Using Activated Charcoal to Inactivate Agricultural Chemical Spills

Prepared by:
Fred H. Yelverton
Crop Science Extension Specialist

Jerome B. Weber
Professor of Crop Science

Gerald Peedin
Crop Science Extension Specialist

W. David Smith
Crop Science Extension Specialist

Published by: North Carolina Cooperative Extension Service

Publication Number: AG-442

Last Electronic Revision: March 1996 (JWM)

Farmers as well as the general public are concerned about the effects of pesticides on the environment. At the sarne time, the agricultural community realizes that pesticides are uital for consistent profitableproductionofreliable, safe, high-quality agricultural commodities.

Large quantities of pesticides are handled by farmers and farm workers; thus pesticide accidents may occur, euen when the most stringent safety guidelines are followed. If a pesticide spill occurs, proper corrective measures can help prevent environmental contamination of soil and water resources.

Inactivating Pesticide Spills

If a pesticide is spilled accidently, if the wrong pesticide is applied, or if a pesticide is applied at an excessive rate, the best solution is to apply a material that will adsorb or inactivate the pesticide. Once the pesticide has been adsorbed, it is biologically inactive and cannot cause environmental contamination by running off in surface waters or leaching into groundwater. Activated charcoal (activated carbon) is the universal adsorbing material for most pesticides. Powdered activated charcoal is made up of very small carbon particles that have a high affinity for organic chemicals such as pesticides. Activated charcoal has a large surface area to which organic molecules can bind. When it is applied to pesticide-contaminated soil, the pesticide molecules are attracted to the charcoal particles and bind to them when they come into contact.

The amount of activated charcoal to apply to a pesticide-contaminated area varies with the chemical characteristics of the particular pesticide. The rate ranges from about 100 to 400 pounds of activated charcoal per acre (2.3 to 9.2 pounds per thousand square feet) for each pound of active ingredient of a pesticide applied per acre. A general rule is to apply about 200 pounds of activated charcoal per acre (4.6 pounds per thousand square feet) for each pound of pesticide active ingredient per acre. For example, if trifluralin (Treflan 4EC) was inadvertently applied to an area at a rate of 1 quart per acre, there would be 1 pound of active ingredient of trifluralin per acre (Treflan contains 4 pounds of active ingredient per gallon and 1 quart is 1/4 gallon, so each quart contains 1 pound). To completely inactivate this area you would need to broadcast apply 200 pounds of activated charcoal (see Table 1 for conversion to square feet). Your county Extension agent can assist you in determining a rate of activated charcoal to apply to a given area.

Activated charcoal can be applied by various methods. It can be applied in the dry form with a lime spreader. However, activated charcoal particles are easily moved by wind, so it may be difficult to distribute the charcoal evenly when applied in the dry form. The easiest method is to suspend the charcoal in water and apply it by hand with a watering can (for small areas) or a power sprayer. Because activated charcoal does not mix easily with water, use a 0.5 percent solution of a nonionic surfactant (equivalent to 1 quart per 50 gallons) to enhance its suspension in the water. Note that charcoal particles are very brasive and can damage spray equipment (paricularly roller type pumps).

Table 1. Conversion from Pounds of Activated Charcoal Per Acre to Pounds of Activated Charcoal Per Thousand Square Feet
Rate of Activated Charcoal (pounds per acre) Charcoal Needed (pounds per 1,000 square feet)
100 2.3
100 4.6
100 9.2
100 18.4
100 36.7
100 73.5

The activated charcoal should be incorporated with a disk or rototiller into the upper few inches of soil so that the activated charcoal will come into contact with the pesticide. Uniform application of activated charcoal followed by thorough mixing is the key to inactivating a pesticide-contaminated area.

On many farms, pesticide levels in soils are quite high in areas where pesticides are mixed. Unfortunately, most mixing occurs close to a water source, and usually in the vicinity of a well. often, pesticides have been mixed in these areas for many years and soil concentrations have accumulated over time. These areas are distinguishable by dead or dying vegetation or the absence of any livingplants. High pesticide levels in soils close to a well can be hazardous because of the high probability that groundwater or well water will be contaminated.

Activated charcoal can also be used to clean up these areas. However, it is impossible to determine the levels of pesticide residues in the soil. In this area, as well as in the case of some pesticide spills, soil pesticide levels may exceed 50 to 100 pounds of active ingredient per acre. Fortunately, these areas usually total only a few hundred square feet. To treat these areas, it is necessary to measure the contaminated area, guess at the level of pesticide residue, and adjust the activated charcoal rate accordingly. If pesticides have been mixed on the site for many years and no living vegetation is visible, assume that the level of contamination is higher than if some living vegetation is visible but shows symptoms of injury or disease . For example, if the contaminated area is 20 feet by 20 feet (400 square feet) and you assume that the pesticide level in the soil is equivalent to 50 pounds per acre, you would need to apply the activated char coal at a 10,000-pound-per-acre rate in order to apply 200 pounds of charcoal per pound of active ingredient. For a 400-square-foot area, you would need to apply and incorporate only 92 pounds of activated charcoal.

Applying too much activated charcoal should not cause problems, and it is therefore always best to guess on the high side . A few weeks after applying the charcoal, plant some type of seed in the treated area. If the seeds germinate and plants look healthy several weeks later, the pesticide spill has been inactivated. If plants still do not grow, the area may need to be retreated.

Activated charcoal is manufactured by many companies, such as ICI Americas, Inc. and West Virginia Pulp and Paper Company. It is available through your local agricultural chemical dealer. Two commonly used agricultural carbons are Gro-Safe (ICI Americas) and NuChar S-A (Westvaco). Activated charcoal usually costs about $1 per pound or less. Contact your local agricultural Extension agent for more information and for assistance in determining rates and sources of activated charcoal.

The use of brand names in this publication does not imply endorsement of the products or services named or aiticism of similar ones not mentioned.

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

AG 442