Carcinogens Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Carcinogens can be defined as potential cancer-causing agents that are found within our natural (air, water, soil), social (lifestyle and dietary choices, voluntary vs. involuntary exposures), and built (synthetic chemicals, pharmaceuticals, radioactive substances) environments. Carcinogens can induce cancer in an organism and as such, the biological environment (genetics, aging, sex) plays a role in the degree of vulnerability to the carcinogen(s) in question. Bacteria, parasites, and viruses have also been implicated for their role in cancer causation; their impact varies depending on the biological environment.

According to the International Agency for Research on Cancer (IARC), the most recent description of the categories of agents includes “both ‘specific’ as well as ‘groups’ of related chemicals, complex mixtures, occupational or environmental exposures, cultural or behavioural practices, biological organisms, and physical agents.” The IARC Monographs provide a complete listing of all of the carcinogens assessed to date.

In an attempt to better understand, potentially lessen, and possibly eliminate human exposure to carcinogens, testing and evaluation of carcinogenic agents are frequently conducted within the field of science. Numerous carcinogens have been assessed by organizations such as the IARC and the U.S. Environmental Protection Agency (EPA). According to J.B. King, there are three main methods for directly testing an agent’s carcinogenic potential in an ethical manner (i.e., not knowingly putting humans at risk of being exposed to carcinogenic agents for experimental purposes). As with any method, each of these tests has its own advantages and disadvantages.

Methods of Testing

The first method of testing is conducted with cultured cells. In order to minimize species variation, human cells can be used. However, when an agent is evaluated in the absence of the complex nature of an entire biological system as in the case with cultured cells the metabolic activation of the test agent may not occur, which can result in false negatives. The main objective for using cultured cells is to test compounds by monitoring their effects on the cell functions that are involved in the process of transforming normal cells into cancer cells (i.e., DNA damage).

The second method includes testing on microorganisms. Using this method, scientists can examine the carcinogen’s ability to generate mutations. The Ames test developed by Bruce Ames in 1975was the first method to use the bacterium Salmonella typhimurium. This bacterium was genetically altered so that it could detect chemically induced mutations. The Ames test is relatively simple to administer and can quickly examine a large number of agents. A limitation with this method is the frequent occurrence of false positive and false negative results. Such inaccuracies can occur because the premise behind this test is that carcinogens are also mutagens. However, this is not always the case. Therefore, the Ames test has been used by many researchers as a screening test for carcinogens prior to testing on animals.

The third and most direct method to evaluate the effect(s) of a carcinogen is through the use of animal models. These tests are conducted primarily to examine the ability of the carcinogenic agent(s) to induce cancer(s) and/or to damage the DNA of animals. However, because humans have different genetic predispositions and are not confined to various controlled environments, they often experience multiple and varied exposures to carcinogens at different doses for various durations and at different points in time throughout their lifetimes. As Curtis D. Klaassen notes, the route of exposure (ingestion, inhalation, absorption, or parenteral), as well as the carcinogen’s ability to metabolize in the body, plays a role in the effect the agent has on the body. These factors make it difficult to draw parallel comparisons among humans, let alone between animals and humans.

Nevertheless, animal experiments are the best available method for testing carcinogens to date. Because different strains of the same species vary in their reaction(s) to carcinogens, it has been suggested by King that different species should be used in animal tests in order to fully understand and more accurately classify carcinogens.

To date, the best available approach for understanding human carcinogenic exposure are those methods used in the field of epidemiology. The association between human exposures to occupational carcinogens and cancer can be traced back to the late 1700s, when Sir Percivall Pott recognized the association between exposure to soot among chimney sweepers (which was later identified as benzo[a]pyrene) and the occurrence of scrotum cancer. Since then, numerous occupational epidemiological studies have been conducted in an attempt to better understand human exposure to specific carcinogens. Research has been undertaken using occupational and health records in conjunction with the testing of blood, serum, and other biological samples.

Hurdles to Investigation

Nevertheless, there are limitations with these types of studies, because the examination of several exposures (such as those found in the natural, social, and built environments) over one’s lifetime are difficult to isolate, despite their critical role in cancer causation. There is also the possibility of delayed effects or a latency period between carcinogenic exposure and the manifestation of cancer. This creates further difficulties in the identification of causative agents. Additionally, as Jack Siemiatycki and his associates note, several earmarked “occupational carcinogens” (i.e., asbestos, radon gas, and benzene) are not strictly monitored or measured in the general environment; therefore, one cannot be certain that these presumed occupational carcinogens are in fact solely the result of workplace exposures. This gives rise to concerns on a micro level, such as deciphering the totality of study findings. It also raises concerns on a macro level such as the implementation of stringent policies and regulatory measures as well as social responsibility.

Other epidemiological studies have been conducted in contaminated sites, such as the Hiroshima and Nagasaki atomic World War II bomb sites and the nuclear fallout accident at Chernobyl in 1986. These sites gave rise to an increase of certain cancers, and these populations became of interest to epidemiologists around the world. Numerous human observational studies have been conducted with the populations of these regions in order to better understand deleterious health outcomes as a result of carcinogenic exposures.

Epidemiological studies have been successful at implicating some cultural practices for their role in cancer causation. For instance, Parviz Ghadirian and associates found that in certain regions of Iran, the custom of eating opium dross, as well as the consumption of contaminated bread containing large quantities of silica fibers originating from extraneous seeds used in the bread, have been suspected as the “initiating” carcinogenic factors for esophageal cancer. Additionally, some cooking practices (including inhalation-exposure to cooking fumes, the consumption of charred meat, the consumption of pickled or moldy foods) have been associated with certain cancers.

The use of epidemiological studies to understand carcinogenic agents is not limited to occupational and/or environmental agents. Several viruses and bacteria have also been implicated in cancer causation. For instance, the bacteria helicobacter pylori (h-pylori) has been found to be associated with stomach cancer. Likewise, some studies have linked the human papillomavirus (hpv) to cervical cancer.

Based on a number of different types of studies that examine carcinogenicity, in addition to other relevant data presented, the IARC assesses carcinogenic agents on an ongoing basis. These carcinogens fall into one of four groups, and can move up and down the ranks as new information becomes available. Carcinogens are categorized as “Group 1 when the agent is carcinogenic to humans; Group 2A when the agent is probably carcinogenic to humans; Group 2B when the agent is possibly carcinogenic to humans; Group 3 when the agent is not classifiable as to its carcinogenicity to humans; and Group 4 when the agent is probably not carcinogenic to humans.” The IARC has reviewed almost 900 agents since 1972. In 2002-03, there was some controversy in the literature among several scholars and researchers regarding possible industry influence in the decision-making process concerning some of the carcinogens reviewed. Notwithstanding, there are numerous carcinogens that are yet to be reviewed that we are voluntarily and involuntary exposed to in our environments every day.

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