US-12618823-B2 - Method of quantifying microplastic mass

Abstract

A method of quantifying microplastic mass in a sample composition, including the steps of pre-treating the sample composition to remove non-microplastic organic matter and extract microplastics thereby providing a pre-treated sample composition, measuring the organic carbon content of a microplastic polymer in the pre-treated sample composition using total organic carbon (TOC) analysis, and quantifying the microplastic mass in the sample composition according to the organic carbon content of the microplastic polymer.

Inventors

• Yiu Fai TSANG
• Yan Laam CHENG
• Ziying Li

Assignees

• The Education University Of Hong Kong

Dates

Publication Date

20260505

Application Date

20230223

Claims (17)

1. 1 . A method of quantifying a total microplastic mass in a sample composition, the method comprising: providing a treated sample composition by removing non-microplastic organic matter from the sample composition and by extracting a microplastic polymer having an organic carbon content from the sample composition, measuring the organic carbon content of the extracted microplastic polymer in the treated sample composition by using total organic carbon (TOC) analysis, and quantifying the total microplastic mass in the sample composition based on the measured organic carbon content of the extracted microplastic polymer.
2. 2 . The method according to claim 1 , wherein the removing the non-microplastic organic matter from the sample composition comprises digesting the sample composition using a digestion reagent for a pre-determined digestion duration, the extracting the microplastic polymer from the sample composition comprises producing a microplastic layer by using density separation, and the providing the treated sample composition further comprises: capturing the microplastic polymer in a filter by filtering the microplastic layer through the filter, and drying the filter with the captured microplastic polymer for a pre-determined drying time at a pre-determined drying temperature prior to the total organic carbon (TOC) analysis.
3. 3 . The method according to claim 2 , wherein the digestion reagent is selected from the group consisting of a 30% hydrogen peroxide solution, a wet peroxide oxidation (WPO) solution, and an acid solution.
4. 4 . The method according to claim 2 , wherein the pre-determined digestion duration is between 2 and 24 hours.
5. 5 . The method according to claim 2 , wherein the pre-determined digestion duration is 2, 4, 6, 8 or 24 hours.
6. 6 . The method according to claim 2 , further comprising adding filtered sodium bromide before the extracting the microplastic polymer from the sample composition, and wherein the producing the microplastic layer by using density separation comprises maintaining the sample composition at 25° C. for at least 2 hours.
7. 7 . The method according to claim 2 , wherein the filter is a glass fiber filter having pores of a 0.4-μm diameter.
8. 8 . The method according to claim 2 , wherein the pre-determined drying time is between 2 and 8 hours and the pre-determined drying temperature is 60° C.
9. 9 . The method according to claim 2 , the drying the filter with the capture microplastic further comprising putting the filter with the captured microplastic polymer inside a treated ceramic boat, putting the filter with the captured microplastic polymer inside an oven and drying the filter with the captured microplastic polymer inside the treated ceramic boat using the oven.
10. 10 . The method according to claim 1 , wherein the total organic carbon (TOC) analysis comprises using a total organic carbon (TOC) analyzer.
11. 11 . The method according to claim 10 , wherein the measuring the organic carbon content of the extracted microplastic polymer comprises inserting the treated sample composition into the TOC analyzer and combusting the treated sample composition at 900° C.
12. 12 . The method according to claim 1 , wherein the extracted microplastic polymer is selected from the group consisting of polyamide 66 (PA66), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS), or a combination thereof.
13. 13 . The method according to claim 1 , wherein the extracted microplastic polymer is one or more extracted microplastic polymers.
14. 14 . The method according to claim 1 , wherein the extracted microplastic polymer is in a powder form or in a pellet form.
15. 15 . The method according to claim 2 , wherein the digesting the sample composition comprises maintaining the sample composition a temperature of 45° C. for 2 hours using a heat plate and stirring the sample composition at a rate of 200-300 rotations per minute.
16. 16 . The method according to claim 10 , wherein the microplastic mass is quantified according to the carbon content of the microplastic polymer and a measured carbon mass from the TOC analyzer.
17. 17 . The method according to claim 1 , wherein the sample composition is wastewater, pond water or sludge.

Description

TECHNICAL FIELD This invention relates to a method of quantifying microplastic mass in a sample composition, in particular the present disclosure is directed to a method of quantifying microplastic mass in a sample composition using total organic carbon (TOC) analysis. BACKGROUND The durable, lightweight, low cost and adaptable nature of plastics has led to their widespread use commercially and in some form in almost all households. However, the widespread use of plastics has resulted in the accumulation of plastic waste in the environment. The rising global population has contributed to a large and continually growing amount of plastic waste generated every day. Plastic waste is broken down into microplastics and these microplastic pollutants have permeated the natural ecosystem, being present in soil, rivers, and oceans, and has caused widespread environmental problems. The presence of microplastics within the food chain is also increasing and can harm ecosystems and human health. The persistence of microplastics in the natural environment and its effects on organisms are the subject of environmental research and scientific interest. To study and understand the abundance, location and effects of microplastics in the natural ecosystem, reliable and effective methods of monitoring microplastics are desired. SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a method of quantifying microplastic mass in a sample composition, including the steps of: pre-treating the sample composition to remove non-microplastic organic matter and extract microplastics thereby providing a pre-treated sample composition, measuring the organic carbon content of a microplastic polymer in the pre-treated sample composition using total organic carbon (TOC) analysis, and quantifying the microplastic mass in the sample composition according to the organic carbon content of the microplastic polymer. For example, the method of the invention is used to monitor microplastic pollutants in wastewater, pond water or sludge for environmental pollution assessments. In the method of the invention, total organic carbon (TOC) analysis is used to quantify microplastic mass in a sample composition. The microplastic polymer may be, for example, a single polymer or a mixture of polymers and can be in the form of a powder or a pellet. In an example embodiment, the microplastic polymer includes polyamide 66 (PA 66), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene combination thereof. Existing analytical techniques used for microplastic quantification are time consuming, typically taking several days to identify microplastic polymer types and determine the microplastic mass contents. The accuracy and viability of these existing analytical techniques may also be hindered by the size, shape, presence of biofilm or other organic pollutants on the microplastic, and they often require the use of expensive analytical instruments to conduct analysis of the small microplastics. Advantageously, the accuracy of the method of the invention is not affected by variable factors of microplastic characteristics such as the broad size range of the microplastic, microplastic polymer types and additives, or different shapes of microplastics. The method of the invention is also quick and inexpensive, only requiring infrastructure commonly available in environmental testing laboratories, thereby saving 75% of sample pre-treatment time and 60% of extraction costs. Further, the invention reliably provides mass-based concentrations of microplastic polymers in sample compositions with different viscosities, i.e., liquid samples or sludge samples, with high recovery rates of the microplastic polymers in the liquid and sludge samples of over 98%. In a preferred embodiment, pre-treating the sample composition includes the steps of: digesting the sample composition using a pre-determined digestion reagent for a pre-determined digestion to duration remove non-microplastic organic matter, extracting the microplastic polymer from the sample composition by density separation to produce a microplastic layer, filtering the microplastic layer through a filter such that the microplastic polymer is captured in the filter, and drying the filter with the captured microplastic polymer for a pre-determined drying time at a pre-determined drying temperature in preparation for total organic carbon (TOC) analysis. Pre-treatment of the sample composition removes undesired non-microplastic organic matter or impurities to ensure the accuracy of the microplastic quantification using total organic carbon (TOC) analysis. Sample composition pre-treatment also extracts or isolates microplastic polymers from the sample composition prior to TOC analysis. Pre-treatment of the sample composition provides a low-cost, fast, reliable and simple way of eliminating undesired organic carbon content in sample compositions without the need for