GSTM1 and anemia (phenotype): Meanwhile, some studies verified the negative associations of PM2.5 with Hb and anemia (Elbarbary et al. 2020; Honda et al. 2017; Mehta et al. 2021; Morales-Ancajima et al. 2019), but other studies found the positive associations (Liao et al. 2019; Wang et al. 2021).