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1. Introduction
Pesticides are one of the most important inputs in agricultural production. They effectively reduce losses caused by insects, diseases and weeds, improving crop yields and their quality1)(2)(3. However, it has been widely demonstrated that, by reaching soil, water and air compartments, they also represent a major threat to environmental sustainability. Non-target organisms such as birds, fish, beneficial insects, plants and others are systematically exposed to pesticides and therefore affected by their toxicity4. Pesticides also pose serious risks to human health. Human exposure can occur directly due to occupational, agricultural, and household use, or indirectly, mainly through contaminated food and water consumption5)(6.
Despite the cumulative evidence generated in the past years and the growing awareness of negative impacts from pesticides; various attempts proposed to mitigate the overuse of pesticides have been practically ineffective. One of the most cited examples is the adoption of integrated pest management (IPM). Moss7 pointed out that IPM implementation has been poor, with little evidence of concomitant reductions in pesticide use.
Moreover, the quantity of pesticide production and consumption has kept increasing annually at the global level. According to the latest data from the Food and Agricultural Organization8, the total pesticide consumption worldwide has risen from 2,047,087 tons in 2000 to 2,611,124 tons in 2020.
Pesticide dependency is a fundamental part of modern agricultural regime and a very complex phenomenon. Even when pesticide resistance has been widely considered as one of the major causes9)(10. Hu11 argues that pesticide dependency is not only a technological issue as pesticide resistance thesis indicates, but rather a man-made issue, with socioeconomic and political reasons for both the country and the farmers, involving multi-dimensions, multi-actors and multi-scales factors.
Consequently, multiple and complex actions at different levels are required when addressing pesticide dependency mitigation12. The actions to be developed in each region or country, as well as their prioritization and urgency, require previous and basic analysis of the intensity of pesticide use, the expected behavior in environmental fate and the associated risks13.
The objective of this work was to analyze pesticide use in Uruguay, combined with the information available on its potential risks with an emphasis on ecological risks.
2. Materials and methods
The information made available by the General Directorate for Agricultural Services (DGSA) from the Ministry of Livestock, Agriculture and Fisheries of Uruguay (MGAP)14, and the Food and Agriculture Organization of the United Nations (FAO)8 corresponding to the last two decades (2000-2022) was used for the diagnosis of pesticide use in Uruguay and other agricultures regions.
For the estimation of the most used active ingredients in the country, a sample was taken using information collected from the DGSA's system of pesticide application registrations from 2019 to 202215. For the potential risks associated with its use, the information reviewed considered the Pesticide Properties Database16, national and international research related to the subject.
3. Results and discussion
3.1 Use of pesticides in Uruguayan agriculture
The use of these products has had a sustained increase since the year 2000, showing very similar trends to those observed worldwide. The total amount of active substances imported varied from 3.9 to 10.6 tons between 2000 and 202114) (Figure 1).
Herbicides were the group that registered the greatest change, representing 89% of the total volume increase in kg or l of the formulates in 202114. While comparing the worldwide use of pesticides in 2020, 53% is the share of herbicides, 18% is the share of insecticides, 23% is that of fungicides, and others account for 7% only8.
It should be clarified that pesticide products imports are not necessarily a synonymous of the use of such product. There is no information on how much of the imported pesticides are truly used in the country, nor if the use is exclusively for agricultural purposes. Despite this, it is an indicator commonly used for global and comparative analyses in this subject17.
The greater use of pesticide products in the country has a strong association with the agricultural area’s growth in this period. Favourable agricultural prices and a rapid generalization of the practice of zero tillage were determinants of agriculture expansion towards non-traditional areas and mainly agriculture intensification process, as a result of massive adoption of double cropping18.
In this way, the increase in pesticide products imports reflects an increase in the intensity of their use, and therefore refers to greater quantities of pesticide products per hectare cultivated and per year. The information collected shows that higher amounts of pesticides per hectare in the periods between 2000 and 2020 varied from 2.58 to 7.97 kg/ha in Uruguay, just as it can be observed in Figure 2 8. There are also marked differences between regions. While in Europe there is a tendency to decrease the intensity of pesticide use, the Southern Cone of South America shows an increasing trend, which is noticeable in the case of Uruguay.
When we analyze the active ingredients comprising the groups of pesticide products imported in 202114) in detail, a clear predominance of a few active ingredients was revealed (Table 1). The most notorious case is that of herbicides, where 88% corresponds to only 5, while 68 active ingredients correspond to the remaining 12%. In the case of imported fungicides and insecticides, this is not so evident, although a few active ingredients still predominate.
Table 1: The most imported active ingredients in Uruguay in 202114
*Mancozeb is also imported in mixtures with metalaxyl. These quantities were not considered because they are not separately reported.
Nevertheless, considering that pesticides are used at very different doses per hectare, kilograms of active substances do not reflect directly the use.
In this context of increasing pesticides imports, but mainly of higher intensity of use, it seems likely that associated risks would also increase, depending on their toxicological and ecotoxicological hazards.
3.2 Toxicology and ecotoxicology characterization of major used pesticides
In an attempt to make a rough estimate of the potential risks of the most commonly used active ingredients in Uruguay, a hazard profile was compiled (Table 2) using information from the DGSA's Register of Application of Pesticide15. It is important to clarify that this hazard profile only considered information on the parameters currently required to register pesticide products in Uruguay19.
Table 2: Toxicological profile according to Pesticide Properties Database16 of the main used pesticides (2019-2022)15
Toxicity scale (Ts): mammals (rat) acute oral LD50 (mg/kg) < 5-50= very hazardous (red); 50-2000= moderately hazardous (yellow); > 2000 = unlikely to present an acute hazard (green). Ts in earthworms (Eisenia foetida) acute 14-day LC₅₀ (mg/kg), > 1000 = Low 10 - 1000 = Moderate < 10 - High. Ts in birds (Oncorhynchus mykiss/ Colinus virginianus) Acute LD50 (mg/kg) > 2000 = low (green); 100 - 2000 = Moderate (orange); < 100 = High (red). Ts in honeybees (Apis mellifera) acute LD50 (µg/bee) > 100 = Low (green); 1 - 100 = Moderate (orange); < 1 = High (red). Ts in fish (Colinus virginianus) acute 96 h LD50 (mg/l) > 100 = Low (green); 0,1 - 100 = Moderate (orange); < 0,1 = High (red); Aquatic invertebrates (Daphnia magna) acute 48 hour EC₅₀ (mg/l) > 100 = Low; 0.1 - 100 = Moderate and < 0.1 = High.
The danger for humans from pesticide products is classified into toxicological categories. These categories are defined according to the acute risk in mammals, resulting from a single or repeated exposure over a relatively short period of time with the pesticide product. Based on this classification, we notice that in the case of herbicides and fungicides predominant substances do not represent a major threat to human health (Table 2). However, in the case of insecticides, those which predominate are highly dangerous to humans.
National epidemiology studies in human toxicology have identified a wide range of conditions and diseases associated with environmental exposure to pesticides. Evidence has been found in the working environment, in rural and urban populations associated with agriculture20)(21)(22; and in the general unexposed population23.
The human health risk assessment is complex due to its strong dependence on periods and levels of exposure, type of pesticides used, and characteristics of the environment and the human communities of the areas where pesticides are applied. Long-term, standardized and validated studies are needed to confirm the link between pesticides and their negative effects on human health. In addition, the risk to human health should be assessed not only for specific active substances and different formulations, but also for the possible cumulative and interactive effects of exposure to multiple pesticides over time24)(25. It is firmly suggested that risk assessment of pesticide-exposed populations use occupational exposure matrices that consider the tasks performed, the crops and active ingredients, and more complete occupational histories, which could reduce errors due to exposure26.
Regarding the ecotoxicological characteristics of the profile (Table 2), the main insecticides used present more toxicity in terrestrial and aerial organisms in relation to the other groups. However, in the case of aquatic organisms, all three groups of pesticide products present toxicity problems.
Ecotoxicological studies are also complex. They are performed with standard organisms generally selected according to the simplicity of their laboratory study. These organisms are not necessarily the organisms of interest in all the environments in which the pesticide product would be applied27.
In addition, much of the information currently included in the pesticide registry is based on toxicity studies under laboratory conditions, focusing on groups of individual organisms and evaluating each active ingredient separately. Although these types of tests allow methodological homogenization and easily comparable results, they may be questionable in their ability to effectively protect ecosystems, given the differences between the assessment conditions and the conditions of real use28)(29.
Currently, and especially in extensive agriculture, pesticides are used in mixtures, and may generate synergistic toxicological effects, greater than those tested individually. In addition, these systems already have pesticide products in the process of degradation, generating cocktails of numerous compound that lead to stressful conditions for non-targeted organisms. In addition, risk assessments assess the effects on individual organisms, but not on population or community level30.
Also, information regarding the potential effects of the resulting secondary metabolites from degradation is very limited. They have their own toxicological and ecotoxicological characteristics and can be even more toxic than the parent compounds31.
Moreover, the risk generated by a compound is not only linked to the dose and metabolites it generates, but is also dependant on its environmental behaviour. A clear example is the persistence or active bioavailability of pesticide residues over time in different environmental compartments, which is strongly dependent on the physio-chemical characteristics of the compound and the variable characteristics of the destination compartment16)(32)(33. In this sense, glyphosate is considered of low risk in soil, among other aspects based on its categorization as non-persistent. At present, it is known that it may persist according to its form of use, to the point that its reclassification as pseudo-persistent is recommended34.
Pesticide residues cause direct and indirect negative effects on non-targeted organisms23, microorganisms, flora, physicochemical, and biological properties of agricultural soil35)(36.
In Uruguay, the presence of pesticide residues has been reported in watercourses and drinking water37)(38, in soil39)(40, in the air41, in beehives and in component parts of beehives42)(43)(44)(45, and in agrifoods46)(47)(48. Furthermore, there are several studies on the effect of the use of pesticide products at the biota level in environmental compartments49)(50)(51)(52)(53)(54)(55)(56)(57.
Based on the toxicological-ecotoxicological parameters and environmental fate of an active ingredient, pesticide products are registered, suspended, restricted or prohibited for their use.
There are currently 2601 pesticide products registered by MGAP in Uruguay. Eighty one of the registered active ingredients (which comprise 330 products containing these active ingredients) are classified as highly hazardous pesticides (HHPs)58. HHPs are defined by the World Health Organisation, the Globally Harmonised System of Classification and Labelling of Chemicals, Pesticide Action Network International and FAO59)(60 as pesticides that pose particularly high acute or chronic risks to human health or the environment. The European Union and many other countries have banned 41 of the 81 active ingredients that are classified as HHPs and that are registered and commercially available in Uruguay58.
Uruguay has only 22 banned active ingredients according to PAN61, similar to Argentina, Chile and Paraguay (18, 27 and 11 active ingredients, respectively), while Brazil has 133 banned active ingredients. Countries from the European Union are more restrictive with the use and registration of pesticide products61. When we relate this information with that corresponding to the effectively used amounts, we notice that the countries with the greatest use of pesticide products are those with the least restrictions.
It is worth mentioning that in countries with more restrictions the environmental risk assessment required for the registration of new pesticide products must be carried out in different cultivation scenarios, soil and climate representative of the region in which they will be used24. Despite the associated costs of these types of studies, they are essential to better estimate the impact of pesticide use on a particular ecosystem.
4. Final considerations
The available information indicates a high intensity of pesticide use in Uruguayan agriculture. It also evidences the presence of pesticide residues in different environmental compartments, and several negative effects have been reported on local non-target organisms.
Improvements on the registration and renewal system of pesticides, as adopted by countries with more restricted regulations, could be an effective strategy to mitigate deleterious effects of pesticides use.
