Management of Contaminants in Feedlot Waste: Development of realistic guidelines

Summary

Project B.FLT.0333 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.