What Information can you give me on how the composting process affects antibiotics in manure and soil amendments?
Answer: Thank you for your recent request for information from ATTRA, the National Sustainable Agriculture Information Service. I am pleased to provide you with information on the resistance of antibiotics and hormones to the composting process and if they are present in animal-based soil amendments.
Many feedstock materials used in the composting process contain chemicals and heavy metals. There are many published studies that have looked into the impacts composting has on heavy metals and chemicals, including pharmaceuticals and pesticides. Research has repeatedly shown that pharmaceuticals break down in compost if the compost is properly managed for moisture, oxygen, temperature, and a good carbon-nitrogen balance. Yet small levels may still exist after composting and may be taken up by plants; eventually posing a treat for food and groundwater supplies. Some antibiotic levels are actually produced by compost microorganisms.
One study that I have read examined the ability of compost to break down ten pharmaceutical and personal-care product residues in biosolids collected from a wastewater treatment plant. The results found that composting for 45 days reduced residues of nine out of ten products by at least 85 percent. Another study performed by the USDA’s Agriculture Research Service, in 2005, found that composting reduced the incidence of estrogen (17B-estradiol) and testosterone in chicken manure by 84 to 90 percent in 139 days. Scientists concluded that the rate of hormone degradation is affected by how well the compost is aerated, and by the moisture level, porosity and particle size of the compost.
Time is another key variable in the reduction of antibiotics and hormones through composting. Most commercial composting facilities compost for at least 60 days and some wait six to eight months. According to many states, you can meet EPA law in five days with in-vessel composting, or 15 days for other systems, but then you need to store it for 30 days as a safeguard.
With the exception of the standards set by the National Organic Program (NOP) for compost used in organic farming systems, national standards, regulated by the EPA, only exist for composts made from biosolids, or solids that have been treated by municipal wastewater treatment facilities. The EPA along with individual state standards for finished compost generally requires regular testing for heavy metals and pathogens. Tests for pharmaceutical compounds and pesticide residues are not required. Biosolids must meet these standards before the compost can be spread on fields or sold to wholesalers and retailers.
It is unclear as to whether or not antibiotics are present in soil amendments derived from animal by-products. I was unable to locate research regarding this topic. However, my thought is that any chemical residues in soil amendments may be targeted by soil microorganisms that activate the nutrients in the soil amendment. In other words, the soil microorganisms will break down residues once the amendments are incorporated into the soil. In addition, the processes of creating bone meal and blood meal may reduce levels of antibiotics and hormones present in the animal source. Bone meal involves steaming the bones to sterilize them, then crushing them into a meal. Whole blood meal is produced by spray drying the fresh whole blood from animal processing plants at low temperatures. The fresh blood is collected in cooling tanks that utilize agitation to prevent coagulation of the fresh blood. The whole blood is then centrifuged to remove foreign material and then circulated through a disintegrator to remove all remaining foreign particles.
Below is a list of a few studies that investigated antibiotic and hormone levels in compost. I have also included the NOP regulations for compost and manure applications (§ 205.203 Soil fertility and crop nutrient management practice standard). This standard also defines the use of animal by-products in organic production. The use of meat meal should fall under the standard on allowed materials for soil fertility. Relevant sections include 205.203( b), and (c)(i, ii, iii).
Rich, Deborah. 2007. “Questioning the Compost Supply Chain.” San Francisco Chronicle. May 5, F-5.
1). Here is a research project that indicated that antibiotics do degrade in compost. The interesting conclusion is that a pile of antibiotic laced manure, left alone to degrade without any manual management after the pile had been created, was just as effective in eliminating antibiotics as managed compost systems (compost that was turned weekly or compost that was maintained in a vessel).
Dolliver, Holly, Satish Gupta, and Sally Noll. 2008. "Antibiotic Degradation in Manure Composting". Journal of Environmental Quality. 37:3: p. 1245-1253.
2). Here's a study showing that antibiotics in manure can be taken up by plants when they are fertilized with animal manures containing the antibiotics. This is the use of raw manure, not compost:
Kumar, K., S.C. Gupta, S.K. Baidoo, Y. Chander, and C.J. Rosen. "Antibiotic Uptake by Plants from Soil Fertilized with Animal Manure." 2005. Journal of environmental Quality. 34:6 p: 2082-2085.
3). Here's another study using Oxytetracychne (OTC) - a broad-spectrum antibiotic used in livestock production. The OTC did not affect the composting process and within the first six days of composting, showed a 95% reduction.
§ 205.203 Soil fertility and crop nutrient management practice standard
(a) The producer must select and implement tillage and cultivation practices that maintain or improve the physical, chemical and biological condition of soil and minimize soil erosion.
(b) The producer must manage crop nutrients and soil fertility through rotations, cover crops and the application of plant and animal materials.
(c) The producer must manage plant and animal materials to maintain or improve soil organic matter content in a manner that does not contribute to contamination of crops, soil or water by plant nutrients, pathogenic organisms, heavy metals or residues of prohibited substances. Animal and plant materials include:
(1) Raw animal manure, which must be composted unless it is:
(i) Applied to land used for a crop not intended for human consumption;
(ii) Incorporated into the soil not less than 120 days prior to the harvest of a product whose edible portion has direct contact with the soil surface or soil particles; or
(iii) Incorporated into the soil not less than 90 days prior to the harvest of a product whose edible portion does not have direct contact with the soil surface or soil particles.
(2) Composted plant and animal materials produced though a process that:
(i) Established an initial C:N ratio of between 25:1 and 40:1; and
(ii) Maintained a temperature of between 131 and 170 degrees for three days using an in-vessel or static aerated pile system; or
(iii) Maintained a temperature of between 131 and 170 degrees for 15 days using a windrow composting system, during which period, the materials must be turned a minimum of five times.
(3) Uncomposted plant materials.
(d) A producer may manage crop nutrients and soil fertility to maintain or improve soil organic matter content in a manner that does not contribute to contamination of crops, soil or water by plant nutrients, pathogenic organisms, heavy metals or residues of prohibited substances by applying:
(1) A crop nutrient or soil amendment included on the National List of synthetic substances allowed for use in organic crop production;
(2) A mined substance of low solubility;
(3) A mined substance of high solubility, provided that the substance is used in compliance with the conditions established on the National List of non-synthetic materials prohibited for crop production;
(4) Ash obtained from the burning of a plant or animal material, except as prohibited in paragraph (e) of this section, provided that the material burned has not been treated or combined with a prohibited substance or the ash is not included on the National List of non-synthetic substances prohibited for use in organic crop production; and
(5) A plant or animal material that has been chemically altered by a manufacturing process, provided that the material is included on the National List of synthetic substances allowed for use in organic crop production established in §205.601.
(e) The producer must not use:
(1) Any fertilizer or composted plant and animal material that contains a synthetic substance not included on the National List of synthetic substances allowed for use in organic crop production;
(2) Sewage sludge (biosolids) as defined in 40 CFR part 503; and
(3) Burning as a means of disposal for crop residues produced on the operation except that burning may be used to suppress the spread of disease or to stimulate seed germination.
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