The Agriculture and Agri-Food Canada Program to Assess and Manage the Transport of Microconstituents in Biosolids-Amended Soils
Abstract:Trace concentrations of various pharmaceuticals and personal care products (PPCPs) are now widely detected in surface waters and in drinking water. The health risks to humans and wildlife exposed to these chemicals is of some scientific and regulatory concern. The potential sources of environmental exposure to PPCPs include effluents from sewage treatment plants, leakage from septic systems and landfills, discharges from pharmaceutical manufacturing facilities and hospitals, and drainage from land that has been irrigated with wastewater or that has been fertilized with biosolids. Biosolids are a valuable source of nutrients for crop growth, and the use of this material as a fertilizer is widespread in many agricultural areas that are in proximity to urban populations. PPCPs that persist through the sewage treatment process and that partition preferentially into organic matter will be carried in sludge and ultimately biosolids.
Land application of both biosolids slurry (“liquid municipal biosolids”; LMB; total solids content usually <3%) and of dewatered municipal biosolids (DMB; total solids content usually >20%) is a common practice in many parts of Canada. The characteristics of DMB and LMB differ in ways that are likely to influence the persistence and the transport potential of PPCPs following their application to soil. LMB applied to unsaturated soil will fill available pore space, ensuring greater exposure of PPCPs to soil microorganisms that may accelerate biodegradation. In contrast, restricted diffusion of oxygen into DMB aggregates, restricted diffusion of PPCPs out of the DMB aggregates into the surrounding soil matrix may enhance the persistence of PPCPs. LMB behaves as a liquid when applied, and can entrain PPCPs within and over the soil at the time of application through, for example, preferential flow. In contrast, large cohesive DMB aggregates remain at the point of deposition on the soil. DMB or LMB can be injected below the soil surface, or surface spread followed by soil incorporation. The two land application methods differ in their capacity to expose PPCPs to the atmosphere where they would be subject to UV irradiation and oxygen, and incorporate PPCPs into the soil matrix where they would be exposed to soil microorganisms. With direct injection, DMB is extruded beneath the soil surface in intact tube-like sections, whereas the surface spreading plus incorporation method mechanically breaks apart the solids into aggregates of various sizes. With LMB, slurry is injected into the subsurface, or simply applied on the surface and then incorporated into the soil. These physical differences should result in differences in tile drain effluent PPCP mass loads among the two land application methods.
Within this context, we have been investigating the transport of selected PPCPs from land that has received commercial rates of biosolids. Our primary objectives are: 1. characterize concentrations and mass transfer of PPCPs via tile drainage and via surface runoff from land that has received biosolids. 2. Characterize differences in transport potential of PPCPs carried in liquid municipal biosolids compared to dewatered municipal biosolids. 3. Characterize the effects of biosolids application methods (eg. surface versus subsurface application) on transport potential. 4. Investigate ratecontrolling factors for persistence and for transport. 5. Use field data to inform models (eg. MACRO for predicting movement of PPCPs to tile drains). 6. Compare the measured PPCP effluent concentrations with reported values for toxicological endpoints and, on this basis, assess risk.
We have primarily employed three different but complementary experimental formats for these studies. Tile drainage transportation experiments have been undertaken on commercial scale fields using commercial application equipment. Runoff transportation work has been done on small field plots receiving commercial rates of biosolids. Runoff was driven with artificially applied precipitation. Detailed PPCP fate experiments have been undertaken in the laboratory using bulk soil incubations. Analytes of PPCPs from field experiments have been identified and quantified using HPLC-MS methods. Fate and persistence work has generally used radioisotope analytical methods, following the disposition of 14C or tritium-labelled parent compounds added to soil. The general classes of PPCPs evaluated in our study include some acidic drugs, neutral/base drugs, ß-blockers, and antimicrobials. Specific analytes examined included acetaminophen, naproxen, ibuprofen, gemfibrozil, carbamazepine, cotinine, fluoxetine, atenolol, sulfamethoxazole, sulfapyridine, triclosan, and triclocarban.
Some of the results obtained to date can be summarized as follows. PPCPs are detected in tile drainage and in surface runoff, sometimes months after application. Maximum concentrations of PPCPs detected in effluent are generally lower following application of DMB than application of LMB. Incorporation of LMB eliminates the potential for loss via runoff. Application of LMB using an Aerway device reduces contamination via tile drainage, compared to surface applied and incorporated. The mass transfer (fraction of chemical applied that is exported) varied widely. Maximum concentrations of PPCPs detected in effluents were generally far below toxic thresholds for a variety of endpoints drawn from the literature.
Document Type: Research Article
Publication date: January 1, 2009
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