Grantee Research Project Results
2014 Progress Report: New Environmental Public Health Indicator Linking Organochlorine Compounds and Type 2 Diabetes
EPA Grant Number: R834795Title: New Environmental Public Health Indicator Linking Organochlorine Compounds and Type 2 Diabetes
Investigators: Chambers, Janice E. , Crow, John Allen , Ross, Matthew K. , Wills, Robert W.
Institution: Mississippi State University
EPA Project Officer: Hahn, Intaek
Project Period: April 1, 2011 through March 31, 2014 (Extended to March 31, 2016)
Project Period Covered by this Report: April 1, 2014 through March 31,2015
Project Amount: $500,000
RFA: Exploring Linkages Between Health Outcomes and Environmental Hazards, Exposures, and Interventions for Public Health Tracking and Risk Management (2009) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Human Health
Objective:
The overall objective of this project is to develop an environmental public health indicator (EPHI) by investigating the linkage between soil residues of a class of persistent organic pollutants (i.e., organochlorine [OC] insecticides and their stable metabolites/degradates), levels of these compounds in people and a disease with which they are implicated, type 2 diabetes. The proposed EPHI would be serum levels of these OC compounds.
There are two linked hypotheses: (1) environmental (soil) levels of OC compounds and serum levels of these compounds in people residing in a region of intense agricultural crop production are greater than levels in soil and people from a less intensely farmed region, and (2) a quantitative relationship exists between serum levels of OC compounds and the prevalence of type 2 diabetes.
Progress Summary:
Aspects of Aim 1, the environmental soil sampling and analysis, were conducted during Year 1 of the project. Soil samples from two regions in Mississippi, the Delta region and a non-Delta region, were collected and analyzed for select OC compound levels. The objective of this aim was to provide the environmental data that would constitute part of the EPHI. The hypothesis underlying this portion of Aim 1 is that environmental (soil) levels of select OC compounds would be higher in the soils from the highly agricultural Delta region than in soils from the less agricultural non-Delta region. The proposed work was to collect 40 soil samples in each of the two locations. We decided to increase that number to 60 to represent more locations in the two regions.
Analysis of OC compounds in serum was performed by gas chromatography/mass spectrometry (GC/MS) following organic solvent extraction. The methodology, developed initially by DPX Labs (Columbia, SC) for analysis of pesticides in fruits and vegetables, was modified in our laboratories for OC extraction from human plasma or serum. An internal standard containing C13 p,p'-DDT and C13 trans-nonachlor in hexane was added to 1 mL of serum. Acetonitrile was added to the sample to precipitate proteins. Following centrifugation, the resultant supernatant was mixed with deionized water and the mixture was aspirated into a DPX disposable pipette solid phase extraction column. OC compounds were eluted from the sorbent matrix, concentrated and resuspended. Concentrations of the target OC compounds were determined by isotope dilution GC/MS. Extracts were analyzed using an Agilent Technologies 6890N gas chromatograph connected to a 5975C triple-axis mass spectrometer. A targeted mass analysis was performed in electron ionization mode using single ion monitoring for the analytes described above. Quantification and confirmation ions were monitored for each analyte and its respective isotopically labeled internal standard. Limits of quantitation were 100 pg/mL serum (14.8 ng/g serum lipid) for trans-nonachlor, oxychlordane and p,p'-DDE. Areas under the curve were converted to pg/mL utilizing a standard curve. Values were adjusted for serum lipid content from the clinical data provided by the Veterans Administration (VA).
The original aims have not changed. The soil sampling and analysis are complete and the human sampling and chemical analysis are in progress.
It was anticipated that the Delta soils would contain higher levels of these legacy OC insecticides (or their degradation products) than the non-Delta soils because of the much higher historical levels of agricultural activity and pesticide use in the Delta compared to the non-Delta. The results, as reported earlier, were consistent with this anticipation, with more Delta than non-Delta soils having OC compound residues and, for the samples that did have quantifiable residues, about tenfold higher levels of DDE in the Delta soils than in the non-Delta soils.
There were 138 diabetics and 124 nondiabetics in the subjects recruited thus far. Only 1 sample had a quantifiable level of oxychlordane, and very few (only about 14%) of the samples had quantifiable trans-nonachlor, but the majority of the samples (about 64%) had DDE (Table 1).
Table 1. Data on Subjects Recruited for the Study
Above Quantitation Limits |
|||||
Total Number |
Average Age |
Oxychlordane |
Trans-Nonachlor |
p,p'-DDE |
|
Nondiabetic |
124 |
66.5 |
1 |
16 |
76 |
Diabetic |
138 |
65.9 |
0 |
20 |
91 |
A wide range of OC compound levels were observed (Table 2). There was a higher average concentration of DDE and of trans-nonachlor in diabetics than nondiabetics on both a volume of serum basis and as adjusted for lipid content; this is the relationship anticipated. However, it must be borne in mind that data collection is still incomplete and the trans-nonachlor data result from a very small number of subjects; therefore, no statistical analysis has been conducted at this point.
Table 2. Serum Concentrations (Averages and Ranges) of Trans-Nonachlor and p,p'-DDE, Expressed on Both a Volume Basis and Adjusted for Serum Lipid
ng/mL Serum |
ng/g Lipid |
|||
Trans-Nonachlor |
p,p'-DDE |
Trans-Nonachlor |
p,p'-DDE |
|
Nondiabetic |
1.64 |
5.61 |
239.0 |
1,042 |
Diabetic |
1.65 |
5.95 |
289.6 |
1,104 |
Range |
0.19–5.12 |
0.09–59.61 |
19.4–825.3 |
8–14,391 |
Because data collection is still ongoing, no statistical analysis comparing levels in diabetics to nondiabetics was conducted, nor was any analysis of the Delta compared to non-Delta subjects or comparing African-Americans to Caucasians. However, the data to date are compiled into Table 3 below. As mentioned above, the overall mean of DDE is somewhat higher in the diabetics compared to the nondiabetics; while the lower ends of the ranges of values from diabetics and nondiabetics were similar, the upper ends of the ranges were considerably higher in diabetics than in nondiabetics. Those subjects from the agricultural Delta region showed much higher average levels of DDE than those from the non-Delta region, as expected, although the higher end of the range of values was in the non-Delta group. We have no information on residence history or occupation of the subjects in the study. Lastly, the African-American subjects displayed considerably higher DDE levels and displayed a much wider range of values than the Caucasian subjects.
Table 3. Serum Levels of DDE From Subjects Residing in Mississippi
Group |
N |
Detects |
Mean |
Range |
|
N |
% |
||||
Normal |
124 |
76 |
61 |
1,042 |
8–9,365 |
T2D |
138 |
91 |
66 |
1,104 |
10–14,391 |
Delta |
92 |
89 |
96 |
1,209 |
8–10,572 |
Non-Delta |
143 |
78 |
55 |
917 |
10–14,391 |
African-American |
112 |
77 |
69 |
1,550 |
8–14,391 |
Caucasian |
151 |
90 |
60 |
679 |
10–3,166 |
The results to date indicate that DDE is rather generally distributed throughout soils in the Delta region, and only infrequently observable in the non-Delta region. In soils that had quantifiable levels of DDE, average levels were an order of magnitude higher in the agricultural Delta region than in the largely nonagricultural non-Delta region. Therefore, the likelihood of exposure to people from dust and consequently contamination of food and water, as well as contact surfaces, will be substantially higher for residents of the Delta than the non-Delta. This environmental parameter is consistent with the hypothesis underlying this project's proposed EPHI. Early results from the human samples indicate higher levels of DDE in the serum of diabetics compared to nondiabetics, which is consistent with the hypothesis underlying this project. If this difference between diabetics and nondiabetics is maintained through the rest of the samples, then DDE concentrations in serum may well be a possible biomarker for risk of type 2 diabetes.
Future Activities:
Subject recruitment through the VA clinic has improved, so subject recruitment will continue into Year 5. The additional research activity will include continuing collection of the human blood samples and processing them for quantification of OC compounds. When data collection is complete, statistical analysis of the data will be conducted, including construction of statistical models that will determine whether the proposed EPHI (i.e., serum levels of OC compounds) is verified.
Journal Articles:
No journal articles submitted with this report: View all 9 publications for this projectSupplemental Keywords:
Exposure, health effects, human health, environmental chemistry, monitoring, analytical, persistent organic pollutants, organochlorine compounds, type 2 diabetes, public health indicatorProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.