Trace Elements in Turfgrass Clippings Collected from Coal Combustion Product-Amended Putting Greens

Maxim J. Schlossberg, Assistant Professor, Department of Crop and Soil Sciences, Pennsylvania State University, University Park 16802

Corresponding author: Maxim J. Schlossberg. mjs38@psu.edu

Abstract

Golf course putting green construction methods rely on homogenous mixtures of coarse and medium-sized sands as root zone media, yet limited availability of mineral sands has increased interest in use of more ubiquitous medium- and coarse-textured components. Coal combustion products (CCP) are currently being used as substitutes and/or amendments of soil in golf course construction, including root zones of putting greens. However, the common practice of clipping disposal by surface land-application raises concern for potential trace element contamination of soil and/or water resources. Three greenhouse studies evaluated the elemental composition of creeping bentgrass (Agrostis palustris Huds. cv. Crenshaw) leaf clippings collected over a 6-, 12-, or 18-month period following establishment of putting greens constructed using CCP, sand-sized bottom ash (BA) and/or fly ash (FA), as substitutes for mineral sand. Results showed levels of As, Cd, Cu, Ni, Pb, Se, and Zn in putting green clippings fell well below pollutant concentration regulatory limits, permitting such clippings to be safely land-applied without requiring maintenance of cumulative pollutant loading rate (CPLR) records onsite.

Introduction

Dependable recreational use of a turfgrass site requires a well-drained root zone mix. Fine-textured soils often have limited macroporosity and do not support heavy traffic and use. When comprising the majority (>70% by mass) of a root zone, sand-sized particles bridge and increase porosity appreciably (15). Desirable physical characteristics of a putting green root mix include 10 to 15% non-capillary porosity, rapid infiltration rate, and a volumetric water holding capacity >10% (18).

Bottom ash (BA), a relatively inert and stable sand-sized (0.15 to 2 mm) aggregate, was produced nationally at an annual rate of 1.6 × 10⁷ metric tons in 2003 (9). In that same year, four times more fly ash (FA), a comparatively fine-textured (< 0.15 mm) coal combustion product (CCP), was generated in the United States (9). Bottom ash and FA have significantly lower bulk densities (0.7 to 1.2 g/cm³) than mineral sands, and their utilization often reduces construction costs by minimizing transport requirements (J. Moore, personal communication, 2002). It is likely for this reason that CCP have been historically used in the construction of golf course putting greens (4) and internally-drained bunker systems (J. Jennings, personal communication, 2001). A golf course currently under construction in Pennsylvania has specified BA and compost mixtures exclusively as tee and putting green root zone media (Fig. 1) (J. Spencer, personal communication, 2005), while similarly constructed golf courses currently operate in Europe (F. Harrison, personal communication, 2005). Numerous experimental studies have identified physicochemical attributes of CCP as soil amendments and/or substitutes (1,8,10,11,12,13).

Fig. 1. Construction of a golf course tee using bottom ash (BA) as root zone media, North York, PA. (Photo by Max Schlossberg).

An important aspect of putting green maintenance, regardless of root zone underfoot, is daily management and disposal of putting green leaf clippings. Bentgrass putting green mowing generates leaf clippings at a daily rate of 10 to 50 kg/ha of dry matter (approximately ½ lb/1000 ft²). With greens, tees, and fairways considered, an average 18-hole golf course can generate 2 to 9 tons of fresh/wet clippings each week of the growing season. Many superintendents effectively manage disposal of these clippings through systematic, onsite land-application (3) using heavy-duty, paddle-type spreaders manufactured explicitly for this purpose.

While seemingly a benign reuse, surface disposal of organic residue is regulated at the state level, with the exception of biosolids and animal manures. Federal standards for biosolid/manure surface application (40 CFR Part 503, under the Clean Water Act) state maximum trace element concentrations allowable for land application of these societal/agricultural byproducts (17). Because the 503 rule underwent extensive multi-pathway risk assessments, followed by a scientific and worse-case scenario approach to develop elemental concentration limits, it has become the de facto standard for land application of organic materials containing potentially hazardous elements. Many state regulatory boards have essentially transferred the 503 rule to standards for land application of composts and/or non-composted yard waste; such as leaves, grass clippings, and other vegetative material (6).

Thus, considering the popularity of clipping spreading and the increasing use of CCP as putting green root zone media, a study of BA- and/or FA-amended putting green root zones was conducted to observe CFR 40 Part 503 pollutant levels in associated creeping bentgrass leaf tissue, and to determine the suitability for onsite disposal of these CCP putting green clippings by unregulated land-application (17).

Root Zone Media and Column Preparation

Bottom ash and FA were collected from electric-generating plants in Georgia. Quartz sand and sphagnum peat moss (SPM) were acquired at local commercial outlets. Chemical properties of CCP used to formulate the root zones were determined in triplicate by Method 3050A (16) and are shown in Table 1. Granulation of the SPM was achieved by passage through a 2-mm sieve. Sand, FA, and BA were air-dried and separated by particle diameter with hand sieves.

Table 1. Chemical properties of coal combustion products (CCP) used to formulate the putting green root zone media.

Chemical properties		Bottom Ash	Fly Ash
Trace element concentration^x	Arsenic (mg/kg dry ash)	2	104
	Cadmium (mg/kg dry ash)	<1	1
	Copper (mg/kg dry ash)	274	200
	Nickel (mg/kg dry ash)	179	94
	Lead (mg/kg dry ash)	6	39
	Selenium (mg/kg dry ash)	2	24
	Zinc (mg/kg dry ash)	70	130
Solution activity	Water pH (1:1)	6.4	8.7
Solution activity	Electrical Conductivity (1:1, dS/m)	0.1	1.2

^× USEPA Method 3050A (16).

All root zones were formulated in the following volumetric particle size distribution: 7% very coarse sand (1 to 2 mm); 42% coarse sand (0.5 to 1 mm); 21% medium sand (0.25 to 0.5 mm); 10% silt, fine, and very fine sand (5 to 250 µm); and 20% SPM. A washed, quartz sand was used to formulate the mineral fraction of a control root zone (CON). Two of three CCP-root zone media treatments were formulated using BA and FA for replacement of sand and silt/fine sand/very fine sand, respectively (BAFA), or BA as a replacement for half of the sand aggregate (by volume) and FA as a replacement for silt/fine sand/very fine sand (BASFA). The remaining CCP-root zone media treatment was comprised of quartz sand with FA as a replacement for the silt/fine sand/very fine sand particles (SFA). Greater detail of experimental methods is provided in a companion publication (11).

Once homogenized, root mixes were transferred to 42-cm long sections of schedule 40, polyvinyl-chloride (PVC) pipe (5.1 cm internal diameter). The columns were closed on one end by a PVC end- cap with a 1.2-cm diameter center hole, and filled with 210 cm³ (10-cm height) of fine pea-gravel. Lastly, each PVC section was loaded with 636 cm³ (30-cm height) of the root zone media in 5-cm high (106 cm³) lifts. Each lift was firmly tamped in efforts to maintain consistent bulk density throughout each column.

Creeping Bentgrass Establishment and Maintenance

‘Crenshaw’ creeping bentgrass (Agrostis palustris Huds.) was seeded in plastic trays (20 kg pure certified seed/ha) for transplant into columns. Each tray was lined with ~2 cm of either bottom ash or sand (in equal parts of 1 to 2 mm, 0.5 to 1 mm, and 0.25 to 0.5 mm), and covered with a thin layer (~4 mm) of a SPM/bentgrass seed mixture.

On 7 October 2000, six replicated columns of four root zone treatments (Study 1) were leached with 400 mL of de-ionized water (DW), and sodded with recently-matured “discs” of creeping bentgrass. The BAFA and BASFA columns received sod propagated in the BA trays, while the SFA and CON columns received sod propagated in the sand trays. In 2001, the remaining 48 columns were split into two additional experiments and initially leached and established as described above on 22 January (Study 2) or 4 March (Study 3).

All putting green columns in the greenhouse were identically irrigated as necessary to prevent wilt and mowed semi-weekly at a height of 1.3-cm (0.5-inches) by frequently-sharpened, stainless-steel scissors. Slow-release fertilizer (Milorganite 6-2-0 Fertilizer, Milorganite, Milwaukee, WI) was incorporated into the root zones to provide N at 53 g/m² and P at 8 g/m² per 10 cm. Neither plant protectants nor supplemental lighting were employed over the experimental periods, thus daily photoperiod did not extend beyond that naturally observed at 32°N latitude (Athens, GA). Maximum photosynthetically-active photon flux density levels recorded in the greenhouse reached 1665 mmol/(m²s) at solar noon on 16 July 2001, approximately 70% of levels measured near-simultaneously outdoors. Greenhouse temperature was maintained in a range favorable for creeping bentgrass growth (10 to 24°C).

Data Collection and Analysis

Creeping bentgrass leaf clippings from Study 1 columns were collected with the described scissors 126, 180, 225, 401, 479, and 537 days after sodding (DAS). Clippings were collected from Study 2 columns 30, 49, 77, 92, 118, 294, and 359 DAS; and from Study 3 columns 16, 78, and 184 DAS. The scissor blades were rinsed and wiped thoroughly after each clipping collection to prevent cross-contamination of samples. Leaf clippings were triple-rinsed with DW, dried at 70°C in a forced-air oven, and acid-digested (5). Trace elemental concentration of CCP and leaf clipping digests were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS; Elan-6000; PerkinElmer, Wellesly, MA). Sample spikes, blanks, and standard reference material (SRM) digests were systematically included to measure analytical accuracy and precision. Recovery levels were contained within a 4 to 9% margin of the spike/SRM concentration. Saturated hydraulic conductivity of the uppermost 7-cm of each root zone was determined in situ upon completion of each study (7).

Each greenhouse study was comprised of 24 experimental units arranged in a completely randomized design. Levels of As, Cd, and Se in leaf tissue digests often fell below detectable limits, resulting in data that failed to meet the normally-distributed assumption of ANOVA. These dependent variables were transformed to rank sums by the PROC RANK procedure of SAS (Version 8.2, SAS Institute Inc., Cary, NC). Once requisite assumptions for parametric analysis were validated, the linear mixed procedure of SAS (PROC MIXED; Version 8.2, SAS Institute Inc., Cary, NC) facilitated analysis of the repeated measures (nested in study) data. Previously determined multiple comparisons of treatments within significant (P ≤ 0.05) main or DAS interactive effects were conducted using Tukey’s studentized range procedure (a = 0.05). Where a significant root zone effect on a trace element level was observed, a predetermined CCP vs. CON contrast statement identified significant variation (P ≤ 0.05) common to the three CCP-substituted root zones.

Experimental Results

Within a two week period following establishment, roots from the creeping bentgrass sod had effectively penetrated the surface of all root zone media, as determined by resistance to manually-applied detachment forces. Though particle size distribution of the root zones did not comply exactly with the United States Golf Association (USGA) recommendations for putting green construction, hydraulic parameters of the root zones measured at the end of each experimental period fell within acceptable ranges (11,18). Mean bulk densities of the CCP-substituted root zone media were 55 to 99% of the 1.35 g/cm³ sand-based control (CON) value. Total digestion of the utilized CCP showed both BA and FA to contribute trace elements to the root zone matrix (Table 1). Excepting Cu and Ni, the FA contained the greater trace element concentrations, particularly levels of As, Pb, and Se. Moreover, the FA showed greater hydrated reactivity than BA (Table 1), which is in agreement with a recently published summary of comparisons (9).

Clipping yields, as dry mass of clippings per mowing event, were observed within a range of 22 to 84 kg/ha over the experimental periods. Despite this wide range of observed shoot growth rate, yield was not significantly affected by study, root zone treatment, or interaction between the two (data not shown). Moreover, no measured variables (including forthcoming tissue concentration data) were significantly influenced by interactions between study and root zone treatments. These results, in tandem with the precluded analysis of a “study by DAS by root zone treatment” interaction term, support the simplified pooling of tissue concentration data across the three studies.

Trace Element Concentrations in Bentgrass Clippings

Leaf tissue levels of Cu, a plant-essential micronutrient, were unaffected by either root zone media or DAS (Table 2). Mean Cu levels (Fig. 2) ranged from 19 to 37 mg/kg (or parts per million), an array slightly above the reference common sufficiency range of plant shoot tissue (2), but well below the Part 503 monthly concentration limit of 1,500 mg/kg (17). Leaf tissue accumulation of Ni (Fig. 2), the most recently-identified plant-essential micronutrient, did not vary among treatments or time period (Table 2) but exceeded the plant shoot tissue common sufficiency range of < 1 mg/kg (2). Lead, a potentially-harmful pollutant that rarely accumulates in plant tissue, was observed in low concentrations (0.5 to 1.5 mg/kg) and showed no association with root zone media composition or time (Table 2). Mean levels of Ni and Pb observed in bentgrass leaf clippings (Fig. 2) were generally 2 orders of magnitude less than the Part 503 concentration limits of 420 and 300 mg/kg (or parts per million), respectively (17).

Table 2. Analysis of variance (ANOVA) of trace element concentrations in creeping bentgrass leaf clippings, by source.

Trace element	Source
	Root zone df = 3	Root zone contrast: CCP vs. control df = 1	DAS^z df = 13	Root zone × DAS^z df = 45
	P < F^y
As^x	***	***	***	***
Cd^x	**	NS	***	*
Cu	NS	NS	NS	NS
Ni	NS	NS	NS	NS
Pb	NS	NS	NS	NS
Se^x	*	*	***	**
Zn	**	NS	***	NS

^z All days after sodding (DAS) terms were analyzed as nested within study.

^y Significance levels are as follows: NS = not significant, * = P < 0.05, ** = P < 0.01, and *** = P < 0.001.

^× ANOVA conducted using rank sums data (some data fell below detection limits).

Fig. 2. Experiment-wide trace element mean concentrations in creeping bentgrass leaf clippings, by root zone treatment [CON, control sand; BAFA, bottom ash (BA) and fly ash (FA); BASFA, sand, BA, and FA; SFA, sand and FA]. Error bars for Zn represent minimum significant differences between root zone treatments (Tukey's studentized range, alpha = 0.05).

Tissue levels of Zn, a relatively ubiquitous trace element and common ingredient in plant protectants, were significantly affected by time or root zone, without interaction (Table 2). Resulting experiment-wide Zn concentrations were significantly greater in bentgrass established to the BAFA root zone than any other (Fig. 2). Regarding the time effect, Zn concentrations (all root zones) reached maximum levels of 202 to 280 mg/kg at 180 DAS, and slowly diminished to levels of 60 to 105 mg/kg by 537 DAS. Tolerance of creeping bentgrass to supraoptimal Zn availability has been reported, and accumulation of Zn in healthy shoots at levels of 1,500 mg/kg has been observed (14). While levels of this plant-essential micronutrient in leaf clippings exceeded all other trace elements measured in the study (Figs. 2 to 4), current regulatory concentration limits are 10 times greater (17) than the maximum level observed in this study.

Fig. 3. Cadmium concentration in creeping bentgrass leaf clippings, by days after sodding (DAS) and root zone treatment [CON, control sand; BAFA, bottom ash (BA) and fly ash (FA); BASFA, sand, BA, and FA; SFA, sand and FA]. Error bars represent minimum significant differences between root zone treatments (Tukey's studentized range, alpha = 0.05).

Fig. 4. Arsenic and Se concentrations in creeping bentgrass leaf clippings, by days after sodding (DAS) and root zone treatments [CON, control sand; All CCP, pooled data of all bottom ash (BA), fly ash (FA), and sand combinations (n = 3)]. Error bars represent minimum significant differences between root zone treatments (Tukey's studentized range, alpha = 0.05).

Of all the trace elements measured in these analyses of bentgrass putting green leaf clippings, Cd exposure poses the greatest risk to mammals. The CCPs utilized contained very minute Cd concentrations (Table 1), yet bentgrass tissue concentrations of 20 to 210 mg/kg (or parts per billion) were observed (Fig. 3). Though a root zone treatment effect on tissue Cd was significant, influence was not confined to either the CCP-amended or control root zones (Table 2). The illustrated data demonstrate wide temporal variations in Cd concentration by bentgrass grown in all root zones, including the CON (Fig. 3). Experiment-wide mean leaf Cd concentration was 69, 55, 92, or 72 mg/kg for the CON, BAFA, BASFA, or SFA root zone treatment, respectively. The greatest concentration of Cd observed was 210 mg/kg (BASFA, 92 DAS), approximately 0.5% of the Part 503 Cd concentration limit of 39 mg/kg (17).

The chemistry and behavior of hydrated As and Se are similar in that they are highly mobile, occur in various oxidative states, and generally concentrate in CCP at levels exceeding natural soil concentrations. Unfortunately, prolonged exposure to As poses significant risk to human health, primarily through inhalation or ingestion pathways. Selenium is an essential mineral in the diets of mammals, but extended exposure to concentrated Se is not recommended. The transient nature of these oxyanionic trace elements is demonstrated by the decline in leaf content to negligible levels after the 126 DAS clipping collection (Fig. 4). Neither As nor Se were detected in tissue collected between 225 and 537 DAS (data not shown). The maximum observed As level of 1.2 mg/kg in bentgrass clippings (SFA, 78 DAS) remains below 3% of the Part 503 As concentration limit of 41 mg/kg (17). The maximum observed Se concentration of 1.5 mg/kg was ~70 times less than the Part 503 limit of 100 mg/kg (17)

Conclusion

Results show creeping bentgrass growth in CCP-amended putting greens to mirror that fostered by traditional quartz sand (CON) root zones. Levels of Cd, Cu, Ni, Pb, and Zn were generally unaffected by elevated trace element concentrations of the root mix . Furthermore, in only two relatively-brief instances did CCP-amended root zones contribute to elevated trace element levels (As and Se) compared to the CON root zone treatment. Despite these specific observations, measured trace element levels in clippings collected from CCP-amended putting greens never broached the tenth percentile of Part 503 pollutant concentration limits regulating land applications. These data considered, unrestricted land application of turfgrass clippings collected from either CCP-amended or traditionally-constructed putting greens is highly unlikely to violate federal and state laws or contaminate soil and/or water resources.

However, it is important to note mercury concentrations were not measured in either of the CCP amendments or leaf clippings. Mercury, a highly-toxic heavy metal that very rarely accumulates in aboveground vegetative plant tissue, was the only Part 503 pollutant (regulatory limit of 17 mg/kg) not measured in the described study (17). It is recommended that managers of turfgrass facilities considering land application of clippings submit multiple samples to a certified laboratory for analysis of regulated pollutants (including Hg). Moreover, some states have exercised their sovereign right to impose more restrictive regulations on land application of organic materials than the federal regulations described here (17). In the interest of public safety and environmental stewardship, turfgrass managers should determine turfgrass clippings composition and consult local and state regulatory officials about permissible land-application of turfgrass clippings before broadcasting organic residue(s) to land, public or private.

Acknowledgments

This research was supported by the Electric Power Research Institute, Palo Alto, CA. The author gratefully acknowledges supporting information provided by James Moore of the USGA Green Section; Jon Jennings, CGCS, at Chicago Golf Club; Fred Harrison of EON-UK Ltd.; and J. Spencer of Jim Spencer Golf Course Shaping & Construction. Likewise, technical assistance provided by Bill Miller, Chris Vanags, Stan Dudka, Gil Landry Jr., Bob Carrow, Lamar Larrimore, Gene Weeks, and Cameron J. Tribble is greatly appreciated.

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