Martha Rhoades

Martha Rhoades

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Title Research Manager
Address 102 Kiesselbach Crop Research Laboratory
1870 North 37th Street
Lincoln NE
68583-0817
Phone 402-472-1633
FAX 402-472-7904
E-mail mrhoades1@unl.edu
Contact Preference

Phone 402-472-1633 Walk-ins 102 Kiesselbach Crop Research East Campus

Office Hours

by appointment

n/a

 

Selected Presentations

An ecological study evaluating the association between county birth defect rates and percent of wells testing positive for nitrate and nitrosatable agrichemical compounds.
  • Presentation Type: Poster Presentation
  • Date: 4/25/2016
  • Abstract: Nitrate and atrazine are two of the most prevalent drinking water contaminants in the U.S. and commonly occur together. Ingested nitrate is reduced to nitrite, which can react with atrazine to form the nitrosamine, N-nitrosoatrazine (NNAT). We previously reported an association between exposure to nitrate and atrazine in drinking water and risk of developing non-Hodgkin lymphoma. Additionally, chicken embryos exposed to NNAT were observed to have heart defects, gastroschisis, caudal regression, craniofacial malformations and neural tube defects, with many embryos having multiple malformations. Atrazine and 18 additional agrichemical nitrosatable compounds (NCs) have been detected in Nebraska wells since 1977. Our poster summarizes the methodology and results of an ecological study evaluating the association between county-level birth defect rates and the percentage of wells testing positive for nitrate and NCs. We seek to clarify how nitrosamines such as NNAT, resulting from simultaneous exposure to nitrate and compounds classified as secondary amines, may pose a health threat and what populations are most vulnerable. We expect this research will provide insight into the potential adverse effects of other NCs, including various medications. The long-term goal of our work is to develop strategies that reduce or prevent adverse health outcomes after exposure to NCs and nitrate in drinking water.
  • Full Citation: Rhoades MG, Howard LM, Steele CE, Shea PJ, Raikes HH, VanWormer E, Travnicek DA, Eskridge KM, Spalding RF, Barnes-Josiah D, Rosenquist TH, Beseler CL. An ecological study evaluating the association between county birth defect rates and percent of wells testing positive for nitrate and nitrosatable agrichemical compounds in Nebraska, USA. Poster. Water for Food Global Conference. Lincoln, NE April 24-26, 2016.
Non-Hodgkin Lymphoma, Birth Defects and Water Quality in Nebraska: The Chicken or the Egg?
  • Presentation Type: Oral Presentation
  • Date: 1/13/2016
  • Abstract: Nitrate and atrazine are common drinking water contaminants (particularly in agricultural communities), which can react to form N-nitrosoatrazine (NNAT) in the human stomach. Little is known about the adverse health outcomes of NNAT or how it is metabolized. In this seminar, I will discuss findings from an epidemiology study assessing the risk of developing non-Hodgkin lymphoma in association with exposure to drinking water containing nitrate and atrazine, and laboratory studies evaluating embryotoxicity of NNAT using a chicken embryo model. I will also share some preliminary findings from an ecological study evaluating the association between birth defect rates and Nebraska wells testing positive for nitrate and a nitrosatable compound. The long-term goal is to develop strategies that prevent or reduce adverse health outcomes caused by nitrosamines formed in vivo after exposure to nitrosatable compounds and nitrate in drinking water. We seek to clarify how nitrosamines (such as NNAT), resulting from simultaneous exposure to nitrate and compounds classified as secondary amines, may pose a health threat and what populations are most vulnerable. We expect this research will provide insight into the potential adverse effects of other nitrosatable compounds, including various medications. This research is potentially paradigm-changing to investigations of the effects of contaminant mixtures on human health, particularly how relatively innocuous contaminants may react to form a harmful product(s).
  • Full Citation: Rhoades MG. January 13, 2016. Non-Hodgkin Lymphoma, Birth Defects and Water Quality in Nebraska: The Chicken or the Egg? Nebraska Water Center 2016 Spring Water Seminar Series.
Nitrosoatrazine Formation and Behavior in Water and Soil.
  • Presentation Type: Poster Presentation
  • Date: 3/30/2011
  • Abstract: The products of xenobiotic reactions may pose risks greater than parent compounds. Products of concern include nitrosamines, which can be carcinogenic, mutagenic, and teratogenic. Nitrosamines may form in soil, lake water, sewage, and agricultural soils after applying nitrogen fertilizer and pesticides containing amine moieties. The herbicide atrazine has secondary amine moieties that react with nitrite to form N-nitrosoatrazine (NNAT). We studied NNAT formation, stability, and adsorption in water and soil. NNAT formed most readily in solution at pH 2-4 and in soil at pH ≤5. Acetic acid and fulvic acid promoted NNAT formation in water at pH 4-7. In soil NNAT formed after 7 d at pH 4 and 14 d at pH 5, but none was found at pH 6 and 7. No NNAT was detected in oversaturated or anaerobic soil, indicating the importance of oxygen in the reaction. Adsorption Kd and Koc values show greater adsorption of NNAT (average Kd = 5.93; Koc = 495) than atrazine (average Kd = 2.71; Koc = 123) in Aksarben silty clay loam at agronomic pH. A larger desorption Kd indicates greater hysteresis of NNAT than atrazine. NNAT half-life in Aksarben soil was approximately 9 d, with degradation to atrazine and other compounds.
  • Full Citation: Wei HR, Rhoades MG, Shea PJ Nitrosoatrazine Formation and Behavior in Water and Soil. 241st American Chemical Society National Meeting & Exposition. Anaheim, California March 30, 2011
Assessing the Formation and Biological Significance of Selected Environmental Nitrosamines Using Model Systems.
  • Presentation Type: Poster Presentation
  • Date: 11/10/2010
  • Abstract: Nitrate and atrazine are known to occur together in ground and surface waters and have been shown to form N-nitrosatrazine (NNAT) after ingestion. Because prior research suggests that exposure to nitrosamines may be related to birth defects, we conducted a pilot study in which chicken embryos were examined for lethality and developmental abnormalities at 5 days (HH stage 27) after treating fertilized eggs with NNAT. While 90% of the NNAT-treated embryos were alive, 23% were malformed, including 10% of those treated with 0.06 µg NNAT (lowest dose tested), but there was no clear dose-response relationship. Visible malformations included heart defects, caudal regression, gastroschisis, microphthalmia and anophthalmia, craniofacial hypoplasia, neural tube defects, and other abnormal growth. Some of the embryos exhibited multiple defects. In contrast, atrazine-treated embryos examined at HH stage 27 were alive and showed no apparent developmental abnormalities. Our observations should be confirmed in a mammalian model and the responsible mechanism(s) defined. Epidemiological studies are also needed to evaluate associations between nitrosamine exposure, as well as simultaneous exposure to the NNAT precursors, atrazine and nitrate, and human birth outcomes.
  • Full Citation: Joshi N, Rhoades M, Bennett GD, Wells SM, Shea PJ Assessing the Formation and Biological Significance of Selected Environmental Nitrosamines Using Model Systems. American Public Health Association 138th Annual Meeting. Denver, Colorado November 10, 2010
Non-Hodgkin Lymphoma Risk in Nebraska and Drinking Water Contaminants: Atrazine and Nitrate.
  • Presentation Type: Oral Presentation
  • Date: 11/10/2010
  • Abstract: The increased incidence of non-Hodgkin lymphoma (NHL) in the Midwestern United States has been associated with agricultural exposures. Recurring themes are nitrate-contaminated drinking water and pesticide exposures. Some reports suggest cancer risk associated with consumption of nitrate-contaminated drinking water is due to endogenous nitrosamine formation. Groundwater provides drinking water to over 80% of Nebraska's residents. Atrazine, a herbicide heavily used to control broadleaf weeds and some grasses, is a nitrosatable compound that has been detected in some groundwater samples. The objective of this study was to determine the risk of NHL due to exposure to drinking water contaminated with nitrate or atrazine alone or in combination. A subset of 140 cases and 192 controls from a case control study conducted during 1999-2002 were included. Water data from 1978-1998 was collected from 98 public water systems and weighted based on well contribution and proximity of residence to water supply. No association was found between risk of NHL and nitrate or atrazine in drinking water. After adjusting for confounders, increased risk of NHL was associated with drinking water contaminated with both atrazine and nitrate (OR=2.5; 95% confidence interval(CI): 1.0-6.2). After adjusting for confounders, the risk of indolent B-cell lymphoma was significantly greater (OR=3.5; 95% CI: 1.0-11.6) for those exposed to nitrate and atrazine contaminated drinking water than those not exposed. It is hypothesized that this increased risk of NHL may be due to in vivo formation of N-nitrosoatrazine after drinking water contaminated with atrazine and nitrate. Further investigation is warranted to verify this association.
  • Full Citation: Rhoades MG, Meza JM, Beseler CL, Vose JM, Shea PJ, Spalding RF Non-Hodgkin Lymphoma Risk in Nebraska and Drinking Water Contaminants: Atrazine and Nitrate. American Public Health Association 138th Annual Meeting. Denver, Colorado November 10, 2010

Educational Background

  • BS - University of Nebraska-Lincoln, Chemistry/Psychology (2001)
  • PhD - University of Nebraska Medical Center, Toxicology (2010)

SNR Mission Area(s)

  • Environmental Science

Professional Organizations

Areas of Interest

  • Environmental Toxicology
  • Drinking Water
  • Ecotoxicology

Currently this page only displays grants that were awarded on 1/1/2009 to the present. If a grant was awarded prior to 1/1/2009 and is still active, it will not be displayed on this page.

Grant Title Nitrate and Atrazine: Is the mixture toxic to the developing embryo?
Starting Date 1/1/2016
Principal Investigators
Martha Rhoades
Ending Date 12/31/2016
Funding Level $10,000.00
Funding Source Research Council Faculty Seed Grant