Biomonitoring is the measurement of foreign agents like chemicals in human tissues, hair, bones, urine, blood, or other bodily fluids.
In the case of chemicals like herbicides, urinary biomonitoring is the most accurate, non-invasive, and cost-effective way of tracking an individual’s exposure to a given chemical. But like most things in nature, biomonitoring is rarely straightforward. Methods must be deployed to accommodate a number of factors in order to accurately approximate exposures from levels measured in a bodily fluid like urine or blood.
Our bodies generally metabolize herbicides as they pass through the body, breaking them down into smaller molecules, some of which may bind to other circulating molecules. This process can create a dizzying array of new chemical forms. One example — aminomethylphosphonic acid is the major metabolite of glyphosate, and is formed through a multi-step process.
Metabolite compounds are sometimes more, and sometimes less toxic than their parent chemical. In other cases, they are equally toxic.
Different metabolites may behave differently in terms of cell penetration, affinity for different tissues, or reactivity with other circulating chemicals. Ideally, biomonitoring methods are used that take into account all these factors in the course of producing an accurate estimate of exposure levels.
One such method calculates “creatinine corrected” levels of specific analytes in urine. This added step is carried out in an effort to eliminate the impact of variability in a person’s urine volume on measured concentrations of chemicals in his/her urine. A widely used method has been developed to compensate for this source of variability. It measures the creatinine concentration in a urine sample, and quantifies the level of the analyte (in the cited paper, 2,4-D) drawing on the creatinine concentration in the urine (Cocker et al., 2011).
Heartland Study Biomonitoring
A key goal of the Heartland Study is to approximate trends in herbicide exposure levels in pregnant women from the mid-1990s and the pre-GMO crop era, to the present time. We will do so by compiling existing biomonitoring datasets, and augmenting them through the collection and analysis of several hundred, and perhaps thousands of additional urine samples from pregnant women and babies living in thirteen target Midwestern states.
While most pesticides lack comprehensive biomonitoring efforts, the Centers for Disease Control (CDC) has conducted monitoring for some insecticides and herbicides over the last 20 or so years as part of NHANES, including the herbicide 2,4-D (a key focus of the Heartland Study). The Heartland team will be working intensively with published CDC data on 2,4-D. We also look forward to the opportunity to access and study glyphosate urinary data from CDC-NHANES testing that is going on in the second half of 2019.
In addition to urine testing, the Heartland Team will also conduct buccal (check) swab biomonitoring in the hope of identifying markers of heritable epigenetic change.