State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.
State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.
Water Res. 2018 Oct 15;143:518-526. doi: 10.1016/j.watres.2018.07.007. Epub 2018 Jul 4.
A series of one-dimensional column experiments were conducted to investigate the transport and retention of micron-sized plastic spheres (MPs) with diameters of 0.1-2.0 μm in seawater-saturated sand. In seawater with salinity of 35 PSU (practical salinity units), the mass percentages recovered from the effluent (M) of the larger MPs increased from 13.6% to 41.3%, as MP size decreased from 2.0 μm to 0.8 μm. This occurred because of the gradual reduction of physical straining effect of MPs in the pores between sands. The smaller MPs (0.6, 0.4, and 0.1 μm) showed the stronger inhibition of MPs mobility, with M values of 11.5%, 11.9%, and 9.8%, respectively. This was due to the lower energy barriers (from 108 kT to 16 kT) between the smaller MPs and the sand surface, when compared with the larger MPs (from 296 kT to 161 kT). In particular, the aggregation of MPs (0.6 or 0.4 μm) triggered a progressive decrease in MP concentration in the effluent. Retention experiments showed that the vertical migration distance of most MP colloids was 0-4 cm at the inlet of column. For 0.6 or 0.4 μm MPs, the particles were concentrated over a 0-2 cm vertical distance. Moreover, the salinity (35-3.5 PSU) did not affect the transport of the larger MPs (2.0-0.8 μm). However, as seawater salinity decreased from 35 PSU to 17.5 or 3.5 PSU, the aggregation of the smaller MPs (0.6-0.1 μm) was dramatically inhibited or completely prevented. Meanwhile, ripening of the sand surface by the MPs (0.6 and 0.4 μm) no longer occurred. By contrast, all MPs in deionized water (0 PSU) achieved complete column breakthroughs because of the strong repulsive energy barrier (from 218 kT to 4192 kT) between the MPs and the sand surface. Consequently, we find that the transport and retention of MPs in sandy marine environment strongly relies on both the MP size and the salinity levels.
进行了一系列一维柱实验，以研究在海水电导率为 35 PSU（实用盐度单位）的海水中，直径为 0.1-2.0 μm 的微米级塑料球（MPs）的迁移和滞留情况。随着 MP 尺寸从 2.0 μm 减小到 0.8 μm，从较大 MPs 中回收的出水中的质量百分比（M）从 13.6%增加到 41.3%。这是由于 MPs 在砂粒之间的孔隙中逐渐减小的物理筛分作用。较小的 MPs（0.6、0.4 和 0.1 μm）表现出对 MPs 迁移的更强抑制作用，M 值分别为 11.5%、11.9%和 9.8%。这是由于与较大的 MPs（296 kT 至 161 kT）相比，较小的 MPs 与砂表面之间的能量势垒（从 108 kT 至 16 kT）较低。特别是 MPs（0.6 或 0.4 μm）的聚集导致出水中的 MPs 浓度逐渐降低。保留实验表明，大多数 MP 胶体在柱入口处的垂直迁移距离为 0-4 cm。对于 0.6 或 0.4 μm 的 MPs，颗粒集中在 0-2 cm 的垂直距离内。此外，盐度（35-3.5 PSU）不会影响较大 MPs（2.0-0.8 μm）的迁移。然而，当海水盐度从 35 PSU 降低到 17.5 或 3.5 PSU 时，较小 MPs（0.6-0.1 μm）的聚集被显著抑制或完全阻止。同时， MPs（0.6 和 0.4 μm）对砂表面的老化也不再发生。相比之下，由于 MPs 与砂表面之间的强排斥能垒（218 kT 至 4192 kT），所有在去离子水中（0 PSU）的 MPs 都完全突破了柱子。因此，我们发现 MPs 在砂质海洋环境中的迁移和滞留强烈依赖于 MPs 尺寸和盐度水平。
