NE1001: Application of Sewage Biosolids to Agricultural Soils in the Northeast: Long-term Impacts and Benefit Uses
Statement of Issues and Justification
Sewage biosolids are a byproduct of water purification. To a large degree, these materials have traditionally been considered waste materials and dealt with accordingly (e.g., buried in landfills, dumped in the oceans). In part due to the environmental degradation resulting from such actions, plus the fact that these materials contain plant-available nutrients and organic matter useful in improving soil structure, recycling these materials through land application is increasingly being viewed as desirable. Simplistically, one might assume that these substances could be considered to be equivalent to commonly used fertilizers and applied to field sites accordingly. Yet, complications with the reasonably simple act of substituting these materials for traditional fertilizers result from their content of inorganic (e.g., heavy metals), organic (e.g., surfactants, solvents), and public health (e.g., viruses and other pathogens) contaminants and variability and uncertainty regarding the availability of nutrients.Use of sewage biosolids via agricultural land application is increasing in the U.S. IN New York State, beneficial use increased from 5% in 1989 to over 50% in 1998 (NYS Department of Environmental Conservation, 1998). This trend is expected to continue. USEPA predicts that in the year 2010 70% of sewage biosolids or 5.7 million dry tons will be beneficially used as compared to 63% or 4.5 million dry tons in 2000 (USEPA, 1999). These materials have been used to supplement agricultural phosphorus and nitrogen sources, to adjust soil pH, and to enhance soil structure and tilth. However, a variety of concerns have been raised that must be resolved to ensure the long-term utility of sewage biosolids as well as the preservation of the limited resources of high quality agricultural soils, particularly under Northeast soil conditions. These concerns include questions of whether currently accepted usage practices (as prescribed by the USEPA 503 standards) are adequate to protect the quality of the soils characteristic of this region, to insure the safety of the crops produced thereon, and to protect groundwater.
Soils of the Northeast tend to be shallow and acidic, making them more sensitive to metal applications than are soils in the Midwest or Western U.S. Furthermore, many crops crucial to Northeastern agriculture (e.g., leguminous forage crops and vegetables) are more sensitive to soil metal contamination than the relatively metal-insensitive crops (e.g., corn) for which most phyotoxicity data have been collected. Dairy is a predominant agricultural industry in many Northeastern states and the sensitivity of ruminant animals to some contaminants such as molybdenum is an important consideration. In addition to these agricultural production concerns, there are questions of potential degradation of groundwater quality. Again this is a particular problem in the Northeastern region due to soil and groundwater conditions, its complex mosaic of high population centers and adjacent agricultural enterprises and the predominant use of private wells to supply water to rural residents. Unanswered concerns relating to mobility of metals and/or pathogens by preferential flow paths in soils receiving sewage biosolids and the impact of currently unregulated toxic organic and inorganic constituents are of particular concern in light of the reliance on groundwater sources.
These concerns highlight the possibility that more protective guidelines for long-term sludge use may be needed for the Northeast compared to other regions with different environmental characteristics. It is therefore of considerable utility and interest to define the conditions under which use of sewage biosolids under Northeastern conditions are beneficial and to define procedures for their processing and utilization that will not compromise the current and future usefulness of soils or groundwater. Achievement of the objectives of this project will contribute to the necessary database for development of appropriate management practices for such conditions.
The variability in composition of sewage biosolids - both of desired nutrients as well as contaminants - is an important factor in management decisions regarding land application. Variability includes differences between wastewater treatment facilities as well as temporal fluctuations from a single sewage treatment plant (STP). Sampling frequencies required under current regulations may be as low as one or two samples per year, depending on the capacity of the treatment facility. An understanding of temporal variability at a facility is necessary for making sound land application decisions (for example, application rates should be based on agronomic rates which depend on nitrogen content and availability, variables which may fluctuate significantly). The adequacy of this frequency of monitoring for making such determinations is unknown.
Regulators, faculty, specialists and extension agents are receiving increasing numbers of inquiries regarding safety, social, and economic issues associated with land application of sewage biosolids. While scientific data are useful in determining the risk of the land application of biosolids, additional social information is required to provide adequate responses to questions regarding "perceived risks" and their implications for all potential stakeholders.
To address the issues cited above, a multi-institution, multidisciplinary, integrated research and extension project is proposed wherein well-documented field sites with histories of long-term sludge application will be examined cooperatively. Emphasis will be placed on assessing sites for soil and water quality, plant growth, and pathogen survival and mobility. Social and political impacts will also be assessed. These data plus existing records will be used to assess: sewage biosolids variability; environmental, agricultural and social impacts of varied application scenarios; and the larger sociopolitical contexts in which land application takes place.
While much scientific research has been accomplished and more is on-going (W-170 project, for example), important questions remain that need to be answered. These include further definition of the suitable loading rates of trace metals (e.g., cadmium, copper, mercury, molybdenum, nickel, lead and zinc) which are regulated by their potential for plant or human toxicity and the presence and risks posed by other toxic inorganic and organic chemicals that are not currently regulated and therefore infrequently monitored, if at all, by producers or land owners recycling sludges. Although frequently considered to be a "non-issue," there is also a growing interest in survival of pathogens, particularly viruses, in sludge materials and receiving soils (Chaprone and Margolin, 2000; Yates and Ouyang, 1992). Each of these concerns is exacerbated by the possible movement into ground and nearby surface waters and/or their incorporation into animal and human food systems.
Because of the continuing controversy regarding land application of sewage sludges, all stakeholders involved with their management (e.g., growers, communities, regulating agencies, scientists, and neighbors) in the Northeast are increasingly seeking information and guidance from the land grant universities. However, currently such guidance is inconsistent due to varied interpretations of the limited data available describing use of such materials on shallow, acidic soils and the need to extrapolate findings from studies of unrelated soil systems. This results in confusion and weakens the impact of the advice provided by the extension services of the land grant universities.
Areas of particular concern are:
- Trace elements
- Nonylphenols
- Groundwater
- Nutrients
- Pathogens
- Social, political and legal impacts
Trace Elements
Concentrations of some trace metals in sewage biosolids have been reduced substantially over the past several decades by improved source management and pretreatment of substances entering the wastewater stream. Yet, concerns remain regarding potential for excessive application of some contaminants from sewage biosolids to susceptible Northeastern soil and crop systems under the existing federal rules (McBride, 1995; Schmidt, 1997; Harrison et al., 1999). Interrelated concerns involving the implications of the trace element contents of biosolids on agricultural soils include not only considerations of the fate of the metals themselves and in crops, but also their impacts on the stability and sustainability of the soil ecosystem itself. For example, it has been shown that measurable differences in soil microbial community structure is demonstrable in orchard soils 20 years after receiving a single application of sewage sludge (within EPA guidelines) (Kelly et al., 1999a). Additionally, little is known about phytotoxicity or accumulation of elements such as molybdenum into several crops crucial to Northeastern agricultural (e.g., forage crops like alfalfa, grains, and vegetables) which are much more sensitive to metals than the well studied crops like corn. The potential for excessive molybdenum to cause harm to ruminant animals such as dairy cows and the prevalence of leguminous forage in the Northeast make research on molybdenum in the Northeast a pressing need.
The report titled Criteria and Recommendations for Land Applications and Sludges in the Northeast (Baker et al., 1985) addressed many of these concerns. However, many of the recommendations of the report (both explicit specific metal loading rates and implicit considerations of soil texture in standards development) were not reflected in current regulations. Examination of long-term sites in sensitive regions, such as the Northeastern U.S., with substantial metal accumulation from sludge applications is needed to develop an improved assessment of the sustainability of long-term applications of the sewage biosolids.
Accurate knowledge of the quality of sewage biosolids and of soils and plants from biosolids-amended sites is critical. Uncertainty due to different analytic methods needs to be reduced in order to make results between studies comparable. Fluctuations over time in the quality of sewage biosolids from a single STP are significant. Growers and their advisors need information on this variability in order to make appropriate decisions regarding application rates.
Nonylphenols
The degradation of common nonionic surfactants such as nonylphenol polyethoxylates in STPs leads to the accumulation of estrogenic nonylphenols in anaerobically digested sludge at levels as high as 4000mg/kg (Bennie, 1999). Although nonylphenol-based surfactants have been phased out in Europe they are still widely used in the United States, where there is neither monitoring nor regulation of nonylphenol concentrations in sewage biosolids. Because application of nonylphenol-contaminated sludges is a possible source of ground and surface water contamination, more work is needed to understand the fate of these compounds in agricultural settings.
Groundwater As cited below, ongoing research at Cornell University has found rates of metal movement higher than typically assumed. Preferential flow and facilitated transport mechanisms are not well understood and may be significant for trace element, pathogen and toxic organic transport, particularly under Northeastern conditions. Additionally, the effects of total ecosystem interactions or feedback (i.e. metals in sludge to soil to feed crops to manure to soil; or soil to groundwater to manure to soil loops) on long-term accumulations or mobility need to be evaluated.
An incomplete understanding of trace metal behavior in a farm system may compromise the long-term viability of farms, impact their immediate environment, and complicate legal liabilities (Goldfarb et al., 1999). In view of the unresolved questions concerning sludge-borne metals, it is evident that there is a necessity to document the long-term total ecosystem mobility and fate of sludge-borne contaminants in the more sensitive soil and water systems typical of the Northeastern U.S.
Nutrients Nutrient balance studies of farm systems in the Northeastern U.S., especially dairy farms, show a large net importation of N, P, and K (Klausner, 1993; Bacon et al., 1990; Dou et al., 1995; Hutson et al., 1998). The use of sewage biosolids is a source of imported N and P. The excess nutrients either accumulate in the system (i.e., increased soil nutrient contents) or are lost to the environment (denitrification, overland flow or tile drainage to surface waters, and leaching to groundwater). Nitrogen mineralization rates are variable (Douglas and Magdoff, 1991). Little work has been done on mineralization rates from sewage biosolids. If the rate is overestimated, crops will suffer from N limitation. Conversely, underestimation of mineralization results in over-application, excess N availability and increased risk of nitrate leaching. In cases where alkaline-stabilized sewage biosolids are used as a lime substitute, the accompanying N and P contents are often not matched by corresponding reductions in fertilizer applications. The temporal variability in nutrient content of sewage biosolids generated even at a single treatment plant makes it difficult to predict appropriate agronomic application rates. Finally, the wide P:N ratio of wastewater sludges (greater than that of manures) means that the overloading of P typical of many farms in the Northeast is exacerbated by the use of sludges in contrast to manures (Klausner et al., 1998). Improved understanding of variability in nutrient content and N mineralization rates of sewage biosolids and of the relationship of wastewater treatment processes to the content and availability of nutrients is needed.
Pathogens Sewage biosolids contain a variety of pathogens, including bacteria, viruses, protozoa, and parasites. Treatment processes reduce the number of such organisms, but do not eliminate them (Goddard et al., 1981; Payment et al., 1982; De Maturnana et al., 1992; Mayer and Palmer, 1996). For sewage biosolid products to be land-applied, they must at least meet Class B standards, indicating that they have been treated with a 'Process to Significantly Reduce Pathogens'(PSRP), such as anaerobic digestion. Many sludge products (i.e., composted, pelletized, or alkaline-stabilized) are further treated by a 'Process to Further Reduce pathogen' (PFRP) so that they meet 'Class A' standards, and have no pathogen-related restrictions on use.
Land application of Class B sludges requires certain management restrictions on use for human food and time delays before animal grazing or human site access is allowed, because viable pathogens may still be present in substantial numbers. The regulations for Class B sludge application are based in part on the assumption that soil is a hostile environment for the pathogens and their populations will quickly be reduced to acceptable levels. However, there is potential for transport of pathogenic organisms through overland flow (Dunigan and Dick, 1980) and leaching (via preferential flow paths) that is not typically addressed in regulations or management recommendations.
Social, Political and Legal Impacts
In the Northeast, with the close proximity of residences to farms and the relative abundance of sewage biosolids from nearby urban centers, land application of biosolids is especially controversial. Social science research indicates that risk perception plays a major role in whether citizens accept hazardous activities, substances and technologies (Juanillo and Scherer, 1995). Without understanding what people think about and how people respond to risk, well-intended policies may be ineffective (Slovic, 1987). The decisions of farmers to land-apply sewage biosolids are not only dependent on scientific issues concerning human and environmental health, but also on how they and their neighbors and local officials perceive potential risks (NRC, 1996).
These risk perception and communication issues involve interactions between various constituent groups, who can be seen as stakeholders; farmers, growers, or other potential appliers; scientists; sludge producers; site neighbors; the public; governments; and the media. Little information about risk perception or case studies about sludge land application could be found in a preliminary literature search. Since this issue is so controversial in the Northeast, research on the perceptions of growers and case studies of land application are needed. In response to local concerns regarding land application of sludges, particularly those sludges originating in a different municipality, a number of municipalities have adopted local ordinances (Goldfarb et al., 1999). These ordinances range from very simple bans to complex laws addressing many specific issues (Harrison and Eaton, in press). Some localities seek to base their laws on scientific data relevant to their community and seek guidance from the land-grant university and cooperative extension. The adoption of local laws can complicate land application programs since requirements may be different from locale to locale.
NEED FOR COOPERATIVE WORK
During the Northeast Regional Agronomy Meeting at Cornell University in July 1996, a session was convened to discuss the issue of application of sewage sludges to agricultural lands. Those in attendance represented NY, NJ, MA, ME, DE, and Canada. To further identify opportunities for collaboration, other state experts were subsequently contacted. From these interactions, a need for cooperative studies to develop appropriate guidance, such as updating the 1985 Criteria (Baker et al., 1985) was identified. Subsequently, under the auspices of NEC-100, these and other interested individuals met in December 1997 and 1998, July 1999 and January 2000 to exchange research results and to investigate common interests and projects. Based on these meetings and on the foregoing analysis of the complexities of impact of sewage biosolid-based materials on Northeastern soils in general, and agricultural systems specifically, it is concluded that further collaborative exploration of the issues is needed. Participation in a cooperative research project, and development of appropriate soil/sludge management practices for regional conditions is essential to provide for the use of sludge materials while insuring the long-term sustainability and optimal quality of the area agricultural soils and systems.
RELATIONSHIP TO CURRENT PRIORITIES
This proposal will primarily address CSREES National Goal 4: Greater harmony between agriculture and the environment. Through this research we will assess the potential impacts to ground and surface waters and to soil quality associated with application of sewage sludges under conditions typical of the Northeastern U.S. In addition, several of the research needs identified in the 1994 ESCOP publication, "Opportunities to Meet Changing Needs" will also be addressed. In particular this multidisciplinary project deals with the following areas identified in ESCOP priorities: 1) Recovery and Use of Waste Resources and 2) Synergy at the Agricultural - Urban Interface.
Last Modified:
unknown
Back to Top