The main crop in the state of Campeche is maize. About 144,000 hectares were cultivated in 2006, and just over 181,000 hectares in 2013 [1
]. In addition to maize, rice, sugar cane, sorghum, jalapeño peppers, habanero peppers, and beans are principal crops in the region.
Aside from maize production, Campeche is the primary soybean producing state in Mexico [2
]. According to current federal figures, the harvested areas and annual production have been growing from 2013–2014. Soybean cultivation doubled (29,200 hectares), with the Hopelchén municipality serving as the main soybean producer in the state [3
]. Ninety percent of the soybean crop produced in Hopelchén comes from commercial and industrial producers, while the remaining percentage comes from subsistence farmers (Agricultural producers under the slash and burn model, mainly for self-consumption) [4
]. In Mexico, the production by commercial operators has led to various criticisms due to the severe deforestation process, excessive use of agro-chemicals, and the use of genetically modified (GM) seeds; produced and mainly distributed by Monsanto, which are resistant to glyphosate herbicide application [5
The main cause of deforestation in the study sites around Hopelchén comes from the expansion of industrial agriculture, accounting for 68% of the forest area lost (75,400 ha). This type of production is present throughout the municipalities, however, it is primarily found in sites with a slight slope, causing a high percentage of deforestation per municipality throughout the state of Campeche from 2000–2013 [7
]. Annual mean rainfall is approximately 1100 mm. During some crop seasons the fields flood, therefore farmers often drill infiltration wells, to prevent flooding. Infiltration wells are constructed to induce the indirect filtration of water accumulated on the surface of the soil substrate [8
]. The Yucatan peninsula is primarily covered with karstic soils, which are extremely permeable; as a result, the infiltration wells directly contaminate the groundwater with pesticides. At the study sites near Hopelchén, there are many illegal absorption wells that are not constructed to code, legally permitted, nor sealed. Water infiltration wells are a serious problem in the region because they contribute to desertification. In 2015, observations reported that the lagoons of Cancabchén and that the Ik Lagoon nearly dried up due to the loss of runoff waters [9
The intensive use of pesticides in Hopelchén for sorghum, tomato, maize, and other crops causes groundwater contamination. Many pesticides have a half-life of several months, which allows them to persist for a long period in the environment. A study conducted in 2010 showed the presence of 2,4-dichlorophenoxyacetic acid (2,4-D) residues in the groundwater at some localities in the state of Campeche, including Hopelchén with 13.8 μg/L [10
]. Pollution in the groundwater from pesticides is critical in karstic areas because substances such as glyphosate with a very low octanol/water coefficient (Kow
= 0.00033), are highly soluble in water, reaching a persistence of up to 170 days at 25 °C under low light conditions, and extending to 315 days at 31 °C in darkness [11
]; these temperature and light conditions are very common in the Yucatan groundwater system.
In Mexico, there is only one study about the presence of glyphosate in both surface water and groundwater from natural protected areas and agricultural areas in the state of Chiapas [12
]. Authors found higher concentrations of glyphosate during the dry season, probably due to reduced dilution from precipitation. The concentrations of glyphosate in groundwater ranged from <0.13 to 18.43 μg/L and from <0.13 to 36.71 μg/L in superficial water (river). Similarly, in a study carried out over a period of 3 years in an area near a Maya mountain protected area in Belize, glyphosate residues were found in the phytotelmic water at seven sites where the range of glyphosate concentrations was from 0.22 to 1.7 μg/L [13
]. The authors mention that at least part of the population acquires its drinking water from systems coming from the Maya Mountain Protected Areas, and therefore populations could be chronically exposed to glyphosate. This study suggests that pesticide drift is occurring in these areas, and its dispersion will reach many places depending on the water systems exposed.
A study conducted in 2004 regarding agricultural production methods and pesticide use among subsistence farmers in four rural communities of Campeche, including Ich-Ek, Crucero San Luis, and Suc-Tuc from the Hopelchén area [14
], showed that acetylcholinesterase (AChE) activity in subsistence farmers was significantly lower (p
< 0.05) than the mean activity determined from individuals in a reference group. In this study, carbamates, particularly carbofuran, seem to be more associated with the symptomatology of pesticide exposure than organophosphates.
-(phosphonomethyl) glycine) is the most widely used broad-spectrum herbicide worldwide and its use in agriculture has increased since its introduction in 1970. It is primarily administered for weed control outbreaks during land preparation or pre-harvest. Thus, genetically modified plants resistant to glyphosate were created for soybean and maize production, assuring that the crops were not affected in the presence of glyphosate [15
Genetically modified soybean cultivation emerged in the Yucatán peninsula in 2001. When the first experimental field was planted in 2010, a total of 12,000 hectares were used as pilot fields for genetically modified soybeans. In 2012, soybean producers requested authorization from the Federal Government to extend the area of genetically modified soybean production to 60,000 hectares. The use of genetically modified products such as soybeans entails the indiscriminate use of glyphosate because the transgenic seed-glyphosate dependency cannot be separated.
Aside from leaching into water systems, pesticides cause mortality in bees [17
]. In the USA, approximately 13 million dollars are lost annually from bee mortality [18
]. Although this is not a focal concern of our study, it is important because many of these crops depend on pollination, and honey is an important economic good produced in Campeche. Bee mortality was observed near glyphosate treated crops between 2012 and 2013. Almost 2000 bee colonies died in the towns of Suc-Tuc and San Luis in the municipality of Hopelchén, Campeche [19
]. Sublethal effects in bees constitute other adverse effects from glyphosate which influence the production of honey. These effects are important because laboratory tests with sublethal concentrations of glyphosate (1.25, 2.5, 5, and 10 ng active ingredient/bee) created a slight decrease of acetylcholinesterase activity of the bee [20
Although the European Food Safety Authority (EFSA) [21
] concluded that glyphosate is unlikely to pose a carcinogenic hazard to humans, the International Agency for Cancer Research (IARC) had classified glyphosate inside the 2A Category, which indicates “probably carcinogenic to humans” [22
]. Some studies indicate a correlation between glyphosate and genotoxic, hormonal, enzymatic type [23
], reproductive [24
], and neurological [28
] health risks to humans.
Humans can directly be exposed to glyphosate as operators, passers-by, or residents of glyphosate applied areas, through the food chain [23
] or human water consumption [31
]. Pharmacokinetic studies indicate that glyphosate absorbed orally is excreted unchanged, predominantly in urine [23
], where it can be measured at μg/L levels [32
]. Thus, urine provides a measure of recent exposure and is considered an ideal matrix in biomonitoring studies [29
Soybean crop expansion in the State of Campeche [6
] as well as in other Latin American and European countries, has negative effects on the environment, especially by polluting water, as well as in human and animal health by the generalized and frequent use of glyphosate [36
]. The goal of this study was to determine the levels of glyphosate in groundwater samples, bottled drinking water, and in the urine of subsistence farmers in different communities around the municipality of Hopelchén, Campeche.
This is the first report regarding the presence of glyphosate in water and urine samples in subsistence farmers inhabiting different agricultural communities in the State of Campeche, Mexico. The concentrations and glyphosate ratios in the matrices evaluated indicate a high exposure to this pesticide. It is very important to conduct a more detailed follow-up study to understand the presence of glyphosate in bottled drinking water, correlated with the glyphosate concentrations in subsistence farmers that used this herbicide, since there is no evidence using this matrix. This is of concern because it could explain another possible route of exposure to this pesticide. The presence of glyphosate in urine is very important even at low concentrations because glyphosate puts human health at risk. Therefore, the potential ecological impact of this pesticide must be considered on a more global, rather than regional, scale.
The results indicate the need to establish a monitoring program for pesticide residues in the Yucatán Peninsula. They also suggest a need to monitor non-target organisms, such as bees, to establish the effect of the predominant agricultural practices currently occurring in Hopelchén.
Also relevant to humans, it is essential to carry out a study that considers the health status of the human population in Hopelchén because glyphosate is among the dozens of widely used pesticides in the industrialized agricultural area. Due to the large cultivation areas and the quantities of pesticides applied, exposure to these chemicals by the population and field workers in the area should be evaluated to avoid diseases associated with these compounds.