Industrial toxicology is the study of the harmful effects on humans by chemicals used in the workplace, the products produced by companies, and the wastes created in manufacturing.
Industrial toxicology is a division of the broader science of toxicology that deals with the adverse effects of all forms of chemicals, physical agents, and processes, including drugs and medications. Originally, toxicology was known as the study of poisons, a focus that marked this science since its earliest beginnings. Only in the middle of the twentieth century did this area of scientific inquiry expand and become more specialized.
Humans have been interested in the harmful effects of substances since they first began foraging for food. Identifying which plants were safe to eat and in what quantity and which ones made humans sick or proved fatal became essential for the species to survive. Written records from as early as 1500 bc in Egypt reveal how civilizations began to systematically categorize harmful substances and use them for hunting, to dispose of enemies of the state, and to execute criminals. Specific metals, hemlock, and opium were known and used for these purposes. Animal and insect extracts and venom were smeared on arrowheads. One of the most famous early poisonings was that of Socrates who was forced to drink hemlock. The Medici family in Italy during medieval times raised poisoning to a fine art.
Early philosophers became some of the first toxicology scientists. Hippocrates, Aristotle, and Theophrastus all wrote of poisons as early as 400 bc. From the time of Galen, in the second century ad, to Paracelus, in the sixteenth century, the emphasis was on forensic toxicology; that is, finding out what substance caused someone's death. Paracelus emphasized that any substance could be a poison at the right dosage, and that it was only a matter of dose to distinguish a poison from a medicine. That precept is as apt in the twenty-first century as it was then because of the general awareness of drug overdoses and side effects of medications.
By the eighteenth century as cities grew and workers became concentrated in specific industries, attention was drawn to the effects of the work environment on disease. Ramazzini's book, Diseases of Workers was the first to identify this problem. Potts also reported the link between chimney sweepers exposed to burned wood ash and increased scrotal cancer in 1775. Orfila, a Spanish doctor, catalogued the properties of known poisons and showed the effects of them on specific organs. He published his findings in 1815.
Though works of this type brought the issue of chemical hazards in the workplace, the science of toxicology continued to be enamored with poisons. Even during World War I, toxicology focused on how chemicals could be used in warfare and how to counteract their effects on soldiers. That branch of toxicology continues into the twenty-first century.
By the 1960s, emphasis turned toward the study of how chemicals work within the human body. Testing not only medications, but also cosmetics and household products, became the new focus. Ultimately, pesticides and industrial chemicals were also studied. Testing protocols were created, and toxicity levels were determined. Industrial toxicologists helped develop safety procedures for working with dangerous chemicals and precautions to prevent harm to workers. They also determined the potential health risks and set maximum limits for exposure.
Forms of toxicity
Industrial chemicals that cause the most harm to the body are classified as irritants, asphyxiants, and systemic poisons. Generally, each grouping corresponds to a common route of entry: the skin and eyes, the lungs, and the digestive system. These sites are the places where absorption of the chemical occurs.
IRRITANTS. Irritants are substances that cause inflammation, rashes, or corrosion of skin. They can also cause pain, swelling, mucus secretion, and muscle constriction. These chemicals can also irritate the lining of lungs and the digestive system, and are called irritants because the corrosive effects occur on epithelial (skin) cells within these organs.
Irritants also include gases such as chlorine, ammonia, and formaldehyde. These chemicals can cause coughing, fluid build up in the lungs, and pain.
Another group of irritants called particulate irritants are composed of minute bits of material produced within the work environment. Pulmonary fibriosis, a common condition for those exposed to these irritants in mining and manufacturing, results in scarring of the lungs, and often disability and death. Coal miners are exposed to silica, which can result in pneumoconiosis, silicosis (black lung disease), and asbestosis. These are serious and potentially fatal illnesses. Alumina, zinc oxide, and silicate dust can irritate the lungs, but this inflammation is not as serious, and workers can recover from exposure. Fine droplets of acids, organic solvents, and petroleum products irritate both the lungs and the skin. Perfume components, cosmetics, creosote, and antibiotics, such as tetracycline, can also make the skin extremely sensitive to ultraviolet radiation in sunlight.
ASPHYXIANTS. Asphyxiants are aerosols or airborne chemicals that are inhaled through the mouth and nose. These chemicals displace oxygen within the lungs, thus inhibiting the amount of oxygen being transported throughout the body to nourish cells. Nitrogen and helium, used to flush vats and tanks before routine maintenance, are examples of simple asphyxiants. They replace oxygen in the atmosphere surrounding a worker.
Chemical asphyxiants create harm when inhaled because they create a chemical reaction in the body. Carbon monoxide, for example, robs the body of oxygen by competitively binding to hemoglobin in the blood and preventing oxygen being transported to tissues of the body. Hydrogen sulfide, on the other hand, paralyzes the muscles in the lung and throat and prevents oxygen from entering the body.
SYSTEMIC POISONS. Systemic poisons are chemicals that are ingested and absorbed by the digestive tract. They are grouped according by their action or by a specific organ of the body that they target. Narcotics and anesthetics reduce central nervous system function, and include organic solvents that make effective anesthetics. One such solvent, diethyl ether, was taken out of the industrial sector and used in surgical procedures because of its anesthetic uses. Other neurotoxic agents may cause irreversible damage to the central or peripheral nervous system and include alcohols, mercury, carbon disulfide, and organometallics, such as tin used in antifungal coatings. Some chemicals, such as organic solvents and some metals, target the kidneys and liver. Since these organs are the body's toxin filters, they have more contact with ingested poisons and suffer greater damage. Another group of systemic poisons, include benzene, lead, and arsenic, which affect the bone marrow and can produce too few red blood cells (anemia) or too many white blood cells (leukocytosis). Certain agents, such as mercury, lead, and carbon disulfide, target reproductive organs. They can alter male fertility or cause spontaneous abortion. Mercury has been linked with birth defects.
One group of systemic poisons, called carcinogens, has been widely publicized. These industrial chemicals have been shown to be linked with an increase rate of cancer among workers exposed to them. Some of them include coke oven emissions, asbestos, benzene, and vinyl chloride.
As Paracelus noted, there is a fine line between a beneficial amount of a substance and a harmful amount. That distinction is determined by the doseresponse relationship or the amount of a substance that a worker can be exposed to that is safe and the point at which the substance becomes a threat. The dose-response relationship of a given chemical is characterized by five different categories. The dose threshold is the minimum amount of the substance needed to produce an effect. The lethal dose (LD) is the amount that will cause death. The toxic dose low (TDL), the lowest dose that causes poisoning symptoms for nonairborne toxins, is found in safety manuals and journal articles. The lethal concentration (LC) is the amount that is lethal. It often has a subscript attached, such as LC50, meaning 50% of those exposed died from this specific amount. Finally, the toxic concentration low (TCL) is the lowest published concentration that produces toxicity for airborne substances.
Factors affecting toxicity
Several factors can determine the toxic dose of a specific substance. The rate of entry, how fast the chemical is absorbed in the body, and the route of exposure, or how it enters the body, can increase or decrease the toxicity of a substance. The length and frequency of exposure are also factors. A worker's underlying health can exacerbate an exposure, especially if a target organ is already diseased. Age and body size are also factors, with older and smaller bodies more at risk. In addition, individual rates of absorption will determine how the chemical is taken up into body tissues, and that will determine how toxic the dose is.
When a substance enters the body, it will be stored, transformed, or excreted. Storage can occur in fat, bone, plasma, or the liver. Fat storage can slow down the effects of a chemical because its release and circulation through the blood is decreased. Longer-term storage usually occurs in the bones and the liver, eventually damaging them. Biotransformation can occur in the liver, thereby changing the chemical composition of the substance. Sometimes, this renders the chemical less harmful; sometimes it does not. The byproducts of biotransformation are usually excreted through urine and feces, and sometimes through breast milk. The danger with elimination through the digestive tract is the potential for reabsorption by the small intestine. This prolongs exposure, especially if the substance has not been substantially biotransformed.
In industry, a worker is exposed to a substance, goes home, and allows the body to eliminate the chemical. This natural process is efficient in most cases. In other situations, a remnant of the substance remains in the body and, over time, toxic levels are built up. This makes it critical that working overtime, and therefore experiencing additional exposure, is discouraged, and that workers take appropriate time off.
How different chemicals in the workplace affect the body varies according to the type and form of the substance, the rate of exposure, and how the body reacts to the substance. Some chemical exposure has a latency period in which no damage seems to occur immediately, but will appear later. Carcinogens, reproductive agents, inhaled irritants, and many systemic poisons will not show harmful effects until many months or years after exposure.
Acute effects occur after brief exposure and appear immediately. Some types of exposure, however, can produce delayed effects. Chronic effects happen after repeated or prolonged exposure, and can appear differently than acute exposure to the same chemical. Most carcinogens produce chronic effects. Repeated exposure can result in cumulative toxicity. As a worker is exposed to repeated doses of a substance, it can build up over time to toxic levels in the body, causing damage or even death. In addition, exposure to two or more substances can result in a more intense effect than exposure to each substance alone. This is called a synergistic response.
The exposure to some chemicals can be reversed after the body has had time to metabolize or eliminate the substance. Other chemicals produce effects in the body that cannot be reversed.
Investigation of toxic exposure in the workplace has led to more exact determinants of toxic dose levels, which in turn have led to the creation of new safety procedures and workers' protection laws. This research has also pushed to eliminate hazards in the workplace. New information and new restrictions in industry have pitted governments against corporations and companies against workers and the unions that represent them. This has resulted in individual and class action law suits centered on specific chemicals in the workplace. Unlike other types of negligence cases, the courts find it difficult to determine whether industrial chemicals caused the health effects specified by a complaint or that the company knowingly placed workers in danger. In addition, unlike food and medications, new industrial substances do not need to pass any sort of tests or inspections before they are used.
Industry, however, does its own testing for the products it makes that will be used directly by consumers. These include household products, personal care items, and cosmetics. Other chemicals are tested only after exposure produces effects within a group of workers.
Testing for the harmful effects or toxicity of a substance is done with human subjects in a controlled environment, by using animal studies, performing microorganism tests, or creating computer models. Sometimes, dose-response data is collected at the site of accidental exposures, such as a chemical spill.
These methods, however, have limitations. Scientific ethics prohibit the use of humans in experiments with chemicals that might prove to be dangerous. Microorganism testing studies the growth patterns of bacteria exposed to a potentially toxic chemical. These kinds of tests are limited in that they do not factor in what the chemical's effect would have on a complex organism such as a human being or an animal. Additionally, data from animals studies do not necessarily transfer directly to humans. Some groups also object to the use of animals as test subjects because they are killed when they are subjected to extraordinarily high doses of chemicals.
Industrial toxicology rose from the age of manufacturing. It has grown because of the scientific creation of new substances and the increasing number of medical insurance claims by workers. Branches of industrial toxicology include pesticide toxicology, agricultural toxicology, and environmental toxicology. Though workers' safeguards are being put into place for some of the known toxic agents, such as asbestos or coal dust, new chemicals are being created in research and development labs every year. Of the 100,000 commercial chemicals in use in 2005, fewer than 1,000 have been studied. It is clear that the field of industrial toxicology will expand in order to investigate new substances and how they affect humans in the workplace.
As a result, health care professionals will probably see more patients with diseases related to chemical exposure. They will need to be aware of the systemic effects of various chemicals, especially heavy metals, and will need to know how to treat these effects or help the patient excrete these substances from the body. Of additional concern is the potential for exposure of health professionals in clinics located in industrial settings.
Absorption— The process in which a chemical enters the tissues and is transported throughout the body.
Biotransformation— The processes by which the body changes a substance for use, storage, or elimination.
Dose— Amount of a substance to which an organism is exposed.
Hazard— The conditions under which a substance can produce a toxic dose.
Toxicity— When the dose of a chemical reaches a level to produce adverse effects.
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Wiley-Vch. Ullmann's Industrial Toxicology. New York: John Wiley & Sons, 2005.
Winder, C., and N.H. Stacey, eds. Occupational Toxicology, 2nd Edition. Boca Raton, FL: CRC Press, 2004.
American College of Toxicology. 9650 Rockville Pike, Bethesda, MD 20814. (301) 634-7852. 〈http://www.actox.org〉.
Center for Research on Occupational and Environmental Toxicology (CROET) at Oregon Health & Science University, 3181 SW Sam Jackson Park Road, L606, Portland, Oregon 97239-3098. (503) 494-4273. 〈http://www.ohsu.edu/croe〉.