Improving cost-efficiency for MPs density separation by zinc chloride reuse

The methodology used to extract and quantify microplastics (MPs) in aquatic systems are still not standardized. Salt saturated solutions, such as sodium chloride (NaCl), zinc chloride (ZnCl2) and/or sodium iodide (NaI), are normally added to separate dense plastics from aquatic samples. However, the most effective reagents are also the most expensive (e.g. ZnCl2 and NaI). To decrease this cost, a reuse process of the salt solutions should be applied. The reuse process has been widely investigated for the NaI solution neglecting the ZnCl2. Hence, the aim of this study was to present a simple methodology to reuse the ZnCl2 solution ensuring the efficiency of the product. Results of the present study showed that ZnCl2 solution could be reused at least five times maintaining an efficiency above 95 %. The ZnCl2 reuse decreases the cost of the methodology. The efficiency of ZnCl2 solution after five filtrations remains above 95 % (all polymers are detected and recovered). The use of this salt solution is the most cost-effective methodology to isolate MPs from aquatic samples. (C) 2020 The Authors. Published by Elsevier B.V.