Development of Green Chemicals for the Agricultural Industry

A tractor sprays pesticides across a field of soy beans. Image Credits: Fotokostic/shutterstock.com

Green chemistry is an increasingly prominent philosophy in the chemical industry. It attempts to quantify the environmental impacts and operational hazards of chemical processes using standardized metrics. It also provides a set of guiding principles to improve the metric performance of each input and operation.

The principles of green chemistry mandate a full lifecycle analysis:

• beginning with the selection of renewable, non-toxic feedstocks;
• the design of safe and energy efficient synthetic procedures
• maximum incorporation of all materials into the product, eliminating auxiliaries when possible;
• generating durable, non-toxic products with preserved function;
• and ensuring the natural degradability of all products and by-products at the end of life.

The principles of green chemistry are especially relevant to the manufacturing of agrichemicals due to their direct impact on human and environment health. However, current agricultural practices are still based on intensive production methods using unsustainable technologies developed during the ‘green revolution’ (a term that predates the modern environmental movement) of the 1940-60s.

This technology is characterized by the extensive use of high yielding crop varieties, chemical fertilizers, pesticides and irrigation. According to market research by FoodThink, 66% of Americans feel the agriculture industry is not transparent about food production practices citing primary concerns of the use of pesticides and insecticides, animal antibiotics, and animal hormones.¹

As consumer focus shifts towards establishing a sustainable and secure food supply, the agrichemical industry will require a second ‘green revolution’ utilizing green chemistry principles to continue providing products relevant to agricultural practices.

Minimum Risk Pesticides

Plants and their associated microorganisms are known to produce a variety of chemical deterrents to protect against parasites and competing organisms. These natural products can also fulfill similar human needs (i.e. pest deterrents in medicine and agriculture), either in their isolated form or after chemical modification.

Development of Green Chemicals for the Agricultural Industry

Tractor spreading fertilizers across a field to encourage growth of crops. Image credit: Fotokostic / Shutterstock.com

A warning sign is displayed to stop people from entering a field where pesticides have been applied. Image credit: Modfos / Shutterstock.com

A group of farmers spray pesticides over a paddy field. Image credit: sakhorn / Shutterstock.com

While the toxicity of natural products must be carefully quantified as with any chemical substance, they usually pose minimal environmental threat compared to synthetics due to their biodegradability.

This critical difference has prompted regulation in 8 Canadian providences banning synthetic pesticides for ornamental purposes in favor of natural pesticides, establishing clear ethical, regulatory and market support for further development of natural pesticides.

Additional economic incentive is provided by an EPA mandate that decreases the amount of data and time required for the registration of “minimum risk pesticides” meeting safety requirements for all ingredients. The list of EPA registered minimum risk pesticides includes:

• Essential Oils – distilled from certain plants have shown good insecticide activity against arthropods and selectively against broadleaf weeds. Eden Research PLC has developed a formulation technology to encapsulate mixtures of geraniol, eugenol and thymol (monoterpene in thyme oil) in a chitosan coated alginate bead, providing the first fungicide to offer natural, effective control of the grey mould, Botyris, on fruit and without adversely affecting honeybee populations.²
   
• Insecticidal soaps – produced by the base-hydrolysis of natural triglycerides to fatty acids which can be further modified to produce organic detergents such as sodium lauryl sulfate. Pelargonic acid is a short chain fatty acid derived from esters extracted from the leaves and flowers of Pelargonium (common germanium). Application of 10-lb per acre of pelargonic acid to yellow squash controlled crabgrass and broadleaf weeds resulting in maximal yields equivalent to manual weeding.³
   
• Fe-HEEDTA – a liquid-based herbicide containing soluble iron strongly chelated by N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEEDTA). Broadleaf weeds preferentially absorb the soluble iron-chelate from solution which eventually decomposes releasing Fe(III) in the plant tissue where it causes oxidative stresses to vital organelles.⁴

Controlled Release Fertilizer Formulations

Although the necessary nutrients for plant growth are usually present in the soil, many factors can affect their availability to plants such as the formation of insoluble minerals in addition to soil properties including water content, pH, and compaction.

To provide nutrients in a plant available form, agrichemists have developed formulation technology that vastly improve the fraction of nutrients in fertilizers absorbed by plants, significantly reduce fertilizer application rates, and minimize runoff to nearby surface water.

• Lignosulfonate based chelators - Agmin Chelates Pty Ltd offers custom micronutrient blends formulated with a lignosulfonate chelator which forms a stable water soluble complex with nutrient molecules to prevent mineralization in the soil and facilitate foliar application directly to the leaves. The lignosulfonate adjuvant is sourced from paper mills as a by-product of the sulfite pulping of wood and functions as a naturally tacky wetting agent and dispersant to enhance adsorption of the fertilizer mixture to the leaves. Gradual biodegradation of the lignosulfonate releases the nutrients for absorption by the leaf.⁵

MU Agriculture Ethics 2014 Documentary. Video Credits: Tyler Morin / YouTube

Biofertilizers contain beneficial soil microbes that colonize plant roots and improve soil fertility by releasing nutrients from organic matter and insoluble (phosphate) minerals; improving soil acidity, cation exchange capacity, and water holding capacity through the formation and exchange of humus; and improving the soil structure by burrowing and aggregating soil particles. Environmentally safe and effective methods of inoculating multiple species of soil microbes into the heterogeneous and non-sterile soil environment can be difficult to achieve.

• Polymer encapsulation ­– of soil microbes in microspherical alginate beads (< 1 mm) is a highly reproducible and efficient formulation strategy to facilitate root colonization in competitive microbial environments, preventing wash down, and improving the stress tolerance of the inoculum. Bac-coat technology developed by the Austrian Institute of Technology has been used to coat maize seeds with encapsulated microbes, showing a 60% improvement in root colonization over non-encapsulated controls. ⁶

Energy Efficiency in the Agrichemical Industry

Increased regulation of industrial greenhouse gas emissions and the rising cost of energy in the coming decades will likely have a dramatic effect on the profitability of the energy intensive manufacturing of conventional fertilizers and pesticides.

The agrichemical industry can guard against such risks by prompt implementation of green chemistry initiatives and expanding natural products research, as outlined in the above sections.

References and Further Reading

1. “Emerging Faith in Food Production,” Sullivan Higdon & Sink FoodThink, 2014.
2. Field trial research conducted by Eurofins Agrisearch, 2006 and 2007.
3. Webber III, C.L.; Taylor, M.J.; Shrefler, J.W. Weed Control in Yellow Squash Using Sequential Post-directed Applications of Pelargonic Acid. Hort. Technology 2014; 24: 25-29.
4. Fiola, D.S. Iron-based Herbicides: Alternative Materials for Weed Control in Landscapes and Lawns. University of Maryland Extension, 2014.
5. Benefits of Foliar Fertilization - Agmin
6. A. Bejarano, U. Sauer, B. Mitter, C. Preininger. Encapsulation of plant-growth promoting bacteria in polymer matrix: Development of new biofertilizers, XXII International Conference on Bioencapsulation, 2014.