Quantification and persistence of ionophore antimicrobials associated with poultry litter

Veterinary anticoccidials, biochemically known as ionophores are used in therapeutic and sub- therapeutic levels in animal feed, for prophylaxis and growth promotion. A significant amount of ionophores have been detected in animal manure like poultry, and surrounding soil and waters as reported in various literature. In our previous study on poultry manure, we quantified four ionophores, namely monensin, salinomycin, narasin and lasalocid at the range of 20-100 µg kg-1. Ionophores have been found to be toxic to different species of flora and fauna including humans. Case studies on poultry farm workers, report, ionophore toxicity at the range of 0.5-5 mg kg-1. Ionophores can also contribute to clinical antibiotic resistance in pathogens by different mechanisms including horizontal gene transfer. As ionophores have been identified as emerging contaminant from manure, contaminating agricultural soils and risking farmers’ health, it is important to study its mobility in soil for further risk assessment. A batch equilibrium study has been performed with a very commonly found ionophore in the mid-atlantic region, called monensin. We found monensin to be strongly sorbed to soil particles containing more clay and organic matter. Soil factors such as pH and CEC were strongly co-related with sorption. Distinct desorption pattern was also observed.

Introduction:

In the United States (USA) more than 11 X 106 kg year-1 of antibiotics are used at sub-therapeutic levels (Hansen et al., 2009c; Mellon et al., 2001). Macrolides, ionophores, and antibiotics are the most commonly used antimicrobials in poultry, dairy and swine production. Animal manure is commonly used as fertilizer in agriculture throughout the world, providing a beneficial reuse for waste from livestock production, which otherwise would be costly to dispose of. Manure can be beneficial to farmers as it helps to increase crop production, improving soil quality and fertility when the manure is land-applied for agricultural purposes. But other undesired constituents such as antimicrobials can also enter the environment with manure application. The United States Department of Agriculture – National Agricultural Statistics Service (USDA-NASS) estimated the amount of manure that was applied to hectares of cropland and pastureland in the USA, based on 2002 and 2007 Censuses of Agriculture. Data shows that poultry manure was applied to 8,94,2061 hectares of land, with more than 50 % of the application occurring in atleast twenty-three States. In the Mid-Atlantic States of Pennsylvania, Virginia, Maryland, and Delaware it is estimated that poultry manure was applied at the manure application rate of 5.71 Mg per hectare to more than 10,00,00 hectares. Broiler chicken (chickens raised for meat) production has increased from 11 billion kg in 1990 to close to 22 billion kg in year 2009. Proportionately, the value of production also increased for the poultry industry. For broilers, value of production increased from 15 billion dollars in 1999 to above 20 billion dollars in 2009 and for layers it increased from 5 million dollars in 1999 to 7 million dollars in 2008 as per the 2002 and 2007 Censuses of Agriculture by USDA-NASS data as illustrated in the Ag-Atlas maps. Thus huge amount of poultry are produced every year in the US and millions of dollars are involved in this poultry industry with increasing production rate. This is directly co-related to huge amount of poultry manure production that is used in different ways. The most popular use of poultry manure is land application as fertilizers. Significant quantities of antimicrobials have been found in manure-amended soils, plants grown in the soils, and associated groundwater, surface water, and sediments (Kim and Carlson, 2006; Kumar et al., 2005a). This implies that antimicrobials from the manure do get transported into various components of the agro-ecosystem and hence have a high potential of entering the food web (Chee-Sanford et al., 2009). Antibiotics are known to cause antibiotic resistance in bacteria including pathogenic bacteria that present a human health concern. As the potential risks of using antibiotics in animal feed are becoming well known the use of alternative antimicrobials such as ionophores are increasing. Poultry companies classify them as ‘non-antibiotic’ compounds, as they are not used as clinical drugs. This has led to some confusion as ionophores have been found to be toxic to non-target species, including soil dwelling flora and fauna, higher animals and even human beings (Dowling, 1992; Hansen et al., 2009c). Ionophores have been popularly used for many decades as anticoccidant in poultry feed, coccidia being a major parasitic disease. They are also used as feed additives in cattle as they increase efficiency in post ruminal digestion by altering rumen microbial population through ion transfers across cell membranes and also known to decrease methane emission from them, methane being a severe greenhouse gas (Russell 2002). Significant levels of ionophores ranging from 0.005 µgml-1 to 50.0 mgml-1 have been found in public waterways, sediments, and soils near confined animal feeding operations (Paginini 2005). There is acute lack of data regarding the use of ionophores like monensin in animal feed, along with, knowledge on their occurrence, fate and transport. There is little published data on the sorption and desorption characteristics of ionophores relative to soil properties. It is important to study the mobility and persistence of these ionophores in the agricultural soils so as to better assess the environmental risks associated with them. This will enable the farmers to improve the feed management practices, so that these compounds are not allowed to accumulate and persist in the agricultural environment. It will not only lead to reduction of environmental and health risks for farm workers exposed to ionophores, but also improve soil and water quality and conserve natural resources which in turn will improve the lives of farm communities. This project deals with determination of sorption and desorption characteristics of the most commonly found ionophore named monensin, in coastal plain soils; that will give mechanistic information about its mobility in the agricultural soil systems, where poultry manure is typically land applied. References: 1. Hansen, M., Krogh, K.A., Bjorklund, E., Halling-Sorensen, B. and Brandt, A. Environmental risk assessment of ionophores. TrAC Trends in Analytical Chemistry, 2009, 28, 534-542. 2.Mellon, M., Benbrook, C. and Benbrook, K.L. Hogging it- Estimates of antimicrobial abuse in livestock. Union of Concerned Scientists Publication, Cambridge, MA, USA, 2001. 3.Kim, S.C. and Carlson, K. Occurrence of ionophore antibiotics in water and sediments of a mixed-landscape watershed. Water Research, 2006, 40, 2549-2560. 4.Kumar, K., C. Gupta, S., Chander, Y., Singh, A.K. and Donald, L.S., Antibiotic Use in Agriculture and Its Impact on the Terrestrial Environment. In Advances in Agronomy; Academic Press; 2005; 1-54. 5.Chee-Sanford, J.C., Mackie, R.I., Koike, S., Krapac, I.G., Lin, Y.-F., Yannarell, A.C., Maxwell, S. and Aminov, R.I. Fate and Transport of Antibiotic Residues and Antibiotic Resistance Genes following Land Application of Manure Waste. J Environ Qual, 2009, 38, 1086-1108. 6.Dowling, L. Ionophore toxicity in chickens: a review of pathology and diagnosis. Avian Pathology, 1992, 21, 355-368. 7.Russell, J.B. and Houlihan, A.J. Ionophore resistance of ruminal bacteria and its potential impact on human health. FEMS Microbiology Reviews, 2003, 27, 65-74. 8.Paginini, European Food Safety Authority. In ESFA J; 2005; 77.