Why is exposure to pesticides 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. Exposure to insecticides, herbicides, and fungicides are commonly evaluated, but most research has focused on insecticides, as they have been developed to be toxic by design.
Other than occupational exposures to farmers, farm workers, and manufacturing workers, most environmental exposure to insecticides is through the dietary pathway, although non-dietary ingestion, particularly in children with frequent hand-to-mouth behavior, and inhalation of resuspended dust particles, can also be significant pathways of exposure.
The insecticides and herbicides 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 insecticides: pyrethroid/pyrethrin insecticides (common for household use) and neonicotinoids and their derivatives;
- The most widely used herbicides: glyphosate, atrazine, and their metabolites; and
- The legacy organochlorine (OC) insecticides such as dichlorodiphenyltrichloroethane (DDT), which have been banned in the United States but are persistent in the environment and still used in some developing nations.
Exposure to smaller amounts of OP insecticides over a long period of time may cause people to feel tired or weak, irritable, depressed, or forgetful. Many OCs impact liver function in animals and are considered possible human carcinogens.
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.
Chronic, low-level exposure to other classes of pesticides has been associated with several adverse health outcomes in children and adults. Respiratory effects of environmental exposure to pesticides have also been reported in studies of both children and adults. However, the associations observed are weak and often not significant. More research is needed to confirm a respiratory risk from exposure to pesticides.
Recent action by the U.S. Environmental Protection Agency (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, and in environmental samples such as dust or wristbands. Many published data exist with which to compare these exposures including general U.S. population data published in Centers for Disease Control and Prevention's (CDC) National Report on Human Exposure to Environmental Chemicals.
The levels of current-use pesticides and their metabolites in urine and blood reflect recent exposure in 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 and/or stability over time may be necessary.
How can exposure to pesticides be measured?
As pesticides comprise a wide ranging classes of chemicals, information pertaining to each and every chemical cannot be covered in this document.
- Analytes (Current use pesticides): 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 2,4-D, glyphosate, and atrazine (and related chemicals) can also be measured, typically as panels of related analytes rather than a single exposure.
- Analytes (Legacy pesticides): Legacy OC pesticides will not be routinely analyzed, but HHEAR has the capability to measure them if needed. They would be measured in blood specimens as the intact chemical or a stable metabolite.
- Methods: Various methods are used for different target chemicals (depending on the chemical class). Most methods use chromatography followed by mass spectrometry.
- Types of biospecimens: For current-use pesticides with water-soluble metabolites, the most common matrix used is urine. As the most current-use pesticides are rapidly metabolized and eliminated, they are not typically analyzed in blood. For pesticides that are measured in urine, urine dilution should be taken into consideration and therefore creatinine and/or specific gravity are recommended to be measured for comparison within and between individuals.
For the legacy OC pesticides, serum, plasma, or whole blood may be used. Other lipid-rich matrices such as adipose and brain tissue or breast milk may also be used. Because OC pesticides are lipophilic, they need to be corrected for blood or other matrix lipids.
- Types of environmental samples: House dust, soil and wristbands are the most common media analyzed, but other media have also been used.
How does HHEAR ensure the quality of its analyses?
Laboratories follow several quality assurance and quality control procedures in the analysis of pesticides. These include procedural blanks, matrix spikes, duplicate sample analysis, and blinded duplicates (when available). If possible, inclusion of field “blanks” can help identify any contamination from collection/storage devices/sources, although this is not a common issue when metabolites are analyzed.
It is important to understand that the urinary metabolites measured can also be derived from metabolites preformed in the environment; some studies suggest up to 70% of the urinary concentration can be derived from this non-toxic exposure.
What sample quality and quantity are necessary?
Typically 0.1-1.0 mL of urine for current use pesticides and 1 ml of serum or plasma for legacy pesticides, or 1.0 gram of dust, or 5.0 grams of soil are used, but a greater quantity may be required if more than one class is to be measured, and for duplicate analysis of samples. Less volume usually translates to lower frequency of detection. Samples must not have undergone repeated free-thaw cycles.
Centers for Disease Control and Prevention. National Biomonitoring Program Factsheet: Dichlorodiphenyltrichloroethane (DDT).
Centers for Disease Control and Prevention. National Biomonitoring Program Factsheet: Organophosphorus Insecticides: Dialkyl Phosphate Metabolites.
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.