Table 1.

Microplastic-extraction abilities of different hypersaline solutions. The + and − signs indicate the adequate (+) or inadequate (−) technique for that type of microplastics. Reference numbers are given in brackets. Typical densities of different polymers are reported in the first row. Prices refer to Merck website (update July 2023).

Salt	Density g/cm3	PET	HD PE	PVC	LD PE	PP	PS	PA	Remarks	Price EUR/kg
		1.32–1.41	0.94–0.96	1.14–1.46	0.91–0.92	0.85–0.92	1.04–1.08	1.12–1.15
Milli-Q water	1	−	−	−	+	+	−	−	1. Easy to use 2. Low recovery rate	32.20
NaCl	1.2	−	+	±	+	+	+	+	1. Easy to use, non-toxic 2. Low recovery rate, requires multiple washings	46.50
ZnCl2	1.5–1.8	+	+	+	+	+	+ [46]	+	1. Reusable 2. Corrosive, strong foaming with organic samples [47,48] 3. Toxic to aquatic life [49]	139.00
NaI	1.55–1.8	+	+	±	+	+	+	+	1. Reusable 2. Reacts with cellulose fibers, hygroscopic, multistep method 3. Eye irritant	396
Sodium Polytungstate	1.4–1.65	+	+	+	+	+	+	−	1. Eye irritant 2. Toxic to aquatic life	266/100 g
Sodium Dihydrogen Phosphate monohydrate	1.4–1.45	+	+	+	+	+	+	−	1. Hazard free 2. Heating is required to achieve desired density [50]	96.60
CaCl2	1.3–1.35	+	+	+	+	+	+ [51]	−	1.Organic matter settles slowly due to high viscosity [32] 2. Ca2+ caused flocculation of organic substances through ion bridging; thus, it is not suggested for organic rich samples [48] 3. Eye irritant	97.60
ZnBr2 dihydrate	1.7	+	+	+	+	+	+	+	1. Toxic to aquatic life, eye irritant	344.00
NaBr	1.37	+	+	+	+	+	+	+ [52]	1. Eye irritant	80.60
Lithium tungstate	1.62	+	+	+	+	+	+	+	1. Recommended by NOAA	79.90/25 g
Potassium iodide	1.7	+	−	+	−	+	−	+	1. Eye irritant 2. Toxic to aquatic life [53]	298.00
K(HCOO)	1.5	+	+	+	+	+	+	+	1. Reusable	96/L
NaCl/NaI	1.2/1.8	+	+	+	+	+	+	+	1. High recovery rate 2. Pretreatment required [54]	−