Extraction of Organochlorine Pesticides from Plastic Pellets and Plastic Type Analysis
Summary
Microplastics act as vector of potentially toxic organic contaminants with unpredictable effects. This protocol describes an alternative methodology for assessing the levels of organochlorine pesticides adsorbed on plastic pellets and identifying the polymer chemical structure. The focus is on pressurized fluid extraction and attenuated total reflectance Fourier transform infrared spectroscopy.
Abstract
Plastic resin pellets, categorized as microplastics (≤5 mm in diameter), are small granules that can be unintentionally released to the environment during manufacturing and transport. Because of their environmental persistence, they are widely distributed in the oceans and on beaches all over the world. They can act as a vector of potentially toxic organic compounds (e.g., polychlorinated biphenyls) and might consequently negatively affect marine organisms. Their possible impacts along the food chain are not yet well understood. In order to assess the hazards associated with the occurrence of plastic pellets in the marine environment, it is necessary to develop methodologies that allow for rapid determination of associated organic contaminant levels. The present protocol describes the different steps required for sampling resin pellets, analyzing adsorbed organochlorine pesticides (OCPs) and identifying the plastic type. The focus is on the extraction of OCPs from plastic pellets by means of a pressurized fluid extractor (PFE) and on the polymer chemical analysis applying Fourier Transform-InfraRed (FT-IR) spectroscopy. The developed methodology focuses on 11 OCPs and related compounds, including dichlorodiphenyltrichloroethane (DDT) and its two main metabolites, lindane and two production isomers, as well as the two biologically active isomers of technical endosulfan. This protocol constitutes a simple and rapid alternative to existing methodology for evaluating the concentration of organic contaminants adsorbed on plastic pieces.
Introduction
Global production of plastics is continuously rising since the 1950's to reach 311 million tons in 2014 with about 40% used in packaging1. In parallel, increasing quantities of these materials are accumulating in the environment, which might pose a serious threat to the ecosystems2. Although already reported in the 1970's, the occurrence of plastic debris in the marine environment has only received a greater attention in the past decade. Especially microplastics, plastic fragments with a diameter of ≤ 5 mm, are now recognized as one of the main marine water quality issues3.
Plastic resin pellets are small granules generally in the shape of a cylinder or a disk and with a diameter of a few mm (e.g., 2 to 5 mm)4,5. They fall in the category of microplastics. These plastic granules are industrial raw material from which final plastic products are manufactured through re-melting and molding at high temperature6. They can be unintentionally released to the environment during manufacturing and transport. For instance, they can be directly introduced to the ocean through accidental spills during shipping4,7,8. They can be carried from land to oceans by surface run-off, streams and rivers. Because of their environmental persistence, plastic pellets are widely distributed in the oceans and found on beaches all over the world4. They can negatively affect marine organisms and can enter the food chain, where their effects are unpredictable6,7. Furthermore, several studies have revealed the presence of environmental contaminants adsorbed onto plastic pellets collected in a coastal environment, which act as vector of these potentially toxic chemicals4,9,10. In fact, there is laboratory evidence suggesting that these chemicals can bioaccumulate in tissues of organisms after being released from ingested plastic fragments11,12.
In order to better assess the hazards associated with the occurrence of plastic pellets in the marine environment, it is necessary to develop methodologies that can determine sorbed organic contaminants. An important step is the extraction of the chemicals from the plastic matrices, which can present heterogeneous physical-chemical characteristics depending on the polymer type, its degradation stage, and pre-treatments. Most of the investigations reported in the literature use maceration or Soxhlet techniques4,5,6,9,13,14,15,16,17,18, which are solvent and/or time consuming. Regarding the growing interest for this issue, alternatives should be developed, for a faster evaluation of organic contaminants adsorbed on plastic pieces. In addition, plastic chemical analysis provides information about the chemical structure of the microplastics. As a result, the predominant types of polymers and copolymers present in the environment can be evaluated. Although plastic fragments are usually made of polyethylene (PE) and polypropylene (PP)5, some sampling locations can present a particular profile where other categories are significantly represented (e.g., ethylene/vinyl acetate copolymer and polystyrene (PS)). FT-IR spectroscopy is a reliable and user-friendly technique for polymer identification commonly used to identify microplastics19,20.
The main aim of the present work is to offer a rapid and simple option for extracting OCPs and related compounds from plastic pellets by means of a PFE. However, the design of the protocol includes all steps leading to the determination of sorbed OCPs, from the sampling of the resin pellets to the analysis of the compounds. The method of identifying the plastic type is also described. The developed methodology focuses on 11 OCPs and related compounds: i) DDT (2,4'- and 4,4'-dichlorodiphenyltrichloroethane) and its two main metabolites DDE (2,4'- and 4,4'-dichlorodiphenyldichloroethylene) and DDD (2,4'- and 4,4'-dichlorodiphenyldichloroethane); ii) the isomer gamma-hexachlorocyclohexane (γ-HCH) as the main ingredient of the pesticide lindane and the two isomers α-HCH and β-HCH released during its production15; iii) and the two biologically active isomers endosulfan I (Endo I) and II (Endo II) present in the technical endosulfan. The studied pesticides are broad-spectrum insecticides, chemically stable, hydrophobic, and classified as persistent organic pollutants (POPs) by the Stockholm Convention21.
Protocol
Representative Results
Discussion
Most studies focusing on organic contaminants associated to plastic pellets have relied on classical extraction methods of the adsorbed chemicals. The Soxhlet apparatus is the most widely used technique with typical extraction times ranging from 12 to 24 h and with high consumption of organic solvents (i.e., from 100 to 250 mL per extraction)23. Maceration extractions require a long contact time between the sample and the organic solvent (e.g., 6 days)4 an…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was funded by IPA Adriatic Cross-border Cooperation Program 2007-2013, within the DeFishGear project (1°str/00010).
Materials
| Alpha–HCH | Dr. Ehrenstorfer, Augsburg, Germany | DRE-C14071000 | H301, H351, H400, H410, H312 |
| Beta–HCH | Fluka, Sigma-Aldrich, St. Louis, USA | 33376-100MG | H301, H312, H351, H410 |
| Lindane | Fluka, Sigma-Aldrich, St. Louis, USA | 45548-250MG | H301, H312, H332, H362, H410 |
| Endosufan I | Supleco, Sigma-Aldrich Bellefonte, PA, USA | 48576-25MG | H301, H410 |
| Endosulfan II | Supleco, Sigma-Aldrich, Bellefonte, PA, USA | 48578-25MG | H301, H410 |
| 2,4'–DDD | Fluka, Sigma-Aldrich, St. Louis, USA | 35485-250MG | H351 |
| 4,4’–DDD | Dr. Ehrenstorfer, Augsburg, Germany | DRE-C12031000 | H301, H351, H400, H410, H312 |
| 2,4’–DDE | Dr. Ehrenstorfer, Augsburg, Germany | DRE-C12040000 | H351, H400, H410, H302 |
| 4,4’-DDE | Fluka , Sigma-Aldrich, St. Louis, USA | 35487-250MG | H302, H351, H410 |
| 2,4’–DDT | Dr. Ehrenstorfer, Augsburg, Germany | DRE-C12081000 | H301, H311, H330, H351, H400, H410 |
| 4,4’–DDT | National Institute of Standards and Technology, Gaithersburg, USA | RM8469-4,4'-DDT | H301, H311, H351, H372, H410 |
| n-Hexane | VWR International GmbH, Graumanngasse, Viena, Austria | 83992.320 | H225, H315, H336, H373, H304, H411 |
| Acetone for HPLC | J.T.Baker, Avantor performance Materials B.V., Teugseweg, Netherlands | 8142 | H225, H319, H 336 |
| FL-PR Florisil 1000mg/6mL | Phenomenex, Torrance, CA, USA | 8B-S013-JCH | |
| Fat free quartz sand 0.3-0.9 mm | Buchi, Flawil, Switzerland | 37689 | |
| Gas chromatograph Hawlett Packard HP 6890 Series gas chromatograph with GERSTEL MultiPurpose Sampler MPS 2XL with ECD and FID detector | Agilent technologies, Santa Clara USA | ||
| Presure fluid extractor, Speed Extractor E-916 | Buchi, Flawil, Switzerland | ||
| Solid phase extractor | Supleco, Sigma-Aldrich Bellefonte, PA, USA | ||
| Concentrator miVac DUO | Genevac SP Scientific, Suffolk UK | ||
| GC capillary column Zebron ZB-XLB (30 x 0.25 x 0.25) | Phenomenex, Torrance, CA, USA | 122-1232 | |
| ATR FT-IR Spectrometer, Spectrum-Two | Perkin Elmer |
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