Introduction
All organisms including human beings are exposed to a myriad of toxins from within the environment .The food we eat, the water we drink and the air we breathe, soaps ,cosmetics and other chemicals used in our daily lives contain toxins. Almost everything within the environment if taken in sufficient amounts can turn out to be poisonous or harmful .Therefore; there is a need to apply quick and cheap methods of testing and to determine the amounts of toxins in substances. Toxicity presents a complex variation between individuals. An amount that can harm one individual may not harm the other person.
Toxicologists often average out this effect by screening a group of test individuals and determining the amount (dose or concentration) which kills half the subjects. This level of toxin (the median mortality, killing 50% of subjects) is called the LC50 or LD50 (Lethal Concentration 50% or Lethal Dose 50%). Screening could be done on any animal, but for a variety of reasons a small aquatic Arthropod (specifically, a Crustacean) is used here: Daphnia. These water fleas are small, but can be seen swimming around in pond water, from which they can be gathered using a very fine (plankton) net. They can be reared in the lab in small cups under natural or artificial light, using natural or artificial pond water.
Despite being tolerant to low amounts of oxygen in the water, Daphnia is extremely sensitive to household chemicals such as detergents.
Objective:
Determining the level of household cleaning agent that is harmful to Daphnia
Hypothesis
The toxin concentration of the 10% will have highest lethal concentration
Materials needed
Materials required for this study included, a culture of Daphnia,6Containers, 1 ml disposable pipettes, cup containing Daphnia water ,graduated cylinder, marking pen and a household cleaning agent. The purpose of 1 ml disposable pipettes was to deliver certainly measured amounts of the cleaning agent into a cup containing Daphnia water.
Methods
Daphnia culture was obtained from the instructor, and each group did a head count of Daphnia present in a cup. Ideally, there were supposed to be 16 individuals. Individuals exceeding 20 inside a cup were returned to the instructor .After this, every group acquired Daphnia water in four containers, which were labeled, 10%, 5%, 2.5% and Control using the marker pen. A small amount of Daphnia water was added in a cup, and the cup labeled “Rinse water”.20 milliliters of cleaning agent from the lab bench was added to the Dracula culture inside the cup, and the amount of the detergent that killed half of the population was recorded in a sheet.
3ml of cleaning agent was acquired using a graded pipette and delivered into a cup.27ml of Daphnia water was added to make 30ml.This was added to the 10% container. The amount of poison and water added to get 5%, and 2.5% was calculated. Four Daphnia were collected using a spoon and siphoned into a clean pipette. Beginning with the control, 4 Daphnia were added to each cup, and the exact time for addition recorded. All the four containers were checked after every 10 minutes for an hour, and the number of Daphnia dead was recorded.Four Daphnia are collected in a plastic spoon by siphoning them with a CLEAN pipette. If all Daphnia dies or does not dies within the 60 minutes, dilutions up and down were done, and the experiment repeated.
Report sheet/results
Summary
As can be seen from the above tabulated data,10% toxin concentration had the highest lethal concentration .Throughout the 60 minutes, there was no single Daphnia which died in the control cup. However, as the concentration of toxin increased the number of Daphnia dying within the 10 minutes interval increased and the time that the Daphnia took to die reduced. The 10% toxin concentration was the most lethal as all Daphnia died within the first observation (10 minutes).
Daphnia was not good substitute for human since human beings are structurally and biologically different from Daphnia. Human beings have specialized organs to excrete poison from the body as compared to Daphnia .However, Daphnia serves a good purpose to show how toxin concentration may affect organisms.
Potential or observed errors associated with this lab.
-Adding too much water can affect concentration of the toxin
-Different sizes of Daphnia can affect how fast toxin kills it
-Inability to measure completely accurately
References
Brown, M. (1999). Laying Waste: The Poisoning of America by Toxic Chemicals. New York, NY: Pantheon Book.
Forsythe, S. (2011). The Microbiology of Safe Food. Hoboken: John Wiley & Sons.
Rossol, M. (2011). Pick Your Poison: How Our Mad Dash to Chemical Utopia Is Making Lab Rats of Us All. Hoboken, New Jersey: John Wiley and Sons.
Schroeder, H. (2004). The Poisons Around Us; Toxic Metals in Food, Air, and Water. Bloomington: Indiana University Press.
