the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Mar 2026
Urban-Rural Inequality in Microplastic Exposure Exacerbates Health Risks for Rural Residents in Northern China
Abstract. Atmospheric microplastics (MPs) and plasticizers are emerging contaminants requiring systematic research on urban-rural exposure inequality. This study examined MPs and plasticizers in PM2.5 across urban-rural and indoor-outdoor environments in Northern China's Guanzhong Plain. The 24 h time-weighted exposure concentrations for MPs and plasticizers were 3.6 and 6.8 times higher, respectively, in rural areas than in urban areas. Polyethylene terephthalate (PET) exhibited the greatest disparity in urban-rural MPs exposure. Plasticizer exposure was overwhelmingly dominated by phthalates, with di(2-ethylhexyl) phthalate (DEHP) reaching exceptionally high concentrations in rural indoor air (≈ 600 ng m-3), far exceeding urban levels (10.4 times). Rural residents experienced consistently higher inhalation exposure to MPs and plasticizers, resulting in substantially elevated health risks, with non-carcinogenic and carcinogenic risks both 6.9 times higher than the urban populations. The volume-normalized oxidative potential (DTTv) was significantly higher in rural than in urban environments (10.8 vs. 1.79 nmol min-1 m-3) and strongly correlated with most MPs and plasticizer species (r > 0.7). Source apportionment revealed that contacting plastic products accounted for 51.7 % of the MPs and plasticizers exposure in rural areas, nearly double the urban value of 27.6 %. In contrast, transportation-related source contributed only 5.9 % in rural areas but 22.6 % in urban areas. These results demonstrate clear urban–rural inequality in MPs and plasticizers exposure and related health effects, highlighting the need for exposure-based and equity-aware assessment frameworks and interventions for air emerging contaminants, especially for disadvantaged rural areas.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-1305', Anonymous Referee #1, 20 Mar 2026
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RC2: 'Comment on egusphere-2026-1305', Anonymous Referee #2, 11 Jun 2026
This study revealed significant urban-rural exposure inequality in terms of airborne microplastics (MPs) and plasticizers in Northern China. Collected PM2.5 samples were analyzed across indoor and outdoor environments. It was found that rural residents face substantially higher contamination levels compared to urban residents. The 24-hour time-weighted exposure for rural residents was 3.6 times higher for MPs and 6.8 times higher for plasticizers compared to those living in urban areas. Specifically, the concentration of plasticizer DEHP reached roughly 600 ng/m³ in rural indoor environments, which is over ten times higher than those measured in urban areas. In addition, rural populations were found to endure consistently higher cancer/non-cancer risk and OPDTT. As revealed by source apportionment, plastic products using was found to contribute the high exposure risk of rural residents. A number of different assessments were performed here. However, current conclusions lack novelty, and the findings need to be more firmly supported.
1. Current title of this manuscript was “exposure inequality for rural residents in Northern China”, but the sampling sites involved in this work were very limited to draw such conclusion. Many important cities in the BTH region were not mentioned. Also, only samples from January were collected and analyzed. But the There is a lack of discussion on the temporal variation. Thus, the representativeness of the conclusion should be reconsidered.
2.The authors reported the comparison between the concentration of microplastics and plasticizers between indoor and outdoor environments. However, there is a lack of discussion on many characteristic impacts of indoor environments. For example, the indoor-outdoor air exchange rates and indoor resuspension effects. Differences in building air exchange rates (rural vs. urban) could substantially influence indoor MP/plasticizer levels in addition to the source influences.
3.In terms of the source apportionment analysis, the limited number of samples and the chemical species (no typical tracing components) measured in this work are likely to bring significant uncertainties in source identification in indoor and outdoor environments. Running Positive Matrix Factorization (PMF) on only 22 urban and 19 rural indoor samples with 13 tracer species risks model overfitting and unstable source solutions.
4.The discussion of health risk is not comprehensive enough. Both OPDTT and cancer/noncancer risks were evaluated. But the relationships among MP/plasticizers, OP, and cancer risks were not discussed clearly. Correlations between DTTm (mass-normalized oxidative potential) and MPs/plasticizers were very weak (r = 0.2–0.4, some near 0). Also, the US EPA has no established RfD (reference dose) or SF (slope factor) values for inhaled microplastics as particulate polymers. The extrapolation of parameters should be clearly justified in terms of their toxicity parameter or routes of exposure.
5.In the conclusion part, the authors stated that“equity-aware frameworks and interventions” but provides no quantitative assessment of potential mitigation measures (e.g., improved rural waste management, ventilation changes, plastic alternatives). The recommendation needs to be clear with specific analysis. Also, inequality and equity are different terms.
Citation: https://doi.org/10.5194/egusphere-2026-1305-RC2
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This study presents a systematic investigation into the urban-rural disparities in exposure to microplastics (MPs) and plasticizers in PM2.5 in the Guanzhong Plain, northern China. The manuscript is generally well-written and provides valuable data on concentration levels, health risk assessments, and source apportionment. The topic is timely and relevant, particularly in the context of environmental inequality and emerging contaminants. However, several key scientific and methodological issues need to be addressed before the manuscript can be considered for publication.
(1) The authors used the dithiothreitol (DTT) assay to assess the oxidative potential (OP) of PM₂.₅ and attributed a significant portion of OP to MPs and plasticizers. However, MPs are insoluble particles and do not directly contribute to DTT consumption in aqueous-phase assays. Similarly, most phthalates (PAEs) are hydrophobic and poorly soluble in water, making them unlikely to directly participate in DTT reactions. The observed correlations between OP and these analytes may be confounded by co-emitted species (e.g., metals, quinones, PAHs). The authors should discuss the mechanistic plausibility of MPs and PAEs contributing to DTT-based OP and acknowledge the limitations of the DTT assay in capturing the oxidative potential of insoluble or hydrophobic compounds.
(2) The bridge plot in Figure 2c appears to be incorrectly oriented. The current representation suggests that urban concentrations are higher than rural ones for certain MPs, which contradicts the data presented elsewhere. The authors should either reverse the direction of the difference or reorder the groups (e.g., urban on the left, rural on the right) to clearly illustrate the rural excess.
(4) Figure 4 reveals an important but underexplored pattern: outdoor concentrations of MPs and PAEs are slightly higher in urban areas, while indoor concentrations are substantially higher in rural areas—by nearly an order of magnitude. This suggests that indoor sources dominate rural exposure. The authors should provide a more detailed discussion of potential indoor emission sources in rural homes (e.g., plastic sheeting, food storage, waste burning, consumer products), such as considering the role of winter ventilation practices in trapping indoor pollutants. If available, include data on housing characteristics (e.g., building materials, heating methods) to support the interpretation.
(4) The current title implies a general conclusion about urban-rural disparities. However, the main findings are driven by indoor exposure differences, which are not reflected in the title. To avoid misleading readers, the authors should either modify the title to include the indoor context (e.g., “Indoor Exposure Disparities…”), or clearly state in the abstract and introduction that the study focuses on personal exposure integrating indoor and outdoor time-activity patterns.
(5) While the authors report strong correlations between OP and MPs/BTs, they do not sufficiently control for other known redox-active species in PM₂.₅ (e.g., transition metals, quinones, EC/OC). This weakens the claim that MPs and plasticizers are key drivers of OP. The authors should include a discussion of potential confounders.
(6) The study is conducted in January 2024 in the Guanzhong Plain, a region with distinct winter climate and heating practices. The authors should explicitly acknowledge that the findings may not be generalizable to other seasons (e.g., summer with different ventilation and source patterns).