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Assessing Chemicals for Cancer-Causing Agents

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  • 0:07 Cancer-Causing Agents
  • 0:55 Sources of Carcinogens
  • 2:15 Assessing Carcinogens
  • 4:43 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

In this video lesson, you will identify sources of cancer-causing agents. You will also learn how scientists determine which substances and chemicals cause cancer in humans.

Cancer-Causing Agents

You have probably known someone with cancer in your lifetime. This is because cancer affects millions of people each year. Cancer is uncontrollable cell growth. Normally, your cells grow at a certain rate and then eventually die. When you have cancer, certain cells keep growing, and growing and growing. This is why a tumor is a good indicator of cancer, because a tumor is just a large mass of cells.

Cancer comes in many different forms and does not discriminate between age, gender or race. Cancer-causing agents are called carcinogens and come from about as many different sources as there are types of cancer. In order to prevent and treat cancer, scientists need to first understand the sources of carcinogens, as well as what makes them cancer-causing agents.

Sources of Carcinogens

The uncontrolled cell growth of cancer occurs because of some change in your DNA, which is like a set of instructions for your body. If your DNA can't tell your cells to stop growing, then they will just keep growing, and this is exactly what carcinogens do. They get in there, and they screw up your body's instructions by mutating your DNA.

Carcinogens come from our environment, and we are surrounded by them all the time. Some carcinogens are from direct sources - like x-ray radiation and tobacco smoke. Tobacco smoke is especially dangerous because it contains over 4,000 chemicals, many of which cause cancer.

Other carcinogens may be difficult to identify because they are only carcinogenic once they have reacted with other chemicals. Dioxins fall into this category, and these chemicals are found in wood preservatives, insecticides and from paper bleaching and electrical fires.

Some carcinogens come from natural sources, such as plants. Aflatoxins are carcinogens that are naturally produced by fungi growing on food. Fungi that produce aflatoxins are most often found growing on grains, peanuts, meat and dairy products. UV radiation from sunlight is another natural carcinogen. UV radiation mutates your DNA and causes skin cancer and cataracts.

Assessing Carcinogens

The list of known carcinogens is a long one, but it wasn't developed by accident. Scientists determine whether a chemical or substance is carcinogenic in three main ways. The first is human studies. What better way to understand the effects of chemicals on our bodies than to study the effects of chemicals on our bodies?

Epidemiologists study large-scale comparisons of groups of people to determine causes, effects and patterns in human disease. Epidemiological studies are much like other scientific experiments. One group of people is the control (non-exposure group), and the other is the experimental group. The difference is that instead of purposefully exposing people to chemicals to see if they cause cancer, epidemiologists simply take advantage of the chance to learn from exposures that have already occurred. For example, epidemiologists study cigarette smokers and non-cigarette smokers to determine what kinds of cancer tobacco smoke causes and how much more likely smokers are than non-smokers to get cancer from cigarettes.

Animal studies are another method used to determine if something is a carcinogen. Mice and rats are excellent test animals for a number of reasons. First, they respond to carcinogens in much the same way that humans do. Second, they have very short lives, so they can show us the effects of carcinogens on a much faster time scale. Lastly, they are easy to work with because they are small and reproduce quickly.

Animals in labs are often given doses that are much higher than what we would be exposed to in the natural environment, and this is for a couple of reasons. A high dose of a substance in a smaller number of mice can produce the desired effect much more quickly than giving a low dose to a large number of mice. It also allows scientists to more accurately estimate dangerous exposure amounts for humans, who are much larger than laboratory mice.

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