8th International Conference on Environmental Science and Technology Lemnos island, Greece, 8 10 September 2003

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SOLID-PHASE MICROEXTRACTION TO DETERMINE THE MIGRATION OF

PHTHALATES FROM PLASTIC WARE TO DRINKING WATER

K. PERDIKEA, E. PSILLAKIS, and N. KALOGERAKIS

Technical University of Crete, Department of Environmental Engineering, Polytechnioupolis, 73100 Chania, Greece

E-mail: epsilaki@mred.tuc.gr

EXTENDED ABSTRACT Phthalate esters are widely used as additives in the manufacture of plastics improving their softness and flexibility. As these compounds are not chemically bound to the plastics, they can easily penetrate these materials and migrate into the food or water that comes into direct contact. The presence of phthalates in drinking water is usually in the low g/L contamination level due to their hydrophobic nature. Today, phthalate esters are included in the priority lists of pollutants in several countries and are being questioned worldwide because of their potential toxicity to humans and the environment. Solid Phase Microextraction (SPME) coupled to Gas Chromatography was used for the determination of phthalate esters in water samples introducing thus a fast and solventless analytical method enabling detection of these compounds in the low g/L concentration levels. The major advantage of SPME over other preconcentration techniques was that it minimized the risk of secondary contamination during sample preparation, a major parameter to consider during phthalate contamination. This paper investigates the extent of phthalates migration from several disposable plastic materials into drinking water. The plastic materials investigated included plastic shakers used for the preparation of iced coffee, plastic cups and plastic straws. The scope of the present work was to investigate for the first time the effect of temperature on phthalate migration establishing thus the safety of these materials when used with hot beverages as well as demonstrating the importance of storage and transfer conditions of plastic materials containing drinking water. Overall, the results revealed that significant quantities of phthalates are expected to be present in drinking water samples coming into direct contact with disposable plastic items at elevated temperatures. The contamination level is higher when a prolonged exposure to such temperatures is applied. Therefore, it is strongly advisable to control temperature during the transfer, storage and/or handling of these materials. Key words: SPME, phthalate esters, drinking water, water analysis

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1. INTRODUCTION

Dialkyl phthalate esters (phthalates) are widely used as plasticizers in the manufacture of polyvinyl chloride to improve flexibility softness, workability and general handling properties. The physical rather than chemical incorporation of phthalates in the polymeric matrix ensures that they are widespread contaminants. Penetration of phthalates into the ecosystem or in wastewater effluents occurs during the production phase and via leaching and volatilisation from plastic products during their usage and/or after disposal. Furthermore, phthalates can easily escape from plastic materials and migrate into the food, water or beverages coming into direct contact with the packaging material [1]. The presence of phthalates in such products depends on the initial concentration of phthalates in the packaging material, contamination during production, as well as transfer and storage conditions [1]. Today, phthalates are included in the priority lists of pollutants in several countries and are being questioned worldwide because of their potential toxicity to human health (in particular on liver, kidney and reproductive system) and the environment. Some of them are known teratogens when administrated repeatedly at low doses and their hepatocarcinogenic and estrogenic activity has been recently documented. The most commonly occurring phthalates are di-2-ethylhexyl phthalate (DEHP), di-n-butyl phthalate (DBP) and butylbenzyl phthalate (BBP) [2,3,14]. In the 80s, the US Environmental Protection Agency (US EPA) and other countries classified the commonly occurring phthalates as priority pollutants and recommended 6 g/L as the maximum contamination level (MCL) for DEHP in water systems and suggested close monitoring of all phthalate contaminants for concentrations above 0.6 g/L [4]. Phthalates contamination is usually in the low g/L level due to their hydrophobic nature. Various pre-concentration techniques, such as Liquid-Liquid Extraction (LLE) and Solid-Phase Extraction (SPE), are commonly used to determine low phthalate concentrations in aqueous samples [5,6]. The main disadvantage of these techniques is that apart form being expensive, time-consuming and labour intensive, they typically result in secondary contamination during sample preparation due to the presence of phthalates in many laboratory products [7,8]. In this context the development of new fast and sensitive analytical methods minimising the risk of phthalate contamination during sample treatment is of paramount importance. Solid-Phase Microextraction (SPME), introduced in 1990 by Arthur and Pawliszyn, is a fast, simple and solventless sample preconcentration method [9]. The commercially available SPME fibre consists of a thin polymeric-coated fused-silica fibre, fitted in a special syringe-type holder for protection and sampling. During SPME sampling analytes partition by adsorption or absorption (depending on the fibre type) from the solution to the stationary phase and are concentrated. After sampling for a well-defined period of time, the fibre is withdrawn and transferred to the heated injection port of a gas-chromatograph (GC) or to a modified high-performance liquid-phase (HPLC) rheodyne valve [8]. SPME has gained the attention of many research groups around the world and over the last decade, it has been applied to the determination of a large variety of volatile and semi-volatile analytes, in several types of environmental matrices [8,10]. Recently, the combination of SPME with GC enabled detection of phthalates at low g/L contamination levels in water samples, minimising the risk of secondary contamination, a major parameter to consider during phthalates trace analysis [10,11].

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The aim of the present studies is to monitor and evaluate phthalates migration from several disposable plastic materials into drinking water. The plastic materials investigated here included: plastic shakers used for the preparation of iced coffee, plastic cups and plastic straws. For the first time the effect of temperature on phthalate migration for these plastic items was investigated establishing the safety of these materials when used with hot beverages as well as demonstrating the importance of storage and transfer conditions of plastic materials containing drinking water. 2. MATERIALS AND METHODS 2.1. Chemicals Standard methanolic stock solutions containing 2000 mg/L of each target phthalate, namely: dimethyl phthalate (DMP), diethyl phthalate (DEP), DBP, BBP, DEHP and di-n-octyl phthalate (DOP) were purchased from Supelco (Bellefonte, PA, USA). A methanol solution of benzyl benzoate (99+ %, Sigma-Aldrich Chemie GmbH) was used as the internal standard. Working standard solutions of 50 mg/L were prepared weekly in methanol. Stock and working standard solutions were stored at 4C. Aqueous solutions were prepared daily by diluting the working standard solution in deionized water. Deionized water used for sample preparation was prepared on a water purification system (EASYpureRF) supplied by Barnstead/ Thermolyne. All solvents were pesticide-grade and were obtained from Merck KgaA (Darmstadt, Germany). 2.2. Disposable plastic ware All disposable plastic items examined here were purchased from a local supermarket. Two brands of coffee shakers were investigated. Brand A was made of polystyrene (PS) and did not contain water in its original packaging. Evaluation of phthalate migration for this particular brand was achieved by adding 200 mL of deionized water each time. Brand B was made of polypropylene (PP) and was vended with water in the plastic shaker. Disposable plastic cups and straws made of PP were also examined. 2.3. Sample preparation and SPME procedure For extraction, a 5 mL water sample was placed each time in 7-mL clear glass vial, equipped with a glass-coated mini-impeller and fitted only with aluminium foil and screw caps with hole, all purchased from Supelco (Bellefonte, PA, USA). Each morning standard solutions of all target analytes were extracted by using SPME in order to ensure consistency. For all quantification experiments, the aqueous solutions were spiked prior to extraction with the exact amount of the internal standard solution. SPME was performed using a manual 65-m polydimethylsiloxane-divinylbenzene (PDMS-DVB) SPME fibre and a SPME fibre holder assembly all purchased from Supelco. The fibre was conditioned in the hot injector of a GC device, before its first usage, according to the manufacturers recommendations. The SPME fibre holder assembly was then clamped at a fixed location above the glass vial containing the stirred (1000 rpm) sample solution. The SPME fibre was then exposed to the aqueous phase and after sampling for 45 min the fibre was retracted and transferred to the heated injection port of the GC-FID where it was left for 5 min.

2.4. GC-FID Analyses Phthalates were analysed using a Shimadzu GC-17A (Ver. 3) Gas Chromatograph-Flame Ionization Detector system. Injections were performed in the splitless mode at 280C with the spilt closed for 5 min (solvent delay time). Helium was used as a carrier gas at a flow-rate of

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1.2 mL/min. The Thermogreen LB-2 septa (Supelco, Sigma-Aldrich Chemie GmbH) were pre-drilled. Analyte separation was performed on a 30m0.25mm, 0.25m SPB-1701 capillary column (Agilent Technologies). The column oven was initially set at 60C and then programmed to 300C at a rate of 10C/min, where it was held for 11 min. 3. RESULTS AND DISCUSSION 3.1. Practical considerations during SPME/GC-FID and methods performance To minimise the effect of secondary contamination associated with the analysis of trace quantities of phthalates a number of measures were taken. All glassware and accessories used in the experiments were washed several times with Suprasolv quality organic solvents [13]. A glass-coated mini-impeller was used as a stirrer and aluminium foil replaced Teflon septa. Furthermore, the thick protector needle of the SPME fibre irreversibly damaged the thermo-resistant Thermogreen LB-2 septa used in the GC instrument. Such damages typically resulted in carrier gas leaks, extraneous peaks and phthalate contamination due to small polymer septa pieces introduced into the inlet liner of the GC injector. Pre-drilling the septa prior to using them and replacing them on a daily basis avoided such damages [14]. Between runs a clean-up procedure for the SPME fibre eliminated the possibility of analyte carry-over between analyses, a major drawback of SPME during phthalates analysis. Accordingly, after desorption, the SPME fibre was immersed in a stirred solvent solution for 5 min and was subsequently transferred to the heated injection port (280C) of another GC until the next extraction [15]. Moreover, blanks were run periodically during experiments to confirm the absence of contaminants [11]. Despite the measures taken, GC-FID analysis of deionized water, revealed the presence of phthalates in deionised water. It was assumed that this background contamination originated from the GC septum or from water purification system used for producing deionised water [12]. Calibration was performed by extracting water samples spiked in the concentration range from 25 to 0.5 g/L for most target analytes. A very good linear correlation coefficient (r2) was found for most phthalates (r2 > 0.9955), except for BBP and DEHP (r2 = 0.9724 and 0.9498 respectively). Repeatability expressed as the relative standard deviation (RSD) of five consecutive replicates ranged between 4% and 10%. The limits of detection (LODs) were determined according to published guidelines by comparing the signal-to-noise (S/N) ratio of the lowest detectable concentration to a S/N ratio of three [9]. They were found in the low-ppb level ranging between 0.03 and 0.4 g/L. Under the present experimental conditions detection of trace quantities of DOP was not possible. 3.2. Analyses of drinking water coming into contact with plastic materials A series of experiments were carried-out in which the effect of elevated temperatures on the quality of drinking water coming into direct contact with plastic ware was investigated. In the first series of experiments the effect of temperature on phthalate migration was investigated for two brands of plastic shakers used for the preparation of iced coffee. These series of experiments attempted to reproduce the high temperatures commonly found in Greece especially during the summer. For the purpose of the present studies both shakers containing 200 mL of water were sealed and left in the oven at 40C for several days. The results on phthalates concentrations are summarized on Table 1. It should be mentioned

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here that Brand A does not contain any water in its original packaging and as such deionised water had to be added. Thus, Day 0 in the case of Brand A corresponds to the background phthalate contamination originating from the deionised water. Brand B on the other hand is vended with water in its original packaging. Day 0 in this case represents the initial phthalate contamination. It should be mentioned here that the company producing Brand B imposes storage of this product in refrigerators at all selling points. As such the initial phthalate contamination most likely corresponds to contamination during the production phase. In all cases nq stands for not quantified and denotes the presence of phthalates in concentrations that could not be quantified at levels below the limits of quantification (0.5 g/L) but still greater than the limits of detection. This means that their presence in the examined water samples could be confirmed but not quantified. Overall, the results revealed that prolonged exposure of these plastic products on elevated temperatures facilitates phthalates migration and results in phthalate-contamination at levels of significant concern. Overall, Brand B yielded lower phthalate contamination than Brand A, despite the fact that it remained at 40C for a much longer period of time. This observation reflects the lower risk rank attributed to PP when compared to PS in the pyramid of plastics. Table 1: The effect of temperature (40C) on drinking water quality coming into contact with plastic coffee shakers

Brand A plastic shaker (PS)

Brand B plastic shaker (PP)

Analyte

Day 0 (g/L)

Day 1 (g/L)

Day 2 (g/L)

Day 12 (g/L)

Day 0 (g/L)

Day 3 (g/L)

Day 6 (g/L)

Day 7 (g/L)

Day 42 (g/L)

DMP 2.84 3.21 2.09 nq 0.74 1.61 DEP nq 2.63 2.95 5.13 nq nq 0.55 0.73 1.65 DBP nq 2.70 3.17 6.22 nq nq 1.38 1.67 2.03 BBP nq nq nq nq DEHP nq 0.67 0.68 0.74 nq

In another series of experiments the two brands of coffee shakers were left outdoors, exposed to real conditions such as heat and sunlight. The temperature during exposure of Brand A ranged from 12 to 28C and for Brand B from 18 to 36C. The results are summarised in Table 2. Table 2: Drinking water quality coming into contact with plastic coffee shakers exposed at ambient conditions

Brand A plastic shaker (PS) Brand B plastic shaker (PP)

Analyte

Day 0 (g/L)

Day 2 (g/L)

Day 37 (g/L)

Day 0 (g/L)

Day 61 (g/L)

DMP 1.65 1.08 0.93 DEP nq 1.31 1.4 nq nq DBP nq 0.90 1.70 nq 2.22 BBP DEHP nq nq nq

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Once again the results revealed that exposure of these plastic materials under elevated temperatures facilitate phthalates migration into water. As expected phthalate migration is not as extensive as it was in the first series of experiments, most certainly because the plastic shakers were not continuously exposed to elevated temperatures. Brand A results in a more significant phthalate contamination when compared to Brand B. Both series of experiments stress-out the importance of temperature control during transfer, storage and handling of these products. Furthermore, the degree of phthalate migration originating from disposable plastic cups and straws was investigated. Because these items may come into direct contact with hot beverages, the experimental conditions had to be changed. Accordingly hot tap water was added in a plastic cup for 30 min. Portion of the tap water was analyzed prior heating it and it was assumed that the presence of phthalates, if any, was below the limits of detection of the analytical method used here. The results (Table 3) revealed that under the present experimental conditions, only DBP could be extracted. In the case of the straws, each item destined for investigation was completely immersed in 100 mL hot tap water and was left there for 30 min. In both brands of straws (Brand 1 and 2) DMP and DBP were found present in the samples. However in the case of Brand 2 the DMP concentration was of significant concern. Overall, the results suggested that the above mentioned plastic items are safe to use only with cold drinks. Table 3: Results on phthalate concentration originating from plastic cups and straws after a 30 min exposure with hot tap water.

Plastic Straws (g/L) Analyte

Plastic Cup (g/L)

Brand 1

Brand 2

DMP nq 2.84 DEP nq DBP nq nq nq BBP DEHP

4. CONCLUSIONS Overall, significant quantities of phthalates are expected to be present in drinking water samples coming into direct contact with several disposable plastic items at elevated temperatures. The contamination level is higher when a prolonged exposure to such temperatures is applied. Therefore, it is strongly advisable to control temperature during the transfer, storage and/or handling of these materials. REFERENCES

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