Adjuvants ensure safety and efficiency in spraying

For years, there has been a debate about whether or not adjuvants should be considered a “related” product under the Agrochemicals Law (Law No. 7.802/89 regulated by Decree No. 4.074/02) and therefore be subject to the same registration process as such products. When in doubt, products classified as adjuvants were registered as such. This debate ended with the publication on November 20, 2017, by the Ministry of Agriculture, Livestock and Food Supply (Mapa), of Act No. 104, which cancels the registration of products registered exclusively as adjuvants, “given that there is no mandatory registration under Law No. 7.802 and Decree No. 4.074”. This attitude, while correct, is reckless.

Adjuvant, by definition, is “any substance or compound without phytosanitary properties, except water, which is added to an agrochemical preparation to facilitate application, increase effectiveness or reduce risks”. Therefore, if it “does not have phytosanitary properties” and is developed to be “added to an agrochemical preparation”, by itself it does not exert any control and, therefore, is not an agrochemical. On the other hand, to “facilitate application, increase effectiveness or reduce risks”, it interferes with the characteristics of the spray solution (mixture of the agrochemical with water), and may alter important aspects of the spraying. This interference may be positive or negative in the spraying process, in the effectiveness of the product and also in the safety of the worker, the environment and the food. For example, an adjuvant can alter the surface tension and/or the viscosity of the spray solution. By altering these characteristics, it will interfere with factors such as droplet size, spreading and evaporation speed, interfering with the technology and safety of the application. In solving the problem, re-registering as an agrochemical would not be a viable alternative, since the efficacy tests required in the registration process do not reflect the functionality of the adjuvants. Therefore, the alternative is to know, analyze and classify the adjuvants by their functional characteristics.

In the Functional Classification, adjuvants can be divided into two large groups: utility adjuvants, which act during the spraying process, i.e., between the tank and the target; and enhancers, which improve the performance of the product after the drop reaches the target. Within these groups are the functionalities of the adjuvant, which are its form of action, such as spreaders, adhesives, penetrants, wetting or evaporation reducers, buffers, chelating agents, drift reducers, etc. In this context, adjuvants perform specific functions, and not generic ones as normally disseminated. In addition, functionality is related to the chemistry, nature and quality of the components, which means that different formulations of the same product, such as vegetable oil, for example, can lead to different results. It is also important to note that some adjuvants can be multifunctional, i.e., have more than one functionality, but there is no single adjuvant that can perform all these functions. Knowing how to select the correct adjuvant is the basis for the effectiveness and economy provided by these products.

To correctly identify the adjuvant, the first step is to analyze the situation and understand “what it is expected to do”, that is, “what functionality should be sought”. Once this is done, some adjuvant options should be analyzed to compare not only the positive effects, but also the negative ones, which could cause problems in the phytosanitary treatment, with the aim of mitigating them, or even opting for another product if this is not possible. Therefore, to seek the correct functionality and how to use the adjuvant, in addition to information from the product manufacturer, it is important to understand its interference in the spraying process and several functionalities can be used as examples of this process.

The surfactant effect of adjuvants has been mistakenly confused with the spreading effect, but the two are independent in a spray. Surface tension is the result of hydrogen bonds, which are intermolecular forces caused by the attraction of hydrogen from a water molecule (H+) with the oxygen from neighboring molecules (O-). Inside the drop, a water molecule is surrounded by others, which causes the attraction to occur in all directions, but on the surface, the attraction occurs only on the bottom, causing a layer to form on the outside with an effect similar to a “trampoline”. The higher the surface tension, the more difficult it is to deform this layer. Thus, a drop with high surface tension when thrown at a target, as in the case of a spray, will have a greater tendency to bounce than to adhere to the target. Breaking the surface tension, by means of a surfactant, gives the drop greater capacity for deformation, absorbing the impact energy and reducing bounce. Roughly speaking, it is like a soccer ball being dropped from a certain height on the ground. The more inflated the ball (greater tension), the greater its ability to bounce. When the ball is deflated (less tension), the bounce decreases, as it deforms upon impact and stops on the ground. The spreading effect is the ability of a droplet to cover a larger area on the target than the original after impact. Thus, spreading can be translated as the area wetted by the droplet after it hits the target. Increasing spreading can be an excellent resource as a tool for reducing the volume of water used in spraying, without losing effectiveness and with a significant reduction in cost, as it allows a smaller volume of spray to provide the same coverage of the target. However, some adjuvants can increase the area wetted by a single drop by more than 30 times. In this situation, depending on the spray volume, drops that would not initially coalesce begin to coalesce on the target, increasing runoff, reducing the amount of product on the plant and consequently the effectiveness of the phytosanitary treatment, leading to a loss of productivity and/or the need for a greater number of sprays per harvest. For these adjuvants, normally classified as “superspreaders”, the application volumes must necessarily be reduced depending on the target coverage required. Furthermore, the spreading effect is an interaction of the adjuvant with target characteristics, such as type and amount of wax. Therefore, the spreading of the same product may vary for different crops.

The wetting or evaporation-reducing effect of water can be considered in two ways: before impact on the leaf or on the leaf. On the leaf, the wetting effect cannot be assessed individually, as it is affected by the spreading effect. In two products with exactly the same wetting effect, the one with the largest spreading area will have greater direct contact with the environment, evaporating more quickly. An adjuvant with good wetting characteristics reduces, for example, the crystallization rate of the chemical product on the target, which can increase its effectiveness. On the other hand, reducing the evaporation of drops on the path between the sprayer and the target increases the product recovery rate, that is, the amount of product actually reaching the target. Therefore, using a good wetting agent can represent an important factor both economically, since it can increase the period of use of the sprayers depending on weather conditions, and in terms of safety and effectiveness, since drops that would evaporate before reaching the target, resulting in the possibility of contamination of the producer and the environment, start to reach it, increasing the amount of product on it. 

However, an opposite effect will be observed if the adjuvant, even with other positive functionalities, increases the speed of water evaporation. In this case, measures to mitigate the risk of evaporation, such as using thicker droplets when possible, paying greater attention to weather conditions or even choosing another adjuvant, must be observed.

The drift-reducing effect of an adjuvant can be analyzed in two ways: either by analyzing the spray volume represented by droplets with a diameter of less than 100 µm (Drift Risk Potential) or by directly assessing drift in wind tunnels. Regardless of the method, drift reduction is usually achieved by increasing droplet size and/or reducing the number of very fine droplets in a spray. Reducing drift, ensuring that more of the spray reaches the target, is undoubtedly desirable and reduces worker and environmental contamination problems. However, several adjuvants can increase drift and the number of fine droplets and, in this case, the negative effect must be evidenced so that the producer can adopt risk mitigation measures and avoid damage to the environment and neighboring crops.

There is also an important consideration. Adjuvants are always “drift reducers” and never “anti-drift”, as this is an erroneous way of communicating or transmitting functionality. An anti-drift product would be one that eliminates drift, that is, that prevents it from happening, which does not exist, while a drift reducer only brings it to lower levels, although it continues to exist.

Several other features that are just as important as those mentioned should be considered, but these clearly exemplify how knowledge of the functional characteristics of an adjuvant is important not only to increase the effectiveness and economy of phytosanitary treatment, but also to reduce losses by limiting its use, changing the way it is adjusted and/or the conditions of use of the sprayer. For this reason, the Engineering and Automation Center of the Agronomic Institute (CEA/IAC), of the Secretariat of Agriculture and Supply of the State of São Paulo, has been dedicated for over 20 years to developing methods to individually evaluate the functionalities of adjuvants, seeking a more technical recommendation for these products, which emphasizes their positive side, but, at the same time, takes due care with the negative side when necessary. 

Regulation

Based on the above, if adjuvants do not qualify as “pesticides or similar products”, they also cannot be “over-the-counter products, without the need for any authorization by MAPA” as specified in item 5 of Act 104, since they can directly interfere with the effectiveness and cost-effectiveness of phytosanitary treatment. Therefore, if not registration, adjuvants need at least regulation. Initiatives in this regard have already been taken in the past by the Brazilian Association of Generic Pesticides (Aenda) and by MAPA itself, but they have not yielded effective results. Basic functionalities need to be scientifically analyzed to serve as technical parameters for their recommendation and use. Since there are no national or international standards for testing and classifying such functionalities, a joint action between MAPA, the National Health Surveillance Agency (Anvisa), the Brazilian Institute of the Environment and Renewable Natural Resources (Ibama), manufacturers, users and researchers, as well as a Study Committee of the Brazilian Association of Technical Standards (ABNT) seeking to develop Brazilian standards, is necessary. If this is not done, and quickly, the losses to agriculture, farmers, workers and the environment could be significant.

*Per Hamilton Humberto Ramos, Viviane Corrêa Aguiar, Ana Flavia Villa e Rafael Kenji Nagami Lima, of the Engineering and Automation Center of the Agronomic Institute