Why is childhood pesticide exposure relevant to health?
Pesticides are among the most commonly used chemicals in the United States. This broad class can include insecticides, herbicides, fungicides, and other classes of chemicals developed to eliminate or mitigate pests. Insecticides, herbicides, and fungicides are the most commonly evaluated, but most research has focused on insecticides as they have been developed to be neurotoxic by design.
Most environmental exposure to insecticides is from the dietary pathway, although non-dietary ingestion, particularly in children with a lot of hand-to-mouth behavior, and inhalation of resuspended dust particles can also be significant pathways of exposure. Children tend to have higher levels of exposure (per kg/bw) to pesticides than do adults and adolescents.
The insecticides most studied include
- The widely used organophosphate (OP) insecticides, sometimes called junior-strength nerve agents because of their shared mechanism of action;
- The newer and potentially less toxic pyrethroid (PYR) and pyrethrin insecticides that are common for household use; and
- The legacy organochlorine (OC) insecticides such as DDT, which have been banned in the United States but which are persistent in the environment and still used in some developing nations.
More than 30 studies have documented an association between prenatal and/or early childhood exposure to insecticides and neurocognitive delays, including decreased motor function, early onset of attention-deficit hyperactivity disorder (ADHD) symptoms, pervasive developmental disorders, and decreases in IQ similar to those seen with lead. Recent action by the EPA has sought the elimination of all residential use of one OP pesticide, chlorpyrifos, the most commonly used agricultural insecticide; however, more than 30 OP pesticides retain active registrations for use including some home and garden uses.
What types of questions can be answered?
Exposure to various pesticides can be estimated by measuring their intact parent chemical and general or “selective” metabolites in urine, blood, and other matrices. Many published data exist with which to compare these exposures including general U.S. population data published in CDC’s National Report on Human Exposure to Environmental Chemicals.
Levels of pesticides and their metabolites reflect current exposure over the last few days. Several longitudinal studies have suggested a high degree of analyte variation in multiple samples taken over time. To relate levels of pesticides or their metabolites to a chronic condition, multiple samples or studies to indicate within-person stability over time may be necessary.
How can exposure to pesticides be measured?
- Analytes: As pesticides are a broad class, all cannot be covered in this document. OP pesticides can be measured as their “general” class metabolites (dialkylphosphates) or metabolites more selective for a specific pesticide (e.g., 3,5,6-trichloropyridinol (TCPY) for chlorpyrifos/chlorpyrifos methyl). Pyrethroids can be measured as their general metabolite 3-phenoxybenzoic acid (3PBA) or other less common metabolites. Herbicides such as 24D, glyphosate, and atrazine (and related chemicals) can also be measured, typically as panels of related analytes rather than a single exposure. Legacy OC pesticides will not be routinely analyzed, but CHEAR has the capability to measure them if needed. They would be measured in blood products as the intact chemical or a stable metabolite.
- Methods: Different methods are used for different target chemicals. Most methods use chromatography followed by mass spectrometry.
- Types of biospecimens: For current-use chemicals with water-soluble metabolites, the most common matrix used is urine. Breast milk may also be a reasonably stable matrix. As the current-use chemicals are rapidly metabolized and eliminated, they are not typically analyzed in blood. For the legacy OC pesticides, serum, plasma, or whole blood may be used. Dried blood spots is another option but the method is not validated. Other lipid-rich matrices such as adipose and brain tissue may also be used. Because OC pesticides are lipophilic, they need to be corrected for blood or other matrix lipids. Because the concentration of urine varies, OP metabolite concentrations are typically corrected so that differences in exposure can be distinguished from differences in urine dilution .
How does CHEAR ensure the quality of its analyses?
If possible, the inclusion of field “blanks” in a study can help identify any contamination from collection/storage sources, although this is not a common issue. It’s important to understand that the urinary metabolites measured can also be derived from preformed metabolites in the environment; some studies suggest up to 70 percent of the urinary concentration can be derived from this nontoxic exposure. Positive and negative controls are included in each analytic run.
What sample quality and quantity are necessary?
Typically 0.1-1.0 mL is used, but a greater volume may be required if more than one class is to be measured. Less volume usually translates to lower frequency of detection. Samples must have not undergone repeated free-thaw cycles.
Mamane A, Raherison C, Tessier JF, et al. Environmental exposure to pesticides and respiratory health. European Respiratory Review. 2015;24(137):462-473.
Muñoz-Quezada MT, Lucero BA, Barr DB, et al. Neurodevelopmental effects in children associated with exposure to organophosphate pesticides: a systematic review. Neurotoxicology. 2013;39:158-168.