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The transport of Pb(II) or Cd(II) in subsurface has been studied in the literature; however; their co-transport in porous media in presence of colloids has not been clearly understood. In this work, a series of column experiments were conducted to study Pb(II) and Cd(II) co-transport in saturated porous media under various experimental conditions with different combination of colloidal solution (montmorillonite colloid, manual loessial soil colloid and humic acid), flow rate (0.1, 0.5 and 1.0 ml min −1 ) and sand grain size (0.4-0.8mm and 0.8-2.0mm). The results showed that increase of flow rate and grain size promoted the mobility of Pb(II) and Cd(II), furthermore, the presences of mobile colloids also enhanced the mobility of the two heavy metals, meanwhile, Cd(II) showed higher mobility than Pb(II) in the columns. Findings from this work enhanced current understanding of the competitive transport and colloidfacilitated transport of heavy metals in saturated porous media.

Mollusk shell matrix proteins are important for the formation of organic frameworks, crystal nucleation, and crystal growth in Pinctada fucata martensii (P. f. martensii). MicroRNAs (miRNAs) are endogenous small non-coding RNAs that play important roles in many biological processes, including shell formation. In this study, we obtained the full-length sequence of Pif97-like gene in P. f. martensii (PfmPif97-like). PfmPif97-like was mainly distributed in mantle pallial and mantle edge. Correlation analysis indicated that the average shell thickness and weight showed a positive correlation with PfmPif97-like expression (P < 0.05). The inner surface of the nacreous layer and prismatic layer showed atypical growth when we knocked down the expression of PfmPif97-like by RNA interference (RNAi). We used a luciferase reporter assay to identify that miR-9b-5p of P. f. martensii (Pfm-miR-9b-5p) downregulated the expression of PfmPif97-like by interacting with the 3′-untranslated region (UTR) while we obtained the same result by injecting the Pfm-miR-9b-5p mimics in vivo. After injecting the mimics, we also observed abnormal growth in nacre layer and prismatic layer which is consistent with the result of RNAi. We proposed that PfmPif97-like regulated by Pfm-miR-9b-5p participates in shell formation of P. f. martensii. These findings provide important clues about the molecular mechanisms that regulate biomineralization in P. f. martensii.

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