ARSENIC LEVELS IN SOIL vs. POPULATION DENSITY OF RUBUS URSINUS
Coral Hall
Sweet Home Project
January 27, 2004
Coral Hall
Abstract:
This project researched, tested, and analyzed data to support the hypothesis that high levels of arsenic found in the soil negatively affect trailing blackberries (Rubus ursisnus) that grow in it. We tested this theory by collecting soil samples from selected areas in Sweet Home, Oregon where additional research has taken place for its high levels of arsenic in its soil. This provided us with areas to collect samples that contained low, medium, and high levels of arsenic in the soil. After the samples were collected, they were prepared and sent to the reactor for INAA (irradiated neutron activation analysis) analysis to find the exact amount of arsenic in each area we observed. For each of these plots we also found the plant density for trailing blackberries by counting the number of stems that grew from the ground in the marked off area, (a 2 yd. x 2 yd. plot). The results we found from our data showed that higher levels of arsenic in soil causes lower levels of plant density for trailing blackberries. This is an important issue to research because many animals and possibly people are at risk if the high levels of arsenic cause common plants to absorb arsenic, causing their leaves and fruit to be poisonous, or prevent them form growing entirely. More research will need to be done in these areas to support our findings and produce important conclusions concerning arsenic levels and its effects on the environment.
Introduction:
The purpose of our group’s research is targeted towards finding the relationship between the level of arsenic in soil, and the density of the plant Rubus ursinus. Our objective is to find the level of arsenic in selected plots of soil in the Sweet Home area by sending soil samples to the OSU reactor, calculating the density of rubus ursinus in that area through careful observations, and comparing the data to find a relationship.
We predict that different levels of arsenic will affect trailing blackberries because arsenic is poisonous to many plants and animals. This means that higher levels of arsenic will result in lower levels of plant density of trailing blackberries.
This information is important to discover because arsenic is poisonous and harmful to living plants and animals when exposed to it in high amounts. Many animals such as birds, deer, skunks, foxes, opossums, coyote, raccoons, black bears, squirrels, and chipmunks all eat from the berries of the plant. (USDA) If the rubus ursinus is effected by the high amounts of arsenic, the animals that each off the plant could be negativly effected as well and face disease or death. The berries might not even grow on a plant that is in soil with a high level of arsenic and could cause some animals to starve or search for food in less secure areas. Farmers and local gardeners are also affected by the impact of arsenic. If higher levels of arsenic in soil results in lower plant density of trailing blackberries, a common, sturdy plant, than other plants and crops could also be affected and prevented from growing, or producing healthy food.
Rubus Ursinus is more commonly known as Trailing Blackberry. This plant is from the rose family and grows in thickets and hedges. (encyclopedia) Blackberries are a great source for iron and vitamin C. (encyclopedia) This helps the animals that feed off its berries to stay healthy.
The Trailing Blackberry grows dark green leaves that are 1 ½ -3 in long and are in leaflets of three, alternating around the stem. (Virginia) The leaves also have prickly thorns all underneath, and a serrated edge. (Virginia) The plant’s branches are long and slender, and can grow up to around twenty feet. (Virginia) The stems start out by growing upward, then they start to arch with maturity and eventually touch the ground and re-root. (Virginia)
Methods:
Because of similar research performed in the spring of 2003, where soil samples were taken from Sweethome and sent to the OSU reactor, we were able to know the order of steps to take to prepare samples for the reactor. The first step in our procedure was to find six areas to use to take our data from. Each area will needed to have similar ground slope, contain rubus ursinus plants, and have distinct levels of arsenic in the soil. Two of the plots needed to have a high level of arsenic in the soil, two had to have a medium level of arsenic, and two dad to have a low level of arsenic in the soil. We selected one of our "low arsenic areas" at Crescent Valley High School where rubus ursinus grows. This gave us a different area to collect data from where arsenic is not found in the soil in high amounts. This data was used as a control to compare with our data from Sweet Home. We took four soil samples from each plot (each plot will be an area of 2 yards by 2 yards). These samples were taken 1 in. from the corner point, inward, towards the center. Each soil sample was taken two inches from the surface and enough soil was taken to fill a regular sized zip lock bag. The four soil samples from each plot weremixed together and placed in one large zip lock bag to gain an average soil sample for the entire plot. The final six soil samples were then prepared and sent to the OSU reactor and analyzed for arsenic using INAA.
Procedure for preparing a soil sample for INAA analysis:
Procedure for preparing sample to be sent to the reactor:
(Wear latex gloves throughout this procedure to avoid contamination of containers and samples. DO NOT USE WATER TO CLEAN ANYTHING!)
WHEN YOU HAVE TWO SAMPLES IN SMALL VIALS:
After the soil samples have been taken, prepared, and sent to the reactor, we will measure the density of rubus ursinus growing in each plot that we took soil samples from. This will be done by careful observation of counting each stem of trailing blackberry plants that grow from the ground in the selected plots. After all our data is collected, we will compare the level of arsenic in the soil with the density of rubus ursinus in that area, and find a relationship between them.
Materials:
To complete this experiment successfully, we will need the following materials.
|
Date to be completed: |
Trip to Sweet-home November 20, 2004 |
First class time after Sweet-home trip |
Second class time after Sweet-home trip |
|
Task: |
Gather soil samples from chosen plots and find the density of Rubus Ursinus in each plot |
Dry soil samples |
Prepare soil samples for the reactor |
Data to be collected:
INAA Analysis:
The process of NAA (neutron activation analysis) is very important to this project. Rare earth elements found in samples are highly radioactive after they have been exposed to neutrons. This means that through the process of nuclear reactions, and the measuring of radioactivity, the identification and amount of different elements can be determined in samples. During this process, the samples placed in the reactor are irradiated. A neutron is launched at a high velocity at the compound nucleus and this non-elastic collision causes the nucleus into an excited state. The compound nucleus will then de-excite to a more stable state by emitting one or more gamma rays. By measuring these gamma rays, a formula can be used to determine the amount of different elements in a sample. The formula is as follows: C (of the unknown) / C (of the standard)=A (of the unknown)/A (of the standard)
C = the concentration, or the amount of an element that a sample or standard is made of
A = the activity, or the number of counts per time passed (this is often divided by the sample’s mass so that the results are in per-gram units).
Standard = a sample that had a known amount of a certain element or elements. This sample is prepared for the reactor like all other samples, and is irradiated at the same time as the unknown sample. Through this process, we were able to determine how much arsenic is in each soil sample that we sent to the reactor. This is important because we were able to have an accurate result of the different levels of arsenic in the soil, allowing us to find the relationship between plant density and the different arsenic levels.
Results:
The outcome of our data shows that areas with soil that has high levels of arsenic in it also show a population density for trailing blackberries that is less than areas where the soil contains less arsenic. In order to organize the data we collected, the following guidelines were used:
Arsenic: Population Density:
High (H) = 31+ ppm High (H) = 8-11stems
Med (M) = 9-30 ppm Med (M)= 4-7 stems
Low (L) = 2-8 ppm Low (L) = 0-3 stems
With these categories we were able to place the data results into the following table:
|
Plot Number |
Blackberry Pop. Density |
Arsenic Level (ppm) |
|
1 |
0* (L) |
47.2 (H) |
|
2 |
7* (M) |
9.5 (M) |
|
3 |
9* (H) |
2.8 (L) |
|
4 |
5* (M) |
19.3* (M) |
|
5 |
1* (L) |
38.9 (H) |
|
6 |
11* (H) |
3* (L) |
This chart shows how the arsenic levels found in the soil and the population density of trailing blackberries in that area are directly related in a linear pattern. The higher the level of arsenic found in the soil, the lower the number is for the plant density of trailing blackberries. This can be shown by the following graph:
Rubus ursinus Population Density Vs. Soil Arsenic Level
During our project, we created a group website to place all our methods, results, and observations. We also practiced drying samples to send to the reactor, and placed results onto spreadsheets for organization. Most of our group time was spent planning out our project, assigning tasks to be completed on individual time (this consisted mostly on research of related topics), and analyzing our results once they returned form the reactor. We also had the privilege to visit the reactor on two occasions. The first time, we were given an informative speech about how the reactor works, and were able to see the reactor as it was turned on. On the second trip to the reactor we worked with the INAA computers and saw the program used to analyze the samples we sent to the reactor. We helped in the long process of taking the results from the measuring program and placing them on a single spreadsheet so that each group has access to the data.
Discussion:
Our hypothesis stating that high levels of arsenic negatively affect trailing blackberries is correct according to the data we collected. In areas where the soil contains high levels of arsenic, the population density for trailing blackberries is less, and in areas when the soil contains low amounts of arsenic, the blackberries population increased. The areas where the soil contained medium levels of arsenic also contained a medium amount of trailing blackberries.
This data makes sense, and can be the result of two explanations: either the trailing blackberries are absorbing the arsenic from the soil and are poisoned from it, or the arsenic blocks the root system from absorbing the needed nutrients for survival. The arsenic could also eat away the nutrients in the soil, preventing the plants from them and making the soil empty. The data we collected shows that high levels of arsenic cause low population density in trailing blackberries, and this could suggest that the plant absorbs the arsenic into its stems and leaves.
During this project several restrictions occurred that altered our findings. If we were to redo this experiment, we would take our own samples from Sweet Home instead of relying on other groups to gather the necessary data. This was an issue because the essential data that we needed for our results, the number of stems growing from the ground of each selected plot, was only observed, and not actually counted. This means that we were provided with the results of "High," "Medium," and "Low," population densities of trailing blackberries instead of the number of stems collected. We had to estimate the number of stems for each plot based on educated knowledge of the number of stems that grew in the plot we used a Crescent Valley. The other biggest restriction was the limit to the number of samples we were able to send to the reactor. Since our group was limited to six samples, we were only able to test each plot once allowing for many different factors to alter our results and not providing very accurate data to draw conclusions from.
This project gave justification to the hypothesis that high arsenic levels in soil negatively affects the population density of trailing blackberries, but more similar research needs to be done to make the claim solid. Since trailing blackberries are affected by arsenic, experiments should be made to test other plants to see if they are affected as well. It is also important to know if the plants are absorbing the arsenic into their stems, leaves, and fruit, or if they are just being blocked from the nutrients they need to survive, stunting their growth. This could be tested by collecting samples of the plants that grow in areas where the soil contains high levels of arsenic and sending them to the reactor to find out if there is now arsenic in the plant as well. This would provide information on how different plants react to the arsenic in soil and help us understand how the arsenic prevents plants from growing in large amounts.
Sources:
Reactor (MURR). http://www.missouri.edu/~glascock/naa_over.htm
http://www2.corvallis.k12.or.us/cvhs/science/samplepreparationprocedureforINA.doc
School, http://www2.corvallis.k12.or.us/cvhs/science/samplepreparationprocedureforINAA.doc
http://www.cnr.vt.edu/dendro/dendrology/syllabus/rursinus.htm
