| 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.
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).