pesticides

[violin30]

Hello, I am just starting with my science fair this year. I am interested in doing something with pesticides. I have been reading quite a lot and have few questions for you please.
1. Is there a database where I can find what pesticides are currently used on fruits and vegetables and what are the side effects they have on animals and humans?
2. And my teacher said it woudl be very complex to experiment with real pesticides. Is there an alternative that I can use instead. I would like to find something that would be a close chemical structure relative.
3. What science fair category a project with pesticide would be most suitable?
Thank you so much for your help.

[deleted-71884]

Hi Violin30,

It's great that you are starting on a science fair project!

As for number 1, you can look at this: http://www.epa.gov/agriculture/tpes.html. The EPA regulates which pesitcides are good to use and which aren't on consumer goods.
Actually, it would be hard and a lot of work to look at a lot of pesticides. It would be best for you to focus on one or two and go more in depth on that specific pesticide than works on many different pesticides and get very scanty results. As for alternatives, there are biodegradable pesticides.
Depending on what you are doing, it could be an environmental, food science, or biological project.

Hope that helps!

-Sam

[deleted-72431]

Hi,
I agree that it will be hard to look at many different pesticides. Perhaps you can focus in on one pesticide-- really find out the structure of it, and how and why it works. What about pesticides interests you? Is it the effect it has on the environment? The fact that pesticides can contaminate food and affect peoples' health? As Sam pointed out, there are biodegradable pesticides. Would you be interested in comparing the efficacy of two different pesticides (perhaps one biodegradable, the other not?)

Lily

[violin30]

Hello, and thank you so much for your replies. I am looking more into effetive ways for removing the pestecides from fruits, apples. I would like to apply pesticide on fruit and then after using diffrenet methods to remove it, measure the consentration of it in liquid. My teacher told me that it would too complex to experiment with real pesticide, that is why I am looking for an alternative that woudl closely resemble pesticide in chemical structure. Maybe it is a good idea to run experiment with biodegradable and non-biodegradable pesticides and compare the results then. Please let me know what you think. Thank you.

[mbadtke]

I love the idea of seeing what removes the pesticides the best! After looking around on the net a bit, it seems like it would be very challenging to measure actual pesticide concentrations. It can be done, but it takes pretty sophisticated and expensive equipment. I have a different idea. What if you used a powder that could be observed with UV light, something like is linked below...

http://www.germwise.com/howtouse.asp

It is totally harmless and not very expensive. You could artificially coat fruit with this substance, then try some different techniques of washing, etc, and then use a UV light to see what percentage of the fruit still has the UV powder.

One issue is how well it would stick to the fruit, but that might be something to experiment with before you start your full project. Have fun!

Matt Badtke

[deleted-72431]

Hey violin30,

I agree, that idea of measuring pesticide removal is pretty neat! Perhaps you could look more into washing methods by considering the "like dissolves like" principle (have you learned about this in your chemistry class?). You could learn about some of the molecules that are used as pesticides and compare their polarity to different solvents, such as water, ethyl alcohol, etc., and form a hypothesis based on this preliminary information.

Feel free to ask more questions!
Lily

[donnahardy2]

Hi,

This is an interesting discussion and definitely a challenging one to do for a science fair project. The other experts have had some really good suggestions. Here are two project ideas from the science buddies website that I believe could be adapted to your idea. The first project includes a specific protocol along with background reading information. The second project idea includes several good suggestions and background reading information and suggestions for alternatives to using vertebrate animals in your project.

https://www.sciencebuddies.org/science- ... p018.shtml

https://www.sciencebuddies.org/science- ... p019.shtml

I hope this helps.


Donna Hardy

[donnahardy2]

Hi,

I found a paper that you might be able to use for your project. Most methods for measuring pesticides require specialized equipment, but this paper describes a method you might use to measure pesticides that contain chloride, bromide and iodide. The method requires only a spectrophotometer and some silver nitrate.

http://www.ncbi.nlm.nih.gov/pmc/article ... 7-0119.pdf

If your school has a spectrophotometer and some silver nitrate, you could the method from this paper to do your analysis; you would still need to choose a suitable pesticide and design your experiment. You would also have to avoid using samples like seawater that contained chloride to avoid interference.

Examples of halogenated pesticides are heptachlor, diuron, endosulfan, and captan. There are others listed on the Stockholm convention on persistent organic pollutants.

http://en.wikipedia.org/wiki/Stockholm_Convention

Lindane is a chloride-containing pesticide commonly used on humans as a treatment for lice and scabies, so might be a good choice for your project.

http://en.wikipedia.org/wiki/Lindane

Diuron is a chloride-containing herbicide that inhibits photosynthesis. This herbicide is very commonly used, so would be of current interest to study for a science project. You could possibly collect your samples by any roadside that shows evidence of spraying for weed control.

http://en.wikipedia.org/wiki/DCMU

http://www.cdpr.ca.gov/docs/emon/pubs/f ... diuron.pdf

Captan is a chloride-containing fungicide that is commonly used on apples. Since apples are commonly eaten by humans, this would be another possible topic for your project.

http://en.wikipedia.org/wiki/Captan

I think you have a really good idea for a project, and I would encourage you to continue exploring for ideas for your experiment. Please check with your teacher, as there are always concerns about safety in working with this type of compound.


Donna Hardy

[violin30]

Dear Miss Donna,
thank you so much fro all the links. I have been reading a lot and have quite a few questions. I will post after I am through the last two papers. Thanks again for you help.
Julia.

[violin30]

Hello,
i have looked into working with Captan and I am allowed to experiment with it under supervision. I can obtain easily as well at 48% concentrate in a powder form. I have been reading the paper on alternative methods of measuring the pestercide, but I am so lost. Most methods for measuring pesticides require specialized equipment, but this paper describes a method you might use to measure pesticides that contain chloride, bromide and iodide. The method requires only a spectrophotometer and some silver nitrate. Can you please explain to me how I am to approach this method or point me in a right direction? Thank you so much.

[donnahardy2]

Hi,

From the material and methods section of the paper that I cited in my previous post, here is the procedure for measuring captan and other halide-containing molecules.

Analytical methods. Chloride, bromide, and iodide were
determined in culture supernatants turbidimetrically (8) by
adding 0.2 ml of 0.1 M silver nitrate solution in 5 M
phosphoric acid to 1 ml of sample and reading the A525 on a
spectrophotometer (Uvikon 860; Kontron, Everett, Mass.).
The range of 10 standards for each analyte from 0.1 to 5.0
mM gave a linear response, with r2 = 0.99. Optical densities
of cell suspensions were measured at 600 nm.

Were you able to open the link and read the entire article? If not, let me know and I will upload it for you.

Does this method made sense to you? Can you get some silver nitrate, phosphoric acid, and some captan to use as a control? Do you have access to a spectrophotometer that will measure OD at 600 nm?

Let me know if you need more explanation on the method.

Donna Hardy

[violin30]

Dear Miss Donnahardy2,
I have not taken chemistry yet, but I did pick up and textbook and I am going though it. I really like the idea of using a spectrophotometer . I am ashamed to say, but I do not understand anything fo the procedure they used. If it not too hard for you, please explain to me exactley what they were doing. I am homeschooled and will try to call the local high school to find out if they have spectrophotometer . I already looked on ebay to see if it can be bought. Some of them are reasonable but some are quite expensive. Thank you again for your help.

[deleted-72431]

Hey Violin30,
One way you might be able to use a spectrophotometer (if your local high school does not have one) is to ask a local university, which will almost certainly have a spectrophotometer. Perhaps you could contact a few professors in the chemistry department and explain what your experiment is, and then ask if they would be willing to support you? Even if they say no, most professors enjoy speaking to students who want to learn more and you may be able to discuss the design and implications of your experiment with them.

-Lily

[donnahardy2]

Hi Violin30,

Do not worry about getting a spectrophotometer. While it would be good to have one because this would allow you to obtain quantitative results for your project, it is possible to construct a standard curve that you can use to estimate concentration. When silver ions are added to captan, a white solid precipitate is formed and this can be seen as cloudiness or turbidity in the sample. If you make a series of dilutions of known concentrations of the fungicide, you will see a series of tubes with cloudiness ranging from clear to opaque, and you can match your samples to the tube of a known concentration of the fungicide. You can be your own spectrophotometer with this method. You would seal the tubes and use them as a standard curve for all of your experiments.

Does this make sense? Or do you need additional explanation?

I think you can start designing your experiment. What problem are you going to investigate?


Donna Hardy

[violin30]

Thank you fro beinh so helpful. I am trying to see what would be most effective way of removing pestecides from apples. Do you think the substances that I would use in my experiment, would interefe with silver ions and captan and I would not be able to tell the color as clearly using the serial concentarations/delutions? Thank you.

[donnahardy2]

Hi Violin,

You should plan to do a preliminary experiment to optimize your experimental conditions so you will get results that are feasible with the method you are using. You can test each substance that you use to clean the apples with the silver chloride first before you decide to use it in your experiment. Many of the cleaners I would consider using, like pure water, hot water and vinegar would not interfere. What method of cleaning apples were you planning to use? We can check for chloride content before you start.

Have you thought about your experimental protocol? How are you going to set up your experiment? This will be challenging.

Donna Hardy

[violin30]

Yes, I have been thinking of how to do the procedure.

[deleted-71957]

violin30,

I actually had the experience for a couple summers to work on a local farm. We used a common system of pesticide application called Integrated Pest Management (IPM). It is often standard procedure on smaller farms that applies pesticides only when it is absolutely needed. I would suggest doing further background research pesticide application to understand the 'bigger picture' of your experiment.

Hopefully that provides some additional information,
Travis Sigafoos

[donnahardy2]

Hi Violin,

Travis has made some good comments that help minimize the amount of pesticide on apples at harvest time. Since the purpose of your project is to determine the best way to remove the pesticide once it has been applied to the apples, I think your experimental protocol is very good. However, I recommend doing a pilot study with one control (no pesticide) apple and one experimental apple with a water wash, just to make sure the experiment will work, and that you are operating in the dynamic range for your analytical method. For your pilot experiment, try taking two x 20 ml aliquots of the wash solution and compare the results of duplicate samples. The pilot experiment will help you to optimize the method so you will get really good results when you do the definitive experiment.


Donna Hardy

[violin30]

Miss Donnahardy, thank you for your advice. I was looking at possible ways of measuring the concentartion of pesticides and came across this idea of using the turbidity meter. What do you think about it? I will apply the pestecide unto my apples, but my question is do I mix captan with silver nitrate in order for percipitate to occur and turbidity meter will be able to read it. Does reaction need any acid for percipitation to happen. In what amounts I need to combine captan, silver nitrate and , maybe, acid? Thank you.

[donnahardy2]

Hi Violin,

Great idea! Do you have a turbidity meter? What is the brand and model? The silver chloride gives a white precipitate that you should be able to read with a turbidity meter. This will give you quantitative results. You will have to set up a standard curve and plot NTU vs concentration of the Captan, but you definitely should be able to correlate NTU’s to concentration of pesticide. The turbidity meter will be a good substitute for the spectrophotometer in the original method.

Donna Hardy

[violin30]

Thank you. You can not belive what a relief it is to hera from you. The turbidity meter comes in a Spark kit. Would you please explain about standard curve and NTU. Thank you so much.

[donnahardy2]

Hi,

Here’s a brief summary that I hope will be helpful A turbidity meter measures the cloudiness or haziness of water due to suspended particles that are invisible themselves. Higher levels of suspended particles will result in a solution of higher turbidity. When colorless silver nitrate is added to Captan, it forms an insoluble precipitate that makes water cloudy. A turbidity meter measures the light that is transmitted through water and results are given as nephelometric turbidity units, or NTU’s. One NTU is equivalent to 1 mg of very small silica particles in a liter of water. Your turbidity meter will be able to measure range of NTU’s and you will have to determine the correlation of Captan concentration to NTU’s. So you will set up a calibration curve of samples containing increasing concentrations of Captan and measure the turbidity. You can plot NTU on the y-axis and concentration of Captan on the x-axis to establish your calibration curve.

To help you get started, you can go back to the original reference and try to reproduce the author's method on the bottom right of page 1615:

http://www.ncbi.nlm.nih.gov/pmc/article ... 7-0119.pdf

The authors used a standard curve of 10 standards with a concentration of 0.1 to 50 mM and reported a linear response with an R2 value (correlation coefficient) of .99. This means that the graph was a straight line below 0.1and 50 mM. I don't know if your turbidity meter is as sensitive as the spectrophotometer used in the reference paper, so you need to test it to make sure it will work. Do you have Captan that is a known concentration? Do you know how to calculate and dilute the sample to a range of 0.1 to 50 mM? Please let me know what you need to know next.


Donna Hardy

[violin30]

Dear Miss Donna, thank you again for the wealth of information. The turbitidy meter is very sensitive. I will be calibrating it every time I use it. I read about calibration curve on wikipedia. I would apprecite if you can guide me through calculation and diluting of samples? I found captan on ebay here is the link. It is powder adn 50% concentartion.
http://compare.ebay.com/like/2006661321 ... s&var=sbar
In the paper that you posted , they added 0.2 ml of 0.1 M silver nitrate solution in 5 M phosphoric acid to 1 ml of sample. So I am assuming that for percipitate reaction to occur I will need phosphoric acid to use. Would I just apply captan to my apples and then swabbing the apples after wash with a swab, I will dip the swab into acid/silver solution? Would that method give me good results?
I looked at Carolina biological and there few different kinds of silver nitrate. What type should I get?
Thank you again for your help. I will wait to hear form you to buy my supplies.

[donnahardy2]

Hi Violin,

I apologize for the delay in responding to your last inquiry. I have been very busy and work and away for a couple of days.

For studies like this, it it better to purchase 100% pure chemicals. Pure Captan does appear to be available from Sigma Aldrich, but the cost is prohibitive. Here is the label for the Captan that you found; it includes 50% fungicide and 50% inert ingredients that are not described.

http://www.southernag.com/docs/labels_msds/cap50w.pdf

Before you purchase this, it would be good to know if the inert ingredients contain any chemicals that would precipitate with silver. If so, this would definitely affect your standard curves. You can try contacting the company, Southern Agricultural Insecticides, Inc and ask about the inert ingredients. It might be best to call and ask for a referral if the person answering the phone does not know. Their phone number is 828) 692-2233. If no information is available, as for the name of the manufacturer of the specific item they are selling.

For the silver nitrate, Carolina Biologicals does offer two forms of silver nitrate that will work for your project.

Catalog number 887788, silver nitrate, 5 grams, would make 300 mL of 0.1 M silver nitrate, which would probably be plenty for your project. Catalog number 850770, a package of 5 capsules, would make 50 ml of a 0.1 M solution each is $5 more, but would be more convenient to use.

You will need to devise a suitable method for rinsing the apples to recover the Captan. I think it would be difficult to swab the entire surface of an apple, but you could try this. I think it might be easier and give more reproducible results if you could first dip the apples in a solution of the Captan and let the apples dry. You could then use a measured volume of deionized water and add an apple and water to a sealed container, like a zip lock plastic bag, and shake well to recover the pesticide. You would then use 1 ml of the water for your samples. You might need to do a small pilot experiment to check and make sure your technique will work. Have you looked for a standard method for preparing apples for pesticide analysis?

Donna Hardy

[violin30]

Thank you for getting back to me. I think, the method with washing apples in a sterile distilled water after applying pestecide would be best. I then can use the rinsing sample, 1 mL, and add it to phosphoric acid and silver nitrate.
I will contact the compnay on Monday to find out about the inert ingredients. I would apprecite any information about the standard method you mentioned below for testing the apples. Thank you again.

[violin30]

Miss Donna,
I called the company and they told me that there are waxes and fillers and other two elements: N-trichloromethylthioylthyo-4-cyclohexene, 2-dicarboximide. I hope, you can tell me if any of these substances will react with silver nitrate. Thank you again.

[donnahardy2]

Hi Violin,

Great work! Yes, the trichloromethylthioylthyo-4-cyclohexene will react with the silver nitrate. The waxes and dicarboximide won't cause a problem. I would need the chemical structure of the "fillers" to know more about these. Captan is insoluble in water so these substances are probably added to improve the solubility of the fungicide.

Here are a couple of articles that describe a method for preparing fruit for pesticide analysis.

http://www.ual.es/personal/intercom/comun/7.pdf

In this paper, the method is described in section 2.2 sample treatment. The fruit is homogenized in a blender, extracted with ethyl acetate and NaOH and blended. The extract was then filtered through anhydrous sodium sulfate, washing eith more ethyl acetate, and evaporated to dryness. The sample was dissolved in methanol and filtered through a .45 micron filter. This method would be too difficult for you to do.

http://www.chem.agilent.com/library/app ... 4068en.pdf


In this paper, the sample is homogenized, acetic acid, acetonitrile, magnesium sulfate, and sodium acetate are added to the sample before it is centrifuged. The acetonitrile is further processed (refer to the flow chart diagram).

I would say that these methods are way beyond the scope of your project, so rinsing the apples as you have described to recover the fungicide would be your best option. Since the Captan is insoluble in plain water, you will probably need to add something to improve recovery of the Captan from the apple. Captan is soluble in chloroform, but I don't recommend that you work with this solvent. The most readily available non-polar solvent is acetone, which is found in fingernail polish remover. I think that perhaps adding 10-20% acetone to the water would help. Acetic acid (vinegar) is also a good solvent and it might work well. Do you think you can get acetone? Do you have a safe place to work with this volatile solvent? If not, then the acetic acid would be a good option.

Donna Hardy

[violin30]

Dear Miss Donna,
http://www.dudadiesel.com/search.php?qu ... 5Qod0xoUpQ
This link is for 99% acetone. Please check it out to see if it is suitbale for the experiment. I do have a place to experiment with it -- fume hood.
In the paper that you posted , they added 0.2 ml of 0.1 M silver nitrate solution in 5 M phosphoric acid to 1 ml of sample. So you suggesting that I would use acetone instead of water to wash my apples and then add 2 mL of that to 0.2 mL of 0.1 M of silver nitrate. Would I use phosphoric acaid as well. Or you were suggesting that acetone woudl be used instead of phosphoric acid and I will still wash the apples in water? Thank you again.

[donnahardy2]

Hi Violin,

The acetone you found would be very good for your experiment. You could also check at a beauty supply store or auto parts store to see if you could find a less expensive option, however, do check to make sure you buy acetone with nothing else added. You will probably want to work with diluted acetone, 10 or 20 % diluted in water. 100% acetone is very flammable and I think that adding a small amount as an organic modifier will improve the recovery of the Captan from the apples. The silver nitrate is prepared in the phosphoric acid separately, and you would add this to the dilute acetone that you rinse the apples with to look for the white precipitate. .

Does this help?

Donna Hardy