Evaluating Pathogen Destruction In Road Kill Composting

BioCycle November 2006, Vol. 47, No. 11, p. 49

Composting appears to work well for managing road-killed deer, however, questions remain about the hygienic quality of the process and product as well as concerns about worker health.

Jean Bonhotal, Ellen Harrison and Mary Schwarz

OVER 25,000 dead deer – plus numerous carcasses of other animals such as raccoons, coyote and fox – are managed annually by the New York State Department of Transportation (NYSDOT). NYSDOT maintains and operates a 15,656 mile highway system of interstates, expressways and connectors which comprises about 15 percent of the state’s total of 111,000 miles of highway. The 25,000 dead deer do not account for deer killed on county and local roads that must be managed by local highway departments.

Disposal options for these carcasses are limited and appropriate disposal is expensive. Carcasses are often left by the road or dumped into low areas. Over the past several years, the Cornell Waste Management Institute (CWMI) has worked with dairy farms to manage mortalities through on-site static pile composting. Regional and local NYSDOT personnel have attended workshops and indicated interest in trying composting to manage road-killed deer. In response, composting of road-killed deer is being piloted at several NYSDOT facilities where it seems to be working well. However, questions remain about the hygienic quality of the process and product as well as concerns about worker health.

The effectiveness of inactivating patho-gens through composting is generally assessed by monitoring the reduction in indicator organisms. Salmonella and fecal coliform are the usual indicator organisms – organisms that the USEPA requires for evaluation of the hygienic quality of sewage sludges. It is widely recognized that the sensitivity of different pathogenic organisms to heat varies significantly and questions have been raised about the use of the current indicator organisms.

Evaluation of the effectiveness of static pile composting to inactivate pathogens in road-killed carcasses requires identification of the pathogens that might be present and analysis of their sensitivity to inactivation by heating. That, combined with time/temperature data from the compost piles, will provide the information needed to assess the hygienic quality of the compost product and help determine end use.

STATIC PILE COMPOSTING WITH WOOD CHIPS
There is a need to evaluate the effectiveness of static pile composting of mortalities bulked with wood chips. Wood chips are an appropriate and easily available material for use in NYSDOT compost piles. Temperatures achieved in static pile composting suggest an adequate degree and duration of high temperatures to significantly reduce the survival of many pathogenic organisms, at least in the core of the piles.

Preliminary investigations by CWMI at several piles in New York State indicate that temperatures of 140°F are reached and that temperatures over 130°F are sustained for more than six weeks. However, temperature and pathogen kill in static compost piles have not been studied to the extent needed to provide confidence. Questions such as “What is the thermal stability/sensitivity of the pathogens that might be present in road-killed wildlife in New York?”, “Are there worker health and safety issues?”, “When is the process finished?” and “Where can the finished product be used?” still need to be addressed.

NYSDOT and local highway department staff who work with carcasses need health and safety information pertaining not only to carcass-borne pathogens, but also on tick-borne diseases such as Lyme disease, Rocky Mountain Spotted Fever, babesiosis and ehrlichiosis. Preliminary indications based on discussion with Cornell Veterinary College faculty indicate that ticks on deer have a relatively low infection rate, at least for Lyme disease, and that handling the carcasses would thus not be a major potential source of exposure. Ehrlichiosis is known primarily in the southern U.S. but has been reported in New York; babesiosis is rare and is mainly coastal. However, relevant data need to be gathered and assessed in order to develop appropriate guidance. Such guidance might address the life cycle, feeding behavior and data regarding infection, coupled with advice on practices to minimize the risks of exposure and infection. This guidance would be relevant to all workers handling carcasses and not just to those engaged in composting.

LITERATURE REVIEW
To answer these questions, a literature review was conducted by CWMI to find data concerning the thermal stability of the pathogens identified. The information and professional opinions helped to determine which pathogens or indicator organisms would be tested in the composts. Complete results of the literature search are posted on the CWMI website, http://cwmi.css.cornell.edu. The following provides a summary.

The literature reviewed on prevalence suggest that the pathogens expected to be found in white tailed deer and other wildlife are as follows: Salmonella – very little to none in deer; E. coli and fecal coliforms – conflicting reports on E. coli O157:H7, but other fecal coliform are present and can be a source of human infection; Clostridium – present, especially in the gut and multiply when the animal dies; Listeria – present, but deer are probably not an important source; Campylobacter – very little to none; Yersinia – wild ruminants may be important carriers; Tularemia (Francisella tularensis) and other tick-borne diseases (as well as rabies) are carried by wildlife, but are more important in the handling of the carcasses rather than the composting process; Coxiella – not prevalent; CWD – present, hard to manage, will most likely not be affected by composting; Leptospira – conflicting reports; Cryptosporidia and Giardia – also conflicting reports, but more likely in younger animals; Mycobacteria – present, but probably in less than five percent of the population. The hardiness of these pathogens is summarized in Table 1.

Extensive review of the literature on inactivation of these pathogens suggests that the temperatures reached in static pile composting of road-killed white-tailed deer will be sufficiently high enough to inactivate the pathogens of importance:

Salmonella – Unlikely to survive in compost where temperatures exceed 50°C over a period of several days to two weeks. In ground meat, a 1 log10 reduction in bacterial numbers can be obtained after 46 minutes at 55°C, 0.8 minutes at 60°C, and 0.1 minutes at 70°C .

E. coli and fecal coliforms – Unlikely to survive in compost where temperatures exceed 50°C over a period of several days to two weeks. In ground meat, a 1 log10 reduction in E. coli bacterial numbers can be obtained after 33 minutes at 55°C, 1.2 minutes at 59°C, 0.5 minutes at 60°C, and 0.1 minutes at 70°C.

Clostridium – Few studies have been done in compost. In ground meat, a 1 log10 reduction in bacterial numbers can be obtained after 5.2 or 16.9 minutes at 59°C and 41.7 minutes at 70°C.

Listeria – In compost, the rising temperature had little effect on eliminating Listeria, but when exposed to the athermic factors (such as alkalinization of compost to pH 8.8) of composting, it was eliminated. In ground meat, a 1 log10 reduction in bacterial numbers can be obtained after 47 minutes at 55°C and 1.1 minutes at 60°C .

Campylobacter – Holding manure at 25°C for 90 days will decrease bacterial numbers to concentrations below detection. In lamb meat, a 1 log10 reduction in bacterial numbers can be obtained after 1.2 minutes at 55°C and 0.3 minutes at 60°C.

Yersinia – Holding manure at 25°C for 90 days will decrease bacterial numbers to concentrations below detection. In milk, a 1 log10 reduction in bacterial numbers can be obtained after 0.5 minutes at 60°C.

Francisella tularensis – Survived less than 10 minutes in liver and cured ham at 56 and 57°C, respectively.

Coxiella – Pasteurization times and temperatures (between 63 and 80°C) needed to kill this organism.

CWD – Extremely high heat needed to inactivate the prion responsible for CWD, will most likely not be affected by composting.

Leptospira – Hardiness level two organism. Should be inactivated at the same temperatures as Streptococcus spp. In ground beef, a 1 log10 reduction in Streptococcus faecalis bacterial numbers can be obtained after 12 minutes at 60°C.

Cryptosporidium and Giardia – Holding manure at 25°C for 90 days will decrease protozoal numbers to concentrations below detection.

Mycobacteria – Hardiness level three organism. Depending on the species, mycobacterium may grow at a wide temperature range from 10° to 65°C, though the optimum growth range for most species is between 29° and 45°C. Deer do harbor Mycobacteria, but only in a very small percentage of the deer population.

In summary, the relative hardiness of the pathogens expected to be found in road-killed deer and other wildlife is – in order from lowest to highest – Campylobacter jejuni < Yersinia enterolitica < Escherichia coli < Listeria monocytogenes Salmonella spp. < Streptococcus faecalis (based on D-values in food from various studies).

FIELD TRIALS
CWMI established six static compost piles to conduct the research. Three are at NYSDOT facilities that also serve as sites for demonstrations and monitoring. Three additional research piles were located at Cornell. All piles contain four deer carcasses bedded in wood chips. It was decided that the portions of the digestive tract that would have the highest pathogen load were the ascending spiral colon and the ceacum (both located after the small intestine). Therefore the entire spiral colon and ceacum of each of the deer that went into the piles were removed, cut up and mixed together, and tested for Fecal coliform, E.coli, Salmonella, Fecal streptococci and Enterococci.

Mycobacterium avian paratuberculosis (MAP), the bacteria that causes Johnes disease in cattle, was also chosen because while not found in deer, it is a tough indicator organism that does not reproduce in the environment. The MAP was in manure from known Johnes positive cows.

Both sets of samples were placed into the carcasses in the research piles in a manner that enables them to be recovered for sampling. Use of nylon mesh bags containing substrate were placed inside plastic balls with holes. Strings were attached to balls for recovery. Triplicate samples were removed from each pile of what is fondly referred to as “deer goo” at weeks 3, 6, 9, 17, 36, 52.

Johnes samples were pulled the week after the deer fecal samples. Compost samples were taken at months 3, 6, 9, 12 and analyzed for density, moisture, water holding capacity, pH, organic matter, conductivity, C:N and Solvita maturity. In addition, compost was analyzed for levels of pathogens at time 0, 3, 6, 9 and 12 months. Compost and deer feces samples were analyzed at Woods End Research Lab; MAP was analyzed at the Cornell University Animal Health Diagnostic Center – Johnes Program. Data loggers were used to record temperatures in four locations in each pile.

All the sampling has been completed over the past year and results are being statistically analyzed and interpreted so that appropriate guidance can be developed. A DVD and educational materials are in production and will include research results, health, safety and compost use recommendations.

This report was prepared by Mary Schwarz, Ellen Harrison and Jean Bonhotal of the Cornell Waste Management Institute in Ithaca, New York. The literature review was done for the New York State Department of Transportation. Visit http://cwmi.css.cornell.edu/Composting.html.

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