Agrochemicals – Using particle sizing to develop green pesticides

In 2015, the global agricultural chemical market was estimated to be worth $214 billion. By 2020, this market is projected to grow to $250 billion due to the increasing need for agrochemicals.1 However, agrochemicals can accumulate in the environment, polluting rivers and poisoning wildlife.

It is important that environment-friendly solutions are developed if humans wish to continue to their large-scale use of agrochemicals.

Fertilizers and pesticides are the most widely used agrochemicals. Pesticides are chemicals that are used on crops to control pests including weeds, insects, rodents, and fungi. Pesticides are not a modern invention although their use has increased substantially over the past five decades.

In ancient times, farmers used to apply substances such as elemental sulfur in order to repel pests. With more than 350,000 different pesticide products currently registered in the US., the chemistries of today’s pesticides are more diverse and advanced.

How Do Pesticides Affect the Environment?

Pesticides act by deterring or killing the target 'pest'. However, pesticides also affect non-target plants and animals, as they are not species-specific. One of the earliest industrially produced pesticides, dichlorodiphenyltrichloroethane (DDT), has been found to persist in the environment and to accumulate in the animal tissues, resulting in toxicity.

As a result, the US Environmental Protection Agency (EPA) banned the use of DDT in 1972. However, DDT is not the only pesticide to have an adverse impact the environment. There is increasing concern about the use of other pesticides and their potential effects on water quality, biodiversity, and soil quality.

Without using pesticides, farmers could lose up to 50% of their crops. Historically, there are many instances of crop failures resulting from pests and significantly impacting societies. During the 1840s, the potato blight in Ireland caused a famine resulting in the death of three million people. As the global population rises and the land available for crop production shrinks, it is not a viable option to ban pesticides and other agrochemicals.

Many environmental regulatory authorities now want farmers to use smaller amounts of pesticides and to use only those pesticides that have a minimal impact on the environment. Therefore, current research is focused on developing more specific and environmentally friendly pesticide formulations.

Developing Environmentally Friendly Pesticides

Commercial agrochemical formulations including pesticides typically contain an active ingredient together with a number of ‘inert’ ingredients such as solvents, surfactants, defoamers, emulsifiers, stabilizers, anti-freeze elements, antimicrobials, pigments, and buffers.

Many commercial pesticides require the use of organic, petroleum-based solvents as they are poorly soluble in water. However, organic solvents are often carcinogenic and toxic. Therefore, the current trends in the development of pesticides include the elimination of organic solvents wherever possible. Potential contenders for environmentally friendly alternatives to oil-based formulations include water-based pesticide formulations.

Water-based pesticide formulations can either be aqueous solutions, water-dispersible granules, suspensions, or emulsions. There has recently been a rapid development of suspension concentrate formulations, which consist of solid particles of a water-insoluble active ingredient dispersed in water with the help of surfactants.

Water-based suspension pesticide formulations are advantageous as they have a high concentration of active ingredients present in them, easy handling and low cost, ease of application, and others. Additionally, they are more environment-friendly compared to organic solvent-based formulations.

The particle size and distribution of suspension concentrate formulations are important properties to consider because they directly relate to the efficacy, stability, and required dosage of the final pesticide product. Smaller particles with a larger surface area can enhance adhesion and penetration of target organisms, improving their efficacy and bioavailability.

For suspension concentrates, stability can be a particular problem, because particles with the active ingredient tend to settle during storage, causing separation. However, stability and particle size are inversely proportional to each other. Therefore, stability can be increased by reducing the active ingredient particle size, since small particle sizes enable the Brownian motion to dominate over gravitational force.

Therefore, particle size distribution becomes an important quality indicator when new, environmentally friendly suspension concentrate pesticide formulations are developed and produced.

Analyzing Environmentally Friendly Pesticide Formulations

It is particularly challenging to analyze the particle size distribution of pesticide formulations given their complex and varied nature.

Bettersize laser particle analyzers provide accurate particle shape and size analysis of suspensions, including novel environment-friendly water-based pesticide formulations.7 The Bettersizer S3 Plus analyzer uses a dual-lens approach with automatic alignment to increase the particle size measurement range, and enhance resolution and accuracy.

Almost all agrochemical formulations can be analyzed using the Bettersizer S3 Plus. These include suspension agents with small particle distributions in the range 0.1 - 10 µm, and larger particles used as water-dispersible granules with a size distribution of 50 - 800 µm.

The instrument can measure particle shape as well as particle size, meaning parameters such as the median particle size (D50), particle size distribution, average particle size, and boundary particle size can all be determined.

A reliable circulation and dispersion system combined with high-speed sampling ensures full dispersibility of all samples, and guarantees accuracy and repeatability. Only a small amount of sample is needed for the analysis, due to the small volume cell used in Bettersize instruments. This makes the instruments suitable for use in research and development laboratories.

Conclusion

The particle size used in pesticide formulations has a large impact on their solubility in environment-friendly solvents. Therefore, particle size analysis should play an important role in developing pesticides that are not highly toxic towards their external environment and that are more specific to certain species.

Bettersize provides various particle shape and size analysis systems, which are well-suited for the analysis and development of new agrochemicals.