Investigating an Efficient Method for Extracting Microplastics from Soil/Sediment Samples

Stephanie Perez Author

08/03/2020 Added

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[00:00:00.720]Hello everyone.
[00:00:01.553]My name is Stephanie Perez,
[00:00:02.880]and I am a junior in civil engineering
[00:00:05.200]at the University of Nebraska Lincoln.
[00:00:07.400]This summer I, with Dr. Bartelt-Hunt,
[00:00:09.232]and her graduate student, Nasarin Naderi,
[00:00:11.510]in investigating an efficient method
[00:00:13.250]for extracting microplastics from soil or sediment samples.
[00:00:17.000]To begin, I'll explain what microplastics are.
[00:00:19.912]Microplastics are tiny particles of plastic
[00:00:21.730]that result from the breakdown of plastic debris,
[00:00:24.310]and they're typically less than
[00:00:25.440]five millimeters in diameter.
[00:00:28.150]Some concerns we have with microplastics
[00:00:30.050]are that micro plastics have the potential
[00:00:31.880]of carrying contaminants.
[00:00:34.750]In addition, microplastics have been found
[00:00:36.640]in animals due to consumption,
[00:00:38.210]and toxic and endocrine disrupting substances
[00:00:41.210]can be released from microplastics.
[00:00:43.490]Now, I'll move on to explain
[00:00:44.730]microplastic contamination in soils.
[00:00:47.541]Microplastics have been found in soils,
[00:00:49.310]and there's a lack of research studying the effects
[00:00:51.480]of microplastic contamination in soils.
[00:00:54.040]In addition, existing microplastic soil
[00:00:56.250]extraction techniques have limitations
[00:00:58.870]or have not been comprehensively evaluated.
[00:01:02.520]So the objective of this research is by implementing
[00:01:05.060]new methodologies based on the known limitations
[00:01:07.240]and techniques we will test three methods
[00:01:09.150]for extracting microplastics from soils to determine
[00:01:12.140]which of the three is the most effective method.
[00:01:15.740]Now I'll move on to explain my experimental methodology.
[00:01:19.140]First, we begin by generating
[00:01:20.740]different types of microplastics.
[00:01:22.830]Once you've generated all types,
[00:01:24.550]we mix them together.
[00:01:25.940]Once mixed, we spike a set amount
[00:01:28.260]of microplastics and sand samples,
[00:01:30.590]and we spike a set amount of microplastics
[00:01:32.940]and dried and milled soil samples.
[00:01:36.180]Then we test our desired method of interest.
[00:01:38.630]Our first method of interest is oleophilic extraction.
[00:01:41.390]Our second is centrifugation without oxidation.
[00:01:44.600]Our third is centrifugation with oxidation.
[00:01:47.320]Once we get the resulting solution from each method,
[00:01:50.690]we filter the solution and save the filters for analysis.
[00:01:55.600]Now I'll explain my extraction.
[00:01:58.810]My first method is oleophilic extraction,
[00:02:01.690]and this method begins by adding soil
[00:02:03.730]and sand samples to our flask,
[00:02:06.890]and we spike them with a set amount of microplastics.
[00:02:09.710]Then we add ultra pure water and canola oil,
[00:02:12.830]and we shake the mixture.
[00:02:15.080]Once our mixture looks something like this,
[00:02:17.110]we pour it into a separatory funnel
[00:02:19.340]where it will separate into layers.
[00:02:21.550]Down here, we should have a sediment layer,
[00:02:23.860]and above that we should have our water layer.
[00:02:27.310]Then above that, we should have our oil layer.
[00:02:30.900]What we hope with this method
[00:02:32.540]is that all the microplastics will accumulate
[00:02:34.840]in the oil layer, and therefore we can discard
[00:02:37.180]our water and sediment layer.
[00:02:40.530]Our second method of interest
[00:02:41.840]is centrifugation without oxidation.
[00:02:44.750]This method begins by adding soil and sand
[00:02:48.040]to your centrifugation tubes.
[00:02:50.210]In this photo, our first three tubes are our sand samples.
[00:02:55.530]Our last three tubes are our soil samples.
[00:02:58.510]Once we add that, we spike them
[00:03:00.870]with a set amount of microplastics.
[00:03:04.008]Then we add deionized water to the tubes,
[00:03:06.500]and centrifuge them using this machine.
[00:03:09.590]After they're centrifuged, we filter the supernatant.
[00:03:13.110]Then we repeat that same procedure
[00:03:15.030]using sodium chloride and zinc bromide.
[00:03:18.560]Our third method of interest
[00:03:19.750]is centrifugation with oxidation.
[00:03:22.590]This method is very similar to our second method,
[00:03:25.550]except that before being centrifuged
[00:03:28.280]our samples are oxidized.
[00:03:31.910]So first we begin by adding soil or sand to our tubes,
[00:03:35.010]and then spiking them with a set amount of microplastics.
[00:03:39.430]Then, to oxidize, first we add two milliliters
[00:03:43.250]of aqueous iron oxide solution,
[00:03:45.360]and two milliliters of 30% hydrogen peroxide solution.
[00:03:50.520]In this photo here, you'll see bubbles forming in the tubes.
[00:03:54.060]This is a reaction occurring due to the mixture
[00:03:57.220]of all those solutions.
[00:04:00.070]Then after that, we place our tubes at an oven
[00:04:02.910]at 65 degrees Celsius for three hours.
[00:04:06.990]In this photo here, these are our tubes
[00:04:09.480]after being oxidized.
[00:04:12.143]The reason we oxidize our samples is to separate
[00:04:16.720]all the organic matter from our soil samples.
[00:04:19.140]So if you look closely at this picture,
[00:04:20.710]you'll see that just that is happening.
[00:04:22.810]Right above the soil a thick dark layer has formed,
[00:04:25.620]and that thick dark layer is all the organic matter
[00:04:28.060]being separated from the soil sample.
[00:04:32.400]After our samples are oxidized,
[00:04:35.439]we centrifuged using deionized water,
[00:04:37.990]and then filtered the supernatant,
[00:04:39.790]and then repeat that procedure
[00:04:41.330]using sodium chloride and zinc bromide.
[00:04:45.210]Now I'll move on to explain our limitations and results.
[00:04:49.680]A couple of limitations we had with our first method,
[00:04:52.350]oleophilic extraction, is that polymers with high densities
[00:04:55.320]were not easily separated in our mixtures.
[00:04:59.290]In addition, the stopcock was often clogged
[00:05:01.850]with sand or soil particles.
[00:05:03.840]This is especially true for our soil samples
[00:05:06.950]due to soil particles being a lot finer
[00:05:10.010]than our sand particles.
[00:05:12.120]Another limitation we had with our second method,
[00:05:16.200]and a limitation really that we had with our first
[00:05:18.560]and second method, is that they both went oxidized,
[00:05:22.570]and because they were oxidized,
[00:05:24.300]microplastics might've been absorbed
[00:05:25.810]by the organic material,
[00:05:27.480]and thus cost less recovery in the end.
[00:05:30.640]For our results, our filters were analyzed
[00:05:32.610]using a light microscope,
[00:05:34.620]and we observed that our third method,
[00:05:36.500]centrifugation with oxidation,
[00:05:38.170]had the highest average recovery rates
[00:05:40.450]averaging over 80% recovery for both soil and sand samples.
[00:05:45.590]As for our first method, oleophilic extraction,
[00:05:48.130]this actually had the lowest average recovery rates,
[00:05:50.640]averaging 30-40% recovery for both soil and sand samples.
[00:05:57.220]To conclude, we learned that organic matter can obscure
[00:05:59.730]and/or absorb microplastics.
[00:06:02.100]We also learned that minimal transfer processes
[00:06:04.660]may lead to higher recovery,
[00:06:06.480]and by transfer processes we just mean transferring
[00:06:09.460]from a beaker to a flask to a tube,
[00:06:13.100]and just minimizing those processes
[00:06:15.360]to potentially have a higher recovery.
[00:06:18.250]We also learned that particles with higher densities
[00:06:20.440]cannot be easily extracted from soil.
[00:06:23.740]So what does this mean for our future work?
[00:06:26.100]Since method three had the highest recovery rates
[00:06:28.220]out of all three methods,
[00:06:30.004]we will use method three, centrifugation with oxidation,
[00:06:33.240]for future microplastic soil extraction studies.
[00:06:38.400]So method three will be used to measure contamination
[00:06:40.980]of microplastics in soils, manure, and biosolids,
[00:06:44.840]to measure contaminations of microplastics
[00:06:46.970]in different soil types,
[00:06:49.560]and to classify recovery rates for different resins
[00:06:52.070]of microplastics or microplastics with ranging densities.
[00:06:58.470]To move on, during the 2020-2021 academic school year,
[00:07:02.190]my UCARE research will focus on the migration of micro
[00:07:05.300]or nanoplastics in soil columns to simulate transport
[00:07:08.360]of microplastics in groundwater systems.
[00:07:11.920]Thank you for listening to my presentation today.

Investigating an Efficient Method for Extracting Microplastics from Soil/Sediment Samples

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Investigating an Efficient Method for Extracting Microplastics from Soil/Sediment Samples

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