Abstract

Microbial contamination in pesticide formulations affects their stability, shelf life, and efficacy. This article examines the causes, consequences, and risk factors of contamination in aqueous SC formulations. The author proposes an antimicrobial strategy for manufacturers to mitigate contamination, preserving formulation integrity and quality, and stands prepared to provide comprehensive assistance for its implementation, contact the author.

GENERAL PROBLEM

The issue of microbial contamination in SC pesticide formulations poses a significant concern for manufacturers. The occurrence of microbial growth can be attributed to several factors, including contaminated raw materials like water or additives used in the pesticide formulation, inadequate hygiene and sanitation practices during the manufacturing process, ineffective choice of preservative or its insufficient concentration to combat the specific microorganisms, and improper storage conditions involving uncontrolled temperature and humidity. The presence of microbial contamination can result in various issues, while the main problems are dramatic increase in viscosity, package swelling and risk to human health.

The impact of microbial contamination in pesticide formulations can have significant repercussions. Such contamination has the potential to degrade the active ingredients within the formulation, resulting in diminished effectiveness against targeted pests or diseases. Additionally, certain microorganisms present in pesticide formulations can pose health hazards to humans, animals, and the environment, triggering allergic reactions, skin irritation, or other adverse effects. Furthermore, microbial growth shortens the stability of pesticide formulations, causing alterations in physical characteristics like color, odor, and viscosity, which consequently shorten the pesticide's shelf life and lead to package swelling.

RISK OF MICROBIAL CONTAMINATION FOR DIFFERENT TYPES OF AIs

Microbial contamination can occur in any pesticide formulation, regardless of the active ingredient type. However, the propensity for microbial infection varies among herbicides, insecticides, and fungicides due to the inherent properties of their active ingredients.

In general, herbicides may have a higher propensity for microbial contamination compared to insecticides and fungicides. This is partly because herbicides are often formulated with adjuvants, which are additives used to enhance their effectiveness. Some adjuvants can provide a favorable environment for microbial growth, increasing the risk of contamination.

In contrast, fungicides, designed to target fungal pathogens, are less susceptible to contamination due to their biocidal activity. They have mechanisms of action that disrupt fungal cellular processes, such as cell walls, membranes, or metabolic pathways. These modes of action can also inhibit the growth and survival of other microorganisms, including bacteria and yeasts, reducing the likelihood of microbial contamination.

Overall, the susceptibility to microbial contamination can be ranked as follows:

herbicides > insecticides > fungicides

It is important to note that this ranking is a generalization and can vary depending on specific formulations and conditions.

ROOT CAUSES OF MICROBIAL CONTAMINATION

Role of contaminated surfaces. Contaminated surfaces of vessels and packages play a crucial role in microbial growth and the overall contamination of a formulation. Microorganisms have the ability to adhere to surfaces and form biofilms, which are structured microbial communities embedded in a protective matrix. Biofilms act as reservoirs for ongoing microbial growth and contamination. Cross-contamination can occur when microorganisms from contaminated surfaces are transferred to the formulation during manufacturing or packaging processes. Failure to adequately clean and sanitize vessels and packages between uses allows residual microorganisms to persist on the surfaces. This can lead to subsequent batches or formulations becoming contaminated. Additionally, compromised packages or containers, such as leaks or damaged seals, provide an entry point for microorganisms from the external environment. Once inside, these microorganisms can contaminate the formulation and promote further growth. It is important to note that while surface microbial growth is a significant concern, microbial growth within the formulation itself can also occur under certain conditions. Such growth can contribute to overall contamination and pose risks to formulation stability and quality.

Role of pH. The pH of a formulation significantly impacts microbial growth in the bulk. Microorganisms generally thrive in neutral to slightly acidic pH conditions. However, both acidic (low pH) and alkaline (high pH) conditions can inhibit microbial growth. For most common microorganisms, a pH range of 4 to 9 is considered less favorable for growth. Within this range, bacteria, yeasts, and molds typically exhibit reduced growth rates or limited survival. It's worth noting that the specific pH range inhibiting microbial growth may vary depending on the microorganism type, as some species have adapted to survive in more extreme pH conditions. In the case of SC pesticide formulations, it is important to highlight that their pH range typically falls within the optimal range of 4-9, close to neutral, thereby minimizing microbial growth.

Storage temperature. The storage temperature of formulations has a notable impact on microbial growth. Microorganisms have specific temperature ranges suitable for their growth and reproduction. Elevated temperatures typically foster microbial proliferation, while lower temperatures can impede or suppress it. Temperatures exceeding 38°C are of particular concern within the danger zone. Such conditions provide an optimal environment for numerous microorganisms to thrive and multiply. It is crucial to recognize that certain pathogenic microorganisms, including bacteria known to cause foodborne illnesses, can flourish within this temperature range. If present in the formulation, they can pose significant health risks.

Risky additives. Certain additives commonly used in pesticide formulations can create favorable conditions for microbial growth if not properly controlled. Among potentially "risky" additives which may support microbial growth are Emulsifiers and surfactants, such as Polysorbate 80, Alkylphenol ethoxylates (APEOs), adjuvants such as crop oils, including petroleum-based oils or vegetable oils, solvents, such as glycols or alcohols, Propylene glycol, that can support microbial growth if present at concentrations above 10-15%. Lower concentrations of Propylene glycol are typically less risky but may still contribute to microbial growth under certain conditions. Common concentration of Propylene glycol in pesticide formulations varies in the range of 5-7%. Certain Stabilizers, such as polyethylene glycols, can serve as a food source for microorganisms if present in formulations at adequate levels.

However, the main additives which are the main sources of microbial contamination are POLYSACCHARIDES which are added to SC formulations as viscosity modifiers. Xanthan gum is one of the most widely used polysaccharides. It is a natural polysaccharide produced by the fermentation of carbohydrates by the bacterium Xanthomonas campestris. Hydroxyethyl cellulose (HEC) is a modified cellulose derivative that is often employed as a thickening agent and viscosity modifier. Carboxymethyl cellulose (CMC) is another cellulose derivative widely used as a viscosity modifier. It is derived from cellulose by chemically modifying it with carboxymethyl groups. Guar gum is a natural polysaccharide derived from the seeds of the guar plant (Cyamopsis tetragonoloba). Locust bean gum, also known as Carob gum, is extracted from the seeds of the carob tree (Ceratonia siliqua). It is a natural polysaccharide used as a thickening agent and viscosity modifier.

Microorganisms present in the formulation can degrade or metabolize these polysaccharides over time, resulting in a decrease in viscosity. This leads to the loss of desired rheological properties, such as uniform particle suspension. Additionally, microbial activity, particularly by bacteria and yeasts, produces byproducts like gases or organic acids. The accumulation of these byproducts increases internal pressure within the package, potentially causing swelling, deformation, or even leakage. Swelling of packages can serve as a visible indicator of microbial contamination.

KNOW-HOW

ANTIMICROBIAL PREVENTING STRATEGY

To tackle the challenge of microbial contamination and its consequences on viscosity stability, preventing swelling of the packages and formulation quality in aqueous SC formulations, the following strategy can be implemented. This strategy aims to minimize microbial growth, maintain desired rheological properties, and ensure the overall integrity of the formulation.

• USE PRESERVATIVES. Incorporate appropriate biocides into the formulation to inhibit microbial growth and protect against contamination. It's important to ensure that the selected biocides are compatible with the polysaccharide and do not compromise its performance. The preservatives should be added to the formulation itself as well as to the polysaccharide premix prepared for the further addition to the formulation to manage its viscosity. Here are some commonly used biocides that are often allowed for use in pesticide formulations. Benzalkonium chloride is a broad-spectrum biocide effective against bacteria, fungi, and algae. It is widely used in various industries, including pesticide formulations. Chlorhexidine is an effective antimicrobial agent against a wide range of microorganisms, including bacteria and fungi. It is commonly used in pharmaceutical and cosmetic products and is also suitable for pesticide formulations. Isothiazolinones is a class of biocides that includes substances like methylisothiazolinone (MIT) and benzisothiazolinone (BIT). They are effective against bacteria and fungi and very often used as preservatives in pesticides. Quaternary ammonium compounds, such as dodecylbenzenesulfonic acid and alkyl dimethyl benzyl ammonium chloride, exhibit antimicrobial properties against bacteria and some fungi. They are commonly used as disinfectants and preservatives.
• OPTIMIZE pH AND TEMPERATURE. Microbial growth is influenced by pH and temperature. By adjusting the pH and temperature of the formulation, you can create an environment less conducive to microbial growth. As mentioned earlier pH range of 4-9 is an optimal for SC formulations. To minimize the risk of microbial growth, it is crucial to store formulations at temperatures outside the danger zone. Temperatures exceeding 38°C provide an optimal environment for microorganisms to thrive and multiply. Typically, refrigeration or cold storage temperatures are recommended to inhibit microbial growth and preserve the stability of the formulation.
• ENSURE HYGIENE DURING MANUFACTURING PROCESSES. This includes maintaining a clean and controlled production environment, using sanitized equipment, and employing proper hygiene practices by personnel. For sanitizing the vessels and equipment used for the xanthan gum premix, the following substances can be suitable: Isopropyl alcohol (IPA), a commonly used disinfectant that effectively kills a wide range of microorganisms. It can be used to sanitize vessels and equipment by wiping or spraying and allowing sufficient contact time; Sodium hypochlorite, a strong disinfectant that can effectively eliminate various microorganisms. Diluted hypochlorite solutions can be used to sanitize vessels and equipment, followed by thorough rinsing to remove any residues; Quaternary ammonium compounds, such as Benzalkonium chloride or Dodecylbenzenesulfonic acid, that can be used as both biocides and surface sanitizers. They can be applied to sanitize vessels and equipment, following the manufacturer's recommended dilution and contact time.
• EXERCISE SPECIAL CAUTIONS WHEN PREPARING POLYSACCHARIDE PREMIX for further incorporation into the formulation. Here is an exemplification of guidelines for safely preparing an antimicrobial-resistant Xanthan gum aqueous premix aimed at managing viscosity in SC formulation.
  • Use purified water for preparation of the premix and ensure a clean and controlled environment. Thoroughly clean and sanitize all utensils, equipment, and the mixing vessel.
  • Gradually add xanthan gum powder to the water and mix thoroughly avoiding clumping or agglomeration. Continue mixing until a homogenous and smooth premix is achieved, ensuring that the xanthan gum is fully hydrated and dispersed in the water.
  • Perform antimicrobial treatment. Incorporate an appropriate preservative into the premix to enhance its resistance to microbial contamination. Ensure compatibility by using the same preservative as the one intended for the formulation.
  • Maintain optimal temperature conditions. Ensure controlled temperatures to minimize microbial growth. Consider laboratory testing of the premix preparation at elevated temperatures (above 80°C) to "pasteurize" the Xanthan gum premix, ensuring its performance and properties remain intact. Implementing this "pasteurizing" method for industrial preparation of Xanthan gum premix is recommended where feasible.
  • Package and store antimicrobial-resistant Xanthan gum premix in a sterile, airtight container or packaging suitable for storage. Label the container with relevant information, such as the date of preparation, concentration, and any other necessary details.
  • Store the premix under appropriate conditions, such as a cool and dry environment, following recommended storage guidelines for Xanthan gum.

  By following this method, you can successfully prepare a stable antimicrobial-resistant xanthan gum aqueous premix for further addition to an SC formulation while effectively managing formulation viscosity. It is important to consult with experts and conduct appropriate stability testing to validate the antimicrobial resistance and efficacy of the premix.

• CONDUCT MICROBIAL TESTING. Regularly test the formulation for microbial contamination during production and storage. Implement a robust microbial testing protocol to detect and identify any microbial growth early on. This will allow for timely corrective actions, such as reformulation or adjustment of preservation strategies
• ENHANCE PACKAGING. Ensure that the packaging is properly sealed to prevent entry of contaminants during storage and transportation.
• STABILITY TESTING. Perform comprehensive stability testing of the formulation to assess its resistance to microbial contamination over time. This will help identify any potential issues and allow for adjustments to the formulation or preservation strategies, if needed.
• CONTINUOUS MONITORING. Implement a system for continuous monitoring of the formulation's viscosity, microbial contamination, and package integrity throughout its shelf life. This will enable early detection of any deviations or signs of contamination, allowing for immediate corrective actions.
• EDUCATION AND TRAINING. Provide education and training to personnel involved in the manufacturing and handling of the formulation. Emphasize the importance of hygiene, proper handling, and adherence to guidelines to prevent contamination.

By implementing these strategies, you can mitigate microbial contamination, improve viscosity stability, maintain formulation quality, and minimize risk of swelling packages in aqueous formulations containing polysaccharides. It's important to consult with experts in formulation development and consider conducting thorough testing and evaluation before implementing any changes to the formulation process.