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In many jurisdictions sludge recovered from the sewage treatment process is a valued fertilizer for crop production. Pre-treatment of sewage sludge prior to land application offers the potential to abate enteric microorganisms that carry genes conferring resistance to antibiotics. Pre-treatment practices that accomplish this should have the desirable effect of reducing the risk of contamination of crops or adjacent water with antibiotic resistance genes carried in these materials. In the present study, we obtained municipal sludge that had been subjected to one of five treatments. There were, anaerobic-digestion or aerobic-digestion, in both instances with and without dewatering; and heat-treatment and pelletization. Each of the five types of biosolids was applied to an agricultural field at commercial rates, following which lettuce, carrots and radishes were planted. Based on qPCR, the estimated antibiotic gene loading rates were comparable with each of the five biosolids. However, the gene abundance in soil following application of the pelletized biosolids was anomalously lower than expected. Following application, the abundance of antibiotic resistance genes decreased in a generally coherent fashion, except sul1 which increased in abundance during the growing season in the soil fertilized with pelletized biosolids. Based on qPCR and high throughput sequencing evidence for transfer of antibiotic resistance genes from the biosolids to the vegetables at harvest was weak. Clostridia were more abundant in soils receiving any of the biosolids except the pelletized. Overall, the behavior of antibiotic resistance genes in soils receiving aerobically or anaerobically-digested biosolids was consistent and coherent with previous studies. However, dynamics of antibiotic resistance genes in soils receiving the heat treated pelletized biosolids were very different, and the underlying mechanisms merit investigation.

Sewage sludge recovered from wastewater treatment plants contains antibiotic residues and is rich in antibiotic resistance genes, selected for and enriched in the digestive tracts of human using antibiotics. The use of sewage sludge as a crop fertilizer constitutes a potential route of human exposure to antibiotic resistance genes through consumption of contaminated crops. Several gene targets associated with antibiotic resistance (catA1, catB3, ereA, ereB, erm(B), str(A), str(B), qnrD, sul1, and mphA), mobile genetic elements (int1, mobA, IncW repA, IncP1 groups -α, -β, -δ, -γ, -ε), and bacterial 16S rRNA (rrnS) were quantified by qPCR from soil and vegetable samples obtained from unamended and sludge-amended plots at an experimental field in London, Ontario. The qPCR data reveals an increase in abundance of gene targets in the soil and vegetables samples, indicating that there is potential for additional crop exposure to antibiotic resistance genes carried within sewage sludge following field application. It is therefore advisable to allow an appropriate delay period before harvesting of vegetables for human consumption.

Municipal biosolids are a useful source of nutrients for crop production, and commonly used in agriculture. In this field study, we applied dewatered municipal biosolids at a commercial rate using broadcast application followed by incorporation. Precipitation was simulated at 1, 3, 7, 21 and 34 days following the application on 2 m(2) microplots to evaluate surface runoff of various pharmaceuticals and personal care products (PPCPs), namely atenolol, carbamazepine, cotinine, caffeine, gemfibrozil, naproxen, ibuprofen, acetaminophen, sulfamethoxazole, triclosan and triclocarban. There was little temporal coherence in the detection of PPCPs in runoff, various compounds being detected maximally on days 1, 3, 7 or 36. Maximum concentrations in runoff ranged from below detection limit (gemfibrozil) to 109.7 ng L(-1) (triclosan). Expressing the total mass exported as a percentage of that applied, some analytes revealed little transport potential (1% exported; triclocarban, triclosan, sulfamethoxazole, ibuprofen, naproxen and gemfibrozil) whereas others were readily exported (1% exported; acetaminophen, carbamazepine, caffeine, cotinine, atenolol). Those compounds with little transport potential had log K(ow) values of 3.18 or greater, whereas those that were readily mobilized had K(ow) values of 2.45 or less. Maximal concentrations of all analytes were below toxic concentrations using a variety of endpoints available in the literature. In summary, this study has quantified the transport potential in surface runoff of PPCPs from land receiving biosolids, identified that log K(ow) may be a determinant of runoff transport potential of these analytes, and found maximal concentrations of all chemicals tested to be below toxic concentrations using a variety of endpoints.

Municipal biosolids are a source of nutrients for crop production. Beneficial Management Practices (BMPs) can be used to minimize the risk of contamination of adjacent water resources with chemical or microbial agents that are of public or environmental health concern. In this field study, we applied biosolids slurry at a commercial rate using either subsurface injection or broadcast application followed by incorporation. Precipitation was simulated at 1, 3, 7, 22, 36 and 266 days post-application on 2 m(2) microplots to evaluate surface runoff of 9 model pharmaceuticals and personal care products (PPCPs), atenolol, carbamazepine, cotinine, gemfibrozil, naproxen, ibuprofen, acetaminophen, sulfamethoxazole and triclosan. In runoff from the injected plots, concentrations of the model PPCPs were generally below the limits of quantitation. In contrast, in the broadcast application treatment, the concentrations of atenolol, carbamazepine, cotinine, gemfibrozil, naproxen, sulfamethoxazole and triclosan on the day following application ranged from 70-1477 ng L(-1) in runoff and generally declined thereafter with first order kinetics. The total mass of PPCPs mobilized in surface runoff per m(2) of the field ranged from 0.63 microg for atenolol to 21.1 microg for ibuprofen. For ibuprofen and acetaminophen, concentrations in runoff first decreased and then increased, suggesting that these drugs were initially chemically or physically sequestered in the biosolids slurry, and subsequently released in the soil. Carbamazepine and triclosan were detected at low concentrations in a runoff event 266 days after broadcast application. Overall, this study showed that injection of biosolids slurry below the soil surface could effectively eliminate surface runoff of PPCPs.

This paper focuses on calibration and validation of a dual-permeability soil water flow model, MACRO, to simulate liquid municipal biosolid (LMB) and precipitation induced vadose zone flow to a monitored tile drain system in a structured silt-loam soil, in southern Ontario Canada. The model was calibrated primarily on the basis of site-measured soil hydraulic parameters (encompassing tillage effects associated with LMB application), and field-monitored soil water content, soil water tension, and tile drain discharge for fall site conditions. LMB application for calibration data sets were carried out using an AerWay SSD system. Overall, daily tile drain discharge, soil water content, and soil water tension were well predicted by the following model calibration of primarily soil hydraulic parameters (specifically soil porosity, saturated hydraulic conductivity and van Genuchten soil desorption curve factors). The calibrated model was then validated using two additional daily data sets for two spring/summer study periods, both employing an LMB application. The modeling results were evaluated in part via statistical measures (i.e. average error and root mean square error); which indicated excellent agreement between daily simulated and measured tile drain discharges, soil water content and soil water tension. Overall, for certain LMB applications the modeling approach that was taken slightly under-predicted the degree of immediate application-induced macropore flow in the top 0.4 m of the soil. Generally, MACRO was found to be less adept at handling what was considered to be true bypass flow as a result of soil cracking during the drier soil conditions.

The consumption of crops fertilized with human waste represents a potential route of exposure to antibiotic-resistant fecal bacteria. The present study evaluated the abundance of bacteria and antibiotic resistance genes by using both culture-dependent and molecular methods. Various vegetables (lettuce, carrots, radish, and tomatoes) were sown into field plots fertilized inorganically or with class B biosolids or untreated municipal sewage sludge and harvested when of marketable quality. Analysis of viable pathogenic bacteria or antibiotic-resistant coliform bacteria by plate counts did not reveal significant treatment effects of fertilization with class B biosolids or untreated sewage sludge on the vegetables. Numerous targeted genes associated with antibiotic resistance and mobile genetic elements were detected by PCR in soil and on vegetables at harvest from plots that received no organic amendment. However, in the season of application, vegetables harvested from plots treated with either material carried gene targets not detected in the absence of amendment. Several gene targets evaluated by using quantitative PCR (qPCR) were considerably more abundant on vegetables harvested from sewage sludge-treated plots than on vegetables from control plots in the season of application, whereas vegetables harvested the following year revealed no treatment effect. Overall, the results of the present study suggest that producing vegetable crops in ground fertilized with human waste without appropriate delay or pretreatment will result in an additional burden of antibiotic resistance genes on harvested crops. Managing human exposure to antibiotic resistance genes carried in human waste must be undertaken through judicious agricultural practice.

a Agriculture and Agri-Food Canada, London, ON, Canada N5V 4T3 b Health Canada, New Substances Assessment and Control Bureau, Ottawa, Canada K1A 0K9 c Department of Biology, University of Western Ontario, London, ON, Canada N6A 5B7 d Ontario Ministry of the Environment, Toronto, ON, Canada M4V 1M2 e Agriculture and Agri-Food Canada, Ottawa, Canada K1A 0C6 f Worsfold Water Qualify Centre, Trent University, Peterborough, ON, Canada K9J 7B8 g Ontario Ministry of Food, Agriculture and Rural Affairs, Stratford, ON, Canada N5A 5T8

The MACRO soil water flow model adequately predicted liquid municipal biosolid (LMB) application and precipitation induced tile discharges. LMB was applied via two different application methods; AerWay SSD (Sub Surface Deposition) and a Kongskilde Vibro-Shank-type injection system. The model was able to satisfactorily simulate wetting-front movement through soil profiles. The model, however, could not reproduce the observed tile discharge values under dry, cracking soil conditions. Modeling results showed that LMB induced flow moved instantaneously through the soil profile to tile drains for the injection method. Tile discharge changes for the AerWay method were not notably detected. Bacteria concentrations in tile water were evaluated for each application approach, and tended to decrease over time presumably due to macropore flushing and dilution effects.

With increasing application of liquid municipal biosolids (LMB) on farm lands, a better understanding of the transport mechanisms by which contaminants reach water sources is required. For this purpose, a onedimensional transport model, MACRO, was used to understand soil water transport mechanisms under macroporous soils. Field measured data were used for calibration purposes. The model predicted that macropore flow dominated tile flow; bacteria transport was also found to be predominately macropore driven. Modeling helped to elucidate: the LMB application rates that reduce the risk of application induced macropore flow of LMB to tiles, the surface soil water contents required to minimize application induced tile contamination from LMB, and tile discharge contributing area. Although cursory at this stage, this modeling exercise was found to be promising with respect to providing information that can be used towards the development of Best Management Practices (BMPs) for land application of LMB.

Selection of appropriate liquid sewage, or liquid municipal biosolid (LMB), land application options can be assisted by modeling LMB transport in the vadose zone. The dual-permeability soil water flow model (MACRO) was used to simulate vadose zone flow and tile drain discharge resulting from LMB application (at 93,500 L ha-1) to agricultural field plots for three seasons using a rolling-tine aeration (AerWay® SSD) slurry deposition system (surface apply over aerator-tilled soil), furrow-based slurry injection system, and surface spread (broadcast) on un-tilled soil followed by incorporation methods. Given the total solid content of the LMB (0.02 to 0.05 g mL-1), we assumed that it behaved, for modeling purposes, as water. The AerWay SSD system, which surface applies LMB immediately over aerator-tilled soil, did not cause measurable or simulated changes in tile drain discharge during any study period condition. For the broadcast + incorporation experiment, preferential flow of LMB to tile occurred within 0.5 h post-application. Modeling did not simulate the small increase in application-induced discharge observed. This discrepancy was likely due to the existence of bypass flow in un-tilled soil. For the injection method, we simulated vadose zone flow processes associated discretely with the application furrow. While the furrow modeling approach adequately reflected tile breakthrough times, there were some overestimations of peak discharge (100%). Mass loads of bacteria associated with the different application methods did not show, nevertheless, marked or consistent treatment effects. Overall, it was felt that the physically based modeling approach employed here could be used to inform water quality risks associated with different methods to land apply LMB.