(Beyond Pesticides, April 26, 2024) Researchers build on existing research when assessing the relationship between long-term exposure to organophosphorus pesticides—widely used in food production and homes and gardens—and the human gut microbiome. In a new study published in Environmental Health, an interdisciplinary research team from University of California, Los Angeles determined, “that exposure to [organophosphorus pesticides] is associated with changes in the abundance of several bacterial groups and differential functional capacity in metabolic pathways supported by the human gut microbiome.”

The study draws upon data from a “Parkinson’s, Environment and Gene study (PEG)” in which 190 participants were asked to submit fecal samples and answer interview questions. “[The study] was initially designed to investigate the etiology of Parkinson’s disease (PD) and participants were recruited in two study waves [‘over the full 10-year exposure window’]: 2001–2007 and 2012–2017. At baseline, [Parkinson’s disease] patients were diagnosed within the past 5 years and randomly selected community controls were also recruited,” the research team shares in their Methodology section. “Since 2017, we invited previous study participants who could be contacted to enroll in a pilot study of the gut microbiome. In addition, we invited a household or community member of [Parkinson’s] patients to participate.” To be eligible for the study, it was determined that the participants did not have the following:

“acute/chronic gastrointestinal conditions; or
an immunocompromised state and/or were taking immunosuppressants;
antibiotic intake continuously or within the past three months”
The collection kit for the research was based on protocol developed under the Microbiome Core of the Goodman-Luskin Microbiome Center. The microbiome was assessed through bacterial DNA found in the fecal samples. A software, PICRUST2 was used to identify 16S RNA markers—“metagenomic profile of the gut microbiome”—to make predictions on relationships between pesticides and its genetic impacts. For the pesticide exposure assessment component, researchers use a geographic information system (GIS) method with data from California Pesticide Use Reports, land-use survey data from California’s Public Land Survey system, and residential use data from the participants. Researchers found “most abundance changes at the genus level associated with high ambient [organophosphorus pesticide] exposure belong to Lachnospiraceae (seven genera were increased and two were decreased) and Ruminococcaceae (3 genera were increased and 2 were decreased) families in the Clostridia class.” This is significant given these two families are related to anaerobic bacteria present in individuals with healthy gut microbiomes as they produce short-chain fatty acids (SCFAs) “critical in maintaining the homeostasis of the gut microbiome including gut barrier integrity, immunomodulation and regulation of the metabolism of lipids, cholesterol, and glucose []. The production of SCFAs is determined by the type of dietary fibers, the fermenting bacteria, the gut environment, and the substrate []. Therefore, it is possible that the observed changes in SCFA-producing bacteria are an indicator of disturbed homeostasis of the gut environment due to chronic [organophosphorus pesticide] exposure, and the body’s response to such changes.”