David E. Stilwell

Dislodgeable copper, chromium and arsenic from CCA-treated wood surfaces.

Chromated copper arsenate (CCA) is commonly used to preserve wood, but its use poses risk of arsenic exposure. In order to evaluate the extent of exposure to As from physical contact with CCA-treated wood, dislodgeable As from treated wood surfaces (as well as Cu and Cr) was determined as a function of weathering time using dampened polyester wipe materials. Six sets of 2.5-m-long CCA-treated boards, three-four boards per set, were purchased from lumber yards and cut into 30- or 60-cm coupons. A total of 44 such coupons were placed outdoors and the dislodgeable CCA components from the surfaces of the wooden coupons were periodically determined over a 1- or 2-year period by a systematic wipe method followed by nitric acid extraction of the CCA components from the cloth. In all 316 samples, appreciable amounts of the three elements, Cu, Cr and As, were detected. The amounts of surface-dislodgeable As, the most potentially hazardous element and the one of major concern in this study, varied from 5 to 122 microg/100 cm(2) with an average value of 37+/-22 microg/100 cm(2). There was considerable variation in As dislodged among coupons, boards, sets and time. Test coupons that tended to release relatively higher (or lower amounts) over time initially, continued to do so over time. However, the amounts of arsenic dislodged over time did not follow a simple pattern. While the As dislodged tended to decrease with time during the first year, it approached the initial value or increased somewhat during the second year, presumably due to surface rejuvenation effects caused by erosion and weathering. When all the data were normalized to the initial values, no trend emerged, as indicated by the average normalized value of 1.0+/-0.4 for As dislodged over time. Apparently, on installations constructed with CCA-treated wood, arsenic may remain available for a number of years.

Elemental Analysis of Composted Source Separated Municipal Solid Waste

▪ Samples from composted source separated municipal solid waste were analyzed for 25 elements, including heavy metals and trace nutrients. The results were compared to a rural soil. The precision and recoveries for the various analytes using microwave digestion and atomic spectroscopic methods were determined. The recoveries ranged from 30 percent to 130 percent, depending on the analyte. The concentrations of the regulated elements were all well below proposed EPA 503 limits. The average values (mg/kg, dry weight) were 2.1(As), 1.2(Cd), 20(Cr), 173(Cu), <2(Hg), <22(Mo), 17(Ni), 92(Pb), <1(Se), and 395(Zn). The sampling strategy followed a two-stage nested design, allowing for assignment of the errors to the various sampling components. The average errors were 7.2% (samples), 3.5% (sub-samples), and 3.6% (replicates) for the compost, and 10.8% (samples) and 4.7% (replicates) for the rural soil. Reducing the grind size dramatically reduced the error between replicates. The implication of these errors, in t...

Evaluating The Suitability Of MSW Compost As A Soil Amendment In Field Grown Tomatoes Part B: Elemental Analysis"

Tomato plants were grown under field conditions in soil amended with 0, 25, and 50 tons/acre of source separated composted municipal solid waste (MSW). The leaves and fruit from these plants were sampled following a dual-stage nested design, and analyzed for 17 elements. Statistical analysis of the results showed that the Na and P contents increased and that the Cd and Be contents decreased in the fruits grown in the amended soil. In the leaves of tomato plants grown in amended soil the Na content increased, and the Cd, Cu, and Mn contents decreased compared to those grown in the control soil. The attenuation of the Cd, Cu, and Mn levels in the tomato tissues was attributed to increases in pH and organic matter in the compost amended soil.

Heavy Metals Leachability as Affected by pH of Compost-Amended Growth Medium Used in Container-Grown Rhododendrons

The leaching of heavy metals from plant growth medium, admixed with different amounts of compost (prepared from sewage sludge and yard waste) at pH 5, 6 and 7 was determined over a six-month period. Twelve-week old rhododendron cuttings were planted in 2-L containers and rainfall was supplemented with irrigation to supply two centimeters of water per day. Leachates collected over each two to four week period were analyzed for Cd, Cr, Cu, Ni, Pb and Zn using atomic spectrometry. The concentrations of Cd, Cu, Ni and Zn in the leachates increased with increasing proportions of compost in the medium and decreased with increasing time of leaching. Decreasing media pH dramatically increased the concentrations of Cd, Ni and Zn in the leachates, but had no effect on the Cu concentrations. For example, as the proportion of the compost in the pH 5 medium increased from 0 to 100 percent, the concentrations of metals (μg L−1) in the leachates collected during the first two weeks increased from 1 to 33 (Cd), 10 to 123...

Leachability of Arsenic from Field Containers Filled With Plant Growth Medium Amended With Biosolids Compost

The leaching of arsenic (As) from plant growth medium, admixed with different proportions of composted biosolids in field containers, was determined over a four-month period. Eight-week-old perennial flowers, Coreopsis grandiflora L, were transplanted in the field in 2-L containers filled with plant growth media. The treatments were replicated three times and rainfall was supplemented to supply 2 cm of water per day. Water percolating through potted plant containers was collected biweekly and analyzed for As using graphite furnace atomic spectrometry. The concentrations of As in the leachates increased with increasing proportions of compost in the medium and decreased with time of leaching, generally remaining below the drinking water standard of 50 μg/L after two months. Leaching of As occurred at a rapid rate initially but then continued at a slow rate. Compared to other metals of concern, as Cd, Cr, Ni and Pb, As in the compost appeared more mobile.

Elemental Analysis of Municipal Solid Waste Compost II. Refuse Derived Fuel Unders

In utilizing municipal solid waste (MSW) as fuel for energy production, about 10 percent remains as a noncombustible small size fraction byproduct called refuse derived fuel unders (RDFU). We assessed the feasibility of using RDFU to produce compost for land applications, in the context of acceptable limits for metals. Periodic random samples from two batches of RDFU obtained during composting were analyzed for the heavy metals Cd, Cu, Pb, and Zn, and for the plant nutrients N, P, and K. The heavy metal content (mg/kg, dry weight) in all samples ranged from 1.7-12.7 (Cd), 201-3217 (Cu), 267-5002 (Pb), 344-2079 (Zn). The total variability of these elements within a batch of RDFU compost was high, with relative standard deviations (RSD) ranging from 20-107 percent. Estimates of the number of samples needed to obtain a 10 percent uncertainty in the averages ranged from 5-138, depending on the analyte and the compost batch. Leachability tests showed little leaching of metals in the RDFU compost. The high vari...