perchlorate detection

[tigertim]

Other than using a mass spectrometer, is there alternative bleep of detecting perchlorate? I am specifically testing lettuce. If not, would you know any labs that may have one in the bay area.

[Louise]

Other than using a mass spectrometer, is there alternative bleep of detecting perchlorate? I am specifically testing lettuce. If not, would you know any labs that may have one in the bay area.

Food and water contamination with perchlorate generally occur at the ppb level, and most bleep are not senstive enough. As you point out, most testing is done with mass spec (actually a more complicated instrument called a LC/MS/MS or an IC/MS/MS) and I believe these two bleep are the only bleep approved by the EPA for the most sensitive detection. The older EPA protocols used just IC but is less sensitive. It is possible that IC is easier to find that the ms systems, but I don't know for sure.
The EPA protocols are here:

http://www.epa.gov/ogwdw/bleep/sourcalt.html

The perchlorate protocol is 314 (IC) and 331 (mass spec).

I found this by searching for "how does the EPA detect perchlorate".

There may be a lab facility available- I will check in with the Expert who knows about this and have him post here.


Louise

[tigertim]

If I were to carry out a project like this, what would be the odds of finding traces if perchlorate in store bought lettuce. It once was a problem a few years ago but I am not sure about the current situation with the contamination.

[jeffreyshu]

I think you will have a difficult time in conducting the test to find perchlorate in lettuce. I think you will have a harder time in finding perchlorate at detectable levels on a random store bought lettuce.

I'm curious as to what's the reasoning of your topic "accumulating toxins" in lettuce. Could you please describe a little bit about your topic so we can better help you with your project?

[Louise]

I think you will have a difficult time in conducting the test to find perchlorate in lettuce. I think you will have a harder time in finding perchlorate at detectable levels on a random store bought lettuce.

I'm curious as to what's the reasoning of your topic "accumulating toxins" in lettuce. Could you please describe a little bit about your topic so we can better help you with your project?

I agree. I had assumed that this was not testing on 'random' lettuce, but rather some sort of hypthosis driven investigation where you knew that perchlorate was around. What is your hypothesis/experimental plan

As you mentioned, the case with lettuce a few years ago got a lot of media attention. The levels were quite high 130 ppb, when water levels are generally 1-10 ppb. So percholate does accumulate in lettuce, if the lettuce is watered with 'dirty' water.


Louise

[deleted-71447]

Hi tigertim,
I am a PhD/researcher working for the US Geological Survey in Menlo Park, CA. One topic of active work for my research branch is the presence of naturally occurring and man-made perchlorate in precipitation, surface water, and ground water. Another active topic is water usage for agriculture in the USA, so there is a lot of expertise in the topic you've mentioned. I'm going to forward your question to people in the research group and see what we can find for you.
Chris

[deleted-71447]

Hi,
Here is the response from my colleague who is an active researcher in perchlorate issues. I'm afraid there are no big surprises - you'll need to keep searching for a mentor with the proper analytical equipment and expertise if you plan to continue with this project.

Regards,
Chris

I love the idea of looking at lettuce, since the distributors and grocers do the legwork for huge geographic coverage. And the cost would be reasonable. However, I'd advise the student to consider a constituent present at higher levels, hence more easily measured.

The levels at which perchlorate becomes a health concern are parts per billion, the realm of analytical nightmares. In "easy" samples, like filtered groundwater, a sophisticated IC-MS-MS procedure is required to resolve environmentally relevant concentrations (ES&T 2000, 34:1862). At higher levels of interfering anions, like in sediment extracts, isotopically labeled spikes have to be added as internal standards to get meaningful results. Plant-tissue extracts additionally contain interfering organics that must be removed via aluminum-oxide adsorption prior to analysis (J. Agric. Food Chem. 2005, 53:369). So this would not be an easy project for the average student, unless he or she was able to hook up with someone already doing this work.

[tigertim]

I have found a chemist who would be able to run the lettuce samples through a IC-MS-MS. The thing is I need to create the samples myself. I know the FDA has a procedure but does anyone have any others. I also need to test lettuce that will have the greatest possibility of having contamination. Would anyone know of any farms of brands of lettuce that will give me the best results?

[deleted-71447]

Hi tigertim,
That's great! Some of the procedures are described in the references in my previous message. Those references are
ES&T 2000, 34:1862
(Translation: Environmental Science and Technology, 2000, volume 34, page 1862.)
J. Agric. Food Chem. 2005, 53:369
(Translation: Journal of Agriculture and Food Chemistry, 2005, volume 53, page 369.)

Some other references that might help are:
Title: Effects of genotype and transpiration rate on the uptake and accumulation of perchlorate (ClO4-) in lettuce
Author(s): Seyfferth AL (Seyfferth, Angelia L.), Parker DR (Parker, David R.)
Source: ENVIRONMENTAL SCIENCE & TECHNOLOGY 41 (9): 3361-3367 MAY 1 2007
Title: Determination of low levels of perchlorate in lettuce and spinach using ion chromatography-electrospray ionization mass spectrometry (IC-ESI-MS)
Author(s): Seyfferth AL, Parker DR
Source: JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 54 (6): 2012-2017 MAR 22 2006
Title: Perchlorate and nitrate in leak vegetables of North America
Author(s): Sanchez CA, Crump KS, Krieger RI, Khandaker NR, Gibbs JP
Source: ENVIRONMENTAL SCIENCE & TECHNOLOGY 39 (24): 9391-9397 DEC 15 2005

To get those articles, you will probably need access to a university library or university internet. Perhaps your chemist mentor can help with that. Let me know if you have any trouble.

I'm told these are not simple procedures, so you will likely need some help and perhaps some specialized equipment for sample preparation.

One potential strength of your project is that produce suppliers do a lot of the work for you. By going to the grocery store, you can sample produce grown all over the country and all over the world. A good starting point might be to study lettuce from a region irrigated with water from the Colorado River, which is contaminated with very low concentration of perchlorate. The brand probably doesn't matter, as long as you can identify where the lettuce was grown.

This is likely to be a very challenging and potentially rewarding project. Please keep us updated about how things are going.

Chris

[Louise]

I have found a chemist who would be able to run the lettuce samples through a IC-MS-MS. The thing is I need to create the samples myself. I know the FDA has a procedure but does anyone have any others. I also need to test lettuce that will have the greatest possibility of having contamination. Would anyone know of any farms of brands of lettuce that will give me the best results?

I don't know how easy it is to buy standard perchlorate solutions. I assume you will need this to calibrate the MS instrument anyway. But one thought I had was that you could grow some lettuce hydroponically in various solutions of perchlorate and then see how much they concentrated it. I.E. 1 ppb solution (similar to levels found in water supplies) leads to 60 ppb in lettuce. This allows you to be certain you are testing bleep that is actually there... You could vary the input of perchlorate and observe the levels in lettuce. Lettuce grows quite quickly (at least leaf lettuce not head lettuce) and it should be easy to rig up some hydroponic flats. You might have to grow these in your chemist's lab though for safety reasons.

I'm still not sure what you hypothesis is with store bought lettuce. Since most distributors buy lettuce from all over, you cannot really test lettuce by geographical location- it is very rare that I see produce labeled with point of origin. [I agree with Chris that this would be the ideal way to group the samples- I found maps of different watersheds and perchlorate contamination levels. It seems logical that there would be a measurable effect on lettuce levels. If you did find lettuce labeled by source that would be fantastic!] Secondly, given the difficultly of the analytical technique, I think this would potentially be very frustrating- if you get 0 perchlorate, is it because there is 0 perchlorate or because you failed to do the extraction or MS correctly? At the very least, you might want to consider growing lettuce with known perchlorate exposure in addition to testing store bought lettuce as a validation of your bleep.


Louise

[tigertim]

I have recieved some information from the chemist I am working with and had a straight foward approach to the experiment which I am a little iffy about. Can someone tell me waht they think about this bleep. Also, lettuce in groceries usually have their point of origin which will help me determine their contamination. Here is the reply from the chemist I am working with:

I do not think you have the supplies to do the extraction as described in this link, am I correct? You need to to get O-18 labeled perchlorate, as well as the super clean carbon column to concentrate the analyte. My thinking is more of a straight foreward approach. You take lettuce, chop them up, use a lot if you think the level of perchlorate is low, extract the lettuce with water, take the water extract and boil down to a small volume, then analyze the residue. This will concentrate the perchlorate, but without a standard, one can not determine the concentration. But on the other hand , you only want to determine which part of the lettuce contains higher level of perchlorate, then this approach is ok. Please read over the procedure, and understand it, think about what I am saying here, and let us discuss.

[deleted-71447]

Tim,
Has this chemist worked before with naturally occurring concentrations (a few parts per billion) of perchlorate? If yes, then I would trust his/her advice. If not, then I am not clear about how much information you have provided to the chemist. For example, is the chemist aware of this:
"Plant-tissue extracts additionally contain interfering organics that must be removed via aluminum-oxide adsorption prior to analysis (J. Agric. Food Chem. 2005, 53:369)."

It may be that the interference will prevent any meaningful results, but I really don't know.

You should be prepared that it won't work and have an alternative plan, such as looking at nitrate which is usually present in much higher concentrations. You should also think more about Louise's ideas and questions about hypotheses and then let us know your thoughts about those.

Whether or not this particular bleep will work, it seems like you have a good mentor here and the potential for a great project.

[Louise]

I have recieved some information from the chemist I am working with and had a straight foward approach to the experiment which I am a little iffy about. Can someone tell me waht they think about this bleep. Also, lettuce in groceries usually have their point of origin which will help me determine their contamination. Here is the reply from the chemist I am working with:

I do not think you have the supplies to do the extraction as described in this link, am I correct? You need to to get O-18 labeled perchlorate, as well as the super clean carbon column to concentrate the analyte. My thinking is more of a straight foreward approach. You take lettuce, chop them up, use a lot if you think the level of perchlorate is low, extract the lettuce with water, take the water extract and boil down to a small volume, then analyze the residue. This will concentrate the perchlorate, but without a standard, one can not determine the concentration. But on the other hand , you only want to determine which part of the lettuce contains higher level of perchlorate, then this approach is ok. Please read over the procedure, and understand it, think about what I am saying here, and let us discuss.

In addition to Chris's comments, which are good (especially the alumna-oxide prep... though that should be simple (and cheap) for your chemist friend) let me add this...

In theory, this sounds okay. Why don't you do some simple calculations though, and make sure you are at detectable levels. If you have x grams of lettuce with y ppb perchlorate (130 ppb should be the upper limit), your extraction is 50% complete (hopefully you can find this value in the literature and hopefully it will be higher than 50%) in Z volume water and you reduce to volume Q needed for IC-MS-MS, what level are you at? Is this enough for the machine to detect? You don't want an experiment where it turns out you need 50 lbs of lettuce to get enough sample! You should discuss these estimates and the assumptions you made with your chemist.

That said, you still haven't said what your hypothesis is. It is hard to judge whether a qualitative approach like this is suitable for you experimental plan. Is qualitative data okay for you?

With regard to point of origin, make sure this is actually where it is grown, and not where it is packaged or the company is based. Most packets of veggies do have an address, but I think frequently this is not the point of orgin. I believe Whole Foods (and some other grocery stores) generally labels with country of origin (and more rarely state), but I've never seen anything more specific unless it was locally grown.

Louise

[tigertim]

For this experiment, my hypothesis is that there will be a greater accumulation of perchlorate towards the base of the lettuce. I believe this qualitative approach is suitable for this project because I don't need to determine the concentration of the perchlorate.

To figure out which part of the lettuce will have the highest amount, what is the best way to divide sections or classify the parts of the lettuce? I will certainly discuss the comments made by Louise to my chemist. Can I also get a link to the maps of different watersheds and perchlorate contamination levels? Does perchlorate decompose at 100C? I believe it is not volatile. I appreciate all the help in the project!

[Louise]

For this experiment, my hypothesis is that there will be a greater accumulation of perchlorate towards the base of the lettuce. I believe this qualitative approach is suitable for this project because I don't need to determine the concentration of the perchlorate.

To figure out which part of the lettuce will have the highest amount, what is the best way to divide sections or classify the parts of the lettuce? I will certainly discuss the comments made by Louise to my chemist. Can I also get a link to the maps of different watersheds and perchlorate contamination levels? Does perchlorate decompose at 100C? I believe it is not volatile. I appreciate all the help in the project!

Again, please run through the calculations with your advisor. If you are sectioning a head of lettuce, then you will have smaller sample amounts. It will be important to control the source of the lettuce (as a controlled variable), since it seems likely that the geographic source will influence the perchlorate levels. Given your hypothesis, I highly recommend that you grow your own contaiminated lettuce. The best way to test your hypothesis is to have a contaminated head of lettuce. The best way to assure that is to grow your own.

Otherwise, here is a map of Ca from 2004 with perchlorate results. I would try to find lettuce grown in highly contanimated spots.
http://www.uwrc.uci.edu/documents/UCI-U ... 061404.pdf

The source of this map is the Urban Water Research Center, UC-Irvine. I would contact them and see if you can get more up to date results. These levels may have changed dramatically now that the EPA requires testing at the ppb level.

As for how to section the lettuce, I don't really know. I'd look up how lettuce grows, and section it that way. Inner vs. outer leaves of head lettuce might be more reasonable than top vs. bottom.

Louise