ADSORPTION PROPERTIES OF HEAVY METALS ON FIVE DIFFERENT MICROPLASTICS

MÓNICA CALERO ; VERÓNICA GODOY; ANA KAREN FLORES TRUJILLO; PEDRO MARTIN; GABRIEL BLÁZQUEZ; Mª ÁNGELES MARTÍN LARA

La Rochelle, Francia

Congreso; International Symposium on Green Chemistry; 2019

The National Center for Scientific Research, French Ministry of Education and Research

The annual global amount of discarded plastics has been reported to exceed 320?million?tonnes currently (Wrightand Kelly, 2017), 10% of which eventually reach and persist in the aquatic environment (Jambeck et al., 2015).Polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS) and polyvinyl chloride(PVC) plastics are easily decomposed to microplastics in an aquatic environment. Currently, microplastics havebecome an emerging global concern, not only because of their hazards but also because of their interactions withother pollutants (Galloway and Lewis, 2016). For example, some heavy metals might be released and adsorbedby the polymer microplastics causing additional pollution to the ecosystem.The adsorption of some heavy metals onto a range of natural materials has been well quantified, but not for themicroplastics, whose interest has been growing more in recent years. In the present work, the adsorption capacityof microplastics composed of PE, PET, PP, PS and PVC on five heavy metals has been studied: chromium,cobalt, copper, nickel and zinc. Dissolutions of 100 mL of each metal with a concentration of 1 mg?L-1 were used,to which 0.1 g of microplastics were added. They were kept stirring at 160 rpm for 7 days, and the adsorptionbehavior was studied at different contact times (between 24-144 hours). Figure 1 shows the adsorption capacitiesof the polymers for chromium (Figure 1A), cobalt (Figure 1B), copper (Figure 1C), nickel (Figure 1D) and zinc(Figure 1E) on the last day of the experimental test (after 144 h of contact). Chromium, copper and zinc are, ingeneral, the metals that are best adsorbed. In the case of cobalt and nickel, the adsorption capacity is very low inall polymers, just reaching 0.2 mg/g. With regard to polymers, PE is the one with the best adsorption capacity,while PET does not adsorb practically any of the metals proposed.Regarding the contact time, Figure 2 shows the adsorption capacities of the polymers and metals that workedbest, in function of time (from 24 to 144 hours). Only polymers and heavy metals that presented an adsorptioncapacity close to or greater than 0.2 mg/g were reported. In view of the results, it can be inferred that, for allpolymers, chromium and zinc present a high adsorption in the first 48 hours of contact, while copper and cobaltincrease more slowly and progressively over the days. Table 1. Adsorption capacities of the most relatedpolymers and metals measured every 24 hours, over 144 hours (seven days).The results of this work allow us to conclude that the microplastics present in the environment, especially PE andPVC, are capable of adsorbing heavy metals present in the medium and carrying them along the trophic chain.