Cornell Waste Management Institute

Organic Contaminants

Many chemicals that are contained in wastewater become concentrated in sludges. This is particularly true for fat-soluble, persistent organic chemicals (familiar examples are PCBs and dioxins and a more recent example is polybrominated biphenyls). Concerns regarding organic chemicals include ecological impacts to soil health and wildlife and entry into the human food chain particularly through accumulation in dairy products. Whether their presence represents a significant risk to people, agriculture and the environment is under debate.

Neither EPA nor NYSDEC regulate any organic chemicals in sludges and there are very few data on the presence and concentration of these types of chemicals in sludges. The priority pollutant scan required by NYSDEC generates some data on organic chemicals, but it does not include most of the persistent organic chemicals.

Of particular concern for dairy farms are the fat-soluble bioaccumulative chemicals, as these may accumulate in the fat tissue and milk fat of dairy animals when they ingest soil or sludge particles during grazing. These chemicals then become part of the food chain for people. Many of these chemicals pose cancer risks as well as developmental risks. Farm families with high consumption of animal products would be at particular risk. There is a lack of research to evaluate the risk of milk or meat contamination.

A new survey to identify the chemicals in sludges is needed since the previous survey done in 1988 is out of date both because of changes in chemical use and because detection limits in that survey were too high for some chemicals to show whether they were present at levels that might pose a health or environmental risk.

Pathogens and Endotoxins

Sludges contain pathogens and endotoxins (potentially illness-causing cell wall materials that remain after certain bacteria die). Endotoxins have not been studied in sludges, but would be expected to be present in both Class A and Class B sludges.

Sludge regulations require treatment to reduce pathogen levels before sludges can be applied to land. While Class A sludges used in agriculture should be essentially free of pathogens, Class B sludges may contain up to 2 million colony forming units/gram of fecal coliform. In addition to bacteria, sludges also contain viruses and may contain parasites. The ability of pathogens to survive sludge treatment and to survive in the environment varies greatly among different pathogens. Little is known about viruses under these conditions. Given their small size, the potential for surviving viruses to reach groundwater or to blow off sludge sites is a concern.

Persons and animals can be exposed to the pathogens that may remain in sludges by directly contacting the sludge or soil to which sludges have been applied. Federal rules require public access to farm fields to which Class B sludges have been applied to be restricted for 30 days. For other sites where the likelihood of public access is high (such as parks), access is to be restricted for one year. Current rules assume that pathogens will be killed due to environmental exposure over the course of a year. The lesser time restriction for farms is due to the expectation that fewer people might be exposed, not due to different assumptions regarding the inactivation of pathogens. Farmers using Class B sludges are thus required to keep people from their land for at least 30 days. However, it might be advisable to restrict access for at least a year. This includes persons who might use the land for hunting. Since workers can also be exposed, information needs to be provided to workers about the need to maintain high standards for hygiene in order to avoid illness. Current rules require grazing animals to be kept off land to which Class B sludges have been applied for 30 days. The adequacy of that waiting period to prevent disease from parasites has been questioned so a large waiting period may be advisable.

Farm Family Health/Workers

Farmers and farm workers working with sludges and on sludged fields should be aware that Class B sludges contain pathogens. While manures also contain pathogens of human concern, the number of different pathogens likely to affect humans is far higher in sewage sludges. The National Institute for Occupational Safety and Health recently issued guidance for workers that suggests hygiene practices to minimize risks of infection from sludge handling.

Beyond practicing good hygiene, of particular concern for dairy farm families is that persistent bioaccumulative toxic pollutants tend to concentrate in animal fats. There is no requirement for testing of sludges for these bioaccumulative toxics so the concentrations in sludges are unknown. High intake of animal products, which is typical for dairy farm families, and exposure of animals to sludges (particularly if sludges are applied to pasture or forages without tilling into the soil, increasing the potential for animals to ingest sludge) would increase risks.

Neighbor Concerns

There are a number of issues which may concern neighbors of land application sites. Sludges may generate significant objectionable odors resulting in complaints. There is the potential for blowing of sludge or sludge contaminants onto neighboring lands or for sludge to run off onto neighboring properties or into waterways. The potential for chemical contaminants or pathogens to contaminate water supply wells is another concern. Neighbors’ pets or children may enter onto sludge sites and thus be exposed and potentially transfer sludge to their homes and families. Sludge delivery traffic can also be a neighbor concern. Be considerate regarding routes, time of day and speed.

Injection or incorporation of sludges is recommended since it will help to minimize offsite transfer via air, runoff or pets and will help reduce odors. However incorporation will reduce the rate at which pathoens will die off.

EPA sets no restrictions on the proximity of sludge application to neighboring property or dwellings. NYSDEC has established a 500 foot buffer from residences and 50 feet from property lines for Class B applications, but none for Class A. There are no data indicating what an appropriate setback would be to address off-site odors and transport of contaminants and pathogens via wind and runoff.