润色这段话：The results of metabolic pathways analysis indicated that the altered metabolites during high and low PM levels were mainly enriched in sphingolipid metabolism pathway Derived from single-pollut

The analysis of metabolic pathways revealed that the sphingolipid metabolism pathway was significantly impacted by high and low levels of PM. Specifically, the altered metabolites were found to be enriched in this pathway. Further investigation using single-pollutant models, revealed that changes in the levels of circulating sphingolipids, specifically those involved in ceramide metabolism, were positively associated with increased exposure to various pollutants, as measured by the interquartile range (IQR).