Field Sampling Tips and Tricks - Filter clogging

When you’re filtering water samples from a water body that has a lot of organic matter or suspended sediment, your filter might clog before you’re able to filter your target sample volume. For example, you want to filter 250 mL, but your filtration rate slows to a very slow drip when you’ve filtered only 150 mL. It’s impractical and sometimes impossible to wait until the target volume has been filtered. And it’s generally a bad idea to let your water sample sit at room temperature because we know that eDNA degrades quickly, especially at warmer temperatures. There are a number of options for dealing with clogged filters:

  • Switch to a filter with larger pore size, such as a 5 micron filter.

  • Consider setting a cutoff time or drip rate for ending filtering. For example, you might end filtering when the drip rate slows to 3 drips every 10 seconds. If you filter less than your target volume, be sure to record the volume filtered for each sample so you can later analyze it to see if the volume influences the amount of eDNA that’s captured.

  • Filter your target volume through multiple filters. For example, if your target is 1000 mL, you could filter four 250 mL subsamples or two 500 mL subsamples. Label all samples carefully to identify the sample and subsample numbers as well as the volume that was filtered for each. Keep in mind that each filter is handled separately during DNA extraction, so this approach can substantially increase the cost of your sampling program.

    -Katherine Strickler, Washington State University