Transport and deposition of microplastic particles in saturated porous media: Co-effects of clay particles and natural organic matter

• Published in: Environmental pollution (1987) Vol. 287; p. 117585
• Main Authors: Li, Meng, Zhang, Xiangwei, Yi, Kexin, He, Lei, Han, Peng, Tong, Meiping
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.10.2021
• Subjects: Clay particles; Co-effects; Microplastic particles; Natural organic matter; Transport and deposition; Microplastic particles; Transport and deposition; Co-effects; Clay particles; Natural organic matter
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2021.117585

Natural colloids such as clays and natural organic matter (NOM) are universally present in environments, which could interact with microplastics (MPs) and thus alter the fate and transport of MPs in porous media. The co-effects of clays and NOM on MPs transport in saturated porous media were systematically explored at both low and high ionic strength (IS) conditions. Specifically, bentonite and humic acid (HA) were employed as representative clays and NOM. 5 mM NaCl and 1 mM CaCl2 solutions were used as low IS conditions, while 25 mM NaCl and 5 mM CaCl2 solutions were employed as high IS conditions. We found that formation of MPs-bentonite heteroaggregates had great effects on MPs transport under different conditions. Without HA, the small MPs-bentonite heteroaggregates formed under low IS increased MPs transport via serving as mobile carriers, while larger MPs-bentonite heteroaggregates formed at high IS led to the decreased MPs mobility. When both HA and bentonite were copresent in MPs suspension, we found that HA could inhibit the formation of larger sized MPs-bentonite heteroaggregates. Particularly, when the two types of natural colloids copresent in MPs suspensions, MPs transport behaviors were similar to those with only bentonite present in MPs suspensions at low IS, while MPs transport was greatly increased at high IS comparing with those only with bentonite in suspensions. Clearly, without HA in suspensions, bentonite played the dominant role on MPs transport under all examined conditions concerned in this study. Instead, when both HA and bentonite copresent in MPs suspensions, MPs transport was mainly controlled by bentonite at low IS, while both bentonite and HA had major contributions at high IS. The results showed that under solution conditions concerned in present study, MPs mobility in porous media would be greatly affected (either enhanced or inhibited) by the two types of natural colloids. [Display omitted] •Clay acts as carrier raising microplastics (MPs) mobility at low ionic strength (IS).•Formation of larger sized MPs-clay clusters decreases MPs mobility at high IS.•IS and Natural Organic Matter (NOM) concentration control co-effects of clay and NOM.•NOM dose not obviously affect MPs co-transport with clay at low IS.•NOM enhances MPs and clay co-transport at high IS via reducing aggregates sizes. Clay particles and NOM induce diverse co-effects on MPs transport/retention behaviors under different solution conditions.