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The page below is a sample from the LabCE course Tissue Processing in Histology. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Xylene Free Processing

Laboratories are making an effort to reduce exposure to hazardous chemicals. Since xylene is a hazardous substance, exposure should be limited. The hazards of this reagent are discussed in depth in the safety section of this course. The growing concern over xylene's toxicity has introduced several alternatives to the market. Below are some xylene substitutes:
  • Prepared from steam distillation of citrus peel, has strong citrus smell
  • Considered an irritant and sensitizer, some people may develop an allergy to it
  • Contaminates paraffin easily, so paraffin must be changed more frequently
  • Biodegradable but NOT water soluble, not sewer acceptable
  • Replaces the xylene clearant in tissue processing

Aliphatic hydrocarbons:

  • Low reactivity, low toxicity (similar to propane and butane)
  • Non-irritant, non-sensitizing
  • Penetrates tissue quickly
  • Intolerance for water, clearing impeded when dehydrants contain water (even moisture in the air)
  • Suitable for tissue processing and staining, but NOT for coverslipping and may not be compatible with mounting media
  • May be recycled, not sewer acceptable

Isopropyl alcohol (IPA):

  • Replaces the xylene clearant in tissue processing
  • Miscible with ethanol, often used as a 20/80 IPA/ethanol mix for dehydration
  • Miscible with paraffin, IPA is eliminated from tissue during infiltration at higher wax temperatures
  • NOT suitable for use on all processors (due to higher temperature)
  • NOT suitable for section deparaffinization and staining
  • Flammable and NOT sewer acceptable in large quantities or in concentrations above 10%

With our in-depth understanding of processing reagents, we can address equipment and other factors affecting the preparation of tissue for the rigors of microtomy and staining.