Biochar for the mitigation of nitrate leaching from soil amended with biosolids

Countries with sewage treatment plants produce on average 27 kg of dried biosolids/person/yr. Concerns about nitrate leaching limit the rate at which biosolids are added to soil. We sought to determine whether biochar, a form of charcoal that is added to soil, could reduce nitrate leaching from biosolids amended soil. We set up 24 (0.5 m × 0.75 m) lysimeters, filled with two soil types (Templeton Silt Loam and Ashley Dene silt loam) and amended with combinations of biochar (102 t/ha equivalent) and biosolids (600 and 1200 kg N/ha equivalent). Pasture and leachates were sampled over 5 months. Nitrate leaching from biochar plus biosolids amended soils were reduced to levels at or below the control treatments. Pasture N concentrations were similarly affected by biochar addition. Future research should focus on unravelling the mechanism responsible for the change in the nitrogen cycle in soils amended with biosolids and biochar.     

Benchmarking environmental and operational parameters through eco-efficiency criteria for dairy farms

Life Cycle Assessment (LCA) is often used for the environmental evaluation of agri-food systems due to its holistic perspective. In particular, the assessment of milk production at farm level requires the evaluation of multiple dairy farms to guarantee the representativeness of the study when a regional perspective is adopted. This article shows the joint implementation of LCA and Data Envelopment Analysis (DEA) in order to avoid the formulation of an average farm, therefore preventing standard deviations associated with the use of average inventory data while attaining the characterization and benchmarking of the operational and environmental performance of dairy farms. Within this framework, 72 farms located in Galicia (NW Spain) were subject to an LCA + DEA study which led to identify those farms with an efficient operation. Furthermore, target input consumption levels were benchmarked for each inefficient farm, and the corresponding target environmental impacts were calculated so that eco-efficiency criteria were verified. Thus, average reductions of up to 38% were found for input consumption levels, leading to impact reductions above 20% for every environmental impact category. Finally, the economic savings arising from efficient farming practices were also estimated. Economic savings of up to 0.13 € per liter of raw milk were calculated, which means extra profits of up to 40% of the final raw milk price.     

Nitrogen transformation in a denitrification layer irrigated with dairy factory effluent

Adoption of land-based effluent treatment systems can be constrained by the costs and availability of land. Sufficient land area is needed to ensure nitrate leaching from applied effluent is minimised. One approach to decrease required land area is to enhance N removal by denitrification. Layers of organic matter (100 mm thick) were installed below topsoil of a site irrigated with dairy factory effluent. These "denitrification" layers were tested to determine whether they could decrease nitrate leaching by increasing denitrification. Four plots (10x10 m2 each) were constructed with a denitrification layer installed at 300 mm below the surface, and N losses were measured in leachate using suction cups every 3 weeks for 19 months. N in leachate was compared with 4 control plots. Denitrifying enzyme activity, nitrate concentrations, and carbon availability were measured in samples collected from the denitrification layers. These measurements demonstrated that denitrification occurred in the layer; however, denitrification rates were not sufficiently high to significantly decrease nitrate leaching. Total N leaching was 296 kg N ha(-1) from control plots and 238 kg N ha(-1) from plots with denitrification layers; a total of 798 kg N ha(-1) was applied in effluent. More than 50% of the leached N to 40 cm was as organic N, presumably due to bypass flow. Other studies have demonstrated that thicker denitrification layers (more than 300 mm) can reduce nitrate leaching from small-scale septic tank drainage fields but this study suggests that it is probably not practical to use denitrification layers at larger scales.     

Controlling Nitrate Leaching in Water Supply Catchments

S prings from a catchment to the north east of Bath to provide up to 80 per cent of the water supply to a population of 96 000. A review in 1984 suggested that within a few years nitrate concentrations in these sources could exceed the limit for drinking water (11.3 mg N/1). Nitrate was being leached from agricultural land and when an opportunity arose to alter the largely arable farming on part of the catchment, guidelines were devised to reduce nitrate leaching. This paper describes the guidelines and the effects of their implementation.     

Kinetics of nitrate and perchlorate reduction in ion-exchange brine using the membrane biofilm reactor (MBfR)

Several sources of bacterial inocula were tested for their ability to reduce nitrate and perchlorate in synthetic ion-exchange spent brine (30-45 g/L) using a hydrogen-based membrane biofilm reactor (MBfR). Nitrate and perchlorate removal fluxes reached as high as 5.4 g N m⁻² d⁻¹ and 5.0 g ClO₄ m⁻² d⁻¹, respectively, and these values are similar to values obtained with freshwater MBfRs. Nitrate and perchlorate removal fluxes decreased with increasing salinity. The nitrate fluxes were roughly first order in H₂ pressure, but roughly zero-order with nitrate concentration. Perchlorate reduction rates were higher with lower nitrate loadings, compared to high nitrate loadings; this is a sign of competition for H₂. Nitrate and perchlorate reduction rates depended strongly on the inoculum. An inoculum that was well acclimated (years) to nitrate and perchlorate gave markedly faster removal kinetics than cultures that were acclimated for only a few months. These results underscore that the most successful MBfR bioreduction of nitrate and perchlorate in ion-exchange brine demands a well-acclimated inoculum and sufficient hydrogen availability.     

Impact of nitrate addition on biofilm properties and activities in rising main sewers

Anaerobic sewer biofilm is a composite of many different microbial populations, including sulfate reducing bacteria (SRB), methanogens and heterotrophic bacteria. Nitrate addition to sewers in an attempt to control hydrogen sulfide concentrations affects the behaviour of these populations, which in turn impacts on wastewater characteristics. Experiments were carried out on a laboratory reactor system simulating a rising main to determine the impact of nitrate addition on the microbial activities of anaerobic sewer biofilm. Nitrate was added to the start of the rising main during sewage pump cycles at a concentration of 30 mg-N L⁻¹ for over 5 months. While it reduced sulfide levels at the outlet of the system by 66%, nitrate was not toxic or inhibitory to SRB activity and did not affect the dominant SRB populations in the biofilm. Long-term nitrate addition in fact stimulated additional SRB activity in downstream biofilm. Nitrate addition also stimulated the activity of nitrate reducing, sulfide oxidizing bacteria that appeared to be primarily responsible for the prevention of sulfide build up in the wastewater in the presence of nitrate. A short adaptation period of three to four nitrate exposure events (approximately 10 h) was required to stimulate biological sulfide oxidation, beyond which no sulfide accumulation was observed under anoxic conditions. Nitrate addition effectively controlled methane concentrations in the wastewater. The nitrate uptake rate of the biofilm increased with repeated exposure to nitrate, which in turn increased the consumption of biodegradable COD in the wastewater. These results provide a comprehensive understanding of the impact of nitrate addition on wastewater composition and sewer biofilm microbial activities, which will facilitate optimization of nitrate dosing for effective sulfide control in rising main sewers.     

Water Source Protection and Protection Zones

This paper discusses Government policy to August 1989 on the use of protection zones to protect UK water sources from pollution by nitrate. It outlines the use of the powers in the Water Act 1989 to declare Nitrate Sensitive Areas, and the procedures that would be followed in declaring such zones. The circumstances are outlined in which compensation would be paid in Nitrate Sensitive Areas and the reasons for departing from the 'polluter pays' principle. UK policy is related to the proposed European Community Directive on the control of nitrate, and the similarities between the two approaches are illustrated.     

Estimating costs and potentials of different methods to reduce the Swedish phosphorus load from agriculture to surface water

This paper reviews 17 measures to reduce phosphorus leakage from Swedish agriculture to surface waters. Our aim is to evaluate the possible contribution from agriculture to achieve environmental goals including the Baltic Sea Action Plan. Using a regional approach integrating the variability in field specific characteristics, typical costs and national potential for the included measures may be estimated without identifying, e.g., suitable individual fields for implementation. The result may be helpful to select suitable measures but may also influence the design of environmental targets before they are determined.We find that the cheapest measures are reduced phosphorus content in animal food and fertilizer application supervision in pig farms, both measures with annual potentials of around 50 t each, and costs of €7 to €11 kg^− 1 yr^− 1. The total potential of the listed measures is an annual phosphorus reduction to surface waters of 242 t. If the most expensive measures are excluded (> €1000 kg^− 1 yr^− 1) and including retention in lakes the phosphorus transport to the sea could be reduced by 165 t yr^− 1. This amount can be compared with the Swedish commitment in the Baltic Sea Action Plan (BSAP) to reduce input to the Baltic Proper by 290 t yr^− 1.     

A Review of Treatment Process Options to Meet the EC Sludge Directive

New UK regulations from June 1989 will enforce the provisions of an EC Directive on the use of sewage sludge in agriculture. Among the requirements is one that sludge should be treated before surface application to farmland. Treatment is needed to reduce 'significantly' both the fermentability of sludge and the health hazards resulting from its use on farms. In the UK, the health risks associated with sludge are principally beef tapeworm ( Taenia saginata and cysticercosis) and Salmonellosis. Research on the effects of various treatment processes on pathogens has shown the conditions required to produce a 90% reduction of T. saginata and Salmonellae. This information has been used as a basis for describing a list of 'effective' treatment processes and process conditions - as given in a new UK National Code of Practice on the use of sludge in agriculture. The uprating of existing treatment plant, or provision of new plant, to meet the Code of Practice recommendations could involve significant costs. A comparison of the economics of each of the 'effective' treatment processes for different population sizes shows a fairly wide range of net present costs. In general, increased sludge quality means increased costs.     

A review of the impact of climate change on future nitrate concentrations in groundwater of the UK

This paper reviews the potential impacts of climate change on nitrate concentrations in groundwater of the UK using a Source-Pathway-Receptor framework. Changes in temperature, precipitation quantity and distribution, and atmospheric carbon dioxide concentrations will affect the agricultural nitrate source term through changes in both soil processes and agricultural productivity. Non-agricultural source terms, such as urban areas and atmospheric deposition, are also expected to be affected. The implications for the rate of nitrate leaching to groundwater as a result of these changes are not yet fully understood but predictions suggest that leaching rate may increase under future climate scenarios. Climate change will affect the hydrological cycle with changes to recharge, groundwater levels and resources and flow processes. These changes will impact on concentrations of nitrate in abstracted water and other receptors, such as surface water and groundwater-fed wetlands. The implications for nitrate leaching to groundwater as a result of climate changes are not yet well enough understood to be able to make useful predictions without more site-specific data. The few studies which address the whole cycle show likely changes in nitrate leaching ranging from limited increases to a possible doubling of aquifer concentrations by 2100. These changes may be masked by nitrate reductions from improved agricultural practices, but a range of adaption measures need to be identified. Future impact may also be driven by economic responses to climate change.     

Evaluating the utility of 15N and 18O isotope abundance analyses to identify nitrate sources: A soil zone study

¹⁵N and ¹⁸O isotope abundance analyses in nitrate (NO₃⁻) (expressed as δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ values respectively) have often been used in research to help identify NO₃⁻ sources in rural groundwater. However, questions have been raised over the limitations as overlaps in δ values may occur between N source types early in the leaching process. The aim of this study was to evaluate the utility of using stable isotopes for nitrate source tracking through the determination of δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ in the unsaturated zone from varying N source types (artificial fertiliser, dairy wastewater and cow slurry) and rates with contrasting isotopic compositions. Despite NO₃⁻ concentrations being often elevated, soil-water nitrate poorly mirrored the ¹⁵N content of applied N and therefore, δ¹⁵N-NO₃⁻ values were of limited assistance in clearly associating nitrate leaching with N inputs. Results suggest that the mineralisation and the nitrification of soil organic N, stimulated by previous and current intensive management, masked the cause of leaching from the isotopic prospective. δ¹⁸O-NO₃⁻ was of little use, as most values were close to or within the range expected for nitrification regardless of the treatment, which was attributed to the remineralisation of nitrate assimilated by bacteria (mineralisation-immobilisation turnover or MIT) or plants. Only in limited circumstances (low fertiliser application rate in tillage) could direct leaching of synthetic nitrate fertiliser be identified (δ¹⁵N-NO₃⁻ < 0‰ and δ¹⁸O-NO₃⁻ > 15‰). Nevertheless, some useful differences emerged between treatments. δ¹⁵N-NO₃⁻ values were lower where artificial fertiliser was applied compared with the unfertilised controls and organic waste treatments. Importantly, δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ variables were negatively correlated in the artificial fertiliser treatment (0.001 ≤ p ≤ 0.05, attributed to the varying proportion of fertiliser-derived and synthetic nitrate being leached) while positively correlated in the dairy wastewater plots (p ≤ 0.01, attributed to limited denitrification). These results suggest that it may be possible to distinguish some nitrate sources if analysing correlations between δ variables from the unsaturated zone. In grassland, the above correlations were related to N input rates, which partly controlled nitrate concentrations in the artificial fertiliser plots (high inputs translated into higher NO₃⁻ concentrations with an increasing proportion of fertiliser-derived and synthetic nitrate) and denitrification in the dairy wastewater plots (high inputs corresponded to more denitrification). As a consequence, nitrate source identification in grassland was more efficient at higher input rates due to differences in δ values widening between treatments.     

Evaluation of the impact of various agricultural practices on nitrate leaching under the root zone of potato and sugar beet using the STICS soil-crop model

The quaternary aquifer of Vitoria-Gasteiz (Basque Country, Northern Spain) is characterised by a shallow water table mainly fed by drainage water, and thus constitutes a vulnerable zone in regards to nitrate pollution. Field studies were performed with a potato crop in 1993 and a sugar beet crop in 2002 to evaluate their impact on nitrate leaching. The overall predictive quality of the STICS soil-crop model was first evaluated using field data and then the model was used to analyze dynamically the impacts of different crop management practices on nitrate leaching. The model was evaluated (i) on soil nitrate concentrations at different depths and (ii) on crop yields. The simulated values proved to be in satisfactory agreement with measured values. Nitrate leaching was more pronounced with the potato crop than with the sugar beet experiment due to i) greater precipitation, ii) lower N uptake of the potato crop due to shallow root depth, and iii) a shorter period of growth. The potato experiment showed that excessive irrigation could significantly increase nitrate leaching by increasing both drainage and nitrate concentrations. The different levels of N-fertilization examined in the sugar beet study had no notable effects on nitrate leaching due to its high N uptake capacity. Complementary virtual experiments were carried out using the STICS model. Our study confirmed that in vulnerable zones agricultural practices must be adjusted, that is to say: 1) N-fertilizer should not be applied in autumn before winter crops; 2) crops with low N uptake capacity (e.g. potatoes) should be avoided or should be preceded and followed by nitrogen catch crops or cover crops; 3) the nitrate concentration of irrigation water should be taken into account in calculation of the N-fertilization rate, and 4) N-fertilization must be precisely adjusted in particular for potato crops.     

Temporal variability of nitrate transport through hydrological response during flood events within a large agricultural catchment in south-west France

The temporal variability of nitrate transport was monitored continuously in a large agricultural catchment, the 1110 km² Save catchment in south-west France, from January 2007 to June 2009. The overall aim was to analyse the temporal transport of nitrate through hydrological response during flood events in the catchment. Nitrate loads and hysteresis were also analysed and the relationships between nitrate and hydro-climatological variables within flood events were determined. During the study period, 19 flood events were analysed using extensive datasets obtained by manual and automatic sampling. The maximum NO₃⁻ concentration during flood varied from 8.2 mg l⁻¹ to 41.1 mg l⁻¹ with flood discharge from 6.75 m³ s⁻¹ to 112.60 m³ s⁻¹. The annual NO₃⁻ loads in 2007 and 2008 amounted to 2514 t and 3047 t, respectively, with average specific yield of 2.5 t km⁻¹² yr⁻¹. The temporal transport of nitrate loads during different seasonal flood events varied from 12 t to 909 t. Nitrate transport during flood events amounted to 1600 t (64% of annual load; 16% of annual duration) in 2007 and 1872 t (62% of annual load; 20% of annual duration) in 2008. The level of peak discharge during flood events did not control peak nitrate concentrations, since similar nitrate peaks were produced by different peak discharges. Statistically strong correlations were found between nitrate transport and total precipitation, flood duration, peak discharge and total water yield. These four variables may be the main factors controlling nitrate export from the Save catchment. The relationship between nitrate and discharge (hysteresis patterns) investigated through flood events in this study was mainly dominated by anticlockwise behaviour.     

Spatial and temporal trends in nitrate concentrations in the River Derwent, North Yorkshire, and its need for NVZ status

Long-term spatial and temporal variations in nitrate-N concentrations along the River Derwent have been examined using Environment Agency data to investigate the relative importance of impacts of atmospheric N deposition, land use, and changes in management. Where moorland and rough grazing dominate upstream of Forge Valley and Malton, over the 20 years since 1988 mean nitrate-N concentrations were initially increasing significantly, but are now levelling off, with peaks at ca. 4.5 mg N l⁻¹. As expected in a catchment in a nitrate vulnerable zone (NVZ), more agricultural land use increases mean nitrate concentrations and the occurrence of distinct winter maxima, though the latter have become markedly less pronounced since 2001. It is suggested that this improvement is a combined effect of imposition of NVZ designation in the lower reaches in 2002, animal number declines associated with the Foot & Mouth outbreak in the region in 2001, and the impact of farmers' responses to increasing fertilizer prices and to beneficial pollutant mineral N inputs from the atmosphere. Minima in nitrate-N concentrations in summer have become much less pronounced over the past decade and are typically ca. 60% higher in concentration than a decade earlier. This probably is attributable to the effects of pollutant-N leaching to depths in soil below the rooting zone when near surface biotic uptake is low in winter. The resultant N mineralization in summer enhances summer nitrate leaching. The Derwent is a relatively clean river; however, its entire catchment was designated justifiably as a NVZ in January 2009, apparently based upon a projected 95 percentile nitrate-N concentration > 11.29 mg l^− 1 for 2010 based upon forward projection of data from 1990 to 2004 for Derwent Bridge. A survey of water quality in March 2009 showed that some agricultural areas are still making a significant contribution to the total nitrate level well downstream, at the point responsible for implementation of NVZ status. At 3 of the 29 sites sampled, nitrate concentration exceeded 60 mg l^− 1.     

Spectral optical monitoring of nitrate in inland and seawater with miniaturized optical components

Miniaturized spectral analytical systems become ever increasingly important for in situ monitoring of natural waters’ nutrients, such as nitrate, phosphate or ammonium. A miniaturized UV spectral photometer has been developed for online detection using liquid core wave guides (LCW), UV transmitting optical fibers, a low-cost miniature polychromator, and a deuterium light source. The LCWs were manufactured by coating the insides of silica glass capillaries with Teflon^® AF 1600. Due to this setup our instrument needs only a few microliters of sample for each measurement. Nitrate can be directly detected by UV absorption spectroscopy in a spectral range between 200 and 350 nm. To separate the nitrate absorption from the superposition of other UV absorbing contaminations, a multi component analysis (MCA) software was applied to the measured spectra. With this developed photometer, nitrate levels can be determined online in inland and seawater or, if needed, in situ. It was evaluated twice in the field and the results for the measured amounts of nitrate in reservoir samples and in the North Sea are also presented in this work.     

Impact of selected agricultural management options on the reduction of nitrogen loads in three representative meso scale catchments in Central Germany

Nitrogen inputs into surface waters from diffuse sources are still unduly high and the assessment of mitigation measures is associated with large uncertainties. The objective of this paper is to investigate selected agricultural management scenarios on nitrogen loads and to assess the impact of differing catchment characteristics in central Germany. A new modelling approach, which simulates spatially distributed N-transport and transformation processes in soil and groundwater, was applied to three meso scale catchments with strongly deviating climate, soil and topography conditions. The approach uses the integrated modelling framework JAMS to link an agro-ecosystem, a rainfall-runoff and a groundwater nitrogen transport model. Different agricultural management measures with deviating levels of acceptance were analysed in the three study catchments.N-leaching rates in all three catchments varied with soil type, the lowest leaching rates being obtained for loess soil catchment (18.5 kg nitrate N ha^− 1 yr^− 1) and the highest for the sandy soils catchment (41.2 kg nitrate N ha^− 1 yr^− 1). The simulated baseflow nitrogen concentrations varied between the catchments from 1 to 6 mg N l^− 1, reflecting the nitrogen reduction capacity of the subsurfaces. The management scenarios showed that the highest N leaching reduction could be achieved by good site-adapted agricultural management options. Nitrogen retention in the subsurface did not alter the ranking of the management scenarios calculated as losses from the soil zone. The reduction effect depended strongly on site specific conditions, especially climate, soil variety and the regional formation of the crop rotations.     

Simultaneous biodesulphurization and denitrification using an oil reservoir microbial culture: Effects of sulphide loading rate and sulphide to nitrate loading ratio

Biooxidation of sulphide under denitrifying conditions is a key process in control of souring in oil reservoirs and in treatment of gas and liquids contaminated with sulphide and nitrate. In this work, biooxidation of sulphide was studied using a representative culture originated from an oil reservoir. Effects of sulphide concentration, sulphide to nitrate molar ratio, and loading rates of sulphide and nitrate on their removal rates and composition of the end products were investigated. In the batch system sulphide removal rate passed through a maximum as sulphide concentration was increased from 2.1 to 16.3 mM, with the highest rate (2.06 mM h⁻¹) observed with 10.7 mM sulphide. Nitrate removal was coupled to sulphide oxidation and the highest removal rate was 1.05 mM h⁻¹. In the continuous bioreactors fed with 10 and 5, 15 and 7.5, and 20 and 10 mM sulphide and nitrate, cell wash-out occurred as dilution rate was increased above 0.15, 0.13 and 0.08 h⁻¹, respectively. Prior to cell wash-out linear increases in sulphide and nitrate removal rates were observed as loading rate was increased. The highest sulphide and nitrate removal rates of 2.0 and 0.92 mM h⁻¹ were obtained in the bioreactor fed with 15 mM sulphide and 7.5 mM nitrate at loading rates of 2.1 and 0.93 mM h⁻¹, respectively. Short residence times and high sulphide to nitrate ratios promoted the formation of sulphur, a desired end product for ex situ treatment of contaminated streams. Combination of long residence times and low sulphide to nitrate ratios, which favours formation of sulphate, is the suitable strategy for in situ removal of H₂S from oil reservoirs.     

Groundwater Nitrate Concentrations from the Old Chalford Nitrate-Sensitive Area, West Oxfordshire

This paper, describes nitrate concentrations in a groundwater catchment currently designated as a nitrate-sensitive area. Although the scheme has been operational for two years, groundwater nitrate concentrations have regularly exceeded the EC maximum admissible concentration of 11.3 mg/1 NO₃-N (50 mg/1 NO₃) from sources draining both arable and grassland management regimes. Nitrate levels from arable areas tend to produce a seasonal pattern of winter leaching and summer uptake, whilst no such pattern or fluctuation is observed from grassland areas. Four processes are defined which regulate nitrate inputs to the saturated zone of the Great Oolite aquifer: (i) availability of 'free'nitrogen, (ii) variations in nitrogen uptake, (iii) leaching of nitrates from the soil environment, and (iv) limited atttenuation within the unsaturated zone.     

Decreasing ammonium generation using hydrogenotrophic bacteria in the process of nitrate reduction by nanoscale zero-valent iron

An integrated nitrate treatment using nanoscale zero-valent iron (NZVI) and Alcaligenes eutrophus, which is a kind of hydrogenotrophic denitrifying bacteria, was conducted to remove nitrate and decrease ammonium generation. Within 8 days, nitrate was removed completely in the reactors containing NZVI particles plus bacteria while the proportion of ammonium generated was only 33%. That is a lower reduction rate but a smaller proportion of ammonium relative to that in abiotic reactors. It was also found that ammonium generation experienced a biphasic process, involving an increasing period and a stable period. After domestication of the bacteria, the combined NZVI-cell system could remove all nitrate without ammonium released when the refreshed nitrate was introduced. Nitrate reduction and the final product distribution were also studied in batch reactors amended with different initial NZVI contents and biomass concentrations, respectively. Both the nitrate removal rate and the ammonium yield decreased when the initial content of NZVI reduced and the initial biomass concentration increased. However, about 27% of the nitrate was converted to ammonium when excess bacteria (OD₄₂₂ = 0.026) were used, which was higher than that with appropriate amount of bacteria.     

The potential steroid hormone contribution of farm animals to freshwaters, the United Kingdom as a case study

The combined farm animal population is considerably larger than the human one in the United Kingdom, implying a possibly important contribution to the environmental load of steroid hormones entering water. To make comparisons on the amount of steroid hormones produced by the different livestock, information was gathered on the structure of the UK farm animal populations and the amount of hormones excreted by animals at each of their life stages. An individual normalised dairy cow excretes two orders of magnitude more, and a normalised pig excretes more than one order of magnitude more steroid oestrogens than a normalised human. In terms of excretion, the combined farm animal population (including sheep and poultry) probably generates around four times more oestrogens than the human population in the UK. The biggest contributor on the animal side is the relatively small dairy cow population. If steroid oestrogens behave like herbicides, in which a worst case loss to surface waters is around 1%, then it could be argued that farm animals are responsible for 15% of all the oestrogens in UK waters. When simulations were made with the MACRO pesticide leaching model, predicted concentrations for field drains failed to exceed 1 ng/L. The rapid biodegradation rates, and high sorption rates taken from the literature and used in the model suggested less than 0.001% of oestrogens would reach the field drains. This survey suggests that direct excretion of steroid hormones by animals into water courses, or discharges from farmyard drains, are likely to be more important sources of contamination rather than via normal agricultural scenarios.