03
Jun
Elevated Exposure to Wastewater Contaminants in Communities Near Ag Fields, Study Finds
(Beyond Pesticides, June 3, 2025) Chemical contaminants in wastewater have long been of concern, especially given the significant costs of upgrading wastewater treatment facilities to remove existing and emerging chemicals. In advancing chemical safety, one of the many regulatory determinations that Beyond Pesticides advocates for, prior to the allowance of any toxic chemical use, is the establishment of a realistic cleanup or disposal strategy. Yet, a plethora of petrochemical pesticides flood the market and contaminate the air, soil, water, and crops before poisoning humans and wildlife. A study in the Journal of Environmental Chemical Engineering uses the detectable levels of metabolites (breakdown products) of pesticides in wastewater to gauge exposure to populations living near flower bulb fields throughout the Netherlands. Wastewater samples were collected from five wastewater treatment plants (WWTPs) located in different parts of the Netherlands, with two of the locations (Tollebeek and Lisse) located near flower bulb fields and the other three representing control areas. The study finds that higher levels of chemicals correlate with proximity to agricultural fields and present a heightened health risk.
The authors describe wastewater-based surveillance (WBS) as a complementary approach to human biomonitoring that they use “to assess the spatial differences in human exposure in areas with relatively high use of pesticides versus reference areas.†By analyzing influent wastewater [coming into wastewater treatment plants] for the presence of several specific human metabolites of triazines, pyrethroids, and organophosphates, the researchers are able to assess exposure to pesticides based on the proximity to flower bulb fields and evaluate the associated health risks.   Â
The authors note: “In this unique study a total of 71 influent wastewater samples were analyzed during the period of pesticide application on flower cultivation, 31 originated from flower bulb areas and 40 from control areas. Higher population normalized mass loads [PNMLs] were found in the flower areas for 2-methyl-6-ethylaniline and hydroxytebuconazole, metabolites corresponding to the pesticides metolachlor-S and tebuconazole, respectively.â€
In utilizing the WBS method, the researchers are able to assess exposure throughout entire communities as opposed to testing hundreds or thousands of human urine samples, as is typical with human biomonitoring studies. The authors explain this, saying: “Wastewater-based surveillance (WBS) and Wastewater-based epidemiology (WBE) are exploratory and complementary tools that overcome some of the limitations of human biomonitoring, such as sampling biases, long realization time, high costs, and ethical issues. The WBS approach can be considered as a large anonymous test which consists of diluted urine from the entire population and thus a single sample can be representative of a large community.â€
The WBS tool has previously been used for public health assessment with SARS-CoV-2 and Monkeypox, as well as with illicit drugs to provide estimates of total drug use in populations. (See studies here, here, here, and here.) In this study, the researchers report that, “The results in this work are presented as surveillance data based on WBS and can give valuable insight into spatial and temporal trends of human exposure to pesticides.â€
Wastewater samples were analyzed for the following biomarkers that are related to pesticides applied in flower bulb cultivation: 2-methyl-6-ethylaniline (2,6-EA); 6-chloronicotinic acid (6-CN); 3,4-Dichloroaniline (3,4-DCA); terbuthylazine desethyl (DES); N-desmethylacetamiprid (N-DMA); asulam (ASU); tebuconazole-1-hydroxy (TEB-OH); boscalid-5-Hydroxy (BOS-OH); 3-phenoxybenzoic acid (3-PBA); 3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylic acid (HCBA) and 4-hydroxychlorpropham-O-sulphonic acid (4-HSA).
These biomarkers correlate with the following pesticides/classes of pesticides: tebuconazole, chlorpropham, asulam, boscalid, pyrethroids, cyhalotrin-lambda, terbutylazine, metolachlor-S, linuron, imidacloprid, thiacloprid, and acetamiprid. In analyzing the data, the authors note, “The concentrations of each biomarker measured in a 24-hour composite sample were multiplied by daily flow rates of wastewater entering the WWTP and divided by the population served by each WWTP.â€
As a result, the metabolites (and associated pesticides) detected in samples from the collection sites near flower bulb fields include 3,4-DCA (linuron) in samples from Lisse, TEB-OH (tebuconazole) in Tollebeek, and 2,6-EA (metolachlor-S) in samples from both Tollebeek and Lisse. Population normalized mass loads (PNMLs) are higher in Tollebeek when compared to the control areas, with the researchers reporting that a “statistically significant difference was observed between Tollebeek and the other municipalities.â€
As the study explains, results from wastewater and urine samples cannot be directly correlated, but the presence of these metabolites in WBS confirms human exposure to pesticides such as the broad-spectrum fungicide tebuconazole, with evidence that populations can be more exposed to these chemicals when living closer to flower bulb fields. “The results obtained in the present study illustrate that a population living near a flower bulb field is exposed to higher pesticide levels than people living in control areas,†the authors write.
They continue: “Here, we have investigated the particular case of flower bulb cultivation, in which a relatively high load of pesticides is being used. Obviously, a wider variety of crops will also be of interest, such as potatoes, other vegetables and fruit trees, that are cultivated in relatively large areas with a high pesticide application rate. WBS can help to assess if residents in these areas are subjected to higher pesticide exposures, as input for further risk assessment.â€
The pesticides that correlate with the detected metabolites in the study are associated with toxicity to aquatic organisms, endocrine disruption, reproductive effects, developmental effects, epigenetic effects, organ damage, neurotoxicity, cardiotoxicity, oxidative stress, and potential cancer. (See more information on these chemicals in the Gateway on Pesticide Hazards and Safe Pest Management.)
The researchers also share additional exposure-relevant research, which includes a Dutch study that finds concentrations of TEB-OH “in 61% of the urine samples (n = 99) collected from residents living near flower bulb fields during the application period in 2017.” The study also reports that “4-HSA was detected more often in urine samples collected from residents living in flower bulb areas (97%) compared to control areas.†Another study notes that, “Pesticide concentrations were 5–10 times higher in outdoor air samples around bulb fields during application periods than in reference areas,†supporting the current study’s data on higher pesticide exposure for populations closer to flower bulb fields.
Beyond Pesticides has previously shared that wastewater treatment facilities are contaminated with a variety of chemicals for which they do not have adequate processes in place to remove before the water is reintroduced in agriculture or even as drinking water. In a Pesticides and You article, the threats to health and the environment after the use of recycled wastewater in agricultural fields are explored. As stated, residues of pesticides, pharmaceutical drugs, and other chemicals in irrigation water can end up on plant surfaces, be taken up by crops, or contaminate the soil, thus increasing human exposure risk and environmental contamination. One study found that 64% of vegetables irrigated with treated wastewater contained traces of contaminants of emerging concern (CECs), including DEET (a repellent) and triclosan (an antibacterial).
CECs can enter municipal wastewater through bathing, cleaning, and the disposal of human waste and unused pharmaceuticals. By using recycled wastewater in agriculture that contains CECs, there are many associated direct and indirect health effects, such as those resulting from the rise in antibiotic resistance in soil bacteria, as has been previously noted with wastewater contaminated with the antimicrobial pesticide triclosan. (See additional information on triclosan and its cross-resistance with antibiotics here, here, and here.)
In the Daily News titled Chemicals, including Pesticides, in Wastewater Discharge Contaminate Oysters in Pacific Northwest, Beyond Pesticides also reports on the heightened threats to aquatic organisms, and the entire food web, with proximity to wastewater discharge pipes. In a Portland State University study, the authors find that the proximity to wastewater sites determines overall oyster health/condition. Impacts on organisms, such as oysters, can have cascading effects throughout entire ecosystems.
As the Daily News summarizes, although communities around the nation are required to treat their wastewater under the Clean Water Act, the wastewater treatment process does not remove all chemical contaminants, even during high-level treatment processes. The ubiquity of certain compounds makes it difficult to extract all pollutants from the water, which can persist in the water for long periods. Often, wastewater facilities will discharge this “clean†wastewater into nearby water sources. However, the combined impact of contaminated wastewater and chemicals already in waterways has detrimental impacts on aquatic ecosystem health. Moreover, some compounds work synergistically (together) with others to increase the severity of the effect. In addition to adverse health effects on marine organisms, these chemicals harm terrestrial organisms relying on surface or groundwater.
The ubiquitous contamination of harmful chemicals, ranging in persistence and toxicity, throughout soil, water, plants, and within organisms is unacceptable. (See more on body burden here.) Beyond Pesticides’ mission is to eliminate the use of petrochemical pesticides and synthetic fertilizers in order to protect the environment and all organisms in it, as well as mitigate the current crises of public health, biodiversity, and climate change, with the use of organic land management practices.
In working with only allowed materials recommended by the National Organic Standards Board (NOSB) and codified by USDA’s National Organic Program under the Organic Foods Production Act (OFPA), there are many health and environmental benefits (see here and here). Take the first step in reducing the amount of toxic chemicals that end up in waterways and in wastewater by growing your own organic food and/or buying organic products.
Create nontoxic lawns and landscapes in your own backyard and in your community, as well as take action to Protect All Waters of the U.S. See additional ways to take action and sign up for Action of the Week and Weekly News Updates delivered right to your inbox here to stay informed.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Bijlsma, L. et al. (2025) Wastewater surveillance for assessing human exposure to pesticides: Investigating populations living near flower bulb fields, Journal of Environmental Chemical Engineering. Available at: https://www.sciencedirect.com/science/article/pii/S2213343725017865.
