemic toxicity (see Box 5.1). Another example might be organ damage following skin absorption of a pesticide while picking fruit.

Acute toxicity represents the immediate harm caused by exposure to a chemical substance. Typically, acute toxicity occurs within minutes or hours of exposure, although with certain chemicals, such as some pesticides, symptoms can take several days to appear. Chronic toxicity represents a substance’s ability to cause harm over a longer period of time. It’s important to note that most chemicals cause both acute and chronic toxicity, although research tends to focus more on acute toxicity. The time between exposure to a chemical hazard and the development of symptoms from that exposure is called the latency period. Many of the consequences of exposures to chemical hazards (e.g., occupational diseases) have a latency period that is measured in years. As we saw in Chapter 2, this delay can confound the relating of diseases to occupational exposures.

Although only a fraction of all chemical exposures result in a worker’s death, toxicity is often measured in terms of a substance’s lethal dose (LD) as determined from animal experiments. For example, the toxicity of a chemical tested on rats via ingestion might be expressed as Oral LD50 (rat): 56mg/kg. What this means is that when rats were fed the substance, half (the ‘50’ after the LD) died shortly after ingestion when given 56 milligrams of the substance per kilogram of animal weight. These LD50 values are measures of substances’ acute toxicity and allow us to compare the toxicity of substances. Substances with a lower LD50 are more acutely toxic than substances with a higher LD50 because lower LD50 substances cause half of the animals to die at lower doses. The toxicity of substances may also be measured based upon their lethal concentration (LC) in the air or water.

These toxicity measures show us that the dose (or amount) of a chemical that enters the body affects whether the chemical exposure causes harm and the degree of harm. For example, some chemicals are relatively harmless in low concentrations, such as the methane gas that can sometimes be found in well water as a result of fracking operations. But, in high concentrations, methane can displace oxygen and cause rapid heart rate, fatigue, nausea, and, eventually, death by asphyxiation. (It is also flammable and potentially explosive.) That said, it is important to note that doses that are too low to cause acute toxicity can still cause chronic toxicity, especially if the dose is repeated over time. Prolonged exposure to silica dust, for example, can give rise to silicosis—a lung disease that impedes respiration—but silicosis may not manifest itself for 10 to 30 years after the exposure.

While toxicity data is helpful in identifying chemical hazards, it is important to be cautious when using it. Lethal dose measures focus on the acute toxicity of a substance and are less useful in assessing a substance’s chronic toxicity or the effect of repeated exposures to low doses. Toxicity experiments also tend to be based upon ingestion of the substance because ingestion- and absorption-based experiments are less expensive than experiments based upon respiration. This bias may reduce the accuracy of the resulting data because most chemicals enter our bodies through respiration or skin absorption. Toxicity data is also based upon animal experiments, and these results may not be perfectly applicable to humans. Perhaps most concerning is that toxicity experiments typically assess the toxicity of a single substance in isolation. This ignores the reality that most workplaces expose workers to multiple chemicals and these exposures may interact synergistically. That is to say, exposures to multiple chemicals may increase the toxicity of each chemical out of proportion to its toxicity in isolation.

As discussed in Chapter 3, controlling chemical hazards begins by identifying worker tasks and environmental factors associated with the location. Subsequently, we must identify and list each chemical a worker is exposed to and the route(s) of entry for that chemical. The potential hazard posed by each exposure and the risk of exposure should be determined along with control strategies. It is important to consider each chemical both independently and in combination with other hazards because differences in absorption and toxicity can suggest different controls. Control strategies used should follow the hierarchy of controls, beginning with elimination (e.g., using non-chemical processes) and substitution (e.g., using a less hazardous chemical), then progressing to engineering controls (e.g., physically isolating workers from the chemical).6

Less effective control approaches include administrative controls that minimize or standardize exposures and the provision of personal protective equipment (PPE). In addition, some workplaces provide special facilities (e.g., showers, lunchrooms) to minimize workers’ exposure to chemicals. Some organizations will also undertake extensive medical and environmental monitoring and record keeping. This can include monitoring the level of a hazard in a specific area (area monitoring), the dose experienced by a worker (personal monitoring), or the presence of a chemical or its metabolic residue in a worker’s blood, body fluids, or tissues (medical monitoring). While not hazard controls per se, monitoring and record keeping can provide data that can help to adjust administrative controls, assess the effectiveness of PPE, and identify early signs of health effects. Box 5.2 discusses the complexities of controlling chemical exposures that result from the growing risk of wildfire due to climate change.

In practice, controlling exposure to chemical substances can be difficult. Workplaces often use multiple chemicals, which may have poorly documented synergistic effects. Further, the ways in which products are used may change over time, thereby reducing the effectiveness of administrative controls such as exposure and handling protocols. For example, a reduction in the number of cleaning staff in a hotel may mean workers must now work faster because their workloads have increased. Prior to the staffing change, workers may have used one chemical product to clean toilets and, subsequently, another product to clean the bathroom floors. To cope with the reduced time the workers are given to clean the entire bathroom, the workers may begin applying both products at the same time, creating the possibility of hazardous chemical interactions. Such a change in practice may be unknown to the employer. This example demonstrates that health and safety can be profoundly affected by other human resource practices, such as job design, staffing, and scheduling.

Toxicity data is used to generate occupational exposure limits (OELs). OELs for chemical hazards represent the maximum acceptable concentration of a hazardous substance in a workplace. As we saw in Chapter 4, there are also OELs for physical hazards such as noise, radiation, and (more rarely) vibration. In theory, workers exposed to a chemical substance at the OEL for their entire working life will experience no adverse health effects. In Canada, each jurisdiction sets its own OELs. Governments typically use or reference guidelines provided by the American Conference of Government Industrial Hygienists (ACGIH), a professional organization that publishes exposure limits. Although some jurisdictions use the most recent ACGIH limits, others use limits set for a specific year (e.g., Alberta uses limits set for 2006), and some jurisdictions develop their own distinct limits. When jurisdictions set their own limits, they often review the ACGIH recommendations, including any scientific data, the technical ability to measure substances at worksites, and the economic feasibility of industry compliance.14 Economic considerations can sometimes lead to the decision not to implement certain limits because of the perceived financial burden on industry.

Provincial and territorial regulations can set four types of OELs, depending on the nature of the substance’s toxicity:

• The threshold limit value – time-weighted average (TLV-TWA) is the maximum average concentration of a chemical in the air for a normal 8-hour working day or 40-hour working week.
• The threshold limit value – short-term exposure (TLV-STEL) is the maximum average concentration to which workers can be exposed over a 15-minute period that should not be repeated more than four times a day, with at least 60-minute intervals between exposures. The TLV-STEL is often higher than the TLV-TWA.
• The threshold limit value – ceiling (TLV-C) is the concentration that should never be exceeded in a workplace.
• The threshold limit value – surface limit (TLV-SL) is the maximum concentration of a substance on a surface that a person might touch. This limit is often used for chemicals that enter the body through the skin rather than through respiration.

OELs for a vapour or gas are often set as parts per million (ppm). Aerosols (e.g., dust, fumes, mist) are normally set as milligrams per cubic metre of air (mg/m3). Fibrous substances (e.g., asbestos) are typically set as fibres per cubic centimetre of air (f/cc or f/cm3). The TLV-SL is expressed in mg/100cm2. Compliance with OELs is often assessed via air sampling. Periodic air samples do not necessarily capture normal working conditions because the act of testing may temporarily change workplace behaviour. This dynamic is called the observer effect.

When establishing OELs, governments often follow threshold limit values (TLVs) published by the ACGIH. The TLVs are the ACGIH’s recommendations for allowable chemical exposure. While it is an arms-length body, concerns about its recommendations have been raised. Nearly one sixth of all the ACGIH’s TLVs have been set based upon unpublished corporate data, which raises concerns about the validity and reliability of the results. Further, the committees that set these standards have included a significant number of industry representatives and consultants—many of whose relationships to industry were hidden while they were members—thereby raising concerns about conflict of interest in the establishment of TLVs.15

The power of the ACGIH has also been challenged in court, with organizations such as the International Brominated Solvents Association and the National Mining Association attempting to prevent the publication of threshold limits, arguing that the published limits “disparage the goods, services, or businesses” and are “not supported by credible science.”16 This case was dismissed, and the ACGIH maintains its ability to publish threshold limits.

Challenges arise when there are no established OELs for some hazardous chemicals or when existing limits are outdated (often too high).17 For example, despite diesel engine exhaust being classified as a suspected human carcinogen by the ACGIH since the mid-1990s, there is no TLV recommendation. Rather, the ACGIH has listed diesel engine exhaust as being under study since 2016.18 Most jurisdictions in Canada do have some exposure limits for diesel engine exhaust, but the limits vary based on other components of the exhaust. That is, the exposure limited is not to the exhaust but to carbon monoxide in the exhaust.19 Even when jurisdictions have established limits, there can be variations in the limits and the industries or workers to which they apply. For example, some jurisdictions have limits on diesel exhaust just for the mining sector. As a result, workers across Canada and even within the same jurisdiction might not receive consistent protections, potentially leading to confusion and uncontrolled hazards in workplaces.

Indeed, many scientists dispute the notion that there is any safe level of exposure for carcinogens and reproductive hazards and recommend an “as low as reasonably practicable” (ALARP) principle instead. In this view, so-called safe levels of exposure reflect simply the point below which scientists are (at present) unable to detect ill effects. Box 5.3 takes on the thorny issue of why the ongoing reduction in OELs—while doubtlessly beneficial to workers—is evidence that OELs have not been very effective at protecting them.

Compounding concerns about the validity of OELs is their usefulness in today’s labour market. OELs assume a standard employment relationship with a single employer and an 8-hour workday. Many workers have more than one job and may experience chemical exposures at each worksite. These combined exposures may exceed OELs or may entail complicated chemical interactions. Yet OHS regulations do not require employers to consider chemical exposures workers experience from other jobs or in the community. Employers may well not even know that workers have a second job, let alone what chemical exposures they have. In this way, the trend toward increasingly precarious employment can create workplace hazards that are essentially invisible.

OELs are typically set without considering other workplace hazards. Nevertheless, the health impacts of exposure to different hazards can be more severe than exposure to an individual hazard at the same level.25 For example, noise exposure can lead to greater hearing loss when combined with exposure to carbon monoxide, a combination often found in steel production.26 And workers exposed to solvents or heavy metals in addition to noise also tended to experience more hearing loss.27 Although the ACGIH recommends that workplaces with multiple chemicals having similar impacts on the body should consider combining their impacts in hazard assessments, this recommendation is not consistently enforced. For example, the exposure limits of chemical A and chemical B should be added to ensure that, when the exposure is combined, it does not go over the OEL. This recommendation requires a substantial and uncommon understanding of chemicals and their properties and thus often goes unheeded.

There is also a gendered dimension to OELs. Most OELs have been set based upon studies of healthy younger men, and the resulting standards are applied to both genders.28 OELs do not take into account individuals’ varying sensitivities to chemicals. The same exposure level may result in no ill effects for one worker, while the next person next might experience health effects.

This critique of OELs raises important questions about the validity of information contained in material safety data sheets (MSDS). An MSDS is supposed to contain information about potential hazards, safe use, storage, and handling practices, and emergency procedures. Manufacturers and suppliers must provide and employers must make available an up-to-date MSDS for any chemicals that are considered controlled products by WHMIS. Often the information in MSDSs is based upon OELs. Inaccurate OELs can undermine the utility of MSDSs, which are the key method by which information about chemical hazards is communicated. Further, analysis of the content of MSDSs has also found them to be incomplete, inaccurate, sometimes out of date, and often incomprehensible to workers.29 These findings raise profound questions about the effectiveness of chemical hazard assessment, recognition, and control efforts. More detailed and accurate information is available in databases provided by organizations such as the Canadian Centre for Occupational Health and Safety (e.g., ChemInfo database), but these resources can be expensive to access and difficult for workers to find.

The health hazards posed by oil sands tailings ponds affect both workers on site and nearby residents. This effect illustrates that the line dividing occupational health and safety from public health is blurry and permeable. Similarly, workplace hazards and environmental hazards often overlap, the key difference being whether the exposure happens as a result of work or not. This potential crossover illustrates the pervasive and intricate nature of chemical hazards, which can manifest in various settings and pose challenges in recognizing them.

Chemical hazards are inherently complex given their interactions with the human body. Assessing the risk of using a cleaning agent, for instance, is more difficult than evaluating risks associated with tasks such as roofing or operating machinery. In addition to the potential that the chemical will immediately affect a worker’s health, we need to be mindful of effects that can arise from prolonged exposure or after a long latency period. The effects can also arise because of exposure to multiple hazards, some of which might be unknown to the workers, some of which might arise outside the workplace.

Write a definition for each bold italic word in this chapter.

Select a workplace with which you are familiar and identify a job task performed by a worker that exposes them to a chemical hazard. For example, you might select an art studio with various materials, solvents, and cleaners.

Using the HRAC process set out in Chapter 3, perform a hazard assessment for this task. Your completed assessment should include:

• ➤ A description of the workplace and the work being assessed.
• ➤ A description of the hazard, which injury it might cause workers, and the mechanism of the injury.
• ➤ The risk of injury that the hazard poses to workers, including probability, exposure, and consequences.
• ➤ Three ways to control the hazard. For each potential control, identify what kind of control it is on the hierarchy of controls, how it would be implemented, and the expected cost and effectiveness of the control.
• ➤ A recommended control or controls based on your analysis, including a justification for why you recommended this control instead of the other options that you developed.

Briefly discuss with a partner or write 250-word responses to the following questions:

1. What does ADME stand for, and how does it help us to understand chemical hazards in the workplace?
2. What are the differences between acute and chronic toxicity?
3. Why can chemical hazards be difficult to control?
4. What are OELs, and how are they useful or not?
5. What is the ALARP principle, and how is this approach to controlling chemical hazards different from OELs?

Write 250-word responses to the following questions:

1. What are two chemical hazards that you have faced in a workplace? Describe each, including the potential health effects. Check to see whether these chemical hazards interact with one another.
2. Which of these hazards posed the highest risk to you and why?
3. Did your employer control these hazards? If so, then how? How could your employer have made the work safer?
4. Do you think that these hazards and the controls that your employer used would have stood up to a worker who refused unsafe work?
5. Which strategies did (or could) you or other workers use to make the work safer?