Environmental Toxicology Paper
Joshua Brechtel
ENV/410
September 14, 2014
Jennifer Ott

Environmental Toxicology Paper
Environmental toxicology deals with the toxicology of environmental chemicals. This can relate to toxic chemicals found naturally but usually man-made chemicals are predominately studied. The effect of these chemicals on the environment and subsequent ecosystems are of great importance in understanding human impact on our planet. Ecotoxicology is a type of environmental toxicology that deals with the effects of environmental toxins on ecosystems, habitats and the organisms that live in those ecosystems. The wide range of organisms and environmental factors requires detailed analysis from multiple scientific disciplines. Toxicokinetics and Toxicodynamics
Toxicokinetics is a branch of toxicology that can be viewed as the study of how the body deals with toxicants at different stages after exposure. These stages are absorption, distribution, and elimination. Toxicokinetics studies the ever changing processes that occur within the body during and after absorption of a toxicant. This includes where and how absorption takes place, how the body distributes the toxicant, the effects of metabolism, the toxic effects rendered and the excretion of the toxicant. “In other words, toxicokinetics is a reflection of how the body handles toxicants as indicated by the plasma concentration of that xenobiotic at various time points.” (Michael A. Trush, 2008, p. 1) Toxicodynamics describes what occurs when a toxicant interacts with a specific entity and the biological effects that take place as a result. These “biological targets” can include DNA, proteins, and a variety of receptors. Toxicants interact with these targets and receptors that lead to alterations that may impact the function of their targets as well as structural damage. Toxicodynamics studies the “how” and “why” of these effects in relation to specific toxicants. In short, “Toxicodynamics refers to the molecular, biochemical, and physiological effects of toxicants or their metabolites in biological systems.” (Michael A. Trush, 2008, p. 1) Steps Involved in Toxicokinetics
As mentioned above, there are different stages or steps involved in how the body deals with exposure to toxicants. Absorption, distribution, and elimination are all processes that occur after a toxicant has been exposed to an organism. Toxicants can be absorbed in different ways. Exposure to a toxicant can be absorbed through contact with the skin. When inhaled, toxicants can be absorbed through respiratory exposure. When ingested orally, toxicants may be absorbed as well. As with all toxicants the dose (amount of toxicant exposed to the organism) dictates the amount absorbed and thus the effects of absorption. After absorption occurs the body distributes the toxicant in a variety of ways which will be discussed further on. Eventually elimination of the toxicant will occur. This may take place through excretion and metabolic processes. Primary Routes of Exposure
Exposure to toxicants may occur through different routes. The three primary routes of exposure are through the skin, respiratory tract and the gastrointestinal tract. Skin is often unprotected by many organisms to include humans and is one of the most common routes for exposure. Many pharmaceutical products are specifically designed to be applied to the skin. Inhalation of toxicants is another common route of exposure. In many cases toxic chemicals go absorbed unnoticed through this route because they are not visible and organisms exposed are unaware that inhalation has taken place. Food and water consumption are the primary ways in which toxicants are exposed through the gastrointestinal tract. Toxicants in food and water can be incredibly important to detect to avoid such exposure. Pathways of Distribution
After a toxicant is absorbed it travels through linings of the cells of the organ in which it was exposed. For example, if the toxicant was ingested during food consumption it would be exposed and absorbed through the gastrointestinal tract and would then be distributed through the interstitial fluid of the gastrointestinal tract. Interstitial fluid is the fluid surrounding the cells of an organ. In order for a toxicant to be distributed to body cells and tissues it must first penetrate small blood vessels and then the actual cells of the target organ. If a toxicant is able to enter the blood capillaries it can then be distributed throughout the entire body through the cardiovascular circulatory system and may then be able to penetrate cells in any organ of the body. If the toxicant is able to enter the lymphatic system it may then be distributed throughout the lymphatic system of the body. Four Mechanisms in Moving Toxicants
The four mechanisms involved in moving toxicants across the cell membrane are passive diffusion, filtration, carrier-mediated transport and engulfing by the cell. Passive diffusion is the mechanism in which the majority of toxicants pass through the cell membrane. Passive diffusion is according to “Biology-online” (2009), “A kind of transport by which ions or molecules move along a concentration gradient, which means movement from an area of higher concentration to an area of lower concentration.” Filtration occurs when toxicants move through the larger pores of cell membranes. As water flows through these large pores the toxicant is distributed if small enough to pass through. Carrier-mediated transport is a form of active transport that allows the toxicant to move through the cell membrane through the formation of a complex. The complex forms on one side of the member than diffuses to the other side of the membrane allowing the toxicant to be released. Lastly, toxicant may move through the cell membrane through the engulfing by cells. Biotransformation
Biotransformation is a process when one chemical is changed into another chemical inside of the body. Metabolism is a primary function of the biotransformation process.According to the “Encyclopedia of Earth” (2012), “Phase I reactions are generally reactions which modify the chemical by adding a functional structure. This allows the substance to "fit" into the Phase II enzyme so that it can become conjugated (joined together) with another substance. Phase II reactions consist of those enzymatic reactions that conjugate the modified xenobiotic with another substance. The conjugated products are larger molecules than the substrate and generally polar in nature (water-soluble). Thus, they can be readily excreted from the body. Conjugated compounds also have poor ability to cross cell membranes.” Some of the major transformation reactions in phase I reactions are oxidation, reduction, hydrolysis and acetylation. Some of the major transformation reactions in phase II reactions are sulfate conjugation, glucuronide conjugation, glutathione conjugation, and amino acid conjugation. Environmental effect of toxicants
Toxicants can have varying impact on the environment depending on the type of toxicant. Carcinogens (cancer causing toxicants) negatively impact animal life within ecosystems by increasing cases of cancer which lower population numbers in various species. Mutagens are toxicants that cause mutations. These mutations can greatly alter the DNA of animal and plant life. Neurotoxins, such as mercury and pesticides, can be incredibly harmful toxicants. When used incorrectly or in large quantities neurotoxins can be extremely fatal for a majority of plant and animal species. Overall, toxicants negatively impact environments by contaminating food and water sources and causing health problems for plant and animal life. Conclusion
In conclusion, environmental toxicology is an important field of study. Understanding the impact of human activity and the related toxicants produced helps to reduce the negative impact of this activity. It is important to understand the ways toxicants are exposed to life and how they react when entering into the body. Route of exposure and the distribution of toxicants within the body allow toxicologists and doctors to determine the impact of exposure and how to properly treat the effects of toxicants. This information also helps to properly identify toxicants and their impact. This helps environmentalists to locate sources of toxicants and determine appropriate levels for these chemicals in the overall effort to reduce their negative impact.

References
Biology-online. (2009). Retrieved from http://www.biology-online.org/dictionary/Passive_Transport
Encyclopedia of Earth. (2012). Retrieved from http://www.eoearth.org/view/article/150674/ Michael A. Trush. (2008). Absorption, Distribution, and Excretion. Retrieved from http://ocw.jhsph.edu/courses/publichealthtoxicology/PDFs/Lecture1_Trush.pdf