BIOSOLIDS—YOU ARE WHAT YOU EAT
Holiday season is upon us, the time for feasting and family. And the time for Part II of the Whole Foods response where a ban on flowers and produce grown in biosolids amended soils was justified based on the available ‘science’ showing the hazards of biosolids. In keeping with the holiday theme of feasting (family is a little too personal and not pertinent here), this month we will focus on food safety: how use of biosolids and manures can impact public health through pathogen transfer from manures or biosolids to soils, waters and food crops. Here it is critical to remember that the first mission of wastewater treatment is the protection of public health. Have we done our job? And how does the risk from using municipal biosolids compare to risks posed by beneficial use of animal manures?
What better way to start the library than with a review of the issue by Chuck Gerba and Jim Smith? The paper starts out with a list of the potential sources of pathogens. These are animal feeding operations, decentralized wastewater treatment, treated effluents and biosolids. From there, the authors cut quickly to the chase- every year the amount of manure produced in the US is about 100x more than the quantity of biosolids produced. More than 150 microbial pathogens have been identified that can be transmitted to humans. According to the Centers for Disease Control, all instances where water borne diseases were documented from 1986-1998 where a microbial agent was seen as the cause were linked to farm animals. In fact, Table 2 of this paper lists cases of disease outbreaks associated with animal manures. The critical components of table two are both the numbers associated with these outbreaks (many effecting more than 10,000 individuals) and the fact that in over 50% of the reported cases there were mortalities as a consequence of the contamination.
From manures, the paper goes on to discuss decentralized wastewater systems where groundwater contamination by poorly sited or poorly functioning systems is the third most common source of groundwater contamination. US EPA estimates that each year over 150,000 cases of viral illness and 34,000 cases of bacterial illness occur as a result of drinking well water contaminated by these systems. Wastewater effluent is the next topic. The authors note the use of effluent without sufficient treatment in certain parts of the US, but more importantly the use of these waters for agriculture overseas is a cause for concern. Viral and pathogen loads into wastewater systems in developing countries are much greater than in the US and so the risks associated with use of effluent also poses a greater hazard.
Finally we get to biosolids. The authors describe the Class A and B requirements and describe how if they are adhered to, the risks associated with either type of material are expected to be low and similar. They discuss the importance of vector attraction reduction as an additional key component of risk reduction. They list ways to treat manures to achieve pathogen reduction as well as potential pathogens of concern in human wastes. They do not list examples of fatalities associated with the use of biosolids because there are none. They do discuss the 2002 NRC report (where they concluded that there were no peer reviewed cases of illness associated with the use of biosolids) that called for more sophisticated techniques to test for pathogen kill to assure the public and to protect public health. The authors note that use of more sophisticated analytical techniques will result in the discovery of new pathogens.
From here we go to the second study by Viau and Peccia where some of these newer techniques have been applied to analyze biosolids for bacterial and viral pathogens. This is the paper that has been referred to in the recent wave of concern about the potential for the Ebolla virus to enter and survive wastewater treatment plants. Here the authors rank a number of treatment technologies for their ability to destroy different pathogens. While Class A technologies reduced pathogens in comparison to the Class B samples from mesophilic anaerobic digestion, quantitative PCR analysis could still detect coliphages and clostridium in the Class A products. Class A still had detectable adenovirus. In addition Legionnaires’ disease, caused by L. pneumophila increased during composting. The authors provide a reference where Legionnaires’ disease was associated with the use of a compost potting mixture. The authors point out that identification of pathogens using q PCR likely overestimates viable organisms. They suggest that male specific coliphages may be a good indicator organism instead of fecal coliforms. They note the potential for bioaerosol transmission of pathogens (something that extensive research by Gerba and Pepper has documented is not a concern). What is important here is that this is a paper about ways to analyze for pathogens that are potentially better than our commonly used current tools. It is not about actual incidences of disease but rather ways to analyze to reduce the POTENTIAL for disease as a result of biosolids use.
The last three papers in the library focus on animal manures. First birds, then cows, and finally closing with pigs. In each of these cases, there is discussion of ACTUAL illness and mortality associated with pathogens from animals and their manures. Illness has resulted from manure contamination of crops and waters as well as actual contamination of meat. The first article focuses on avian flu and includes a discussion of how animal operations have grown increasingly large and increasingly concentrated geographically. They note the absence of regulations to protect workers in these facilities. They use data from the avian flu epidemic in Thailand to show that larger scale operations actually pose a greater risk than small flocks. From there to cows, with a discussion of E. coli. Once again, we hear about how confined operations can increase the risk of disease. Animal diet can increase the concentration of these pathogen in the feces. Time of year and other factors also impact how much E. coli is in cow manure. With up to 30% of all cows asymptomatic carriers of this bacteria, these are good things to know. In addition, a high grain diet with incomplete digestion of grains and grains in the animal bedding create a vector attraction problem associated with the manure. Pigs are much better with regards to E. coli, but they have other problems. The authors focus on Canada where a pig production industry geared towards export is exploding. The recommendations for organic certified growing are detailed. The absence of regulations for use of manure in Canada is also noted. Did you know that in the US close to 15% of all foodborne illness is associated with pork products? The paper includes data on survival times of different pathogens in soil, water and manure. They conclude by recommending a 90 day retention time at 25 C as a way to eliminate pathogens in manures.
What we see in this month’s library is that while there are concerns about the POTENTIAL for land application of biosolids to result in illness, there are annual cases of ACTUAL disease and death associated with contamination of food and water from pathogens in animal manure. This is due to two factors: the significantly greater quantity of manures in relation to biosolids and the lack of rules and regulations requiring that the concentrations of disease causing organisms in these manures be treated prior to land application.
So remember, watch what you eat and Happy Holidays!
Sally Brown University of Washington