Airborne Microplastic Concentrations in Five Megacities of Northern and Southeast China

[NNadir]

The paper to which I'll refer in this post without too much discussion of the implications, which should, in any case, be obvious, is this one: Airborne Microplastic Concentrations in Five Megacities of Northern and Southeast China (Xuan Zhu, Wei Huang, Mingzhu Fang, Zhonglu Liao, Yiqing Wang, Lisha Xu, Qianqian Mu, Chenwei Shi, Changjie Lu, Huanhuan Deng, Randy Dahlgren, and Xu Shang Environmental Science & Technology 2021 55 (19), 12871-12881)

Many people who care about the environment are aware of the problem of microplastics, particularly in bodies of water and in landfills. The effort to deal with plastic waste by recycling has proved to be largely a failure, and these dangerous petroleum and dangerous natural gas products have accumulated on a large scale.

The issue about which I have not thought, but perhaps should have thought, is the problem of airborne microplastics. The cited paper brought this problem to my attention, and I thought I'd briefly refer to it in this space.

From the paper's introduction:

Since the middle of the last century, global plastic production and use have increased exponentially. (1,2) Owing to their chemical stability, discarded plastic products have accumulated in the environment and are found even in the most remote regions on Earth. (3) It is estimated that by 2050, there will be 1.20 × 10^11 million tons of plastic waste accumulated in landfills or natural environments, the latter creating a serious threat of plastic pollution.

The "million" in this text is probably an error, since this would imply 10^17 tons. On the other hand, 120,000,000 tons seems to low.

For reference, the amount of carbon dioxide dumped by humanity each year while we all wait, decade after decade for the grand so called "renewable energy" nirvana that did not come, is not here and won't come, is roughly 35 billion tons per year as dangerous fossil fuel waste, with another 10 billion tons per year deriving from land use changes.

We can take these figures with a grain of salt without detracting with the measurements taken by the authors of the paper.

(4) In recent years, small-size (1–5000 μm) plastic particles, termed microplastics (MPs), have been found to be ubiquitous in aquatic (freshwater and marine) and terrestrial environments worldwide. This widespread distribution of MPs in our environment generates great concern for the potential ecological and human health risks associated with these pollutants. (5) The sources of MPs in the environment are generally divided into two categories: primary and secondary MPs. The former includes manufactured small-size plastic raw materials (e.g., feedstock for plastic products) and plastic particles used for various abrasion purposes, such as skincare and personal care products, while the latter includes particles originating from the mechanical weathering, photooxidation degradation, and biodegradation of larger plastic materials. (6) MPs are easily ingested by many aquatic and terrestrial organisms owing to their small size and may pass through the food chain to higher trophic levels. (7,8) As a result, ingestion exposure has motivated a myriad of studies focused on the health risks of MPs. (9,10)

In addition to ingestion exposure, inhalation may be another important pathway for MP exposure. Increasing evidence shows the widespread occurrence and transport of MPs in the atmosphere, with some studies positing that MP intake via inhalation may exceed ingestion via dietary consumption. (11) Quantifying the exposure intensity of airborne MPs is essential for evaluating human inhalation risk. (12) However, most studies examining airborne MPs are based on passive measurements of atmospheric deposition or accumulation in the surface dust layer. (13,14) MP concentrations measured by active pump sampling accurately reflects the air exposure intensity directly, (15−17) but the data concerning airborne MP concentrations derived from active pump collection are still rare. (12) The paucity of MP concentrations suspended in the atmosphere makes it difficult to accurately assess MP exposure risks to humans, especially since the limited data collected to date using different methodologies range by ∼4 orders of magnitude. (11,12,18) Moreover, the maximum reported exposure concentrations of airborne MPs may significantly underestimate the true exposure intensity. This is mainly due to the difficulty in detecting/enumerating MP particle sizes less than 30–50 μm using current methodologies, whereas the size distribution of airborne MPs may increase significantly at smaller sizes (10 million population) comprising urban agglomerations in northern and southeast China. We also explored potential relationships between airborne MP concentrations and routinely monitored air pollution indicators (e.g., PM2.5, PM10) to determine whether these routinely measured parameters could be used as a proxy for estimating MP concentrations. The relationship of airborne MPs and socioeconomic factors, such as population and GDP, were also investigated as potential covariates to explain spatial patterns in MP concentrations. This study informs potential human health risks associated with MP inhalation exposure and explores various factors contributing to differences in airborne MP concentrations and characteristics in densely populated urban centers.

Some graphics from the paper which ought to be self explanatory:



The caption:

Figure 1. Location of studied cities (yellow stars). JJJ represents the Jing-Jin-Ji (Beijing–Tianjin–Hebei) urban agglomeration, and YRD represents the Yangtze River Delta urban agglomeration.

The caption:

Figure 2. Average airborne MP concentration at each sampling site. Blue sites are located in the urban area, and green sites are located at the urban–rural fringe. (a) Beijing; (b) Tianjin; (c) Shanghai; (d) Nanjing; and (e) Hangzhou.

The caption:

Figure 3. Airborne MP concentration (mean ± SD) for the five megacities. Samples with different lower case letters are significantly different at P < 0.05.

The caption:

Figure 4. Size distribution (mean ± SD) of airborne MPs in the five megacities. Samples with different lower case letters are significantly different at P < 0.05.

The caption:

Figure 5. Percentage of fibers and fragments in different size classes of airborne MPs. (a) Beijing; (b) Tianjin; (c) Shanghai; (d) Nanjing; (e) Hangzhou; (f) total = pooled data.

The caption:

Figure 6. Polymer composition of airborne MPs: (a) Beijing; (b) Tianjin; (c) Shanghai; (d) Nanjing; (e) Hangzhou; and (f) total.

The caption:

Figure 7. Relationship of airborne MP concentration and selected air quality components across the five megacities. (a) PM2.5; (b) PM10; (c) SO2; (d) NO2. All relationships were nonsignificant (P > 0.05).

The PVC component is of interest to me, since PVC is a "heavier than water" polymer, the use of which sequesters chlorine, allowing for the industrial accumulation of bases such as hydroxides, which are useful for the capture of carbon dioxide. (The composition of PVC is roughly 56% chlorine by weight.) PVC is often not a single use polymer, and although its production is not currently huge, only on a few tens of millions of tons per year, it does have some properties that make it environmentally less odious, perhaps in some settings, even benign or indeed, even positive.

The ubiquitous distribution of MPs in the atmosphere is considered as a potential health risk to humans. (50) Some atmospheric deposition studies, (40) along with our study, showed a disproportionate abundance of smaller MPs (down to a few to ten microns) in air samples. Many of these smaller MPs fall within the size range of inhalable particles. (31) Even though most of the larger inhalable particles are subjected to mucociliary clearance in the upper airways, some may escape this clearance mechanism and be deposited in deep lung tissues, especially those particles smaller than ∼5 μm. (51) Plastic particles tend to avoid clearance and show extreme durability in physiological fluids, likely leading to their persistence and accumulation following inhalation. (52) In fact, synthetic plastic fibers have been found in human lungs, (53,54) and several workers in plastic processing factories experienced breathing and health problems (e.g., coughing, dyspnea, wheezing, occupational asthma, etc.), possibly linked to chronic MP exposure. (55,56)

In addition to the relatively larger plastic fibers, which are easy to be observed and therefore get more attention, our results showed that smaller MPs were dominated by nonfiber fragments. The various size and shapes of MPs are expected to strongly influence MP interactions with body tissues/fluids and the ability of the body to eliminate MPs from the respiratory/digestive systems. The polymeric composition of MPs will also affect the fate (i.e., accumulation/degradation) of MPs within the various body tissues.

I hadn't thought much about this issue, but perhaps it should have been obvious.

This is a real problem. I believe that there is an engineering solution to solving the problem but nobody, I think, wants to hear me beat my horse.

I wish you a pleasant workweek.

[leighbythesea2]

1. Looks

To be a lot at that smallest size particle. At all the sites. This is eye opening.
And there it is, in the lungs, forever.