Biosolids are the by-product of urban wastewater treatment. When spread on arable or grassland, and provided that they are treated to the approved standards, they may offer an excellent source of nutrients and metals required for plant and crop growth. They can be used as an aid in the development of a soil?s physical and chemical characteristics. They increase water absorbency and tilth, and may reduce the possibility of soil erosion (Meyer et al., 2001). Land application of biosolids to agricultural land can be relatively inexpensive in countries such as the Republic of Ireland (hereafter referred to as Ireland) and the U.S.A, as such by-products are defined as wastes. An alternative, but costly, option in such countries is to pay tipping fees for their disposal. For countries that acknowledge their nutrient replacement potential (e.g. the U.K), there is an associated cost for their usage.
The amount of sewage sludge being applied to land in the EU has dramatically increased. This is as a result of Directive 91/271/EEC (EEC, 1991), which states that the sludge produced from wastewater treatment plants ?shall be reused wherever appropriate? and the Landfill Directive, 1999/31/EC (EC, 1999), which requires that, by 2014, the disposal of biodegradable municipal waste via landfill is to be reduced to 85 % of the total amount produced in 1995. Consequently, the land application of biosolids provides a sustainable and beneficial alternative to landfilling. Although Germany and the U.K. are two of the largest producers of sewage sludge in the EU, Ireland, the U.K. and Spain are at the forefront of EU countries in terms of the percentage of sludge reused on agricultural lands. This is in line with national and EU policy, which warns against over-reliance on landfill and supports resource efficiency and re-use of waste (EPA, 2012). In addition, the minimisation, recycling and recovering of waste is one of the six key goals as set out by the EPA (EPA, 2007; referenced in EPA, 2012). In some countries e.g. Norway, producers of biosolids are responsible for both the quality and content of the biosolids; they must not contain organic pollutants, pesticides, antibiotic or other organic substances which may present health and environmental hazards associated with the use of the product. Stabilisation and disinfection (hygienisation) of all biosolids are required prior to land application and must be ploughed-in when applied to arable land. Re-use of land after biosolid usage must also be considered e.g. grazed grassland needs up to 3 years to recover after biosolid applications before it can return to grazing conditions. This may also be the case for potatoes and soft fruits, but is not the case for cultivation of cereals for human consumption.
In Ireland, the application rate of biosolids to land is governed by EU Directive 86/278/EEC (EEC, 1986), and is enacted in the ?Codes of Good Practice for the Use of Biosolids in Agriculture? (Fehily Timoney and Company, 1999), which set out limits for metal application, and S.I. 610 of 2010, which sets out nutrient (P and N) limits for various crops grown in Ireland. These guidelines do not consider the relationship between biosolid application rates and surface runoff of nutrients, suspended sediment (SS), pathogens, emerging contaminants (EC), or metals; nor do they consider the dose-response relationship between associated hazards and human health. Generally, when applying biosolids based on these guidelines and depending on the nutrient and metal content of the biosolids, P becomes the limiting factor for application. In the U.S.A., the application of biosolids to land is governed by The Standards for the Use or Disposal of Sewage Sludge (U.S. EPA, 1993), and is applied to land based on the nitrogen (N) requirement of the crop being grown and is not based on a soil test (McDonald and Wall, 2011). Therefore, less land is required for the disposal of biosolids than in countries where it is spread based on P content. Evanylo (2006) suggests that when soil P poses a threat to water quality in the U.S.A., the application rate could be determined on the P needs of the crop. A consequence of excessive application rates could be nutrient losses where an application is followed by a rainfall event, or excessive heavy metals transfer from spreading lands along the export continuum to a waterbody with subsequent adverse effects to the environment (Navas et al., 1999).
Release of pathogens into the environment is another concern associated with the land application of biosolids (Gerba and Smith, 2005). Zerzghi et al. (2010a) conducted a study on plots that were treated with 20 annual land applications of 8 and 24 t dry solids (DS) ha-1 of AD Class B liquid biosolids (containing 8 % DS) in order to establish the potential for soil microbial activity. Surface soil samples (0-30 cm), analysed 10 mo after the final application, showed no bacterial or viral pathogens present. In the same study, Zerzghi et al. (2010b) found that the microbial activity increased with increasing application rate of biosolids on the plots, but the bacterial diversity of the soil was not impacted negatively following the applications.
One of the major stumbling blocks in the use of biosolids as a low-cost fertiliser is the issue of public perception (Apedaile, 2001). In Ireland, companies that produce products for the food and drinks industry will not allow the use of the raw materials produced from agricultural land which has been treated with biosolids (FSAI, 2008; Board Bia, 2009). This limits their use as a fertiliser at the current time. During wastewater treatment, the sludge component of the waste becomes separated from the water component. As the survival of many microorganisms in wastewater is linked to the solid fraction of the waste, the numbers of pathogens present in sludge may be much higher than the water component (Straub et al., 1992). Although treatment of municipal sludge using lime, anaerobic digestion or temperature may substantially reduce pathogens, complete sterilisation is difficult to achieve (Sidhu and Toze, 2009) and some pathogens, particularly enteric viruses, may persist. Persistence may be related to factors such as temperature, pH, water content (of biosolids), and sunlight (Sidhu and Toze, 2009). Survival patterns of pathogens in biosolids are difficult to determine, and a lack of a standardised approach to pathogen measurement makes it difficult to quantify their impact. This is particularly the case in studies that have attempted to quantify their impact on surface runoff following landspreading. For example, Zerzghi et al. (2010) conducted a study on plots that were treated with 20 annual land applications of 8 and 24 t dry solids (DS) ha-1 of anaerobically digested (AD) Class B liquid biosolids (containing 8% DS) in order to establish the potential for soil microbial activity. Surface soil samples (0?30 cm), analysed 10 mo after the final application, showed no bacterial or viral pathogens present. However, in another study, an increase in the instances of food poisoning was reported following application of biosolids containing E. coli O157 in the UK (Jones, 1999). Although the US EPA categorise pathogens ?of concern? in biosolids (US EPA, 2001), this list is continuously evolving with advances in detection methods.
Limited amounts of work has been conducted on the environmental or health impact of landspreading of biosolids in Ireland. The project proposers have previously developed a method for the calculation of the maximum legal rate at which biosolids should be applied to land, which takes into account the soil P index, the dry solids and the nutrient and metal content of the biosolids, and a quick laboratory method to evaluate their impact on the release of P and metals to surface runoff (Lucid, Fenton and Healy, submitted paper). They showed that AD biosolids may be applied to land within maximum legal application limits without any adverse risk of runoff of P or metals. Thermally dried biosolids released high amounts of dissolved reactive phosphorus (DRP) and manganese (Mn) into the supernatant water in a laboratory-based runoff test. Lime stabilised biosolids released low amounts of DRP into the supernatant water, but exceeded the legal limit for Mn (when applied at the maximum legal application rate, based on a P index 1 soil) and iron (Fe) (when applied at twice the maximum legal application rate). These results, while indicative only, allow comparison to be made between amendments when applied at the same rate. The impact from EC (i.e. contaminants which do not have a regulatory standard) arising from human use (natural toxins, veterinary medicines, hormones and transformation products of man-made chemicals used in agriculture; OECD, 2012) and which may be contained in biosolids and lost in surface runoff, subsurface drainage and shallow groundwater, have not been investigated.
A number of knowledge gaps concerning the application of biosolids to soil exist: (1) The findings of the previous study by the proposers have been verified at laboratory-scale (using a rainfall simulator) (Lucid et al., submitted paper), but need to be evaluated at plot-scale to also take into account the risk of pathogen or EC loss (OECD, 2012) (2) the impact of spreading based on N and P application rates across a variety of soil P indices, and the possible impact that spreading on the N requirement of the crop could have on subsurface and surface runoff. Spreading based on crop N requirement, as recommended in America, would have the advantage of using less land, but would risk environmental and health impacts, which need to be modelled and assessed (3) the mobility of EC and pathogens, the influence of solubility and sorption behaviour of the EC, the influence of pH, organic carbon content and cation exchange capacity (CEC) of the soil matrix, and the influence of climatic conditions such as temperature and rainfall intensity, on the runoff potential of EC and pathogens. Previous work by UCD has focused on evaluation risks from the spreading of sludge potentially containing antimicrobials and also in relation to spreading meat and bone meal (Harris et al., in review). This expertise will complement the nutrient and hydrology experience from partners in Teagasc and NUIG.
Therefore, the aims of this study are to: (1) undertake a thorough literature review of the spreading of biosolids on land to include analysis of potential impacts on environmental and human health
(2) examine, under controlled conditions in the laboratory and field, the impact of the landspreading of biosolids (on grassland) on surface runoff/subsurface drainage/shallow groundwater of nutrients, solids, metals, pathogens and some specified EC identified in the literature review (either natural toxins, veterinary medicine, or hormones arising from animals), when spread based on N and P application rates (3) to model and conduct a risk assessment of potential hazards of human health concern, using data generated in 1 and 2 above. Note: in relation to objective (2), the EC to be examined will be biocides (triclosan and triclocarbon).

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Healy, M.   "Measurement and modelling of health impacts arising from the landspreading of biosolids". Associated datasets and digitial information objects connected to this resource are available at: Secure Archive For Environmental Research Data (SAFER) managed by Environmental Protection Agency Ireland https://eparesearch.epa.ie/safer/resource?id=04b4d5f5-d55e-11e5-ab63-005056ae0019 (Last Accessed: 2025-01-24)

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SAFER-Data Display URL	https://eparesearch.epa.ie/safer/iso19115/display?isoID=3116
Resource Keywords	biosolids; emerging contaminants; landspreading; sludge; treated sludge; metals; nutrients.
EPA/ERTDI/STRIVE Project Code	2012-EH-MS-1
EPA/ERTDI/STRIVE Project Theme	Land-use, Soils, and Transport
Resource Availability:	Public-Open
Limitations on the use of this Resource	NONE
Number of Attached Files (Publicly and Openly Available for Download):	10
Project Start Date	Monday 1st April 2013 (01-04-2013)
Earliest Recorded Date within any attached datasets or digital objects	Friday 10th January 2014 (10-01-2014)
Most Recent Recorded Date within any attached datasets or digital objects	Wednesday 17th February 2016 (17-02-2016)
Published on SAFER	Wednesday 17th February 2016 (17-02-2016)
Date of Last Edit	Monday 21st May 2018 at 17:33:49 (21-05-2018)
Datasets or Files Updated On	Monday 21st May 2018 at 17:33:49 (21-05-2018)

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Description of Geographical Characteristics of This Project or Dataset
These data originate from a field scale study on the landspreading of four types of biosolids (anaerobically digested biosolids originating from two sites - one in Ireland and one in the UK; thermally dried, and lime stabilized). In addition, for comparison, dairy cattle slurry was also land applied in the study, to compare surface runoff losses of nutrients, metals, suspended solids, and pathogens.

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