Research Accomplishment Reports 2010

Fate, Transport, and Ecological Effects of Livestock Antibiotics in Manure-Amended Agroecosystems

E. D'Angelo
Department of Plant and Soil Sciences

 

Non-Technical Summary

Arsenic and other antibiotics are widely fed to broiler chickens, and high concentrations of these compounds are commonly found in poultry litter. While poultry litter is considered a valuable fertilizer source when applied to agricultural soils, repeated and intense applications of litter can also contaminate surface and groundwater with arsenic and other livestock antibiotics, which poses health risks to people living in areas where poultry manure is used as a soil amendment. Little is known about the factors that regulate the occurrence and effects these compounds in the environment (e.g. bacterial diversity, development of antibiotic resistant bacteria, carbon and nutrient cycling, etc.).

Under certain environmental conditions, human and animal pathogens can acquire antibiotic resistance by genetic mutation and gene transfer from ARB. Objective 1 of this project will show whether livestock antibiotics affect soil bacteria diversity at different topographic positions (soil catenas) in the landscape. Results from this project will be useful for making improved management decisions about when and where to apply manure in order to maximize the benefits and minimize the ecological/health risks. Thus, the proposed research has a direct impact on both production agriculture and natural resource management in Kentucky and the nation.

Information about As levels and speciation in poultry manure determined in Objective 2 is critical for assessing health risks associated with applying large amounts of manure to the environment.

Information about the effect of tillage and manure application timing on As migration to the subsurface as addressed in Objective 3 would be useful for (i) predicting the fate and ecological effects of As and (ii) developing widely applicable best management practices that will maximize the benefits and minimize the health/ecological consequences of land application of manure wastes.

Results from the project will be disseminated through several outlets in order to inform scientists, Kentucky agricultural producers, and the public about the ecological and health consequences of applying poultry manure with As to agricultural fields. Results from the project will be (i) published in two refereed scientific journals, (ii) published as a Ph.D thesis, (iii) presented at local, regional, and national scientific conferences (e.g. American Society of Agronomy), (iv) published as two extension publications (e.g. Soil Science News and Views) and (v) posted on the extension Plant and Soil Sciences department web site.

2010 Project Description

Mentored graduate student who conducted research to investigate the effect of antibiotics on nitrogen cycling and microbial community composition in soils.

2010 Impact

A large portion of antibiotics that are commonly fed to poultry at subtherapeutic levels are excreted in manure and are found in the litter. Most of the litter is land applied, so there is interest in determining whether antibiotics in this material affect microbially-mediated nutrient transformations in soils. To test this possibility, a series of experiments were undertaken to determine the level at which the three antibiotics would have adverse effects on nitrification, denitrification, microbial growth and community composition in nine soils collected along a topographic gradient.

It was discovered that bacitracin did not inhibit nitrification in the soils at any concentration up to 500 mg/kg compared to the zero level control. Roxarsone inhibited nitrification at >150 mg/kg in the shoulder and back slope positions and at 500 mg/kg at all the positions, but not at lower concentrations. Virginiamycin inhibited nitrification at >5 mg/kg in the shoulder, >15 mg/kg at backslope and >50 mg/kg at all positions. Bacitracin inhibited denitrification at 500 mg/kg soil, however, virginiamycin and roxarsone did not inhibit denitrification at concentrations up to 500 mg/kg. Bacitracin did not affect any of the 60 FAMEs compared to the zero level control. Roxarsone and virginiamycin at 1 mg/kg also did not affect any of the FAMES. Roxarsone at 100 mg/kg, however, increased two monounsaturated FAMEs (16:1ω7 and 18:1ω7) and decreased one monounsaturated FAME (16:1ω9), and virginiamycin at 100 mg/kg increased two monounsaturated FAMES (16:1ω7 and 18:1ω7) and decreased branched monounsaturated FAME (i17:1ω7) and polyunsaturated FAME 26:0. Analysis of poultry litter revealed that it contains about 2, 50, and 0.33 mg kg-1 litter of bacitracin, roxarsone, and virginiamycin, respectively.

If litter with these levels of antibiotics were applied at the typical rate of 5 Mg litter/ha and 5 cm soil incorporation depth, then antibiotic concentrations in soils would be expected to range from 0.003-0.4 mg antibiotic/kg soil. Since these concentrations are far below those that affected nitrification, denitrification, and microbial community composition determined in this study, it seems unlikely that application of poultry litter with antibiotics would have a strong impact on these soil microorganisms and processes.

2010 Publications

M.S. THESIS Banerjee, S. Effects of three livestock antibiotics on nitrification, denitrification, and microbial community structure in soils along a topographic gradient. University of Kentucky. 2010.