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The pharmaceutical industry is conducting research to evaluate the pathways and fate of active pharmaceutical ingredients from the consumer to surface waters. One potential pathway identified by the researchers is the disposal of unused pharmaceutical products that are discarded by consumers in household trash and disposed of in municipal solid waste landfills. This study was designed to evaluate relative amounts of surface water exposures through the landfill disposal pathway compared to patient use and flushing of unused medicine pathways. The estimated releases to surface water of 24 example active pharmaceutical ingredients (APIs) in landfill leachate were calculated for 3 assumed disposal scenarios: 5%, 10%, and 15% of the total annual quantity of API sold is discarded and unused. The estimated releases from landfills to surface waters, after treatment of the leachate, were compared to the total amount of each example API that would be released to surface waters from publicly owned treatment works, generated by patient use and excretion. This study indicates that the disposal of unused medications in municipal solid waste landfills effectively eliminates the unused medicine contribution of APIs to surface waters; greater than 99.9% of APIs disposed of in a landfill are permanently retained. Integr Environ Assess Manag 2013; 9: 142–154. © 2012 SETAC
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The detection of trace concentrations of human pharmaceutical compounds in surface water and groundwater continues to receive considerable attention in the technical literature and popular press. The improved precision and accuracy of analytical methods for trace organic chemicals, which includes pharmaceutical products and many other types of consumer products, has led to concerns about potential exposure of humans to these chemicals through the drinking water pathway and to aquatic biota that are in surface waters that receive treated domestic sewage. Research is being conducted by the pharmaceutical industry to evaluate the pathways and fate of active pharmaceutical ingredients from the consumer to surface waters. Potential pathways identified by the researchers are the disposal of unused pharmaceutical products by consumers in household trash that is disposed of in municipal solid waste (MSW) landfills and flushing unused medicines directly to public sewerage systems.
This study compares the relative contributions to the total mass of medicines found in the environment from patient dosing with the mass that results from landfill disposal and from flushing of unused medicines. The definition of unused medicines in this study is limited to unused products that are disposed of by patients or health care providers. Only the active pharmaceutical ingredients (API) in prescription and generic drugs are evaluated in this study. Bulk quantities, surplus, or expired APIs generated by wholesalers or pharmacies are specifically excluded from this analysis because they are returned to their manufacturers and are generally not discarded in municipal landfills. Only landfills defined and regulated as MSW landfills by Subtitle D of the Resources Conservation and Recovery Act (RCRA) are evaluated in this study. Because all active MSW landfill cells in the United States must meet the Subtitle D regulations under federal law, all such landfills are included in this evaluation.
The research compares the API releases in treated landfill leachate to the environmental loadings to surface waters from patient use of pharmaceutical products. In addition, an evaluation of the relative contribution of medicines to surface water based on an assumed scenario where all unused medicines are disposed of by flushing to municipal sewerage systems is evaluated. When the term “conservative” is used to describe an assumption used in this evaluation, it means that the assumption is expected to overestimate the releases of APIs through the pathway being described.
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The estimated releases to surface water of APIs in landfill leachate, for the 24 example APIs, are shown in Table 5 for 1 of the 3 disposal scenarios evaluated in the landfill study. As shown in Table 5, the total annual purchases of these 24 APIs is greater than 9.5 million kg. Metabolism and POTW removal reduce this annual purchased mass by approximately 80% to 82%, for the range of patient use assumed for this study. Table 5 presents the leachate mass loadings to surface water for 3 unused API disposal rates—5%, 10%, and 15% of total annual quantity sold is assumed to be discarded unused to landfills—and compares the landfill leachate loadings in treated effluents to the total amount of each API released to surface waters after patient use and wastewater treatment. The assumed MSW sorption efficiency is 0.01, which results in the greatest estimated releases of APIs in the leachate.
Table 5. Impact of landfill disposal on total surface water load of selected pharmaceutical active ingredients due to patient dosing (0.01 sorption efficiency)
|Compound||API quantity purchased (kg/y)||Loss by human metabolism (%)a||POTW removal (%)a||5% API disposed||10% API disposed||15% API Disposed|
|API mass in POTW effluent due to patient use (kg/y)||API mass in POTW effluent from unused medicine in landfills (kg/y)||Total load resulting from landfill disposal (%)||API mass in POTW effluent due to patient use (kg/y)||API mass in POTW effluent from unused medicine in landfills (kg/y)||Total load resulting from landfill disposal (%)||API mass in POTW effluent due to patient use (kg/y)||API mass in POTW effluent from unused medicine in landfills (kg/y)||Total load resulting from landfill disposal (%)|
|Acetaminophen||5 691 120||10||98||97 318||61.2||0.06||92 196||122.5||0.13||87 074||183.7||0.21|
|Ciprofloxacin||85 440||11||74||18 782||1110.7||5.58||17 794||2221.4||11.10||16 805||3332.1||16.55|
|Doxycycline||32 784||0||0||31 145||88.7||0.28||29 506||177.4||0.60||27 866||266.1||0.95|
|Erythromycin-H2O||64 283||0||66||20 763||0.0||0.00||19 671||0.0||0.00||18 578||0.0||0.00|
|Gemfibrozil||231 530||24||44||93 612||115.2||0.12||88 685||230.3||0.26||83 758||345.5||0.41|
|Ibuprofen||1 035 229||78||90||21 636||53.2||0.25||20 498||106.4||0.52||19 359||159.6||0.82|
|Metformin||1 597 887||0||7||1 411 733||150.9||0.01||1 337 431||301.7||0.02||1 263 130||452.6||0.04|
|Paroxetine metabolite||19 474||0||89||2035||0.0||0.00||1928||0.0||0.00||1821||0.0||0.00|
|Ranitidine||100 417||6||30||62 770||5.7||0.01||59 467||11.4||0.02||56 163||17.1||0.03|
|Sulfamethoxazole||314 389||88||24||27 239||1.3||0.00||25 805||2.5||0.01||24 371||3.8||0.02|
|Tetracycline||68 569||0||0||65 141||8.9||0.01||61 712||17.8||0.03||58 284||26.7||0.05|
|Trimethoprim||64 450||15||29||36 951||0.1||0.00||35 006||0.1||0.00||33 061||0.2||0.00|
|Aggregate||9 544 488|| || ||1 907 324||1659||0.09||1 806 938||3318||0.18||1 706 553||4977||0.29|
The APIs shown in Table 5 with the highest potential mass releases to surface water through the landfill leachate pathway are those with low partitioning coefficients (log Kp <1.0), no biodegradation in landfills, and minimal or no removal at a POTW.
The estimated leachate release to surface water of acetaminophen, which has the largest sales of any of the 24 example APIs, is very low because although this API has a low log Kp, its mass in leachate is predicted to be reduced substantially by biodegradation in an MSW landfill and the quantity remaining in the leachate is very effectively biodegraded in the leachate treatment step.
Ibuprofen has relatively high POTW removal (90%), but is sold in very large quantities, has a moderately low Kp, and has data for biodegradation showing 50% reduction in landfills. It is significantly metabolized by patients (70%), and therefore the proportion of ibuprofen in the discharge to surface water that originates from unused medicine disposal in landfills is higher than that of acetaminophen.
Table 5 also compares the annual API mass released to surface water through landfill disposal to the total mass of API released to surface water from patient use. Even at the greatest assumed disposal rate of unused medicines in landfills, the landfill leachate pathway to surface water is dwarfed by the surface water releases due to patient use and excretion of the 24 example APIs.
The sensitivity analysis of the leachate API mass discharged to surface water (after metabolism and POTW treatment for the quantity used by patients) is carried out using the MSW sorption efficiency and the quantity of unused medicines disposed of in landfills and is shown graphically in Figure 1. The purpose of Figure 1 is to demonstrate that the calculated mass releases of API in landfill leachate are not very sensitive to changes in either the mass of medicine discarded unused or the efficiency of the sorption process in landfills. A 100-fold decrease in MSW sorption efficiency results in about a 8-fold increase in the leachate API mass discharged to surface water. This analysis indicates that the sensitivity of the leachate API mass to the sorption efficiency of the materials in the landfill is much less than 1:1. As expected, the total mass of API in the leachate is a linear function of the quantity of API disposed of with municipal trash. The calculated total annual releases of API to surface water ranges from 0.06% to 0.29% of the releases due to patient use of the medicines.
Disposal of unused medicines by flushing them to public sewerage systems has been a historically recommended practice. Comparison of the relative contribution of APIs to surface water from landfill disposal of unused medicines to disposal of medicines by flushing to the sewer demonstrates the relative efficiency of the 2 approaches for reducing API contributions of unused medicine to surface water.
For this comparison, the estimated aggregate annual surface water releases of the 24 example APIs were calculated by assuming that all unused medicines were disposed of in public sewerage systems. The total surface water release in this calculation is a result of patient use and excretion and disposal of unused medicines to the sewerage systems. The surface water discharge estimates are calculated using the methodology described for landfills (POTW treatment). All API mass quantities are adjusted, as appropriate, to account for the salt fraction of the product if the product is distributed as a salt. The discharges from POTWs due to patient use are based on the mass of API sold, the percentage metabolized, and the percent removed by POTW treatment.
Table 6 presents the calculated surface water discharges of the 24 example APIs assuming unused medicine disposal rates of 5%, 10%, and 15% of annual purchases and a 0.01 sorption efficiency. The percent increase in the total annual surface water discharge of the 24 example APIs that would be caused by unused medicine disposal in sewers, using landfill disposal of unused medicines as the base case for comparison, is 12.2%, 20.3%, and 27.0% for the 5%, 10%, and 15% disposal rates, respectively. This analysis indicates that encouraging the disposal of unused medications in municipal solid waste landfills will decrease the surface discharges of APIs compared to flushing unused medicines to sewers.
Table 6. Impact of unused medicine disposal method on total surface water load of selected pharmaceutical active ingredients
|Compound||5% API disposed||10% API disposed||15% API disposed|
|Unused API discarded to sewer (kg/y)||API mass in POTW-treated effluent (kg/y)a,b||API mass from used medicine disposal (kg/y)||Total load resulting from sewer disposal (%)||Unused API discarded to sewer (kg/y)||API mass in POTW-treated effluent (kg/y)a,b||API mass from used medicine disposal (kg/y)||Total load resulting from sewer disposal (%)||Unused API discarded to sewer (kg/y)||API mass in POTW-treated effluent (kg/y)a||API mass from used medicine disposal (kg/y)||Total load resulting from sewer disposal (%)|
|Acetaminophen ||284 556||103 009||5691||5.5||569 112||103 578||11 382||11.0||853 668||104 147||17 073||16.4|
|Ciprofloxacin||4272||76 511||4272||5.6||8544||76 981||8544||11.1||12 816||77 451||12 816||16.5|
|Codeine ||755||13 661||755||5.5||1510||13 737||1510||11.0||2264||13 812||2264||16.4|
|Diltiazem ||7465||3941||2239||56.8||14 930||6091||4479||73.5||22 394||8241||6718||81.5|
|Doxycycline||1639||32 784||1639||5.0||3278||32 784||3278||10.0||4918||32 784||4918||15.0|
|Erythromycin-H2O||3214||64 283||3214||5.0||6428||64 283||6428||10.0||9642||64 283||9642||15.0|
|Gemfibrozil||11 577||100 095||6483||6.5||23 153||101 651||12 966||12.8||34 730||103 207||19 449||18.8|
|Ibuprofen ||51 761||26 812||5176||19.3||103 523||30 850||10 352||33.6||155 284||34 887||15 528||44.5|
|Metformin ||79 894||1 486 035||74 302||5.0||159 789||1 486 035||148 603||10.0||239 683||1 486 035||222 905||15.0|
|Paroxetine metabolite ||974||2142||107||5.0||1947||2142||214||10.0||2921||2142||321||15.0|
|Ranitidine ||5021||66 285||3515||5.3||10 042||66 496||7029||10.6||15 062||66 707||10 544||15.8|
|Sulfamethoxazole||15 719||51 560||15 719||30.5||31 439||65 393||31 439||48.1||47 158||79 226||47 158||59.5|
|Tetracycline||3428||68 569||3428||5.0||6857||68 569||6857||10.0||10 285||68 569||10 285||15.0|
|Trimethoprim||3223||39 239||2288||5.8||6445||39 582||4576||11.6||9668||39 925||6864||17.2|
|Aggregate||477 224||2 148 394||130 266||6.1||954 449||2 172 443||260 532||12.0||1 431 673||2 196 492||390 798||17.8|
Figure 2 compares the surface water discharges of the 24 APIs that were evaluated for 3 cases: 1) all unused medicine disposal is by flushing to the sewer, 2) all unused medicine disposal is to municipal solid waste landfills, and 3) unused medicine is disposed of elsewhere (i.e., not flushed to the sewer or sent to a landfill) and surface water releases are solely due to patient use.
Figure 2. Comparison of surface water discharges from landfill and sewer disposal of unused medicines (0.5 sorption efficiency).
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These are the boundary cases for unused medicine disposal (i.e., 100% of unused medicines going to one or the other disposal route, not split between both). The quantities of unused medicines are based on 3 percentages of total annual sales (in kg) for each of the 24 APIs evaluated. The contribution of patient use of the medicines, with unused medicines disposed of elsewhere, is also shown on Figure 2 for comparison. As shown, if unused medicines are disposed of in landfills the total surface water contribution is essentially the same as the contribution from patient use alone.
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The 2 most convenient methods that patients can use to dispose of unused medicines are: 1) disposing of them with household trash, or 2) flushing them down the toilet. In some locations, take-back programs are beginning to be available to the public. However, participation in these programs is low. The relative importance of the 2 most common disposal methods for unused medicines to total surface water discharges of the 24 example APIs is shown in Table 6. The comparison of the calculated mass discharges is presented in Table 7.
Table 7. Relative importance of sewer flushing and landfill disposal of unused medicines (0.5 MSW sorption efficiency)
|Unused medicine disposal method||Percent of total surface water release due to specified disposal method of unused medicinesa,b|
|5% unused||10% unused||15% unused|
The landfill contribution to surface water from unused medicines is calculated by accounting for partitioning of each API to the organic and inorganic solids in the landfill and biodegradation of the API in the landfill, if applicable. It is assumed that the leachate is transferred to a POTW for treatment or treated and discharged at the landfill site. The surface water contribution of unused APIs due to flushing to the sewer is calculated by assuming that the unused mass of API is discharged to the sewer without any metabolism of the chemical. The unused API contribution to the surface discharge is calculated as the mass of unused medicine at each percentage disposal rate multiplied by its percent removal at the POTW.
As shown in Table 7, if unused medicines are flushed to the public sewerage systems such disposal would constitute 6.1%, 12.0%, and 17.8% of the total surface water discharges (including patient use and excretion) for the 5%, 10%, and 15% unused medicine quantities, respectively. The reason why the unused medicine disposal in the sewer causes a larger increment of surface water releases than the unused percentage of total API purchases is that patient use includes metabolism of a number of the APIs before they are excreted, thus reducing the total quantities of those APIs that are sent to the sewer.
Patient use of medicines is the principal source of the surface water discharges of APIs regardless of the disposal method for unused medicines. Landfill attenuation of APIs and subsequent landfill leachate treatment by POTWs or BAT facilities results in substantially lower estimated total discharges of API to surface waters when unused medicines are disposed of by landfilling as opposed to by flushing to the public sewers. Essentially, there is no difference in the surface water releases of these 24 APIs between the disposal of unused medicines in landfills and disposal of unused medicines elsewhere.