Progress 10/01/99 to 09/30/04
Outputs
The major part of this project involved pesticide residue, formulation, and animal drug analysis carried out for individuals, companies, agronomists, regulatory agencies, and in support of local veterinary toxicology. The total sample numbers for the duration of the project are given by calendar year as follows: 2000 (1346); 2001 (1267); 2002 (1417); 2003 (1647); and 2004 (1756). During the project interval, the laboratory developed analytical capability in LC/MS/MS methodology for a number of compounds, primarily polar herbicides. Because of the widespread use of glyphosate on a variety of crops, alleged herbicide injury on sensitive crops due to glyphosate drift or contamination has been one of the major complaints encountered by the laboratory, and this laboratory was therefore very interested in having a good alternative method for determination of this compound. A method based on the LC/MS/MS determination of glyphosate as its 2,4-dinitrophenyl derivative was
developed and thus far shows good sensitivity and selectivity and has a wider dynamic range for quantitation than the GC/MS method we commonly use. Comparison of many foliage samples with varying glyphosate concentrations by the LC/MS/MS method and by GC/MS showed comparable results for both, with less matrix-related signal enhancement in LC/MS/MS. However, GC/MS methodology is perhaps better proof of identity due to the availability of several ions for monitoring, and it appears more adaptable to situations such as glyphosate contamination of liquid fertilizers. A collaborative project with the Department of Plant Science studied the effects of applications of low rates of dicamba and 2,4-D to soybeans, simulating drift or tank contamination, on visible injury, yield, and analytical residue levels as a function of time after application. The significance of this work in pesticide residue analysis was that it is important to sample soon after exposure of crops to these growth
regulator herbicides (within a couple of weeks) since plant tissue residues will soon degrade to what might be considered a background residue level.
Impacts
The study of dicamba and 2,4-D residues on soybeans, correlated with visual symptoms and yield loss, is of significance to crop consultants, insurance adjusters, and others who try to assess effects of herbicide damage due to drift, tank contamination, or other exposure. Results would seem to indicate that residue data are very time-sensitive and will have to be carefully considered with regard to their validity for diagnostic or predictive use. An alternative method for glyphosate analysis using LC/MS/MS methodology was developed to increase accuracy and reliability of the test results.
Publications
- Andersen, S.M., Clay,S.A., Wrage, L.J. and Matthees, D.P. 2004. Soybean foliage residues of dicamba and 2,4-D and correlation to application rates and yield. Agron. J. 96: 750-760.
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Progress 01/01/03 to 12/31/03
Outputs
The Pesticide Laboratory analyzed the following samples: 1089 residues, 349 drugs in feed, 77 pesticide formulations, 65 animal remedies, and 67 fatty acid profiles, of which about a third of the drugs and residues, and all remedies and formulations were regulatory. This year again, there were numerous complaints related to glyphosate and phenoxy herbicides, and to a lesser extent with other agricultural chemicals. A collaborative project with the Department of Plant Science involved a study of the effects of dicamba and 2,4-D on soybeans at low application rates, simulating drift, not only assessing the visual symptoms of injury and effects on yield, but also measuring residue levels as a function of time after exposure. It was observed that residue levels dropped very quickly after initial application, even after a week. However, a reasonably good correlation between residue levels (dry matter basis)and application rates remained for up to 12 days for 2,4-D (r=0.81
at 12 days after treatment and r=0.33 at 24 days, p=0.01) and 24 days for dicamba (r=0.85 for 12 days and r=0.70 at 24 days). Residues were observable long after application, but at 48 days after treatment, the levels no longer correlated well with the amount of exposure (r=-0.07 for dicamba and r=-0.20 for 2,4-D). Similarly, decrease in grain yield as a percent of control correlated with herbicide levels for residue measurements up to 12 days after treatment for dicamba (r=-0.86 and r=-0.69 at 24 days for p=0.01) and for 2,4-D (r=-0.83 but only -0.25 at 24 days). This is of significance in residue analysis, since some samples may be submitted long after probable exposure. In other work, activated carbon was evaluated as a potential selective adsorbent in sample cleanup of some pyrethroid and other low polarity pesticides. It was found that minor changes in substituents on the pesticide molecular structure made a great deal of difference in recoveries. In addition, while elution could
be accomplished going either from weak solvent to strong solvent or vice versa, the recoveries again were different even for the same compound with the same solvents if eluted in a different order. The behavior of activated carbon as an adsorbent is thus not very predictable, but some specialized applications may be promising.
Impacts
The study of dicamba and 2,4-D residues on soybeans, correlated with visual symptoms and yield loss, is of significance to crop consultants, insurance adjusters, and others who try to assess effects of herbicide damage due to drift, tank contamination, or other exposure. Results would seem to indicate that residue data are very time-sensitive and will have to be carefully considered with regard to their validity for diagnostic or predictive use.
Publications
- Dwivedi, C., Guan, X., Harmsen, W.L., Voss, A.L., Goetz-Parten, D.E., Koopman, E.M., Johnson, K.M., Valluri, H.B., and Matthees, D.P. 2003. Chemopreventive effects of alpha-santalol on skin tumor development in CD-1 and SENCAR mice. Canc. Epidem., Biomarkers, and Prevention 12: 151-156.
- Guan, X., Hoffman, B., Dwivedi, C., and Matthees, D.P. 2003. A simultaneous liquid chromatography/mass spectrometric assay of glutathione, cysteine, homocysteine, and their disulfides in biological samples. J. Pharm. Biomed. Anal. 31: 251-261.
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Progress 01/01/02 to 12/31/02
Outputs
The Pesticide Residue Laboratory carried out analyses on a wide variety of analytes and sample types, including 61 animal remedies(regulatory), 83 animal drug samples for individuals, 66 regulatory formulation samples, 12 other formulations, 57 veterinary drug and pesticide samples,834 residue samples for individuals, and 304 regulatory residues. This year again, suspected crop injury from glyphosate and phenoxy herbicides were among the most common complaints. In collaboration with the Department of Plant Science, a study is being conducted on the effects of low level exposure of dicamba and 2,4-D on soybeans in terms of visible symptoms, yields, and the residues detected as a function of time following exposure. While the project is continuing, it is evident that the residues not only decrease with time, as expected, but the relative differences between application rates, while large initially, become very small within about three weeks. This is of significance in
legal cases involving alleged injury from plant growth regulator herbicides. In other research, it appears possible to determine shikimate, the plant metabolite accumulating with glyphosate exposure, using the same heptafluorobutyl trifluoroacetyl derivative used for glyphosate. Initially, though, it appears that shikimate was strongly elevated mainly in rather heavy exposures, so the utility of this measurement in assessment of suspected injury from low level glyphosate exposure seems questionable, particularly when glyphosate itself can be detected at quite low levels. Finally, the Pesticide Residue Laboratory is developing residue analytical capabilities with its LC/MS/MS system.
Impacts
The Pesticide Residue Laboratory and the Department of Plant Science are investigating the plant symptoms, effects on yield, and herbicide residues found after various time intervals following low level exposure of soybeans to dicamba and 2,4-D. This was done partly to understand the relationship between what a pesticide analysis finds and what happens in the field, since this type of herbicide drift is a common problem sometimes leading to legal action. Numbers of samples analyzed for the year by the laboratory were also reported.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
Most of the year's effort was related to the operation of the pesticide analytical laboratory, where about 825 residue samples were analyzed (230 of these regulatory samples) for individuals, agencies, and in veterinary toxicology support. Our formulation and drug laboratory analyzed 365 regulatory samples for drugs, remedies, and pesticide formulations, while 77 additional samples were analyzed for individuals or for veterinary toxicology. Glyphosate and phenoxy herbicide incidents have still tended to dominate complaints of suspected herbicide injury to plants because of widespread use, but newer compounds are being encountered as well. It was hoped that it might be possible to determine herbicide residues and abnormal amounts of plant metabolic products (e.g., glyphosate and shikimate) simultaneously using LC/MS/MS, but in the case of glyphosate, this has not yet worked out since daughter ions did not form for MS/MS analysis. Monensin in complex sample matrices was
determined by LC/MS/MS, with results agreeing well with a post-column detection method. At this time, the laboratory is working toward more LC/MS/MS methodology for pesticide residue analysis with a recently acquired instrument.The laboratory also provided analytical support for an on-site investigation of a multiple livestock poisoning incident. In a project assisting a food science investigator, I helped set up an HPLC-electrochemical detection measurement for isoflavone compounds in order to work around an interference problem. The pesticide residue laboratory is in planning stages for a proposed water monitoring project for a wide variety of pesticides and their metabolites.
Impacts
The pesticide analytical service laboratory is heavily involved in state regulatory actions on a continuing basis. There is considerable economic impact of herbicide damage to agriculture, and much of our work is done in an effort to resolve questions on suspected herbicide injury. Residue work also is done in support of some food products for export which must meet certain requirements.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
The pesticide analytical laboratory performed analyses on 382 regulatory residues for the SD Department of Agriculture, 556 other residue analyses for individuals or companies, 49 samples in support of veterinary toxicology, 115 formulations and remedies, and 244 drug analytes in animal feeds. The majority of residue analyses were related to complaints of apparent herbicide injury to crops or ornamentals, with a large number involving suspected damage by glyphosate or growth regulator herbicides. The issue of whether presence of herbicide residues indicates actual plant injury has arisen, and the suggestion has been made that biochemical markers could be employed in addition to herbicide residue detection. For example, elevation of shikimate has been reported in connection with glyphosate exposure, even in the absence of overt injury. On the other hand, glyphosate residues were found in a field situation where shikimate levels were described as normal. Resolving this
will require a lot more data, but the required determination of small polar molecules should be easier to perform using tandem mass spectrometry. Acquisition of a liquid chromatograph interfaced with a tandem mass spectrometer (LC/MS/MS system) was a major objective during the past year, and this is expected to be in place for 2001.
Impacts
As part of our land grant mission, this laboratory performs a wide variety of pesticide analyses, including efforts to detect pesticide poisoning in livestock, determination of herbicide damage in crops, and to provide analytical support to state agencies. We would also like to find whether there are characteristic chemical markers in plants that have been affected by herbicides that would give residue data more significance.
Publications
- No publications reported this period
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