This protocol describes the extraction of organochlorine pesticides absorbed on plastic pellets sampled from beaches, as well as the chemical analysis of the plastics. Plastic pellet sampling. Before going in the field, prepare your sampling materials.
Carefully clean the stainless steel tweezers and the containers, and you will also need gloves, zip bags, the identity beach form, and eventually an icebox. Once onsite, investigate the area to find the pellets. Did you see them?
Wearing gloves, collect the plastic pellets from the beach with the tweezers. In order to have representative results, it is advised to sample 50 to 100 pellets per location. However, if the required number of pellets cannot be reached, collect the maximum pellets possible and specify it in the identity beach form.
Plastic pellets are usually found along the high and low tide lines of sandy beaches. Also, check any potential accumulation areas of stranded material. Sometimes, the pellets can be found sticking to fresh seagrass on beaches, after a storm for instance.
At the end of the sampling, wrap the collected pellets in aluminum foil. Glass bottles can be used as an alternative or eventually paper bags. Do not forget to fill in the identity beach form.
Once in the laboratory, gently wipe off any particles, dry the pellets, if necessary, prior to storage, and store them in dark at low temperature. Extraction of organochlorine pesticides from plastic pellets. Using tweezers, sort the pellets by color.
Gather 10 pellets of similar color, which will constitute one replicate. To this end, create visual references, white/transparent, whitish/yellowish, yellow/orange, amber/brown, and pigmented. Weigh the sample on an analytical balance.
Switch on the pressurized fluid extractor. Download the extraction method, and warm up the instrument to 60 degrees centigrade. While the instrument is warming up, prepare the extraction cell.
First, place the bottom filter and a frit in the extraction cell, and close it. Fill approximately half the cell with quartz sand, using a funnel. Since it is exposed to the same extraction conditions as the samples, special care must be taken to use ultra-clean sand.
Add the 10 weighed pellets. Add quartz sand up to one centimeter to the top of the cell. Insert the top filter in the cell, and place the cell in the instrument.
Place the collecting vessels in the instrument, and start the extraction method. Once the sequence is completed, empty the extraction cell in a cleaned glass Petri dish. Then, retrieve the 10 pellets in the sand.
Store them until further analysis for plastic identification. Concentration and clean-up of the extract. Transfer the obtained extract from the collecting vessel to a glass tube.
Place the tube in a rotating concentrator for 20 minutes at 35 degrees Celsius. In this way, you will concentrate the extract to one milliliter. In the meantime, prepare the solid-phase extraction by placing a waste tube in the rack and a Florisil cartridge on the manifold in the close d-valve position.
Turn the vacuum on at the source, and add four milliliters of hexane in the cartridge to activate the sorbent. Open the valve, and let the solvent pass through the entire sorbent bed. Then, close the valve, and allow the sorbent to soak in hexane for five minutes.
Open the value, and let the sorbent pass through, but close the valve before the sorbent dries off. When the sample is concentrated, transfer it to the cartridge with a glass Pasteur pipette. Gently open the valve and let it pass through slowly.
One to two drops per second is the appropriate speed. Rinse the glass tube containing the extract with half a milliliter of hexane, and add it to the cartridge when the extract has passed through. When the entire solvent has passed through, close the valve, and turn off the vacuum.
Replace the waste tube by a collecting tube, and use a clean solvent guide needle. Add nine millimeters of solvent composed of 10%acetone and 90%hexane. Turn on vacuum at the source, allow the sorbent to soak in the solvent for one minute.
Open the value, and collect the entire eluate and the collecting tube. Place the collecting tube in the concentrator, and evaporate the solvent for nine minutes at 35 degrees in order to reach one milliliter of eluate. Transfer the concentrated eluate in an amber vial, using a glass Pasteur pipette.
Analysis of the cleaned and concentrated extract. Download the analytical method on the control software of the gas chromatograph equipped with a micro electron capture detector. The injection is done in splitless mode.
Place the vial containing the cleaned and concentrated extract in the autosampler rack, and run the method. Inject two microliters of samples. Plastic type identification.
In order to identify the plastic polymer type, transfer the pellets in a glass Petri dish, and place the dish in a plastic bag. Hold one pellet, and cut it with a scalpel. The plastic bag prevents the loss of pellets.
Cutting the pellets allows an easier identification of the polymer than processing uncut pellets. The measurement is carried out on a Fourier transform infrared spectrometer. Place the fragment on the attenuated total reflectance crystal, and screw the sample holder.
Scan the sample, and record its spectrum. Identify the plastic type by comparing the obtained spectrum to a spectral library. In this example, the sample was made of polyethylene.
In black, the spectrum of the sample, and in red, you can see the reference spectrum. Polyethylene, as shown in this example, is the most common polymer type of plastic pellets found. The second most spread category is polypropylene.
Ethylene/vinyl acetate copolymer is the third most common. Polystyrene is also occasionally found. After the analysis, identify the different compounds on the chromatogram by their retention types, and write down the corresponding peak areas.
As can be seen from this example of spiked pellets, all 11 pesticides have been extracted. To calculate the concentrations of the pesticides absorbed on pellets, you will need to determine the calibration equations and the recoveries from the solid-phase extraction and concentration steps by using standard solutions. Here is an example of a chromatogram of plastic pellets collected on a beach in Greece.
Eight pesticides out of 11 were detected. For example, lindane has a retention time of about 9.92 minutes and a recovery of 96%according to standard solutions. On this chromatogram, lindane was detected at the retention time 9.915 minute with a peak area of 3, 270 arbitrary units.
The area is then recalculated according to the recovery. Then, the concentration of the one milliliter extract can be calculated based on the calibration equation. Finally, taking into account the mass of the 10 pellets, the concentration of lindane in this sample was 5.33 nanograms per gram of pellets.
The median concentrations of several replicates are then determined, and results can be plotted by compound categories, HCHs, DDTs, and endosulfans. Here is an example of plastic type identification for a pool of 10 pellets. The issue of microplastics and associated contaminants is a growing concern, and this simple protocol allows a rapid determination of 11 organochlorine pesticides and their related degradation products on plastic pellets found on beaches.
