3.2 Liquid Formulations: Chemistry, Performance & Handling

3.2 Liquid Formulations: Chemistry, Performance & Handling

Pesticide active ingredients (a.i.) are rarely applied in their pure, technical-grade chemical state. Pure active ingredients may be insoluble in water, chemically unstable under ambient conditions, highly toxic to handlers in concentrated forms, or impossible to disperse evenly across target foliage. To overcome these limitations, manufacturers formulate technical chemicals by combining the active ingredient with inert ingredients—such as organic solvents, mineral carriers, emulsifiers, wetting agents, stickers, and stabilizers.

Liquid formulations represent one of the most common physical states used in commercial, agricultural, and turf applications across North Carolina. Understanding the unique physical chemistry, carrier interaction, agitation demand, and hazard profile of each liquid formulation is critical for safe application, equipment longevity, and maximum biological efficacy.

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1. Emulsifiable Concentrates (EC / E)

An Emulsifiable Concentrate (EC or E) is a liquid formulation consisting of an oil-soluble active ingredient dissolved in one or more petroleum-based organic solvents, combined with a synthetic emulsifying agent (emulsifier). Because oil and water are naturally immiscible, the emulsifier—a specialized surfactant with both lipophilic (oil-attracting) and hydrophilic (water-attracting) molecular regions—enables the solvent droplets containing the pesticide to disperse evenly throughout water carrier.

+-----------------------------------------------------------------------------+
|                   EMULSIFIABLE CONCENTRATE (EC) DISPERSION                  |
|                                                                             |
|   [ CONCENTRATE IN BOTTLE ]              [ DILUTED IN WATER TANK ]          |
|   +-----------------------+              +-----------------------+          |
|   | Petroleum Solvent     |              | Water Carrier         |          |
|   | + Active Ingredient   |   + Water    | + Micro-droplets of   |          |
|   | + Emulsifier (Clear)  | -----------> |   Oil Suspended       |          |
|   | (Clear Amber Liquid)  |   Agitation  | (Opaque Milky Emulsion|          |
|   +-----------------------+              +-----------------------+          |
+-----------------------------------------------------------------------------+

Physical Behavior & Appearance

• When poured into a water-filled spray tank, an EC spontaneously forms a milky white, opaque emulsion.
• Unlike true solutions, an emulsion is a suspension of tiny liquid oil droplets within water. Once thoroughly mixed, it requires only minimal agitation to prevent phase separation (oil floating to the surface) during brief operational pauses.

Operational Advantages

• High Active Ingredient Concentration: Typically contains 2 to 8 pounds of active ingredient per gallon, reducing container volume and shipping costs.
• Ease of Handling: Easy to measure volumetrically and pour; readily disperses in water.
• Non-Abrasive: Contains no abrasive mineral particles, causing minimal mechanical wear on pump impellers, pressure regulators, and spray nozzle orifices.
• Invisible Residue: Leaves little to no visible chalky residue on treated crops, ornamental plants, or structural surfaces.

Hazards, Equipment Risks & Disadvantages

• Elevated Dermal Absorption: The organic petroleum solvents dissolve the natural protective lipids and oils in human skin, accelerating the transdermal absorption of the toxic active ingredient into the bloodstream. Handlers must wear chemical-resistant gloves (barrier laminate, nitrile, or Viton) and eye protection.
• Phytotoxicity Risk: Petroleum solvents are inherently phytotoxic to sensitive plant foliage. Applying EC formulations during high ambient temperatures (>85°F to 90°F) or intense sunlight significantly increases the risk of leaf scorch and foliar burn.
• Equipment Degradation: Solvents cause rapid swelling, softening, and structural degradation of natural rubber hoses, neoprene seals, Buna-N gaskets, and plastic tank fittings.
• Flammability & Odor: Many EC formulations have low flash points and release strong petroleum fumes, requiring storage in ventilated, fire-resistant chemical storage facilities.

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2. Solutions (S) and Soluble Liquids (SL / LC)

A Solution (S) or Soluble Liquid (SL / LC) consists of a substance that dissolves completely in a liquid carrier (typically water or a water-miscible solvent). In a true chemical solution, the active ingredient molecules disperse evenly at the molecular level, creating a homogenous, single-phase liquid.

+-----------------------------------------------------------------------------+
|                      TRUE SOLUTION (S/SL) CHARACTERISTICS                   |
|                                                                             |
|   +-----------------------+              +-----------------------+          |
|   | Soluble Liquid (SL)   |   + Water    | Clear, Transparent    |          |
|   | Active Ingredient     | -----------> | Single-Phase Solution |          |
|   | Dissolved in Water    |   Stir Once  | (Molecules Never Settle|         |
|   +-----------------------+              +-----------------------+          |
|   * No agitation required once mixed     * Zero nozzle abrasion             |
+-----------------------------------------------------------------------------+

Physical Behavior & Handling

• Visual Clarity: Forms a completely clear, transparent liquid when diluted in water (though dyes may impart color, the mixture is never cloudy or milky).
• Agitation Requirements: Requires initial thorough mixing. Once dissolved, the active ingredient never settles out or separates, eliminating the need for ongoing agitation during spraying.
• Equipment Impact: Completely non-abrasive to pumps, pressure regulators, and nozzles. Will not clog fine mesh line strainers (100-mesh) or nozzle tips.
• Disadvantages: Soluble liquids formulated with water carriers are prone to rapid leaching through porous sandy soils into groundwater aquifers if applied before heavy rainfall.

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3. Flowables (F / L) and Suspension Concentrates (SC)

Many pesticide active ingredients are solid crystalline chemicals that are insoluble in both water and organic petroleum solvents. To formulate these compounds as liquids, manufacturers mill the solid active ingredient into an ultra-fine dry powder (typically 1 to 5 microns) and suspend it in an aqueous liquid base containing wetting agents and thickeners, producing a Flowable (F), Liquid (L), or Suspension Concentrate (SC).

+-----------------------------------------------------------------------------+
|                   FLOWABLE / SUSPENSION CONCENTRATE (F / SC)                |
|                                                                             |
|   +-----------------------+              +-----------------------+          |
|   | Viscous Liquid Base   |   + Water    | Solid Insoluble       |          |
|   | + Finely Milled Solid | -----------> | Particles Suspended   |          |
|   |   Active Ingredient   |   Continuous | In Water Carrier      |          |
|   | (Thick Like Cream)    |   Agitation  | (Requires Agitation!) |          |
|   +-----------------------+              +-----------------------+          |
|   * Settles into dense sludge if agitation stops; highly abrasive to brass   |
+-----------------------------------------------------------------------------+

Physical Behavior & Handling

• Viscosity: Supplied as a thick, viscous liquid resembling heavy cream or liquid paint. Must be shaken thoroughly prior to measuring.
• Dilution: Forms a cloudy, opaque physical suspension of solid particles dispersed in water.
• Agitation Mandate: Requires continuous, moderate mechanical or hydraulic agitation. If agitation stops, the dense solid particles settle to the bottom of the tank, forming a hard, compacted sludge layer that is exceptionally difficult to re-suspend.

Abrasiveness & Equipment Wear

Because Flowables and Suspension Concentrates contain millions of microscopic mineral/chemical solid particles, they act as an abrasive slurry under high pressure. They cause rapid erosive wear on soft metal nozzle tips (brass and aluminum) and pump rollers. Applicators spraying flowables should utilize hardened stainless steel, ceramic, or polymer nozzle tips.

+-----------------------------------------------------------------------------+
|                      NOZZLE MATERIAL WEAR RESISTANCE                        |
|                                                                             |
|   Brass         [====]                          (Fastest wear / Low life)   |
|   Aluminum      [======]                        (Poor wear resistance)      |
|   Polymer       [================]              (Good wear resistance)      |
|   St. Steel     [========================]      (High wear resistance)      |
|   Ceramic       [========================================] (Maximum life)   |
+-----------------------------------------------------------------------------+

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4. Microencapsulated Formulations (ME / CS)

A Microencapsulated formulation (ME or Capsule Suspension, CS) consists of liquid or solid active ingredient encased inside microscopic plastic or polymer capsules (5 to 50 microns in diameter), suspended in an aqueous carrier liquid.

+-----------------------------------------------------------------------------+
|                    MICROENCAPSULATED (ME / CS) FORMULATION                  |
|                                                                             |
|              +-----------------------------------------------+              |
|              |            POLYMERIC CAPSULE WALL             |              |
|              |      (Permeable plastic shell breakdown)      |              |
|              |                                               |              |
|              |         +---------------------------+         |              |
|              |         |     ACTIVE INGREDIENT     |         |              |
|              |         |  (Slow, timed-release     |         |              |
|              |         |   diffusion over days/wks)|         |              |
|              |         +---------------------------+         |              |
|              |                                               |              |
|              +-----------------------------------------------+              |
|                                                                             |
|   * Size (10-30 microns) mimics pollen grains -> Extreme honey bee hazard!  |
+-----------------------------------------------------------------------------+

Mode of Action & Advantages

• Controlled Residual Release: Once sprayed onto target surfaces, the water carrier evaporates, leaving the microcapsules behind. The active ingredient slowly diffuses through the capsule walls or is released as the polymer shell degrades from sunlight and moisture, providing weeks of extended residual pest control.
• Reduced Handler Toxicity: The polymer barrier encapsulates the chemical, significantly lowering dermal toxicity and odor during mixing and loading operations.
• Reduced Volatilization: Prevents volatile active ingredients from vaporizing into the atmosphere in hot weather.

The Critical Honey Bee Toxicity Hazard

[!WARNING] Critical North Carolina Exam Concept: ME Pollinator Hazard The physical size of microencapsulated capsules (10 to 30 microns) is virtually identical to natural floral pollen grains. Foraging honey bees (Apis mellifera) pick up microcapsules via electrostatic charges on their body hairs, pack them into their pollen baskets (corbiculae), and transport them directly back to the hive. Once inside, nurse bees feed the contaminated "pollen" to the queen, developing larvae, and brood, resulting in catastrophic colony collapse. ME formulations must NEVER be applied to blooming crops, weeds in bloom, or during active pollinator foraging hours.

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5. Ultra Low Volume (ULV) Formulations

Ultra Low Volume (ULV) concentrates are specialized liquid formulations containing near-100% active ingredient (often 80% to 95%+ a.i.). They are designed to be applied at extremely low volumes—often fractions of a pint to one-half gallon per acre—in their pure, undiluted state without water carrier.

Application Dynamics & Hazards

• Specialized Equipment: Requires specialized rotary atomizers or cold-fog aerosol generators engineered to produce uniform, microscopic droplets (10 to 30 microns).
• Use Cases: Commonly used in aerial and truck-mounted public health vector control (mosquito eradication) and specific rangeland/forestry treatments.
• Severe Drift & Inhalation Hazards: Because droplets are microscopic and water is not present to weight them down, ULV droplets remain suspended in the air for extended periods, creating extreme inhalation hazards for applicators and bystander drift risks.
• Solvent Aggressiveness: High chemical concentration quickly corrodes standard spray equipment, degrading plastic tanks, sight gauges, and rubber hoses.

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6. Comprehensive Liquid Formulations Comparison Matrix