Highly hazardous pesticides in Nayarit, Mexico: a retrospective review

Abstract

According to the Food and Agriculture Organization of the United Nations (FAO), Mexico uses more than a quarter of Central America's agricultural pesticides. Furthermore, Mexican regulatory agencies still do not recognize the classification of highly hazardous pesticides (HHP) under the Regulations on Registrations, Import and Export Authorizations, and Export Certificates for Pesticides, Plant Nutrients, and Toxic or Hazardous Substances and Materials (PLAFEST) regulation; no explicit national HHP definition exists. The aim of this review was to identify active ingredients (a.i.) historically used in Nayarit that are classified as HHP by internationally accepted classification systems and highlight the differences between them. Seven bibliographic resources, identified through a literature search conducted between October 2024 and July 2025, reported the pesticide sales or use patterns in Nayarit between 1987 and 2021. One hundred and twenty-five different a.i. were observed, of which 44 (35.2%) are HHP according to criteria defined by the FAO and the World Health Organization (WHO). In comparison, 82 (65.6%) are HHP according to the Pesticide Action Network International (PAN). Although most pyrethroids are highly toxic to bees, most of them are not recognized as HHP by FAO/WHO. Organophosphorus and carbamates are the main chemical families of HHP used in Nayarit. Glyphosate, an individual a.i. rather than a chemical family, was also identified as HHP. Dicofol, an organochlorine listed in Annex A of the Stockholm Convention for the global elimination of its use, was reported in retailer sales records. This review demonstrates the differences in the selection of HHP at a state-level assessment revealing that the criteria proposed by PAN allow the inclusion of a greater number of pesticides, in terms of their environmental effects, and a broader understanding of the presence of multiple HHP identified across the available evidence, indicating the potential for mixed pesticide exposure. We consider that a transparent and nationally adopted HHP identification framework is the first step to develop risk prevention strategies and promotion of sustainable alternatives.

Introduction

A pesticide is defined as “a substance or mixture of substances intended to control any pest, including vectors that transmit human and animal diseases, unwanted species that cause harm or interfere with agricultural and forestry production, as well as defoliants and desiccant substances” (1).

Historically, pesticide use has evolved through three broad periods (2, 3). The first, spanning ancient civilizations, relied on natural compounds such as sulfur, arsenical and mercurial compounds, and pyrethrin derived from chrysanthemum flowers to control pests and disease vectors. The second period, from 1870 to 1945, introduced synthetic inorganic compounds, including copper- and sulfur-based antifungals. The third period began after 1945 with the widespread adoption of synthetic organic pesticides, exemplified by the organochlorine (OC) 1,1,1-trichloro-2,2-bis-(4-chlorophenyl) ethane (DDT), extensively used for vector-borne disease control (4–6).

In Mexico, the introduction, expansion, and use of synthetic pesticides are related to the “Green Revolution,” established in Mexico during the 1940s through an intensive agricultural model based on monocropping and the importation of seeds, fertilizers, pesticides, irrigation technologies, and foreign investment. The expansion of irrigated agriculture associated with the Green Revolution has been linked to increased pesticide loads in water irrigation systems (7).

Pesticides are classified according to several criteria: origin (natural and synthetic), pest control (e.g., herbicides, insecticides, fungicides, bactericides, rodenticides, nematicides, among others), chemical structure (e.g., organophosphate [OP], pyrethroid [PYR], carbamate [CB], OC, among others), environmental persistence (e.g., non-persistent [0–12 weeks], moderately persistent [1–18 months], persistent [up to 20 years], or very persistent [>20 years]), acute toxicity (lethal dose 50 [LD₅₀] (e.g., Ia extremely hazardous, Ib highly hazardous, II moderately hazardous, III slightly hazardous, or U unlikely to present acute hazard)), according to the World Health Organization (WHO 2020), among others (8).

In 2023, 3,728,427 tons of pesticides were used worldwide for agricultural purposes. Of this total, 53.9% were herbicides, 20.9% fungicides and bactericides, 20.4% insecticides, and 4.8% classified as others (9). In the Americas, 1,836,279 tons of pesticides were used (70.9% herbicides, 14.6% fungicides and bactericides, 9.8% insecticides, and 4.7% classified as others). According to the FAO statistical data portal, Mexico is located in Central America, a region where 98,587 tons of pesticides were used for agricultural purposes in 2023, of which 37,298 tons (37.8%) were used in Mexico. Of the total pesticides used in the country, 63.8% were used to control fungi and bacteria, 22.9% were used for insects, and 13.3% for weeds and grasses (9).

This difference may be explained by the structure of Mexican agriculture, which is characterized by a high proportion of intensive horticultural and fruit production, including crops such as tomato, chili pepper, avocado, berries, citrus, and others. These high value crops are particularly vulnerable to fungal and bacterial diseases under Mexico's warm and humid climatic conditions, requiring frequent applications of fungicides throughout the growing season. However, it is important to take into account that this information is related to frequency of use rather than quantity.

At the regional and state levels, accurate data on pesticide usage remains limited. However, efforts have been made to determine the pattern of pesticide sales and use, primarily for agricultural purposes (10). In Mexico, the tons of pesticides used are reported in the FAO statistical database, based on importation of commercial products; however, the extent of national regulatory offices does not cover the amount of specific active ingredients imported, exported, or used on national territory. Nayarit is a key state in Mexico due to its significant contribution to both domestic and export food production. An estimate of 1,668,243 hectares of agricultural surface and forestry land-use makes for a total of 82,494 farming and forestry production units (FFPU), placing Nayarit in 20th place for active FFPU surface in 2022. Despite this comparatively smaller production surface, Nayarit is among the Mexican States with the highest agricultural pesticide use, ranking 3rd in insecticide and fungicide use and 4th in herbicide use (11–14), underscoring the relevance of this state as a subject for historical and retrospective analysis of pesticide use. The main crops of Nayarit are rice, tobacco, eggplant, beans, mango, and pineapple. According to the most recent survey conducted in the state, insecticides are the most used and sold pesticides (45.9%), followed by herbicides (30.5%), fungicides (20.1%), and others (3.5%) (15).

The Food and Agriculture Organization of the United Nations (FAO) defines Highly Hazardous Pesticides (HHP) as “pesticides that are acknowledge to present particularly high levels of acute or chronic hazards to health or environment according to internationally accepted classification systems such as World Health Organization (WHO) or the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), or their listing in relevant binding international agreements or conventions. In addition, pesticides that appear to cause severe or irreversible harm to health or the environment, under the conditions of use in a country, may be considered to be and treated as highly hazardous” (16). Within the GHS classification, Category 1A refers to substances known to have hazard potential for humans, based primarily on human evidence, while Category 1B refers to substances presumed to have hazard potential for humans, based primarily on animal studies.

Since 2008, the Joint FAO/WHO Meeting on Pesticide Management (JMPM) has recommended eight criteria to identify an HHP; a pesticide must meet at least one of the following: (1) WHO Hazard Classification classes Ia (extremely hazardous) or Ib (highly hazardous); (2) GHS carcinogenicity categories 1A or 1B (known or presumed human carcinogen, respectively); (3) GHS mutagenicity categories 1A or 1B (known or presumed human germ-cell mutagen); (4) GHS reproductive toxicity categories 1A or 1B (known or presumed human reproductive toxicant); (5) listing in Stockholm Convention Annexes A, B, or D; (6) listing in Rotterdam Convention Annex III; (7) listing under the Montreal Protocol; or (8) evidence of a high incidence of severe or irreversible adverse effects on human health or the environment, a criterion whose specific characteristics remain formally undefined by WHO, FAO, and the United Nations Environment Programme (UNEP) (17).

The International Pesticide Action Network (PAN) adopts these criteria and expands them into four groups; a pesticide must meet at least one of the following: acute toxicity (JMPM criterion 1, or classification as “Fatal if inhaled” [H330] under the GHS or EU); long-term effects (JMPM criteria 2–4, or classification as carcinogenic, probable/possible carcinogenic, or an endocrine disruptor under IARC, EPA, or EU/GHS criteria); environmental toxicity (at least two of persistence, bioaccumulation, or high aquatic toxicity under Stockholm Convention indicators, or high toxicity to bees under EPA criteria); or international conventions (JMPM criteria 5–7) (18).

In 2020, Central America placed 3rd after South Asia and Southeast Asia in lethal pesticide intoxications worldwide, and second in non-lethal intoxications in the Americas and the Caribbean (19). From 2000 to 2021, a total of 7,984 cases of death were attributed to acute pesticide poisoning in Mexico, and Nayarit placed 7th in the mortality rates from pesticide poisoning (20). A report from Pesticide Action Network and Alternatives in Mexico (RAPAM) identified 210 active ingredients authorized by COFEPRIS that appear on international HHP lists. Among these, 45 are probable carcinogens, such as glyphosate, and 45 endocrine disruptors, like asulam, dimethomorph, mancozeb, and pentachlorophenol, which are still allowed in Mexico but are banned in many other countries (21).

Over the past two decades, several studies have reported the use of HHP in different states of Mexico, compiled in a 2017 national report (10). In 2007, 58.1% of pesticides used in Los Altos de Chiapas were classified as HHP, with 49.1% banned in other countries. In 2008, in the Yaqui Valley of Sonora and the Culiacan Valley (Sinaloa), HHP usage was 43% and 54.6%, respectively. In Guanajuato's Bajío region, 85.1% of insecticides, 66.6% of herbicides, and 41.7% of fungicides used in 2015 were classified as HHP. Also in the same year, it was reported that 59.4% of the pesticides used in Yucatan and Campeche were HHP, and 44.5% of these are banned in other countries (10). In Nayarit, a biomonitoring study conducted in 2025, including analysis of hand-washing samples from children, detected several HHP such as carbendazim (0.04 µg/L), thiabendazole (0.030 µg/L), thiamethoxam (0.007 µg/L), imidacloprid (0.885 µg/L), bifenthrin (0.008 µg/L), chlorpyrifos (0.031 µg/L), diazinon (0.004 µg/L), and malathion (0.003 µg/L), and the glyphosate metabolite aminomethylphosphonic acid (AMPA) (4.73 µg/L) (22). Additionally, our research group investigated the presence of chlorpyrifos in soil, water, and fish samples from Santiago Ixcuintla, Nayarit in 2023, with an average concentration of 4,614.2 ng/L detected in water samples (23).

The use of HHP in the state of Nayarit reflects broader trends in agricultural intensification and the persistent reliance on chemical pest control in crop production. Historically, pesticide use in the region expanded during the mid-20th century, driven by the Green Revolution and the promotion of industrial agriculture, particularly in crops such as sugarcane, maize, sorghum and tropical fruits (13, 24, 25). Many of the compounds adopted during this period, such as OP and CB, are now recognized as highly hazardous due to their acute toxicity, environmental persistence, and potential impacts on human health, especially among rural and farming communities (18, 26).

The aim of this review is to identify the active ingredients historically documented for pest control in Nayarit that meet the criteria for classification as HHP, based on both the FAO/WHO and PAN International frameworks, and to highlight the differences between these classification systems. This analysis contributes to ongoing efforts to reduce the use of hazardous substances and promote sustainable agriculture in the region.

Methodology

A narrative historical review was carried out, combining documentary research with the analysis of current data sources to explore the evolution of HHP use in agricultural practices in Nayarit.

Data sources and selection criteria

The literature search, conducted between October 2024 and July 2025, was designed to identify studies reporting pesticide sales and usage patterns in the state of Nayarit. Data were collected from multiple sources, including: PubMed, SciELO, and EBSCOhost. No temporal restrictions were applied, as one of the purposes of this review was to examine the historical use of pesticides a.i. in the region. The search terms and Boolean operators used in both English and Spanish were: “(pesticides/plaguicidas) AND (Nayarit) AND (humans/humanos)”; “(pesticides/plaguicidas OR agrochemicals/agroquímicos) AND (Nayarit) AND (workers/trabajadores)”; “(pesticides/plaguicidas OR agrochemicals/agroquímicos) AND (Nayarit) AND (pattern/patrón).” Search terms were interchanged to expand the identification of pertinent resources, including “pattern/patrón”, “sales/venta”, “use/uso”, “workers/trabajadores/jornaleros”, “humans/humanos”, and “containers/envases”. Additionally, Google Scholar was searched using the “intitle” operator to restrict results to records containing at least one of the search terms in the title. Google Scholar results were screened by title and abstract against the inclusion and exclusion criteria described above.

Theses focused on pesticide-related studies were also searched through the library website of the Universidad Autónoma de Nayarit; however, none met the inclusion criteria, as they addressed the effects of pesticide exposure on environmental matrices (e.g., terrestrial or aquatic organisms, soil, sediment, water, or food) rather than sale or use patterns. Available government reports similarly focused on recommended compounds and pest management practices for specific crops rather than documenting sale or use patterns, and were therefore not included.

Sources were included based on the criteria: i) original articles or books reporting pesticide use or sales patterns; ii) geographically limited to localities in the State of Nayarit; iii) publications written in Spanish or English. As the exclusion criteria were articles and bibliographic resources that: i) only quantified the presence of pesticides in environmental matrices without reporting the frequency of pesticide use or sale; ii) studies limited to evaluating the effects of pesticides in in vitro and animal models. To avoid duplication, studies reporting redundant data on pesticide use or sales were excluded, except when complementary information was provided in separate publications.

This review considered pesticides used for both agricultural purposes and vector-control programs, given their shared regulatory classification and potential relevance to human and environmental health in Nayarit.

According to the inclusion and exclusion criteria, a total of seven references were selected from the 62 initial search results (from EBSCOhost [41 results], PubMed [12 results], Google Scholar [eight results], and SciELO [one result]); 55 publications were excluded (Figure 1). Duplicate records identified across the four databases were removed prior to eligibility screening. Because several sources originated from the same research group, potential overlap in field-campaign period, sampled population, and reported active ingredients across the seven included sources was systematically assessed and is presented in Supplementary Table S1.

Figure 1

Because references 15 and 30 derive from the same study population (Supplementary Table S1), they were treated as a single independent study (n = 6) when reporting the number of sources documenting each active ingredient, although both are cited individually in Table 1. Active ingredients were identified and reported using their International Organization for Standardization (ISO) common name (27), as opposed to trade names or chemical names, to enable consistent identification and avoid duplicate counting across the seven included sources. This consolidation was performed by one author and reviewed and confirmed by the remaining coauthors. Chemical family and pest-control category assignment, as well as origin classification (synthetic, inorganic, or biological), were verified against established pesticide databases. Active ingredients were classified by origin as synthetic, inorganic, or biological (bioinputs), following the definitions established in the cited databases; bioinputs were considered plant, animal, or microbial products capable of improving the productivity, quality, or health of crops (28). The reported a.i. were classified as HHP according to the criteria established by the Joint FAO/WHO Meeting on Pesticide Management and the criteria proposed by PAN.

Percentages reported throughout this review refer to the proportion of active ingredients identified within the compiled evidence and should not be interpreted as measures of application frequency, sales volume, treated area, or exposure intensity, for which denominator data were not available. Percentages were calculated as the number of active ingredients in each category divided by the total number of active ingredients identified (n = 125). In this context, hazard refers to the intrinsic toxicological or environmental properties of an active ingredient, as established by the classification criteria described above, and is distinct from use, which refers to reported sale or application.

This methodological approach aims to address the limited availability of public data on pesticide use in Mexico. Existing official data are restricted to information on authorized pesticides, their formulations, and intended uses. There is no public registry documenting actual pesticide application, quantities used, or specific geographic locations - despite the potential for mixed pesticide exposure in agricultural areas, based on the co-occurrence of multiple HHP identified in this review.

Flow diagram was constructed using Microsoft Office PowerPoint, and additional artwork and illustrations were created using GraphPad Prism v.8 software (GraphPad Software, San Diego, CA, USA).

Results

The review identified a total of seven studies conducted between 1987 and 2021 that document pesticide sales and use patterns in the state of Nayarit (15, 29–34). As mentioned above, HHP definition and criteria were established in 2008; this does not mean that before this time, the a.i. and pesticide formulations weren't highly hazardous to health or the environment. In this review, a.i. used or sold previous to 2008 were classified as HHP if they met the current criteria accepted by FAO/WHO or proposed by PAN. These sources reported the use of 125 different a.i. belonging to 44 chemical families historically documented for pest control in Nayarit. These sources differ in study design and the type of evidence used to document pesticide sale or use, including retailer sales surveys, self-reported use, biomonitoring, empty-container counts, and institutional records of authorized agricultural inputs; the evidence type, scope, and inherent limitations of each source are summarized in Supplementary Table S2.

In the 1980s, pesticide use in Nayarit intensified in response to agricultural expansion. Historical records and local health studies document the extensive use of OP, CB, and OC, many of which were later restricted or banned in other countries (35). Nonetheless, their presence continued in some rural regions through informal markets and limited enforcement.

HHP identified across historical and current sources

Based on their origin, 88.0% of a.i. were classified as synthetic, 8.0% as bioinputs, and 4.0% as inorganic salts. Bioinputs are considered plant, animal, or microbial products capable of improving the productivity, quality, or health of crops (35). In terms of use, 50.4% of the a.i. were insecticides, followed by fungicides (29.6%), herbicides (17.6%), and bactericides (2.4%). The chemical families with the highest number of identified active ingredients were OP (16.8%), PYR (12.0%), CB (10.4%), inorganic salts (4.0%), triazoles (4.0%), carboxamides (4.0%), OC (3.2%), benzimidazoles (3.2%), strobilurins (3.2%), and amides (3.2%). Other families, such as antibiotics, dinitroanilines, neonicotinoids, picolinic acid derivatives, alcohols, avermectins, triazines, and ureas, each account for less than 3.0% of a.i., while 26 additional families were represented by a single a.i. (Table 1).

According to Díaz-Romo and Salinas-Álvarez (29), in the municipality of Santiago Ixcuintla, 37 different a.i. were used as agricultural pesticides between 1987 and 2001, of which 45.9% are currently considered HHP by FAO/WHO. In contrast, 64.9% are considered as HHP according to the criteria proposed by PAN. Seven years later, our research group reported the pattern of sale and use of pesticides in Nayarit (15, 30), the presence of 42 new a.i., of which 20 are considered HHP by FAO/WHO and 36 by PAN. Additionally, Bernal-Hernández et al. (31) and Paredes-Céspedes et al. (32) reported the use of 12 different pesticides that were applied by individuals belonging to Wixárika indigenous communities. All of the a.i. had already been reported previously in Nayarit and are classified as HHP according to the PAN, compared to 83.3% of the a.i. that are HHP under the FAO/WHO criteria. For mestizo communities occupationally exposed to pesticides, the use of 16 different pesticides was reported for vector control, five of them not being reported before, according to the available literature. Three of them are classified as HHP by the PAN and none by the FAO/WHO (33).

The latest pattern of pesticide sales and use in Santiago Ixcuintla, Nayarit (34), showed the addition of 40 pesticides that had not been reported in previous years (four HHP by FAO/WHO and nine by PAN). Compared to the first published report, eight pesticides have been used consistently for more than 20 years. Six are HHP (two OP, two CB, one N-phosphonomethylglycine, and one dinitroaniline) according to PAN, and four (two OP and two CB) meet FAO/WHO criteria.

Authors highlighted glyphosate as one of the pesticides with high reported sales in the northwest region of Nayarit as of 2021, although the data were not provided (34). This statement is presented as a qualitative observation reported by the study authors and was not treated as a verified quantitative finding in this review. Historically, only eight pesticides were used for more than 20 years: methamidophos and monocrotophos (OP), carbofuran and mancozeb (CB), glyphosate (N-phosphonomethylglycine), trifluralin (dinitroaniline), atrazine (triazine), and oxytetracycline (antibiotic). Of the total pesticide a.i. reported in Nayarit, 72.0% of these were listed in at least one of the six studies, 12.8% in two, 8.0% in three, and 4.0% in four resources. As for those observed in five reports, all of them [OP [methamidophos and methyl parathion], CB [carbofuran], and the N-phosphonomethylglycine [glyphosate]] are classified as HHP by either FAO/WHO or PAN (Table 1).

Of the 82 active ingredients classified as HHP according to PAN, 73 remain currently authorized for use in Mexico; of these 61 (48.8% of the 125 total a.i.) are banned or restricted in at least one other country due to their acute toxicity, chronic health effects, environmental persistence, or their listing in international binding conventions (36).

Comparison of classification systems

According to FAO/WHO criteria, 35.2% of the total pesticides used in Nayarit are classified as HHP. Where 33.6% are synthetic pesticides, and 1.6% are bioinputs. On the other hand, according to PAN criteria, 65.6% of the total a.i. are classified as HHP, 61.6% are synthetic, 3.2% bioinputs, and 0.8% inorganic compounds (Figure 2).

Figure 2

Figure 3 shows the distribution of HHP chemical families according to FAO/WHO and PAN criteria. The OP is the family with the highest number of HHP, followed by CB, OC, and benzimidazoles. It is important to note that in the case of PYR family, most of a.i. are not considered as HHP by FAO/WHO but are recognized as HHP by PAN criteria due to their significant environmental effects. In addition, PAN includes pesticides from twelve different families not considered by FAO/WHO, such as amides, carboxyamides, chlorophenoxy, chloronitriles, dinitroanilines, inorganic salts, N-phosphonomethylglycine, phenyl pyrazoles, pyrroles, spinosyns, strobilurins, and sulfoximides.

Figure 3

Among the a.i. identified in the pesticide use and sale patterns in Nayarit, 61% meet more than one HHP criterion. In this context, pentachlorophenol (PCP) fulfilled four FAO/WHO criteria, while benomyl met three of them. Approximately 32% of HHP met two criteria, and the remainder met only one. Following PAN criteria, PCP met seven criteria, 9.7% of the active ingredients met four criteria, 20.7% met three, 30.5% met two, and the remainder met only one. Of the a.i. meeting four PAN criteria, 62.5% were OP, 25.0% CB, and 12.5% OC (Table 1).

Regarding acute toxicity, FAO/WHO does not consider the GHS “fatal if inhaled”, thereby excluding seven (six synthetic and one inorganic salt) of the a.i. that have been used as pesticides in Nayarit.

Concerning chronic toxicity, FAO/WHO excludes 25 synthetics a.i. from the HHP classification, as it only considers those that fall into the GHS classifications 1A or 1B for carcinogenicity, mutagenicity, and toxicity to human reproduction. PAN, for its part, considers pesticides that met these criteria, in addition to those that are carcinogenic (Group 1) and probable carcinogenic (Group 2A) by the IARC, and a.i. that are carcinogenic to humans (Group A), probable carcinogenic to humans (Group B), and “probably carcinogenic to humans at high doses” by the EPA. PAN also considers endocrine disruption criterion in accordance with Regulation (EC) No. 1107/2009 (a.i. suspected of being carcinogenic to humans [Category 2] and also suspected of being toxic to human reproduction [Category 2], proposed by the EU or the Japanese GHS) and as stipulated in Regulation (EU) 2018/605.

A key difference between the FAO/WHO criteria and those proposed by PAN International for identifying HHP lies in the consideration of environmental hazards. PAN International includes pesticides that pose a high environmental concern, defined as meeting at least two of three criteria (very persistent, very bioaccumulative, or very toxic to aquatic organisms), as well as pesticides considered hazardous to ecosystem services because of their high toxicity to bees, based on the US EPA acute toxicity criterion (LD₅₀ < 2 μg/bee). In contrast, these environmental criteria are not independently used by the FAO/WHO framework to identify HHP. Consequently, 44 synthetic active ingredients, three bioinputs, and one inorganic salt reported as being used in Nayarit were not identified as HHP under the FAO/WHO criteria. Notably, 22 of these active ingredients (20 synthetic pesticides and two bioinputs) met PAN International's criterion for high toxicity to bees. Therefore, their identification as HHP under the PAN framework reflects an environmental hazard to pollinators and ecosystem services and should not be interpreted as evidence of equivalent hazard to human health.

A positive point in the historical analysis of pesticide use in the region is that, based on sales and use patterns (determined by counting empty containers at primary collection centers and in open fields) in the main agricultural area of Nayarit, methyl parathion appears to no longer be used for insect control. In contrast, the presence of dicofol, a pesticide listed in Annex A of the Stockholm Convention on Persistent Organic Compounds selected for global elimination of use (37), has been reported.

Mexico does not have an official definition for HHP in its normative instruments, and this lack of recognition allows the importation and use of chemicals classified as HHP solely by legal omission. Supplementary Figure S1 shows the Mexican states where the use, sale, or presence of HHP has been studied. This map is presented for descriptive and contextual purposes only, as the underlying reports combine different evidence types (e.g., surveys, container counts, and residue analyses) that are not interchangeable indicators of pesticide use, following the same distinction applied to the sources included in this review (Supplementary Table S2). In these reports, the authors use the term “Highly Hazardous Pesticide” to refer to those that meet the criteria established by FAO/WHO or the criteria proposed by PAN. Of the 15 reports presented, seven are included in the compilation “Highly Hazardous Pesticides in Mexico” by Bejarano-González (10). Meanwhile, 66.7% of the studies are based exclusively on usage or sales patterns established through surveys conducted with pesticide dealers (individuals dedicated to the sale of agrochemicals) or workers responsible for applying pesticides to various crops (15, 38–46).

Pesticide use patterns in regions of two federal entities (Nayarit and Sonora) were established through the joint efforts of applying structured questionnaires and counting empty containers in primary collection centers and abandoned in open fields (34, 47) and represent 13.3%; a proportion that also represents those studies in which the use of HHP was evidenced due to the presence of residues of these pesticides in food (48, 49). Only one research study determined the pattern of HHP use in Sinaloa by counting empty containers in primary collection centers and in open fields (50), and another one showed the use of HHP in the Laguna region through pesticide residues in soils (51).

In Nayarit, the patterns of sale and use of pesticides have been established by applying structured questionnaires to urban retailers and fumigators in 19 of the 20 municipal capitals, mestizo farmers (Santiago Ixcuintla), indigenous Wixárika farmers (Santiago Ixcuintla and Tepic), as well as the counting of empty containers in primary collection centers and abandoned in open fields, it is important to highlight that this last methodology has only been applied in the municipality of Santiago Ixcuintla (34).

Limitations

This retrospective assessment of pesticide use was based on seven published sources spanning several decades. Although these publications represent the most comprehensive information available for the study region, part of the evidence originates from our own research group, and potential overlap in field-campaign period, population, and reported active ingredients across sources was assessed and is presented in Supplementary Table S1.

The geographic coverage and temporal distribution of the studies are also heterogeneous, with irregular sampling periods that may not fully capture changes in pesticide use over time. Information obtained through interviews or questionnaires may be affected by recall bias, and information derived from pesticide sales records or empty pesticide containers has inherent limitations as well, since these data do not necessarily reflect actual pesticide application practices and may underestimate products acquired through informal or unregistered markets. In addition, the available literature generally did not report quantitative information on pesticide application rates, total amounts applied, or crop-specific usage.

Changes in pesticide nomenclature, hazard classifications, and regulatory frameworks over time represent a further limitation. To facilitate comparisons across studies, the classification of HHP was harmonized using current PAN and FAO/WHO criteria; however, this retrospective application of modern classification systems may not fully reflect the regulatory or hazard status of pesticides at the time they were reported.

This review was also limited to sources identified through the search strategy described in Methods and may be subject to publication and language bias, as those published studies in languages other than English or Spanish were not considered.

The sources compiled in this review further differ in the type of underlying evidence used to document pesticide sale or use (Supplementary Table S2); sales and empty-container data indicate potential availability, possession, or past use rather than confirmed current application, whereas self-reported and biomonitoring data reflect individual-level exposure that may not generalize to broader use patterns in the region. Exposure and health risk are not assessed in this review, as they would require dose, route, frequency, and duration data not available from the compiled sources. Accordingly, the evidence compiled in this review indicates potential availability, application, environmental release, or occupational and community exposure to HHP, but does not establish concentration, dose, route, frequency, duration, mixture composition, or population-level exposure or risk.

Finally, the presence of a pesticide in the reviewed literature should be interpreted as evidence of occurrence, but not of continuous use, actual application frequency, or human or environmental exposure. The findings provide a historical synthesis of the pesticides documented in the available literature and identify priorities for future environmental monitoring, exposure assessment, and epidemiological studies using standardized methodologies.

Policy recommendations and future directions

In conclusion, local assessment of HHP sales and use patterns reveals important limitations in the FAO/WHO classification criteria, which exclude numerous hazardous pesticides due to their risks to health and the environment. In contrast, the PAN classification system provides a broader assessment of this problem by including environmental damage and human health. Harmonizing the criteria for identifying HHP is a critical first step toward engaging competent authorities and multiple sectors of the population in defining goals aimed at reducing pesticide use and preventing associated risks, through the promotion of sustainable, environmentally friendly alternatives that do not harm human health. It is important to highlight that even if a pesticide is not currently classified as HHP by internationally accepted classification systems, the evidence of its harmful effects to human health and the environment reported by the scientific community should be taken into consideration to restrict or ban their production, importation, and use.

Comparative analysis between the FAO/WHO and PAN International frameworks reveals important discrepancies in the classification of certain active ingredients. While both systems agree on some critical substances, PAN International includes a broader range based on endocrine disruption and environmental harm. This divergence highlights the need for harmonized national guidelines aligned with precautionary principles.

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