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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.
This page was last updated on 07/07/2017
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