Toxicology

Toxicology Toxicology- is the study of chemical Risk The advances of modern chemicals to improve human life have come along way Insecticides, herbicides and fungicides. But, in addition to these benefits, there have been by products that do the exact opposite. The large number of chemicals releases into the environment raises questions about the effects on us and other organisms.

Types of harmful Chemicals There are 5 categories of harmful chemicals: Neurotoxins Carcinogens Teratogens Allergens Endocrine disrupters All of these are found in pharmaceuticals; Makes you think the next time you grab night quill

Types of Chemicals of major Concern Lead Found in paint and gas It’s a Neurotoxin and it impairs learning, nervous system disorders and death Mercury Fish consumption Neurotoxin and it damages the brain, kidneys, liver and weakens the immune system. Arsenic Carcinogen. Found in ground water Cancer

Types of chemical Radon Alcohol Phthalates Found in water and it’s a carcinogen Lung Cancer Alcohol In beverages it’s a teratogen Causes fetuses with reduced fetal growth, brain and nervous system Damage. Phthalates Found in plastics and cosmetics. Its an endocrine disruptor Feminization of females.

Neurotoxins Neurotoxins- are chemicals that disrupt the nervous systems of animals The purpose for this chemical is to interfere with insects nervous system. That is why neurotoxins are sometimes called insecticide. Insects and animals are highly sensitive to neurotoxins. Animals can be completely paralyzed, not able to get oxygen. Lead and mercury are neurotoxins. Lead is no longer a huge problem because of the elimination of lead in gas and paint in the 70’s Mercury is still a huge problem.

Carcinogens Carcinogens are chemicals that cause cancer or heightens the percentage of getting cancer They cause cell damage which leads to the DNA to be mutated This causes mitosis to not shut off. This leads to uncontrolled cell-growth Carcinogens that causes mutations to happen to the DNA is what's known as a mutagen. Not all carcinogens are mutagens. The most well known includes asbestos, radon, formaldehyde and in tobacco.

Teratogens Teratogens are chemicals that interfere with the normal development of embryos or fetuses. The most famous is Thalidomide. This was prescribe to pregnant women during the late 1950s and early 1960s to combat morning sickness The result was 10s of thousands of mothers around the world gave birth to defected babies. The drug was taking of the market in 1961. The most modern Teratogen is Alcohol. Excessive alcohol consumption reduces the growth of the fetus if pregnant Damages the brain and nervous system. Called fetal alcohol syndrome.

Allergens Allergens- are chemicals that cause allergic reactions. Allergens are able to cause an abnormally high responses from the immune system. In some cases difficulties in breathing and death. Generally, it causes allergic reactions in a small fraction of people. Those that causes allergens are peanuts, milk and several drugs like penicillin and codeine.

Endocrine Disruptors Endocrine Disruptors- are chemicals that interfere with the normal functioning of hormones. Endocrine are natural hormones that is manufactured in the endocrine system. They’re released in the bloodstream in very low concentrations. These endocrines bind to receptors that regulates certain functions in the body. Releasing of testosterone and estrogen.

Endocrine Disruptors Water pollution can contain certain hormones Either from animal-rearing facilities, hormones from human birth control pill in sewage. Also, pesticides that mimic animal hormones. Scientist have found that male fish, reptiles and amphibians are becoming feminized. These males have low sperm count, which reduces populations within those ecosystem. These endocrine disruptors turns testosterone into estrogen. This has the same effects on human males. A higher risk of breast cancer in women.

Test to determine concentration of chemicals To assess the risk a chemical poses to an organism, scientist use certain methods. Dose-response studies Prospective studies Retrospective studies

Dose-Response Studies Dose-response studies expose animals or plants to different amounts of a chemical and then observe a variety of possible responses including mortality or changes in behavior or reproduction. These chemical amounts can be measured as concentrations within their foods, air or water. Also, can be measured as dose of a chemical. This is the amount of chemical that is absorbed or consumed by an organism. Most dose responses studies only last for 1 to 4 days. This is due to the efficiency of the doses. Because of the short durations, they’re called Acute studies

Dose Response Studies The Does-response studies usually measures the mortality rate of the specimens. When the data are graphed it usually forms a S-shaped curve. At low dosage, specimens do not die. At slightly higher levels, few individuals die. The dose at which an effect can be detected is called The Threshold. At this dosage, individuals that die are usually poor in health or genetically not very tolerant to the chemical As the dosage increases, more individuals will die. At the highest concentration, all individuals die.

LD50 A helpful measurement for comparing the harmful effects of different chemicals is the LD50 LD50- Lethal dosage that kills 50% of the specimens. This is important for assessing the relative toxicity of a chemical. Scientist can determine whether a new chemical is more or less lethal in comparison to other chemicals that are being used.

Test Specimens The amount of death that a chemical causes can differ among species and among different groups of species. Mammals, birds, fish and invertebrates. Mice and Rats are used for Dose-Response studies instead of humans. The results are than equaled to all mammals Pigeons are used for all birds Trout are used for all fish.

Dose Response Experiments It is important to note that not all Dose response experiments measure death as a response. In many cases, they test other harmful effects that a chemical might have. Is it acting as a teratogen, carcinogen or neurotoxin that could alter the behavior of an individual? These are called sublethal effects. This is to determine the effective dose that causes 50% of the individuals to display the harmful, but nonlethal, effect. This is called ED50 (Effective Dosage)

Testing standards There are several agencies set up to regulate experiments. EPA-Environmental Protection Agency The effects of chemicals on humans and wildlife The Toxic Substances Control Act of 1976 gives the EPA the authority to regulate many chemicals. Excluding food, cosmetics and pesticides. Pesticides are regulated under another law. Federal Insecticide, Fungicide and Rodenticide Act of 1996 This act states that the pesticide will not cause harm to the environment.

Test Standards (Cont.) As it was eluded at the beginning, scientist can not test every organism. Instead, they devised a system of testing a few species that are thought to be among the most sensitive in the world. Bird, mammal, fish and invertebrate. The theory is that if they can find a way to protect the most sensitive of animals from chemicals, then they can protect all the other types of organism. Therefore, if any regulations that are devised to protect it would automatically protect all other species in the group.

Testing Standards There are no groups set up for amphibians. There were no regulations set up, yet, to regulate amphibians and reptiles. Now, scientist use fish for aquatic amphibians and reptiles. Birds for terrestrial amphibians and reptiles. Because amphibians and reptiles are experiencing population declines, there’s an increased in testing these two groups as well.

Cont LD50 and ED50 are used by agencies like EPA. They can determine the concentrations in the environment that should cause no harm. IN order to obtained a safe concentration is by taking the LD50 and dividing it by 10. LD50 /10 The logic is that if the LD50 causes 50% of death, then 10% should cause few or no animals to die. With humans there has to be extra care. Humans are tested so mice and rats are you used. Once the LD50 or ED50 is found it is divided by 10 to determine safe concentration for rats and mice. Then the value is divided by 10 again because rats and mice may be less sensitive than humans.

Cont. Once that value is found, it is then divided by 10 again to ensure an extra level of caution. IN other words, the LD50 or ED50 obtained by rats and mice are divided by 1000 to set the safe values for humans. Chronic Studies Even though some toxicology studies are only conducted for a few days, some are conducted for longer periods of time. These experiments are called Chronic Studies.

Chronic Studies These usually last from an organism is very young to when it is old enough to reproduce. For some species chronic experiments can take several months Like fish The goal of chronic studies is to examine long-term effects of chemicals. Including their effects on survival and their impacts on reproduction.

Retrospective versus prospective studies. Another approach to certain experiments, instead of dose-response, is to examine large populations of humans or animals who are exposed to chemicals in their everyday lives. This can determine those exposures are associated with any health problems. Such investigations fall within the study of epidemiology. Field of science that strives to understand the causes of illness and disease in human and wildlife populations.

Cont. There are two ways of conducting this type of research: Retrospective studies and prospective studies. Retrospective studies Studies that monitor people who have been exposed to a chemical at some time in the past. In the studies, scientists identify a group of people who have been exposed to a potentially harmful chemical. Then they’re compared to a second group that was not exposed to the chemical.

Retrospective studies Both groups are then monitored for many years to see if the exposed group experiences greater health problems than the unexposed group. Example is an accidental release of methyl isocyanate gas in Bhopal, India in1984. 36,000 kg of gas spread through the city of 500,000 inhabitants. 2,000 people dies that night and another 15,000 died later from effects related to the exposure. Scientist have been monitoring two decades to determine if survivors of the accidents have developed any additional health problems over time.

Cont. The retrospective studies have found that approximately 100,000 people are still suffering illness from the accident. Higher rates of respiratory symptoms, genetic abnormalities, infant mortality, kidney failure and learning disabilities.

Prospective Studies Prospective studies- monitor people who might become exposed to harmful chemicals in the future. Ex. Scientists might select a group of 1000 participants and ask them to keep track of: Food they eat Tobacco they use The alcohol they drink They do this for the next 40 years. As time passes the researchers can determine if the habits of the participants have any association with future health problems

Prospective studies and Synergistic interactions Prospective studies can be challenging. This is because of participants habits could cause many other health problems. Habits could be associated with socioeconomic statuses This can cause synergisitc interactions When two risks together cause more harm than one would expect based on their individual risks. example,. The health impact of carcinogen such as asbestos can be much higher if an individual smokes tobacco. Studies of lead in children are often conducted using prospective studies. Ex. Harvard studied the effects of lead on children’s intelligence

Synergetic interactions 276 children in Rochester, New York, were followed from 6 months to 5 years of age. At the age of 5, children can take reliable IQ tests. In addition to lead exposure, the researchers also accounted for other factors that might affect childhood IQ. Mother’s IQ