Fig. 1

Representative images of the eight steps in the sample extraction and preparation process: 1. The dried sediment sample is transferred to a Pyrex® dish ready to be weighed 2. The sample is quantitatively transferred over a no. 6 metal sieve into a density gradient using zinc chloride solution 3. The sample begins to settle in the density gradient 4. The sample in density gradient is exposed to light vacuum to reduce the content of floating organics in the supernatant 5. The upper layers of the density gradient are transferred to a clean beaker for Fenton reaction 6. The sample undergoes Fenton reaction, and more zinc chloride is added after the reaction is complete 7. The second density gradient settles overnight 8. The upper layers of density gradient are pipetted onto Anodisc® filter and filtered by vacuum. The filter with sample is rinsed and dried