Immobilization of Two Veterinary Antibiotics in Soils and Manure Amended Soils Using Drinking Water Treatment Residuals: A Greenhouse Study

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Abstract

Numerous studies have reported occurrence of tetracyclines (TCs) in soil, manure, groundwater, and surface-water. Results from our batch and incubation studies showed that Al-based drinking water treatment residuals (Al-WTR) could be a promising “green” amendment for TCs-rich-soils. Our previous studies revealed high sorption capacity of Al-WTR for tetracycline (TTC) and oxytetracycline (OTC). In this study, the effectiveness of Al-WTR in immobilizing TTC and OTC in manure-fertilized soils and soils under dynamic conditions in a year-long greenhouse column setting was evaluated. Two soil types – one primarily inorganic (Immokalee) and the other dominantly organic (Belleglade) – were selected based on varying physico-chemical properties and reactivity toward TCs. Bermuda grass (Cynodon dactylon) were used as control plants and corn (Zea mays L.) were used as test plants. Soil and manure samples were spiked with different concentrations of TTC/OTC (0-22.5 mg kg^-1) and amended at three rates (0-50 g kg^-1) of Al-WTR. Results showed that, compared to unamended (no Al-WTR) soils and manure fertilized soils, mobility of TTC/OTC significantly (p<0.001) decreased (44-68%) across all WTR treatments. Presence of plant cover decreased leaching of TTC/OTC (6-9%) compared to control columns with no plant cover. A physico-chemically dependent leaching behavior was observed. Immokalee soil showed highest leaching, followed by Belleglade soil, and manure-fertilized soils. The results from the greenhouse column study will possibly help to develop a novel low-cost remediation system for TCs in antibiotics-contaminated soils.

Capsule: Aluminum water treatment residual amendment significantly lowers tetracycline mobility in soil.

Keywords:  Tetracyclines, Soil Remediation, Al-based Drinking Water Treatment Residuals (Al-WTR), Cost-effective sorbent, Greenhouse Column Study.

Abbreviations: Tetracyclines (TCs), Tetracycline (TTC), Oxytetracycline (OTC), Chlortetracycline (CTC), Water treatment residuals (WTR), Veterinary antibiotics (VAs), Concentrated Animal Feeding Operations (CAFOs)

1. Introduction

Veterinary antibiotics (VAs) are primarily used to either treat or protect from infectious diseases, or enhance growth of animals at concentrated animal feeding operations (CAFOs) (Boxall et al., 2003). Since early 2000, VAs have been submitted to environmental risk assessment, due to increasing concern about their ecological and human health risk potential. VAs are partially metabolized in the gut of the animals and considerable given dose is excreted either unchanged, as conjugates with other compounds, or as some active metabolites in manure (Kumar et al., 2005a; Winckler and Grafe, 2001; Williams-Nguyen et al., 2016). During storage (storage ponds, treatment lagoon, etc.) of manure at CAFOs further degradation of VAs occur. However, large amounts of VAs still reach the soil and water system via application of manure to soil as fertilizers and accidental leakage or leaching from waste storage (McEachran et al., 2015; Ostermann et al., 2013; Stoob et al., 2007; Szogi et al., 2015; Topp et al., 2008). As a result, several VAs have been detected in aquatic and terrestrial environments (Hou et al., 2015; Sura et al., 2016; Wei et al., 2016).

Tetracyclines (TCs) are broadly used for various infectious diseases treatment and prevention at the CAFOs. Studies have shown that TCs can enter the soil and water system in substantial concentrations through reclaimed wastewater used for irrigation (Shenker et al., 2011; Tanoue et al., 2012) or by repeated land application of manure/biosolids (McClellan and Halden, 2010; Bassil et al., 2013). Further, they tend to accumulate in soils (Hamscher et al., 2002 and 2005; Kay et al., 2004), generating potential environmental and human-health risks (McEachran et al., 2015; Oberle et al., 2012; Munir and Xagoraraki, 2011; Daughton and Ternes, 1999). Tetracyclines are active compounds even at nano concentration levels (ng L^-1). They have shown to significantly affect the endocrine systems as well as the developmental stages of terrestrial and aquatic organisms (Puckowski et al., 2016; Zhang et al., 2013; Allen et al., 2010; Sarmah et al., 2006).

Tetracyclines levels in the groundwater, surface water, surface soils range from a few micrograms to milligrams (Wei et al., 2016; Hamscher et al., 2002; Aga et al., 2005). Kumar et al. (2005a) reported antibiotic low levels to > 200 mg kg^-1 or L^-1 in manure with concentration in ranging between 1-10 mg kg^-1 or L^-1.  Hamscher et al. (2005) reported Oxytetracycline (OTC) at cocnetration of 270 μg kg^-1, tetracycline (TTC) at 443 μg kg^-1, and chlorotetracyclines (CTC) at 93 μg kg^-1 in soils amended with manure. Winckler and Grafe (2001) reported 450–900 μg kg^-1 TCs in agricultural soils, and Hamscher et al. (2002) reported high levels of TTC (20 mg kg^-1) in the top soil which were fertilized via application of liquid manure.  A study by Kay et al. (2004) reported OTC at a concentration of 1691 μg kg^-1 in soils amended with manure for two consecutive years and a concentration of 613.2 μg L^-1 in drain flow through agricultural waste discharge into aquatic systems. Sarmah et al. (2006) reported surface and groundwater contamination by release of TCs from soil surface to the aquifer via mineral horizon. Further, a bioaccumulation study carried out by Kumar et al. (2005b) showed uptake of TCs (0.002 to 0.017 µg kg^-1 fresh plant weight) by plants that were grown in soils amended with VAs-rich manure. Boxall et al. (2006) showed uptake of various VAs (3 to 38 µg kg^-1 fresh weight) in plant tissue and leaves in plants grown in a sandy soil. Similarly, various recent studies have shown uptake of VAs in plant tissues, leaves, fruit, etc. on plants grown on soils spiked with TCs or on TCs rich manure amended soils (Bassil et al., 2013; Chitescu et al., 2013; Tanoue et., 2012; Wu et al., 2010). Potential adverse impacts of TCs include toxic reactions, allergic reactions, chronic toxicity because of extended low-level intake, development of antibiotic resistant bacteria, and disruption of the digestive system (Bártíková et al., 2016; Pan and Chu, 2016; Kumar et al., 2005b;). Thus, there is a great need to develop remediation techniques to immobilize and stabilize TCs to avoid their transportation, and leaching in to the aqueous environment, uptake or ingestion by plants/animals, and thereby prevent associated human health risks.

Our earlier studies showed high affinity of Al-WTR for TCs in aqueous medium in a batch setting (Punamiya et al., 2013; 2015) and in manure, soils, and manure fertilized soils in short term static incubation setting (Punamiya et al., 2016). Al-WTRs are by-products of drinking water treatment process where alum is used as the primary coagulant (Makris et al., 2010). In the one year long greenhouse study, we assessed the effectiveness of Al-WTR in immobilizing TTC and OTC in soils and manure fertilized soils in a dynamic column setting involving soil, manure, water, and plants. The objectives were; i) to evaluate long term effects of Al-WTR on TTC and OTC mobilization in two soils and manure fertilized soils with varying physico-chemical properties, and ii) to evaluate the effect of Al-WTR on TTC and OTC uptake by plants and TC concentration in leachates over that period of time.

2. Materials and Methods

2.1 Soils, manure, and Al-WTR collection, sampling, preparation, and characterization

Two soils with different physico-chemical properties (Immokalee Spodosols series and Belleglade Pahokee Muck series), cattle manure, plants Corn (Zea mays)] and [Bermuda grass (Cynodon dactylon), and Al-WTR were used in this study. Corn and Bermuda grass seeds were obtained from USDA with >90% germination rate. Soil, manure, and Al-WTR collection are detailed in the supplementary information. Before the initiation of the study Al-WTR, manure, and soils, were characterized for selected physicochemical properties using standard methods and protocol as discussed in Punamiya et al. (2013, 2016).

2.2 Study design and soil amendments

The detailed column design is illustrated in Figure S1. In brief, 80 columns were made from PVC pipes. Leachate was collected in the 1L bottle using an outlet connected with a tube.

Column were filled with play sand (0.18 m) at the base and top soil/soil amended with manure (0.15m).

Immokalee and Belleglade soils were spiked with TTC or OTC in form of tetracycline hydrochloride and oxytetracycline hydrochloride (USP grade, ≥99%, Sigma-Aldrich) to achieve final TTC/OTC load of 2.25 and 22.5 mg kg^-1, respectively. In another set of treatments, soils were fertilized with TTC/OTC rich manure at a rate of 11.2 Mg ha^-1 to simulate a realistic field loading rate.  After equilibration, the soils were mixed with Al-WTR at two rates 25 and 50 g kg^-1, respectively. Columns were filled with the soil/manure fertilized soils-TTC/OTC-Al-WTR mixture after thorough mixing. For samples spiked with TTC/OTC, there were a total of 32 columns with Al-WTR treatments (2 TCs × 2 concentrations × 2 soils × 2 rates of Al-WTR × two replicates). In addition, 16 control columns without Al-WTR, with and without plants (2 soils × 2 TCs × 2 plants × 2 replicates) were also prepared. A randomized block design was used for arrangement of the columns within the greenhouse. The columns were rotated weekly to account for changes in sunlight and greenhouse temperature. Bermuda grass was used a control plant, corn was used as the test crop.

Composite sampling was performed to collect soil samples from top 10-cm surface. The first soil sampling was conducted at time zero (immediately after spiking), followed by 0.25, 0.5 y, 0.75y and 1y of equilibration time (time final). After each sampling, soils were extracted and analyzed for total TTC and OTC using HPLC (details in the following section). The columns (with plants) were over-watered at two events (after 0.25y and 0.5 y) to help leaching. The leachate was collected for each column and analyzed for soluble TTC and OTC. Plant samples were harvested after time of maturity i.e. 0.5 y. Columns were retained for another 6 months without plant cover to understand the effect of soil/Al-WTR aging on TTC and OTC fractionation and mobility. Columns (without plants) were leached twice (after 0.75y and 1y), and leachates were analyzed for soluble TTC and OTC.

2.3 Sample Extraction and TC Analysis

Plant samples were extracted for TTC and OTC using citric acid and methanol (Boxall et al., 2006). After harvesting at maturity, corn kernels and leaves were analyzed for TTC/OTC. TTC/OTC concentration were measured in the extract. The concentration was calculated as the ratio between TTC/OTC in plant biomass (fresh weight) and its concentration in the soil solution. Soil samples were extracted using citric acid, oxalic acid, and methanol/water mixture for total TTC and OTC (Wang and Yates, 2008). Mobility/accessibility of TTC/OTC in the soil was calculated as amount of TTC/OTC extracted from the soil at estimated time interval compared to amount spiked at time zero. While calculating mobility of TCs leaching of TCs was taken into account (subtracted from total concentration).  The amount TC analysis was performed using HPLC (Finnigan surveyor plus, Thermo Scientific) according to Punamiya et al. (2013) and Fritz and Zuo, (2007). Thermo X-series Inductively Coupled Plasma Mass Spectrometer (ICP-MS) (Thermo Electron) was used to perform elemental analysis.

2.4 Statistical Analysis

JMP IN version pro 10 (Sall et al. 2005) was used to perform statistical analysis on the data obtained during the study. Two way or three way analysis of variance (ANOVA) was conducted. Treatment differences were considered significant at 95% (α= ≤ 0.05) and 99 (α= ≤ 0.01) % confidence interval. Data are expressed as mean of two sample (n =2) and with one standard deviation.

3. Results and Discussion

3.1 Solids Characterization

Belleglade (Pahokee Muck series) and Immokalee series (Spodosol) soils were used in the greenhouse study based on their variant physico-chemical properties. Table 1 shows the selected physico-chemical properties of the soils, Al-WTR, and manure. Immokalee soil is sandy nature with very low charged surfaces (e.g., amorphous Fe/Al oxides), is expected to have low retention capacity (Gu and Karthikeyan 2005; Datta and Sarkar, 2005; Figueroa and MacKay, 2005;), and can be expected to release high levels of the spiked TCs into the environment. Belleglade soil was slightly acidic-neutral (pH 6.45) with high soil organic matter (85%) and high concentrations of Ca, Fe, Al, and Mg in comparison to Immokalee soil, indicating higher TCs retention potential (Gu and Karthikeyan, 2005; Figueroa and MacKay, 2005). Both soils have diverse salinity and cation exchange capacity which may affect TC sorption (Ter Laak et al., 2006; Sassman and Lee, 2005; Bao et al., 2010).

Al-WTR was acidic (6.1) and amorphous (about 75% total Al) in nature. The total carbon values (185 g kg^-1) are in agreement with organic carbon concentration in various Al-WTRs across the country (USA) (Ippolito et al., 2011). The organic matter content of Al- WTR was 240 g kg⁻¹, which is higher than both soils. Cattle manure used in the study was acidic (pH 6.1) with high organic matter (250.5 ± 2.5 kg^-1) and total P content (4.5 ± 2.1 kg^-1). Total Ca+Mg ranged between 0.11 to 0.15 g kg^-1. No detectable background levels (method detection limit (MDL) 1  10^-3 mmol L^-1) of TTC and OTC were found in the soils, manure, and Al-WTR used in the greenhouse study.

3.2 Effect of Al-WTR in Immokalee and manure amended Immokalee soil

Immediately after spiking (time zero), there was no significant (p > 0.05) in TTC/OTC mobility in Immokalee soil (unamended control), fertilized with manure, and amended with Al-WTR (treatments) at two rates (25 and 50 g kg^-1). However, the trend changed after 0.25 year of equilibration for both TTC/OTC concentrations and Al-WTR rates (Figures 1 and 2). After equilibration period, the effect of Al-WTR amendment on TTC and OTC mobility on soil and manure amended soils became significant (p < 0.001), with decreased mobility compared to the unamended soil (Figure 1). Further, with increase in the equilibration time from 0.25 to 0.5 year, the effect of Al-WTR amendment became pronounced on TTC and OTC mobility. At the end of 1 year equilibration period, TTC mobility rate decreased by 58-64 % and 72-79% in Immokalee soil, 63-69% and 79-84% in manure fertilized Immokalee soils amended with 25 and 50 g kg^-1 Al-WTR, respectively compared to unamended control at both the TTC concentrations tested (Figure 1). Similar mobility behavior was seen for OTC. However, the rate of OTC stabilization by Al-WTR was slightly lower compared to TTC. After 1 year of equilibration period, the OTC mobility rate decreased by 54-60 % and 69-74% in Immokalee soil, 60-66% and 75-80% in manure fertilized Immokalee soils amended with 25 and 50 g kg^-1 Al-WTR, respectively compared to unamended control (Figure 2). Immokalee is a sandy soil with very low SOM (8.40 ± 0.2 g kg^-1); whereas, manure has very high SOM (250.5 ± 2.5 kg^-1) (Table 1). The relatively low rate of TTC and OTC mobility seen in the fertilized Immokalee soil compared to unfertilized Immokalee soil can be explained by contribution of high organic matter from the manure, enhancing the binding of TTC and OTC. Similar sorption behavior was observed by Wang and Yates (2008) in TCs kinetics and degradation study in a sandy loam soil fertilized with fresh animal manure. They attributed the observed behavior to the higher moisture content in the manure and introduction of organic content from manure in to the soil. Further, Wang et al. (2006) observed similar behavior in kinetics and degradation study of sulfadimethoxine in manure amended soils. There was no significant effect (p > 0.05) of initial TTC and OTC concentrations observed on the rate of mobility by Al-WTR in Immokalee and manure fertilized Immokalee soil. Moreover, Al-WTR application rate had a significant effect (p < 0.001) on the rate of TTC and OTC stabilization in both the TTC/OTC concentrations tested in manure fertilized  and unfertilized Immokalee soil. The observed results are in agreement with our previous short-term incubation study (Punamiya et al., 2016) conducted with Immokalee and TTC/OTC rich manure fertilized Immokalee soil in absence of plants amended with Al-WTR with different initial concentrations of TTC and OTC.

3.3 Effect of Al-WTR in Belleglade and manure amended Belleglade soil

Belleglade soil and manure fertilized Belleglade soil without Al-WTR application showed a significant difference (p < 0.005) in TTC and OTC mobility compared to Immokalee soil controls. This can be explained by the high amount of soil organic matter (85%) and high concentrations of Ca, Fe, Al, and Mg in comparison to Immokalee soil indicating higher TC retention potential and lower mobility (Figueroa and MacKay, 2005; Gu and Karthikeyan, 2005). However, similar to Immokalee soil treatments, no significant difference (p > 0.11) in Al-WTR amended Belleglade soil and unamended controls was seen at time zero (Figure 3 and 4). At the end of 1 y equilibration period, the TTC mobility rate decreased by 67-71 % and 75-81% in Belleglade soil, 72-75% and 82-87% in manure fertilized Belleglade soils amended with 25 and 50 g kg^-1 Al-WTR, respectively compared to controls at both the TTC concentrations tested (Figure 3). In case of OTC, the mobility behavior was similar to TTC. However, as observed in Immokalee soil, the rate of OTC stabilized by Al-WTR was slightly lower compared to TTC. After 1 y, the OTC mobility rate decreased by 64-69 % and 72-76% in unfertilized Belleglade soil, 70-74% and 80-85% in fertilized Belleglade soils amended with 25 and 50 g kg^-1 Al-WTR, respectively compared to unamended control (Figure 4). As compared to Immokalee soil treatments, the difference between rate of TTC and OTC stabilized in unfertilized and fertilized Belleglade soil was relatively low. This is mainly due to the physico-chemical properties of Belleglade. Further, application of manure would not have significantly changed the soil properties in terms of SOM content, total P, and total Ca+Mg, which may contribute to the rate of mobility. There was no significant effect (p > 0.05) of initial TTC and OTC concentrations observed on the rate of mobility by Al-WTR in fertilized and unfertilized Belleglade soil. However, as observed in case of Immokalee soils, Al- WTR application rate had a significant (p < 0.001) effect on the rate of TTC and OTC mobility in both the TTC/OTC concentrations tested. The observed results are in agreement with the previous short term incubation study (Punamiya et al., 2016) conducted with Belleglade and TTC/OTC in the absence of plants amended with Al-WTR. The effect of Al-WTR in stabilization and reducing mobility of TTC and OTC in fertilized and unfertilized Belleglade soil was significantly (p > 0.05) higher compared to Immokalee soil, due to differences in their physico-chemical properties (Table 1). Studies have showed that various physico-chemical properties such as pH, CEC, clay content, (Bao et al., 2010; Sassman and Lee, 2005; Kulshreshta et al., 2004; and Ter Laak et al., 2006), Al and Fe hydrous oxide (Gu and Karthikeyan 2005; Figueroa et al., 2004; Figueroa and MacKay, 2005),  SOM (Bao et al., 2009), humic materials (Pils and Laird, 2007; Gu et al., 2007) presence of complexing metals and competing ligands (Jia et al ., 2009; Wang et al., 2010; Zhang et al., 2011; Zhao et al., 2012) etc. may affect the fate and transport of TCs in the soil system.

3.4 TTC/OTC in leachates and plants: Effect of Al-WTR

The effect of different Al-WTR amended rates (0, 25, and 50 g kg^-1) on leaching of TTC (Figure 5A and 6A) and OTC (Figure 5B and 6B) was investigated as a function of initial TTC and OTC concentrations (2.25 and 22.5 mg kg^-1) after 0.25 and 0.5 year of equilibration time in Immokalee and Belleglade soils fertilized with TTC/OTC rich manure in presence and absence of Bermuda grass (control plant) and corn (test crop). Soils fertilized with manure and spiked with TTC/OTC without Al-WTR amendment were used as control. In the unamended Immokalee soil (no Al-WTR), the highest amount of leaching was observed; due to the sandy characteristics, low SOM, and low Fe, Ca, Al, and Mg concentration. In the presence and absence of plant cover, 25-32% and 38-42% TTC and OTC leached from Immokalee soil after equilibration period of 0.25 and 0.5 year. However, in unamended Belleglade soil relatively low amount of leaching was observed; 15-20% and 20-25% in presence and absence of plants after an equilibration period of 0.25 and 0.5 y. Application of Al-WTR in Immokalee and Belleglade soils significantly (p < 0.01) decreased the downward movement of TTC and OTC and reducing mobility. Similar trend was observed for manure fertilized Immokalee and Belleglade soil; however, the amount of leaching was lower than soils unfertilized with manure; due to increase in the organic matter content and increase in the TTC and OTC binding manure treated soils (Wang and Yates, 2008).

Further, the effect of Al-WTR was investigated on uptake of TTC and OTC by corn (test crop). After harvesting at maturity, corn kernels and leaves were analyzed for TTC/OTC. In soils amended with Al-WTR there was no uptake of TTC/OTC in corn kernel and leaf samples (Tables 2 and 3).  Also, the uptake of TTC/OTC in control soils (no Al-WTR) was minimal (< 0.1 % of the initially added TTC/OTC concentration). Kumar et al. (2005b) studied the uptake of CTC in various vegetables from manure-amended soil with antibiotic concentration in manure ranging from 25 to 125 mg kg^-1. The study reported uptake of CTC was in range of 0.002 and 0.017 mg kg^-1 fresh pant tissue weight. Other studies have also reported minimal uptake of VAs in plant tissue in manure-fertilized soils (Dolliver et al., 2008; Boxall et al., 2006;). However, the uptake varies depending on the compound, plant species, plant physiology and growth stage, soil properties, and environmental conditions.   LC/MS/MS analysis was performed on one sample (corn kernel and leaf extracts) for TTC and OTC to confirm degradation or any transformation of TCs in plant tissue.  LC/MS/MS analysis of the corn kernel and leaf extracts did not reveal any known daughter compounds or metabolites of TCs. The percentage recovery was calculated from the total of TTC/OTC in the soils, lost in the leachate, and uptake in the plants of TTC (Table 2) and OTC (Table 3).  The percentage recovery ranged between 85 to 91% for Immokalee soil and 86 to 92% for Belleglade soil (Table 2 and 3). The residual 12-18% of TTC and OTC can be attributed to loss by photodegradation, removal by microbes, and potential unextractable fraction in manure, soils, and Al-WTR.

3.5 Extraction/Treatments: Effect of Al-WTR

Experiments were conducted to assess possible release of TTC and OTC from Immokalee and Belleglade soil treated with manure and amended with different Al-WTR rates at high initial TTC (Figure S2) and OTC concentration (Figure S3) as a function equilibration time. Four different extraction/treatments were used: 1 mol L^-1 KCl (competing ion effect), DI water (soluble water extraction phase), 0.25 mol L^-1 EDTA (chelating agent) and methanol (role of hydrophobicity), at time zero, 0.5, and 1y equilibration time. At time zero, no significant difference (p > 0.05) was observed in the amount of TTC and OTC released/extracted between the Al-WTR amended Immokalee and Belleglade soils, which were fertilized with manure or left unfertilized compared to controls (no Al-WTR application) (Figure S2A and S3A). The DI water extraction ranged between 64-75% and 52-60 % of the initial TTC and OTC concentration (22.5 mg kg^-1) for Immokalee and Belleglade soil fertilized or unfertilized with manure, respectively. The soluble form signifies the TTC and OTC fraction that may be lost via surface runoffs and leaching or is accessible for plants to uptake.  In case of unamended Immokalee soil (no manure, no Al-WTR) nearly 75% of the TTC/OTC was in soluble form, which was expected due to the sandy characterisitcs and low Ca, Fe, Mg, and Al, concentration of the Immokalee soil. The application of manure and Al-WTR in Immokalee soil at time zero did not exert any significant effect on lowering the TTC and OTC soluble fraction. With the treatment of 1 mol L^-1 KCl and methanol, the extraction was in the range of 58-73% and 60-75%, respectively. As expected, highest extraction was attained via treatment of EDTA, 75-83% of initially added TTC/OTC in Immokalee soil fertilized with manure and amended with Al-WTR (Figure S2A and S3A). However, the addition of Al-WTR at both the rates tested significantly decreased (p < 0.01) extraction by all treatments at 0.5 and 1 year of equilibration time for TTC (Figure S2B and S2C) and OTC (Figure S3B and S3C) indicating immobilization of TCs. After 1 year of equilibration time, KCl, methanol, and EDTA extraction reduced to 8-10%, 11-13%, 14-16%, and 17-20% of initial TTC (Figure S2C) and OTC (Figure S3C) concentration, respectively; whereas, control unamended with Al-WTR extraction were 48-55% (DI water), 54-57% (KCl), 59-62% (Methanol), and 63-72% (EDTA). In case of unamended Belleglade soil (no manure and Al-WTR) 65-69% of the total TTC/OTC was in soluble form, which was relatively lower than Immokalee soil (Figure S2A and S3A). The application of manure and Al-WTR in Belleglade soil at time zero did not exert any significant effect (p > 0.05) on lowering the TTC and OTC soluble fraction as seen for Immokalee soil treatments. The extractions of TTC and OTC by KCl, methanol, and EDTA at time zero were 59-70% and 62-72% and 72-78%, respectively. However, extraction of TTC and OTC in fertilized and unfertilized Belleglade soil by all the four treatments tested significantly reduced (p < 0.05) in Al-WTR amended Belleglade soil compared to the unamended soil after 0.5 and 1y of equilibration time. After 1y, KCl, methanol, and EDTA extraction reduced to 7-9%, 9-11%, 12-14%, and 16-19% of initial TTC (Figure S2C) and OTC (Figure S3C) concentrations, respectively; whereas, controls unamended with Al-WTR extractions were 42-45% (DI water), 49-55% (KCl), 52-58% (Methanol), and 63-66% (EDTA). Al-WTR application rates did not have a significant effect (p > 0.1) in decreasing the release of TTC and OTC by different extractions tested in both Immokalee and Belleglade soils.  Al-WTR was highly effective in decreasing the release of TTC and OTC from Immokalee and Belleglade soils, under a dynamic column set up with soil, water, manure, and plants.

3.6 TCLP analysis of soils and manure applied soils amended with Al-WTR

TCLP was determined for soils and soils fertilized with manure amended with different rates of Al-WTR in presence of plants (USEPA SW-846 Method 1311). TCLP was determined to confirm that the elemental (metals and metalloids) concentrations were below the USEPA limit for their safe disposal or land application. The TCLP values (Table S1) tested for all metal and metalloids were below the criterion (40CFR 261.24) and below the USEPA criteria values of bio-solids, thus, allowing safe disposal and/or land application of Al-WTR. Al and Fe does not fall under USEPA hazardous waste criteria therefore the limits of Al and Fe were compared to the solid industrial waste. The values for Al and Fe were also well below the threshold values of safe solid industrial waste disposal. One of the problems related with Al-WTR soil application may be the toxicity from Al to plants and restriction of growth (especially roots). The plant dry biomass of corn plants (without corn cob and kernel/seeds) harvested after full maturation period grown in Immokalee and Belleglade soils were recorded (Table S2). The data from plant dry biomass shows there was no significant (p > 0.2) effect of Al-WTR application rates on the plant biomass compared to control (no Al-WTR application). Several long term field and greenhouse studies have shown similar results, where no Al toxicity, reduced yields or increased phytoavailability was observed on plants at similar application rates used in the current study (Silveria et al., 2013; Oladeji et al., 2009). In addition, several states use WTRs as soil amendments or as a soil conditioner and to prevent excess P from leaching into surface water bodies. The use of WTRs as a soil amendment have shown several benefits; it helps to improve soil structure, increase moisture retention capacity, and enhance the availability of nutrients to plants ((El-Swaify and Emerson, 1975; Bugbee and Frink, 1985; Heil and Barbarick, 1989). Further, several studies have reported field application of the WTRs for agronomic and ecological benefits (e.g., Agyin-Birikorang et al., 2007; Jacobs and Teppen, 2000;). The plant biomass was higher for Belleglade soil when compared to Immokalee soil as expected based on the physico-chemical properties of both the soils. Also, application of manure to the soils increased the mean plant biomass.

4. Conclusions

Considerable efforts have been made to understand the fate and transport of VAs in the soil and water environment; but few attempts to develop sustainable strategies for remediation have been made. The present study is an effort to reuse an industrial waste by-product in the form of Al-WTR to immobilize TCs.  Our previous batch sorption and incubation settings studies demonstrated effectiveness of Al-WTR as a sorbent for TTC and OTC. The current study demonstrated that Al-WTR can effectively stabilize and immobilize TCs in soils and manure treated soils in a dynamic greenhouse column setting for 1y. Al-WTR amendment reduced the mobility of TTC and OTC, potentially decreasing the risk associated with TCs leaching into water sources, and being available for plants to uptake. Further, long-term (≥ 3 years) simulated field-based studies with repetitive application of TC rich manure, cyclic crop rotation, under field conditions are needed to validate the current findings.

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Figure Legends

Figure 1: Effect of Al-WTR application rates (0, 25, and 50 g kg^-1) on mobility of TTC at two initial concentrations, 2.25 (A) and 22.5 (B) mg kg^-1 as a function of equilibration time in Immokalee soil and Immokalee soil fertilized with TTC-rich manure. Immokalee soil spiked with TTC without Al-WTR amendment was used as control. Data are expressed as mean of two replicates ± one standard deviation.

Figure 2: Effect of Al-WTR application rates (0, 25, and 50 g kg^-1) on mobility of TTC at two initial concentrations, 2.25 (A) and 22.5 (B) mg kg^-1 as a function of equilibration time in Belleglade soil and Belleglade soil fertilized with TTC rich manure. Belleglade soil spiked with TTC without Al-WTR amendment was used as control. Data are expressed as mean of two replicates ± one standard deviation.

Figure 3: Effect of Al-WTR application rates (0, 25, and 50 g kg^-1) on mobility of OTC at two initial concentrations, 2.25 (A) and 22.5 (B) mg kg^-1 as a function of equilibration time in Immokalee soil and Immokalee soil fertilized with OTC rich manure. Immokalee soil spiked with OTC without Al-WTR amendment was used as control. Data are expressed as mean of two replicates ± one standard deviation.

Figure 4: Effect of Al-WTR application rates (0, 25, and 50 g kg^-1) on mobility of OTC at two different initial concentrations, 2.25 (A) and 22.5 (B) mg kg^-1 as a function of equilibration time in Belleglade soil and Belleglade soil fertilized with OTC rich manure. Belleglade soil spiked with OTC without Al-WTR amendment was used as control. Data are expressed as mean of two replicates ± one standard deviation.

Figure 5: Effect of Al-WTR application rates (0, 25, and 50 g kg^-1) on leaching of TTC (A) and OTC (B) at an initial concentration of 22.5 mg kg^-1 after 0.25 and 0.5 year of equilibration (with plants – P) and 0.75 and 1 year of equilibration (without plants – NP) in Immokalee and Belleglade soils and soils fertilized with TTC/OTC rich manure. Soils spiked with TTC/OTC without Al-WTR amendment were used as controls. Data are expressed as mean of two replicates ± one standard deviation.

Figure 6: Effect of Al-WTR application rates (0, 25, and 50 g kg^-1) on leaching of TTC (A) and OTC (B) at an initial concentration of 22.5 mg kg^-1 after 0.25 and 0.5 year of equilibration (with plants – P) and 0.75 and 1 year of equilibration (without plants – NP) in Immokalee and Belleglade soils and soils fertilized with TTC/OTC rich manure. Soils spiked with TTC/OTC without Al-WTR amendment were used as controls. Data are expressed as mean of two replicates ± one standard deviation.

Table 1: Selected general physico-chemical properties of Immokalee and Belleglade soils, cattle manure, and Al-WTR used in the greenhouse study. Data are expressed as mean of three replicates ± one standard deviation.

Nd; Not determined

^a EC = Electrical conductivity

^b CEC = Cation exchange capacity

^c OM = Organic matter

†= Below Method detection limit

^§ Datta and Sarkar, 2005

Table 2: Mass balance of TTC in Immokalee and Belleglade soils, and soil fertilized with manure at high initial TTC concentration (22.5 mg kg^-1) rate. The percent recoveries are calculated from TTC remaining in the soils, manure fertilized soils, TTC in leachates, and TTC accumulation in plants.