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Management of Contaminants in Feedlot Waste: Development of realistic guidelines

Project FLOT.333 has undertaken an assessment of the risks from pathogens and chemicals in manures to exposed human populations and explored their fate and transport with a view to understanding the form and scale of risks and developing risk management recommendations for MLA reflecting this understanding. It has done this by: 

​ 1. Measuring the levels of contaminants within major/priority manure waste-streams at operational feedlots; 

2. Conceptualizing the hazards and the exposure pathways; 

3. Combining this information with dose response literature; 

4. Using risk models, which integrate this information, characterized the absolute and relative risks arising under a range of representative exposure scenarios;

5. Developing management recommendations designed to minimize risks consistent with the emerging exposure picture and current manner in which feedlots are operated. 

The exposure scenarios modelled reflect a review of the literature, the data collected on feedlot contaminant levels and their inactivation/decomposition during management, visits to feedlots to understand current waste management practice, a provisional exposure pathway assessment and conservative/balanced selection of input assumptions in the risk models constructed. The foci of the assessment were: 

1. Major feedlot waste streams likely to contain high loads of zoonotic pathogens and chemical contaminants: o fresh faeces; o pen manure; o harvested manure; o aged manure; o composted manure; o carcass compost; and o (secondarily) site run-off; 

​2. Priority contaminants identified in the initial literature review and via discussions with lot feeders as to their current operation practice comprised: 

o 10 zoonotic pathogens; 

o 5 bacterial indicators (not necessarily hazardous but having lifecycles indicative of pathogens); 

o 13 endocrine disrupting compounds (steroidal hormones); 

o 4 parasiticides; 3. Risks arising from aerosol and dust exposure (inhalation and ingestion) to the following populations: 

o On-farm workers; 

o On-farm visitors; 

o Off-farm users of waste products; 

o The public in situations where exposure appears most likely. 

The work program undertaken to underpin the risk assessment included the following activities: 

​1. A literature review to prioritize experiments and identify appropriate/logistically feasible assay techniques and other experimental methods: 

2. Contaminant assay development and adaptation in particular: 

a. Development of quantitative Polymerase Chain Reaction (qPCR) assays for measuring the abundance of pathogens and microbial indicators in wastes; 

b. Adaptation of established microbial culture assays used for indicators. 

c. Development of extraction methods and assays for the key trace organic compounds of concern. 

3. A survey of contaminant levels in major wastes: 

a. At 5 feedlots (3 in Queensland, 1 in NSW and 1 in Victoria); 

b. During two seasons (winter and summer); 

4. Measurement of the rate of inactivation (pathogens) or decomposition/disappearance (chemicals): 

a. in manures as a function of temperature(20, 37, 50 and 60 oC), over time (up to 4 months); 

b. in response to exposure to solar radiation (short term disinfection only); 

c. in situ(background levels); in microcosms (background levels); in microcosms (inoculated model microorganisms); 

d. in run-off ponds; 

5. Characterization of aerosols generated at feedlots during a relatively dry period (2 Feedlots, late spring 2009): 

a. measured at the centre of one feedlot virtually continuously over 4 days (treated as ambient particle content); 

b. measured immediately downwind of 29 different activities at 2 Feedlots generating aerosols on a small, medium and large scale. 

The management recommendations developed are based on a combination of hygiene first principles, risk probability estimates based on the new data outlined above, and discussion/observations/inspection of Feedlot operations.


Title Size Date published
947.7KB 01/06/2011
14.4MB 01/06/2011

This page was last updated on 07/07/2017

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