Improve biosolids usability by accessing effective and economical drying and pelletizing resources. Diversification of end-use products is important to Class A biosolids marketability. Heat drying and pelletization fosters diversification—helping potential buyers in more markets take advantage of your product through more efficient use, management, and transportation.

Recycling  |  Concerns

Questions and Answers About Risks

40 years of peer-reviewed scientific research shows that, when conducted according to regulations, biosolids recycling is safe and beneficial to crops and soils. EPA  conducted a comprehensive risk assessment that evaluated the health risk to the general population as well as to a highly-exposed individual, such as a person who would have direct contact with biosolids land application sites for a lifetime. To date, there have been no documented negative impacts to public health or the environment where a biosolids program met all the federal and state regulatory requirements.

EPA Risk Assessment

In 1988 the EPA conducted the National Sewage Sludge Survey, which sampled municipal sludges from 200 cities across the nation and tested for about 400 different pollutants. Most of these pollutants were found at very low levels. The EPA used this survey information and national research data to select pollutants for the risk assessment under the 40 CFR 503 rules. The EPA risk assessment looked at 14 possible pathways that land application of biosolids could impact the environment (Table 1).

Table 1 - Exposure Pathways for Biosolids Land Application*

Exposure pathway	Description
1. Sludge-soil-plant-human	Consumers in regions heavily affected by land application.
2. Sludge-soil-plant-gardener	Farmland converted to home garden use.
3. Sludge-soil-child	Farmland converted to future residential use, and child-ingested soil.
4. Sludge-soil-plant-human	Farm households eating a major portion of meat products from animals fed crops grown on sludge-amended soils.
5. Sludge-soil-animal-human	Farm households eating a major portion of meat from animals grazing on sludge-amended soil.
6. Sludge-soil-plant-animal toxicity	Livestock eating food or feed grown on sludge-amended soil.
7. Sludge-soil-animal toxicity	Livestock ingesting soil while grazing.
8. Sludge-soil-plant toxicity	Crops grown on sludge-amended soils.
9. Sludge-soil-soil biota toxicity	Soil biota living in sludge-amended soils.
10. Sludge-soil-soil biota-predator	Animals eating soil biota.
11. Sludge-soil-airborne dust-human	Tractor operator exposed to dust.
12. Sludge-soil-surface water-fish-humans	Water quality criteria for all beneficial uses of surface water.
13. Sludge-soil-air-human	Farm households breathing fumes from any volatile pollutants in sludge.
14. Sludge-soil-ground water-human	Farm households drinking water from wells.

*Reference - EPA Risk Assessment for 40 CFR 503 Rules⁸. 1993.

The EPA risk assessment evaluated the health risk to the general population as well as to a highly exposed individual, such as a person who would have direct contact with biosolids land application sites for a lifetime. The aggregate health risks to the U.S. population from all biosolids land application is much lower than many other common activities in our everyday lives. The aggregate health risks per one million (1,000,000) persons is less than one person for biosolids land application compared to 42 persons for motor vehicle accidents (Table 2).

Table 2 -The Relative Risks of Activities*

Annual risk of death per one million population
Smoking 1 pack per day	277
Motor vehicles accident	42
Alcohol consumption (light drinkers)	5
Eating peanut butter (4 tbsp. per day)	<1
Biosolids land application (all exposure pathways)	<1

* References - EPA Risk Assessment for 40 CFR 503 Rules. 1993. Wilson et al.14 1987.

Trace elements

Since the late 1970s, pre-treatment requirements have been established and implemented to require companies and facilities to reduce or remove the metal constituents before they enter the sanitary sewer system. This has resulted in significantly-decreased levels of heavy metals in biosolids.

Chemicals

The scientific evidence shows that through the variety of physical and biological processes involved in treatment, composting, and/or land application, almost all trace chemicals either degrade or volatilize. The few that are more persistent are at very low levels – similar to levels found in background soils and manures – and do not create any increased risk to public health or the environment.

In developing current regulations, EPA considered about 200 toxic organic compounds. After conducting extensive risk analyses on the 31 that were the most threatening, the agency concluded that they appeared so rarely, or at such low concentrations that they did not need regulations.

Declines of chemical detection in biosolids are due to pretreatment, chemical bans, and the phasing out of chemicals. Residues from the chemicals have declined over the past 20 years. Benzene for example was detected in 93% of biosolids samples in a survey conducted during the late 1970s, but in only 3% of samples from the late 1980s. Detection of persistent pesticides such as chlordane, dieldrin, heptachlor, and hexachlorobenzene were detected in 16% of the 1970s samples, but none of the 1980s samples.

Pathogens

Human disease-causing organisms may also be of concern. Research has shown no increase in health problems at wastewater treatment facilities or on farms where biosolids are used. The potential for exposure diminishes as environmental conditions such as heat, sunlight, desiccation, and other microorganisms destroy pathogens that may be present in biosolids

Odors

Most Class A biosolids products (e.g. compost, fertilizer pellets) are basically odor free or have a slight earthy smell. Some bulk Class B biosolids products have odors similar to animal manures used to fertilize farm fields. As with manures, when bulk Class B biosolids are land applied, some odors are possible, but they are temporary.

Storm water runoff

In order to prevent water pollution, site restrictions are required. These include maintaining buffers along waterways and surface waters and restricting slopes where biosolids can be applied.

Groundwater Contamination

The Biosolids Use regulations required at least 18 inches of soil depth to bedrock or groundwater. In this way, the soil acts as a protective layer to filter nutrients from entering to groundwater. Furthermore, biosolids application rates are limited to the plant available nitrogen, which can be used by the crop. In this way, there are no excess nitrates to leach into the groundwater.

*** Note:  Web site text prepared in part with use of information provided by the Virginia Department of Health, the Biosolids Institute, and the North East Biosolids and Residuals Association, U.S. Environmental Protection Agency, Water Environment Federation, National Biosolids Partnership, and Biosolids.com.