To limit the potential for metal contamination in crustal subsurface borehole observatories, fiberglass and resin-coated steel pipe were used for the first time in scientific ocean drilling during Integrated Ocean Drilling Program (IODP) Expeditions 327 and 336. Here, we summarize the carbon, nitrogen, and iron leaching characteristics of the various materials used and considered for the observatory construction, as these substrates may potentially induce or inhibit in situ microbial growth. We also report on the fluorescence properties of several dopes and sealants used in observatory construction, as these may interfere with DNA-based fluorescence observations on observatory microbial colonization experiments.