Fate and Bioavailability of Emerging Micropollutants from Biosolid-Amended Agricultural Soils

<p>NON-TECHNICAL SUMMARY: <br/>Polycyclic synthetic musk fragrances (SMF) are used extensively in personal care products, detergents, and industrial applications. Because of their resistance to heat, water, and oil, polyfluoroalkyl substances (PFASs) are used in non-stick cookware, stain-resistant fabric, food packaging, paints, fire-fighting foam, and industrial surfactants and emulsifiers.The recent environmental detection of these micropollutants has raised concern because of evidence of environmental persistence, the risk of bioaccumulation, and the potential for toxicity, carcinogenesis and endocrine disruption. One potential environmental pathway of concern is through the agronomic land application of industrial and municipal biosolids. A recent study found biosolid concentrations of SMFs and PFASs to be in the ppm and ppb concentrations respectively, with both compound
classes appearing on multiple high priority watch lists. Little is known, however, about the environmental fate of these compounds within the 4 million dry tons of biosolids that are land-applied for their agronomic benefit each year. This project seeks to address the USDA priority and AFRI challenge area of food safety by filling in scientific gaps and quantifying the fate and bioavailability of two high priority classes of micropollutants - SMFs and PFASs - from biosolid-amended agricultural soils. The information gleaned from the proposed study will help us to better assess the potential risk of the land-application of biosolids to ecological and food safety, aid in the development of best management practices of biosolid waste disposal and associated risk management plans based on trade-offs, and address stakeholders who have expressed concerns about biosolid safety.We hypothesize
that biosolids will provide a source of SMFs and PFASs where they will be available for plant uptake from the vadose zone, potentially impacting both human food and feedstock safety. To test this hypothesis, we have 3 primary objectives:Objective 1: To quantify the aerobic degradation kinetics of SMFs and PFASs in biosolids and biosolid-amended soils. A batch aerobic microcosm study will be used to test the hypothesis that SMFs and PFASs will persist in soils and biosolids after land-application.Objective 2: To quantify the bioaccessibility of SMFs and PFASs from biosolids by measuring desorption kinetics. A batch desorption study will be used to test the hypothesis that SMFs and PFASs in biosolids will leach from the biosolid matrix into the vadose zone where they will be available for plant uptake.Objective 3: To quantify the bioavailability and potential bioaccumulation of SMFs and
PFASs from biosolid-amended soils. Greenhouse and field sampling studies will be used to test the hypothesis that SMFs and PFASs from biosolid-amended soils are available for bioaccumulation in plant roots and tissues where they may potentially enter the food chain.While primarily focused on research, this project will also include extension and educational outreach including: mentoring K-12 students and undergraduate researchers, developing undergraduate and graduate learning modules, outreach to local stakeholders through the Lafayette Science Café series (which is open and advertised to the public) and to a broader audience through the release of a Purdue Extension Bulletin on our findings.
<p>APPROACH: <br/>Galaxolide and tonalide will be used as model SMFs. Final selection of the specific model PFASs and precursorswill be based on those detected in the biosolid acquired. If a key model-compound of interest is not present in sufficient concentration, biosolid will be amended with the compound using talc as a carrier.For Objective 1, laboratory batch aerobic degradation microcosm studies will be used to test the hypothesis that SMFs and PFASs will persist after biosolids land-application. Briefly, at least 2 differing agricultural soils will be collected, passed through a 2 mm sieve, characterized, and stored in the dark at 4°C. Prior to biosolid amendment, soil will be added to 125 mL amber glass bottles and preincubated at 75% field capacity for 1 week. Soil microcosms will be amended with biosolid, crimped with airtight rubber septa, gently shaken to
mix the soil and biosolid, and stored at room temperature in the dark until time of sacrifice. Soil moisture will be monitored gravimetrically throughout the study. Treatments include: a no biosolid soil blank; 3 biosolid amendment treatments approximating the lower, optimal, and upper bounds of typical field application; and biosolid without soil to quantify the stability of the compounds within the biosolid matrix. The optimal biosolid amendment rate will be determined based on the nutritional needs of a model crop (e.g., corn) taking into account biosolid and soil nutrient analysis, with the lower and upper bound rates equivalent to 0.5 and 4 times the optimal rate, respectively. Sterile (autoclaved) soil controls will be used to discern biotic and abiotic transformations. All treatments and controls will be in triplicate. At time of sacrifice, the headspace will be sampled for
volatile parent compounds and metabolites using an airtight syringe fitted with 2 dry solid phase extraction cartridges (SPE) in serial and eluted with solvent. A separate headspace sample will be collected for O2 and CO2 analysis to confirm the microcosms are aerobic and viable. In the event that O2 levels fall below 50% of ambient air, interim headspace measurements of the remaining microcosms will be taken and the headspace purged and re-aerated. The soil microcosms being sacrificed will be extracted using ultrasonic assisted solid-liquid extraction followed by the clean-up of the solvent extracts using SPE to remove co-extracted lipids and matrix constituents.For Objective 2, alaboratory batch desorption study will be used to test the hypothesis that SMFs and PFASs in biosolid will leach from the biosolid matrix into the vadose zone where they will be available for plant uptake.
Briefly, desorption reactors will be prepared in 50 mL centrifuge tubes for the following: a no biosolid soil blank; biosolid alone to quantify the desorption kinetics from the biosolid matrix; and 3 biosolid-soil mixtures approximating the lower, optimal, and upper bounds of typical field application to approximate the bioaccessibility in a mixed matrix. Mass to volume (M/V) ratios will be optimized based on soil characterization. A 5 mM CaCl2 solution prepared in sterile ultrapure DI water spiked with 1 g/L sodium azide as a chemical sterilizer will be added to each reactor. All reactors will be prepared in triplicate and rotated in the dark. At each sampling period, the reactors will be centrifuged, a 0.5 mL aliquot of aqueous phase removed from each and replaced with 0.5 mL of CaCl2-azide solution, and returned to the rotator. The SMFs and PFASs will be extracted from the aqueous
phase using SPE. At the end of the study, the aqueous phase will be removed and analyzed, the solid phase will be extracted, and a mass balance performed.For Objective 3, greenhouse and field sample validation studies will be used to test the hypothesis that SMFs and PFASs from biosolid-amended soils are available for bioaccumulation in plant roots and tissues where they may potentially enter the food chain.The Greenhouse experiments will utilize in-ground soil beds. Plants will be provided with supplemental lighting supplied by 1000W high pressure sodium light fixtures with a 16 hour photoperiod to mimic the optimal outdoor photoperiod and allow the plants to reach physiological maturity. Irrigation will be used to replace water lost through evapotranspiration and maintain crop-specific optimal soil moisture conditions. The greenhouse soil will be characterized for physiochemical and
soil fertility properties prior to use including background SMF and PFAS concentrations and between plantings. Plots will be equipped with leachate collectors to capture excess irrigation water. Leachate will be extracted using SPE and analyzed for SMF and PFAS parent and metabolites to estimate leaching potential. Three crops of agronomic value will be used to assess the potential for plant uptake: red clover (Trifolium pratense) which is used as a forage crop, and corn (Zea mays) and soybean (Glycine max) which are used for livestock feed, human consumption, and industrial uses. These crops will be planted in series to mimic crop rotations over a 16-month period. The rotation will consist of red clover followed by corn, soybean, and red clover. All crops will be planted at the conventional plant densities used in field production. The second planting of red clover will be used to close
out the study and allow for the assessment of the differences in uptake between a virgin soil amended with biosolid and a seasoned soil containing both legacy concentrations of SMFs and PFASs and newly amended biosolid. Time to maturation is estimated at 75 d, 140 d (including a 30 d drying period), and 120 d, respectively. Red clover and soybean seed will be inoculated with rhizobia at time of planting. Four treatments will be randomized in each of 3 replicates within each of (at least) 4 trenches (blocks). Treatments will consist of a control with no biosolid amendment and 3 rates of biosolid application representing the lower, optimal, and upper bound rates typical of land application. The optimal rate of biosolid amendment will be determined based on the nutritional needs of each crop taking into account biosolid and soil nutrient analysis, with the lower and upper bound rates
equivalent to 0.5 and 4 times the optimal rate, respectively. Biosolid will be mixed into the soil 10 days prior to each planting. After reaching maturity, plant tissue and root samples will be collected as follows:Corn: the grain, stover, and first 20 cm of rootsSoybeans: the pods, stover, first 20 cm of the tap root, and first 20 cm of rootletsRed clover, the above ground biomass and first 20 cm of rootsAll plant samples will be collected, prepared, stored, and analyzed separately. All SMF and PFAS concentrations will be be reported on a dry weight basis.A field sample validation study will be implemented in collaboration with the Metropolitan Water Reclamation District of Greater Chicago's Stickney Water Reclamation Plant (MWRDGC), to assess plant uptake under natural growing conditions. Archived biosolid and plant tissue samples (e.g., sweet corn and high value crops including
tomatoes, carrots, etc.) from an ongoing 3 year study on PFAAs will be analyzed for SMFs and PFASs and precursors. Forage and cover crop tissue samples (including our model crops) and corresponding biosolid samples (at time of amendment) will also be collected from MWRDGC partner farms over 2 growing seasons from both fields receiving biosolid-amendment for the first time and fields undergoing long-term application. All plant samples will be collected, prepared, stored, and analyzed. Plant sample processing and analysis of extracts will take place in our laboratory at Purdue University.For all studies, liquid and solid phase extracts will be concentrated in a nitrogen evaporator and reconstituted prior to analysis on the GC-MS or HPLC/MS/MS. Procedural controls will be used to account for any laboratory background contamination.