Chemicals Used for the Aerial Eradication of Illicit Coca in Colombia and Conditions of Application

The aerial spray mixture currently used in the U.S.-supported program of aerial eradication of coca in Colombia contains three components: water, an EPA-registered formulation of the herbicide glyphosate, and a surfactant (Cosmo-Flux 411F). These components are mixed together into a spray mixture in the following percentages: 55 percent water, 44 percent glyphosate formulation, and 1 percent Cosmo-Flux 411F (see Figure 1 below). This diluted mixture is applied to coca at the rate of 2.53 gallons per acre. This application rate is within the glyphosate manufacturer's recommendations for both the amount of concentrated formulation per acre and the amount of total spray volume per acre for woody plants and hard-to-control species. Coca is a hardy, woody bush that falls into this category.

Figure 1: Coca Spray Mixture

Commercial glyphosate formulation:

The commercial glyphosate formulation used in the spray mixture is registered with the U.S. Environmental Protection Agency (EPA) for sale in the United States for non-agricultural use and contains 41 percent glyphosate salt and 59 percent inert ingredients. Approximately three fourths of the inert ingredient content are water and the remainder is a surfactant blend. A surfactant is essentially a soap that enhances the ability of the herbicide to penetrate the waxy cuticle of the leaf surface. Surfactants are commonly used with herbicide formulations to improve the effectiveness of the product. This commercial glyphosate formulation used against coca is registered, produced, and sold in Colombia, where the State Department's Bureau of International Narcotics and Law Enforcement Affairs (INL) purchases it for the Government of Colombia (GOC) for use in the GOC's spray program. Further information on the chemical composition of this commercial formulation is proprietary and is retained by the manufacturer; it is not publicly available and the manufacturer has not provided it to the Department. Figure 2 is a breakdown of the commercial glyphosate formulation by major components.

 Figure 2: Commercial Glyphosate Formulation


From the standpoint of coca control, properly selected surfactants make the glyphosate far more effective than if the active ingredient were applied alone. Research by the United States Department of Agriculture's Agricultural Research Service (USDA-ARS) has demonstrated that certain surfactants enhance glyphosate penetration through the waxy cuticle on the coca leaf surface. Appropriate surfactants decrease the surface tension of the adhering spray droplet (causing them to spread further on the leaf surface). Generally, this is good, since the herbicide is less susceptible to runoff loss and greater surface coverage leads to more uptake of the herbicide. The "right" surfactant may form a chemical shield around small clusters (micelles) of the herbicide and enhance their penetration through the cuticle and into the leaf tissue.

In order to function, glyphosate must move from the site of application (the leaf surface) toward the actively growing meristematic tissue - the new shoot tips and the new roots. Here, the herbicide glyphosate finally does its job, blocking an enzyme that is essential for plant growth but absent from humans. Surfactants are a critical component of the herbicide mixture, allowing the glyphosate to reach this actively growing tissue in the coca plant. They may also stabilize the product droplets, reducing water evaporation, and thereby reducing spray drift.

The commercial glyphosate formulation used in the spray program contains 180g/l of surfactant as part of its inert ingredients. As noted above, USDA-ARS research in the greenhouse and in the field (in Colombia, Panama, and Hawaii) showed that commercial glyphosate formulations with surfactants performed better against coca than other glyphosate without surfactants. Nevertheless, when coca ground-truth verification (see "Eradication Oversight" section below) was first done in October 1997, ratings showed mean control of coca within aircraft spray swaths to be about 70%. This was considered unacceptably low, since the goal was to eliminate the illicit crop and force the growers to abandon further coca production. To improve swath control, USDA-ARS scientists recommended two options, not mutually exclusive. One was to increase the level of glyphosate formulation in the spray mixture. The second was to add an additional surfactant to boost control without necessarily requiring a higher dose of herbicide. Previous USDA research had explored possible surfactants, not available in commercial glyphosate formulations, that might enhance phytotoxicity against coca. Several candidates that enhanced herbicide "efficacy" were selected by the GOC for further consideration.

In consultation with the GOC's Environmental Auditor to the spray program, USDA-ARS scientists recommended that any product to be added to the herbicide tank mixture be acquired from a Colombian source, if possible. This would ensure that it was a product already registered by the appropriate GOC regulatory authority, the Colombian Farming and Livestock Institute (Instituto Colombiano Agropecuario, or ICA), and almost certainly already used in Colombian agriculture. Cosmo-Flux 411F was selected as the additional surfactant because it met the above requirements and most closely matched the most effective U.S. products that had been tested by the USDA-ARS in Beltsville and Hawaii as additives to glyphosate for use against coca.

Cosmo-Flux 411F:

Cosmo-Flux 411F is manufactured in Colombia by a private company. Its use in Colombia is not limited to the GOC's eradication program - Cosmo-Flux 411F is often used as an additive to herbicide sprays for manual and aerial application to crops. Cosmo-Flux 411F is approved for use with herbicides and is registered with the ICA under ICA's lowest toxicological risk category, Category IV - "lightly toxic." The Colombian Ministry of Health has also classified Cosmo-Flux 411F as "slightly toxic" (in opinion No. LP-0573/1993). The active components of Cosmo-Flux 411F are polyol fatty acid esters and polyexothylated derivatives, which are seventeen percent of the product. The remaining 83 percent is made up of inert liquid isoparaffins.

Cosmo-Flux 411F is produced, sold, and purchased for the GOC in Colombia but is not sold in the United States. The EPA Office of Pesticide Programs does not regulate Cosmo-Flux 411F - or other adjuvant products not labeled as pesticides. EPA, however, regulates the use of such adjuvant chemicals if they are purposefully formulated with and are a part of manufactured pesticide products for use in the U.S. - a common practice. INL asked the EPA's Office of Pesticide Programs to review the complete chemical constituents of Cosmo-Flux 411F to learn what EPA knew about the ingredients so that INL could better assess safety concerns related to the use of this product in the spray program. EPA determined in September 2001 that all of the ingredients of Cosmo-Flux 411F are exempt under 40 CFR 180.1001 from the requirement of tolerances when included in pesticides applied to food, feeds, and livestock. That information reconfirmed the GOC's conclusion that Cosmo-Flux 411F was appropriate for use against coca in Colombia. The Colombian manufacturer of Cosmo-Flux 411F recommends its use in a dose ranging from 0.5 to 1.5 percent. The illicit crop eradication program's use of a spray mixture that is 1 percent Cosmo-Flux 411F is thus within the manufacturer's recommendation.

Figure 3 illustrates the components of the final spray mixture by percentage. Water makes up approximately three quarters of the mixture, a fact that substantially reduces the toxicity of the other ingredients. Glyphosate salt (ispropylamine salt) is the second leading ingredient at 18% of the spray mix. Finally, the surfactants (those within the commercial glyphosate formulation plus Cosmo-Flux 411F) make up approximately 8 percent of the mixture.

Figure 3:  Final Coca Spray Mixture

Spray mixing and handling:

The commercial glyphosate formulation, Cosmo-Flux 411F, and water are mixed at forward air bases by mixers/loaders who are members of the Colombian National Police (CNP). The mixers/loaders are trained by the CNP, the U.S. Embassy's spray advisor, and by designated spray pilots. They are trained on the relevant precautions for handling the chemicals in the spray mixture, first aid, and use of personal protective equipment that applicators and other handlers of glyphosate in its concentrated formulation must wear. These include long-sleeved shirts and long pants, waterproof gloves, shoes and socks, and protective eyewear.

Storage and disposal of spray mixture:

Special care is taken in the management of the commercial glyphosate formulation, which is more concentrated than the spray mixture. Appropriate measures are taken to ensure that glyphosate is not allowed to contaminate water, foodstuffs, or natural areas through its storage or disposal. Storage is in manufacturer-approved plastic barrels in covered areas with good ventilation, away from water sources. At the main spray bases, chemical storage is in a concrete storage shelter approximately 50 centimeters high with a 10-degree incline for the collection of any residues. In addition, sawdust, sand, dirt, clay or other absorbent material is readily available for immediate use in case of glyphosate spills. A drainage system, designed to prevent water contamination via run-off or leaching into the ground, collects water storage, mixing, and loading areas in trenches that carry it to a stabilization pools, which are eventually discharged into a specially selected lot to facilitate natural degradation.

Aircraft and spray equipment:

Aviators currently spray coca with the single-engine T-65 "Thrush" aircraft built by the Ayers Corporation for agricultural spray operations and with the twin-engine OV-10D "Bronco" aircraft converted from a military observation aircraft to an aerial spray aircraft. INL is currently taking delivery of a third type of spray aircraft, the Air Tractor AT-802, which is a single-engine agricultural spray aircraft similar to the T-65.

The spray nozzles are standard, agricultural nozzles selected and adjusted to minimize the number of small droplets that can drift downwind from a sprayed coca field. These nozzles produce a volume mean diameter (VMD) between 300-1,500 microns. This droplet size was reached after considerable INL and USDA testing and is consistent with the label instructions recommending coarse sprays that are less likely to drift. The aircraft spray systems are electronically calibrated to disperse a specified quantity of gallons of spray mix per hectare, compensating for variances in ground speed. These are calibrated upon installation and are checked each day during the mechanic's daily inspection and the pilot's preflight inspection. In addition, during actual spray operations the pilot monitors the spray system by observing the readings of the spray pressure and the spray flow rate gauges. Onboard computer and digital global positioning systems (D/GPS)-driven equipment (SATLOC and Del Norte) automatically record each aircraft's actual flight parameters, including differential-GPS track, airspeed, altitude (mean sea level), application rate, and precise geographic location (longitude and latitude coordinates) at the time of aspersion. This allows precise evaluation of each spray event in order to ensure that spraying is conducted within proper target areas and within specified parameters. As part of the end-of-mission check, the mission planner and pilots review the spray logs for any inconsistencies in the recorded spray data.

Spray pilots:

Eradication pilots must have approximately 3,000 total flight hours before they are considered for the spray program and can receive preliminary training in illicit crop eradication. Most of these pilots also have at least 1,500 hours of commercial aerial application (crop dusting) experience. The INL Air Wing contractor trains the spray pilots who are Colombians, third-country nationals, and U.S. citizens. Eradication training focuses extensively on the visual identification of coca fields from the air as well as the technical aspects of crop spraying.


Detailed aerial reconnaissance of cultivation areas precedes all spray missions. Aerial reconnaissance is performed using a multispectral digital imaging system (MDIS) that identifies crop type through the reflected sunlight in the infrared portion of the electromagnetic spectrum. This airborne camera system is calibrated daily and linked to global positioning systems (GPS) equipment that enables fields to be geo-referenced and accurately plotted onto aviation maps for mission planning purposes. As explained below, this equipment is for mission planning and reconnaissance and is not in any way a substitute for positive visual identification of coca fields by the spray pilot during the actual spray mission.

Most of Colombia's coca crop is cultivated in the lowlands east of the Andes; here, the terrain is generally flat or marked by gentle, rolling hills. The more agile T-65 is used for spraying in areas with steeper topography. Coca is often grown in monocrop fields cut out of the triple canopy rainforest of the Amazon Basin. In this context the precision of the pilots is crucial, as is the use of a herbicide mixture that allows for rapid restoration of natural vegetation once the coca has been killed. The reemergence of native vegetation occurs very quickly after glyphosate application, ensuring that soil erosion will be minimal.

Spray parameters:

Spraying is conducted in Colombia under rigid parameters laid out by the GOC's Environmental Auditor to the spray program. Missions are cancelled if wind speed at the airport is greater than 10 m.p.h., if relative humidity is below 75 percent, or if temperature is over 32� Celsius (90� Fahrenheit) - to avoid drift that might come from a temperature inversion. Spray missions are planned so as to avoid spraying wet coca; the goal is to have no rain on the targeted fields from two hours before to four hours after the spraying. Spraying most often takes place in the morning when weather conditions are favorable in the spraying area, although spraying can take place any time of day when the above conditions are satisfied. Poor atmospheric conditions often are the cause of mission cancellations. For example, in 1998 and 1999, spraying took place on an average of 125 days out of the year. During the other 240 days, the spray planes were grounded, with the majority of cancellations due to bad weather.

While flight lines are programmed using the reconnaissance procedures outlined above, pilots are instructed and trained to activate their aircraft spray systems only when they have positively identified coca directly in their spray line. Spray planes are under continual risk from hostile ground fire, yet the pilots spray as low over the coca fields as obstacles (e.g. trees) and security conditions will permit. The altitude above spray targets while spraying is normally less than 100 feet. Under the conditions in which the aerial eradication program is carried out in Colombia, spray pilots face great risks. Over the seven years of the aerial coca eradication program in Colombia, three spray pilots have lost their lives by striking their aircraft against the ground or trees while trying to spray as close to the illicit crop as possible.

The pilot of each eradication aircraft is responsible for deciding when damage to non-target foliage is likely to occur and to take every measure to avoid such collateral damage and spray only within the boundaries of the coca field. Pilots are licensed and trained to be conscious of wind direction and speed during spray operations to avoid unintentional damage to any legal crops. According to Colombian law, food crops that are interspersed with coca are subject to spraying. Nonetheless, great care is taken to avoid spray damage to legal crops and the spraying of any area that does not contain coca. While every effort is made to minimize human and mechanical mistakes, occasional errors are unavoidable. The GOC has implemented improved procedures to investigate claims of spraying of legal crops and to compensate owners if damage is found to be credible.

Spraying and human and environmental health:

Glyphosate is one of the most widely used agricultural herbicides in the world. It has been tested extensively in the United States, Colombia, and elsewhere. EPA approved glyphosate for general use in 1974 and re-registered it in September 1993. In its latest comprehensive review of studies on glyphosate, the EPA concluded that proper use of glyphosate, as permitted in the U.S., would not cause unreasonable adverse effects in humans or the environment.

The product label advises that the concentrated formulation of the glyphosate product causes irreversible eye damage, is harmful if swallowed or inhaled, and may cause skin irritation. These precautionary statements are determined according to EPA policy and are based on the results of testing on laboratory animals. INL does not believe that the spray program exposes humans who may be present in a sprayed field to such risks. This is because the irritation and toxicity potential of the individual ingredients are reduced when diluted during mixing (the final product is approximately 75 percent water) and the mixture is dispersed when sprayed. Thus humans who may be present under the swath of the plane are not exposed to levels that approach the commercial glyphosate formulation in its concentrated, undiluted form. The symptoms of such exposure are likely to be short-term and reversible. Furthermore, any one individual field is unlikely to be sprayed more than one time in a year, lowering the levels of repeated potential human exposure.

To minimize human exposure to the spray mixture, pilots are instructed to avoid flights over towns and populated areas and, during spray missions, to avoid spraying near people, homes, or occupied buildings.

Studies on livestock (cows, goats, and chickens) show livestock absorb limited amounts of glyphosate. Permitted levels of glyphosate in/on crops and livestock for human consumption are published in the Code of Federal Regulations, Title 40 (40 CFR), Section 180.364. EPA has concluded that consumption of crops treated with glyphosate and livestock fed with forage treated with glyphosate in the U.S. does not pose a dietary concern when residues are below these published tolerances. With respect to environmental impact, EPA concluded, based on required and available scientific studies, that glyphosate is not persistent in soil, does not build up after repeated use, and is biologically degraded over time by soil microbes. Because it binds tightly with the soil, glyphosate is unlikely to leach into underground drinking water. These qualities make glyphosate a well-suited herbicide for use against coca in Colombia.

Studies have shown glyphosate itself to be "practically non-toxic" to fish, however some glyphosate end-products may contain other ingredients that may increase the toxicity to fish when they are exposed. In accordance with the instructions on the product label, pilots are instructed to avoid all bodies of water when spraying coca. 

Eradication oversight:

Spray pilot oversight is carried out by several entities. Pilot performance is monitored by the GOC's Environmental Auditor, the Colombian National Police (CNP), INL's Office of Aviation, the Narcotics Affairs Section (NAS) of the U.S. Embassy, Department of State contractor personnel, USDA weed scientists, and the GOC's National Directorate of Dangerous Drugs. The Environmental Auditor, the CNP, and the contractor personnel are continually on-site in the bases or airports from which the spray planes operate and in most cases accompany the spray missions themselves. All of the above-mentioned offices actively participate in the ground truth verification of randomly selected, previously sprayed fields. These verifications usually take place twice a year. During this process, one of the important elements is an assessment of potential overspray or non-target drift, essential indicators of spray pilot (and herbicide) precision. These ground truth verification missions have found very few instances of spray pilot error and have reported that pilot accuracy is excellent and overspray minimal.

Unfortunately, human and mechanical error is possible and mistakes are made on occasion. In the past, many complaints of erroneous spraying of legal crops have proven groundless after subsequent investigation. However, INL believes that the credibility of the spray program is enhanced by a speedy and fair review of all complaints and by just compensation for any legal crops that were indeed sprayed in error. With support from the United States, the GOC's process of investigating harm to legal crops has recently been improved to provide for faster investigation and resolution of complaints.