Jointly published by Elsevier Science S. A , Lausanne and Akad#miai Kiad6, Budapest

Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 192, No. 2 (1995) 289-297

C H A R A C T E R I Z A T I O N O F H O U S E H O L D P L A S T I C S F O R H E A V Y M E T A L S U S I N G N E U T R O N A C T I V A T I O N A N A L Y S I S

S. LANDSBERGER, D. L. CHICHESTER

Department o f Nuclear Engineering, University o f lllinois, 103 South Goodwin Avenue 214 Nuclear Engineering Laboratory, Urbana, lllinois 61801 USA

Highly enriched concentrations of several heavy metals have been found in municipal solid waste incinerator (MSWI) ash. In an effort to identify possible sources of these metals in MSWI ash, a variety of disposable household plastic products was examined for heavy metal content. Using both thermal and epithermal neutron activation analysis (NAA) along with Compton suppression techniques, concentrations of several trace and heavy metals including Ag, As, Au, Ba, Br, CA, Cr, Ca, Fe, Mn, Ni, Sb, Se, Sn, Sr, V, W and Zn were determined. Results indicate a wide range of concentrations for these elements, with large variations in plastics of similar color and intended use. As limits dealing with heavy metal content of consumer products are lowered, NAA techniques will provide a useful method for verification of product compliance.

The disposal of municipal solid waste (MSW) is a growing concern in many parts of the world. Sanitary landfills for the disposal of MSW are nearing capacity while, as public concern grows, the licensing of new landfills is becoming more and more difficult. The response that many communities have taken to help alleviate this problem is to incinerate their waste. With the ability to reduce waste volumes by as much as 90 percent, incineration can significantly extend the waste-accepting lifetime of a landfill.l,2

During the incineration process, heavy metals present in MSW become concentrated in the bottom and fly ashes as the organic portion is combusted and thus removed. The ability of these ashes to leach heavy metals when exposed to water has been the focus of several studies. 3-7 Results from these studies indicate that many landfill bound municipal solid waste incinerator (MSWI) ashes have the propensity for leaching heavy metals in excessive concentrations, often failing regulatory leaching tests and thus requiring handling and disposal as a hazardous material. Owing to these results, investigations into the sources of heavy metals in MSW streams will be useful in making decisions regarding MSW disposal.

The composition of MSW has also been investigated by several researchers.3,r 9 In general, it has been reported that about 5-10% of MSW is composed of plastic wastes; the variation between different waste sites stemming from several factors including different consumer shopping trends in the sampling area and the time of year. This plastic component is important in the discussion of heavy metals in MSW because of the use of metal-based pigments and stabilizers in the plastics manufacturing process.10,n Aware of this practice, various state and federal agencies have enacted laws regulating and limiting the use of these metal-based products, n In response to these regulations, several plastics processors are developing colorants free of heavy metalsA 2 However, recent studies indicate many plastics currently on the market still contain metals in non-trivial concentrationsA3,14 This is especially important when the tendency of the incineration process is to enrich metals in the combustion ash.

In light of these findings, it was decided to investigate a large sampling of household plastic products likely to enter the MSW stream. Neutron activation analysis (NAA) was chosen as

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S. LANDSBERGER, D. L. CHICHESTER: CHARACTERIZATION OF HOUSEHOLD

the tool to use for this analysis based on a number of factors. The NAA process requires little sample preparation, thus avoiding the need for sample dissolution or acid digestion required by other analysis techniques. This technique can provide a possible useful tool for quality assurance and quality control in plastics production. As Parry 15 has pointed out, plastic, which is predominately made of the non gamma emitting elements hydrogen and carbon~ forms a perfect matrix for the study of metal concentrations and thus is a prime candidate for NAA.

Experimental

Sampling and Preparation: Plastic samples wer e purchased from local grocery and drug stores. The samples were chosen to reflect a broad range of consumer goods and uses. In addition, selection was done so as to have several groups of products with similar uses and several groups of products similar in plastic type, e.g., polystyrene and high-density polyethylene and color. The variety in plastic type and color found in the samples is listed in Tables 1 and 2. For identification purposes, plastics were sorted by their recycling code number when known and also into one of twelve color categories.

Table 1 Classification and distribution of samples analyzed by use and plastic recycling code

Plastic Use Recycling Code Totals 1 2 3 4 5 6 7 Unknown

Bags 1 1 4 6 Cleaning Supplies 6 2 8 Food Containers 1 4 1 2 2 10 Lab Equipment 1 2 3 Personal Hygiene 1 5 1 4 1 12 Plasticware 5 2 4 11 Pens 4 4 Toys 5 5 Other 2 2 4 Totals 2 23 1 3 10 4 3 17 63

Recycling Codes 1 - PETE (polyethylene terephthalate) 2 - HDPE (high-density polyethylene) 3 - PVC (polyvinyl chloride) 4 - LDPE (low-density polyethylene) 5 - PP (polypropylene) 6 - PS (polystyrene) 7 - Other

Samples were also categorized into 8 general categories according to either the sample's purpose or, when the sample was part of a package, in the case of bottles and some bags, the product contained in the sample. After documentation, these products were emptied of their contents. Where appropriate, paper and plastic labels were removed along with any adhesive backing. After rinsing with de-ionized water seven times, the specimens were cut into small, thin strips approximately 20 mm by 2 mm in size using case-hardened steel snips. The strips were then placed into small polye~iaylene vials, weighed and heat sealed. Typical weights ranged from 0.8 to 1.8 g. Samples with inhomogeneous coloring were entirely shredded and then mixed to produce an approximately homogeneous sample. Following previous work, hard

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Table 2 Classification of plastic samPles by use and color

Plastic Use Plastic Color * Totals Red Org. Yel. Gr. Blue Prp.' Blk. Wht. Mul. Bin. Opq. Cir.

Bags I 1 2 2 6 Cleaning Supplies 1 1 2 3 1 8 Food Containers 1 1 1 1 4 2 10 Lab Equipment 1 1 1 3 Personal Hygiene 2 ! I 2 1 2 1 1 1 12 Plnsticware 1 1 1 1 3 4 11 Pens 1 1 i 1 4 Toys 1 2 ~ 1 5 Other t 1 1 1 4 Totals 8 6 5 7 7 1 2 6 9 4 2 6 63

* Org. = Orange, Yel. = Yellow, Gr. = Green, Prp. = PurPle , Blk = Black Wht. = White, Mul. = Multi, Brn. = Brown, Opq. = Opaque, Cir. = Clear

General Plastic Product Categories 1. Plasticware (cups, plates, utensils,...) 2. Food Container (candy wrapper, tortilla chip bag, orange juice bottle,.,.) 3. Cleauing Supplies (laundry detergent bottles, dish soap bottle,...) 4. Bags (garbage bags, freezer bags, lawn bags,...) 5. Personal Hygiene (shampoo bottles, toothpaste dispenser,...) 6. Pens (various colored pen caps) 7. Toys (water gun, dart gun,...) 8. Other (telephone, pantyhnse)

and difficult to cut plastics were embrittled in liquid nitrogen and then smashed, the broken pieces being used for analysis.! 4 Six samples were prepared for each type of plastic to be analyzed. All utensils were 'thoroughly' cleaned after each' preparation. The plastic reduction process was not found to introduce measurable contamination.

Irradiation: As a neutron source, the University of Illinois Advanced TRIGA Reactor was used. This reactor has a maximum steady state power level of 1.5 MW and is equipped with a pneumatic transfer system for thermal and epithermal short irradiations, an epithermal cadmium-lined irradiation tube (CLNAT) for medium/long irradiations and a rotary specimen assembly, or "lazy Susan" (LS), for medium/long irradiations. For short irradiations the reactor was operated at a power of 1500 kW with a corresponding thermal neutron flux of 1. lx l 013 n'cm-2-sec -1 and an epithennal flux of 6.3 x 1011 n-cm-2-sec -I. For medium irradiations the reactor was operated at a power of 500 kW with a corresponding epithermal neutron flux of 2. lxl011 n-cm-2-sec -1. Long irradiations were performed at a power of 250 kW with a thermal neutron flux of 5.6x1011 wcm-2.sec "1. This lower flux was chosen to prevent melting o f t h e plastics.

To investigate those elements with short-lived activation products and advantageous thermal cross sections (Al, Ca, C1. Ca, Mn, Na, Ti and V), the pneumatic transfer system was used. Samples were irradiated from between 10 to 120 seconds, with decay times from 100 to 400 seconds and a counting time of 600 seconds. For those elements with more favorable epithermal cross sections (Ba, In, Si, Sn and Sr), the cadmium-lined pneumatic transfer system was used. Typical irradiation times were 120 seconds with decay times of 1000 seconds and counting times of 600 seconds.

Determination of the elements As, Au, Br, Cd, Mo, Sb, Sin, U, W and Zn, all medium-lived activation products, was conducted by irradiation in the CLNAT system. Ten samples were

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irradiated per week over a seven week period for 3 hours and then allowed to decay for 1-2 days. The samples were counted for 3 hours in the Compton suppression system.

Long-lived elements such as Cr, Se, Th, Ag, Cs, Ni, So, Fe and Co were determined for samples irradiated for eight hours in the LS rotary specimen assembly and allowed to decay for 2-3 weeks. These samples were counted for 3 hours.

Data Acquisition: Data acquisition for this experiment used three detectors. For thermal and epithermal short-lived analysis, two high purity germanium detectors with 13% and 19%

Table 3 Elements analyzed, method of analysis used and activation information

Method ELEMENT of

Analysis * Ag 4 AI 1 As 3 Au 37 Ba 2 Br 3 Ca 1 Cd 3T CI 1 Co 4 Cr 4 Cs 4 Cu 1 Fe 4 In 2 Mn 1 Mo 3"f Na 1 Ni 4 Sb 3 Sc 4 Se 4 Si 2 Sm 3 Sn 2 Sr 2 Th 4 Ti 1 U 3 V 1 W 3 Zn 31"

Nuclear Activation Equation

109Ag(n,y) 110mAg 27AI(n,y)28AI 75As(n,y)76As

197Au(n,~t) 198Au 138Ba(n,7) 139Ba 81Br(n,,y)82Br 48Ca(n,,y)49Ca

114Cd(n,7 ,13- ) 115mln 37C1(n,7)38C1 59Co(n,7)60Co 50Cr(n,,/)51Cr

133Cs(n,7) 134Cs 65Cu(n,,/)66Cu 58Fe(n,7) 59Fe

115in(n,~, ) 116mln 55Mn(n,,/)56Mn 98Mo(n,y)99Mo 23Na(n,y)24Na 58Ni(n,p)5~Co

121Sb(n,7)122Sb 45Sc(n,y)46Sc 74Se(n,y)75Se 29Si(n,p)29Al

152Sm(n,y) 153Sm 124Sn(n,y) 125mSn

86Sr(n,y)87mSr 232Th(n,7,13-)233pa

50Ti(n,y)51Ti 238U(n,~,,jS-)239Np

51V(n,y)52V 186W(n,7) 187W 68Zn(n,y)69mzn

Gamma Peak (keV) 657.8 1778.9 559.2 411.8 165.8 776.6 3083.0 336.6 1642.0 1332.4 320.0 795.8 1039.0 1098.6 1097.1 1810.7 140.6 1368.4 810.3 564.0 889.4 264.6 1273.3 103.2 332.0 388_5 311.8 320.0 277.5 1434.4 685.7 438.7

Method 1: Thermal Short at 1500 kW Method 3: Epithermal Medium at 500 kW Method 2: Epithermal Short at 1500 kW Method 4: Thermal Long at 250 kW

tCompton suppression technique used.

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efficiency were used. Medium-lived epithermal analysis was performed with a high purity germanium detector with 19% efficiency in conjunction with a NaI(T1) detector. This arrangement allows the rejection of gamma-rays coincident with Compton events within a window of 100 ns, thus reducing Compton scattered photons and the background in general. This Compton suppression mode, as shown in previous work dealing with epithermal medium- lived analysis, has been proven to significantly lower detection limits for several dements. 16 For the analysis of dements with multiple gamma emissions, this process is not used for obvious reasons. For long-lived analysis, a gamma detector of 24% efficiency was used along with a sample changer. Data collection was handled by ORTEC PC based sottware and hardware. A summary of the four acquisition methods used for analysis along with the pertinent neutron activation information is provided in Table 3.

Data Analysis: At the University of Illinois, the NADA code is used to analyze data and determine elemental concentrations. 17 For concentration determination, reference materials from the National Institute of Standards and Technology (1632a, 1632b, 1633a, 1633b and various NIST elemental stock solutions) and CANMET (Gold Ore CH-2) were used as follows. For each set of sample irradiations liquid standards for individual dements along with several geological reference materials were irradiated. Then, under conditions identical to those for the samples, the liquid chemical reference materials were analyzed and used to make a standards library with which the unknown samples could be compared and analyzed. Exceptions were for bromine and gold, the standards libraries for these two elements were made from the analysis of geologicalreference materials, 1632a and CH-2, respectively. For each method of irradiation, the geological reference materials were separately analyzed as if their elemental concentrations were unknown. This test served to assure the quality of the data obtained and to maintain quality control. Geological reference materials were used for analysis due to the lack of any certified plastic reference materials. Differences in the neutron fluence were determined using cobalt flux wires.

Results and discussion

Sixty-four plastic samples were analyzed; however, for some specimens, not all elements were able to be determined. One sample contained so much CI that, following the thermal short irradiation, it was elected not to perform an epithermal short irradiation. No further investigations were performed for this sample. For the medium irradiations, three samples melted and could not be counted. For the long irradiations, done at a lower power level, one sample melted and therefore could not be counted.

As indicated in Table 4, the range of concentrations determined for many elements was quite large, varying from a few parts per billion to several percent. Also, not all samples had elemental levels great enough to be determined. For example, Ag was found only in two samples and then only in very trace amounts. In Table 4, the column listing "Samples Below the Minimum Detectable Limit (MDL)" refers to the number of samples below their own particular MDL. With samples above the MDL, concentrations for a particular element usually span the entire range, which indicates the large compositional variation among specimens.

Concerning the distribution of elements within a specific sample, Table 5 provides information on 25 different plastic products. Due to space constraints, only the elements As, Cd, Cr, Sb, Se, Sn, V and Zn are listed. These elements were all found in large concentrations for several of the samples listed. For the maximum concentration determined for a particular dement the value is shaded.

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S. LANDSBERGER, D. L. CHICHESTER: CHARACTERIZATION OF HOUSEHOLD

T a b l e 4

o f c o n c e n t r a t i o n

Maximum M~nimum lqumber Number of

Element Units Sample Sample of Samples

Concentration Concentration Samples Below

MDL MDL Analyzed MDL

Ag p p b 53.0 • 15.5 49.1 30.9 4. 12.6 41.0 63 61

AI ppm 39400 4. 900 220 1.02 4. 0.05 0.04 64 1

As ppb 851 4. 11 11 2 .824.0 ,25 0.78 61 10

Au ppb 7.66 • 0.34 0.54 0.035 4. 0.005 0.012 61 4

Ba ppm 15227 4. 798 57 3.00 4. 1.05 3.40 63 36

Br ppm 65.8 4. 3.3 0.1 0.0858 4. 0.0044 0.0200 61 0

Ca ppm 70800 4. 2600 210 3.21 4. 1.44 1.74 64 7

Cd ppm 4802 • 66 1.5 0.0218 4- 0.0024 0.0066 61 12

Cl ppm 41764 • 1802 195 3.65 4.0.48 0.88 64 1

Co ppm 72.6 • 0.4 0.2 0.0604 • 0.0041 0.0081 63 1

Cr ppm 1034 4. 5 0.5 0.0860 • 0.0297 0.0964 63 8

Cs ppb 408 4. 10 24 47.8 4. 3,4 8.6 63 6

Cu ppm 474 + 19 50 0.236 4. 0.090 0.292 64 4 3

Fe ppm 13806 4. 147 26 4.50 4. 1.53 4.85 63 4

In ppb 15.4 • 1.0 3.0 0.104 4. 0.044 0.142 64 47

Mn ppm 120 4. 9 1.5 0.0437 • 0.0152 0.0420 64 18

Mo ppm 122 4. 1 0.1 0.00788 4. 0.00215 0.00699 61 31

Na ppm 1900 + 100 i09 2.37 + 0.42 1.08 64 5

Ni ppm 6.75 4. 2.22 7.28 0.864 • 0.305 0.982 63 55

Sb ppm 306 4. 4 0.07 0.003:37 4. 0.00014 0.00036 61 2

Sc ppm 3.45 • 0,04 0.01 0.00328 • 0.00023 0.00054 63 3

Se ppm 11014. 8 1.0 0.0645 4. 0.0236 0.0769 63 26

Si ppm 356164. 1305 2987 51.5 + 22,2 71.8 63 27

Sm ppm 1,81 4. 0.02 0.01 0.000409 • 0.00021 0.00006 61 6

Sn ppm 37.1 4. 0.9 2.5 0.0743 -~ 0.0280 0.0909 63 40

Sr ppm 125 • 4 8.8 0.725 • 0.278 0.900 63 40

Th ppm 5,13 + 0.03 0.03 0.0163 4. 0,0020 0.0061 63 4

Ti p p m 25000 • 1100 50 11.6 • 1.8 5.6 64 15

U ppb 923 • 22 60 1,64 4. 0.38 1.23 61 28

V ppm 24.9 4. 1.8 1.8 0.00324 • 0.00125 0,00397 64 27

W ppb 804 • 54 168 1.14 • 0.40 1.30 61 9

Zn ppm 354 + 5 5 0.252 4. 0.045 0.140 61 13

MDL: Minimum Detection Limit

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S. LANDSBERGER, D. L. CH1CHESTER: CHARACTERIZATION OF HOUSEHOLD

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Some trends between sample classification and elemental concentration can be seen. For example, soda bottles have similar concentrations for several elements. Additionally, products sometimes employ Sb and Zn to increase the flame retardent properties of plastic, as found in the telephone casing listed in Table 5.18 However, these trends can not be generalized to all products, as demonstrated by the variations in garbage bags and pen caps. It might seem logical that samples similar in color would have similar elemental concentrations, at least for elements used in pigments, such as Cd, Co, Cr and Zn. Again though, while some relations Can be identified, such as the presence of Co in some blue colored plastics, the presence of Ti in some white plastics and the presence of Cd in some red plastics, fewer samples follow these trends than do not. The same is true for different types of plastics. Plastics made of PETE were found to contain high levels of Sb, but for HDPE type plastics, the most numerous analyzed, no elemental trends could be found.

Perhaps the most important information that can be gleaned from Table 5 concerning MSW and MSWI ash is the identification of products with large concentrations of heavy metals. These products, following the enriching behavior of the incineration process, have the potential to contribute a large amount of heavy metals to the ash while at the same time transforming these metals to a form more readily able to enter the environment. Many of the items investigated were found to have one or more of the elements listed in Table 5 at a concentration of 1 ppm or greater. Further, while more research needs to be done to determine the extent to which an incinerator enriches various elements from plastic combustion, concentrations of 50 ppm or more for As, Cd, Cr, Sb, Se and Zn, as found in various items analyzed in this study, are certainly of concern with regard to MSW and MSWI ash. 14

Conclusions

Neutron activation analysis was found to provide an effective method for determining the concentrations of 32 elements in plastic. In the plastics analyzed, elemental concentrations were found to range from a few parts per billion to several percent. While some limited trends could be seen between plastic use, color and type and the concentrations of a few elements, no general trends were found relating these areas. Overall, several products with large concentrations of one or more heavy metals were identified and listed. As demonstrated by this study, NAA also has the potential to serve as a tool for the analysis of plastic for other purposes, such as in quality control for manufacturing or in the determination of concentrations for the enforcement of legal regulations.

The authors would like to thank Assir Dasilva for his assistance with this project. Funding for this investigation was provided by a grant from the Illinois Office of Solid Waste Research, [OSWR Contract No. 09-011].

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(1990) 377. 14. P. BODE, J. Radioanal. and Nucl. Chem., Articles, 167 (1993) 361. 15. S. J. PARRY, British J. NDT, 34 (1992) 533. 16. S. LANDSBERGER, D. WU, J. Radieanal. and Nuel. Claem., Articles, 167 (1993) 219. 17. S. LANDSBERGER, W. D. CIZEK, P. DOMAGALA, J. Ra, dioanal, and Nucl. Chem., Articles, 160

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