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β-sitosterol is a naturally occurring plant compound called a phytosterol. It is found in many species of plants, including trees that are used to make paper, and it is often released in effluent at pulp and paper mills. β-sitosterol is also found in many plant-based foods we eat, in dietary supplements, and in paper products we use (such as toilet paper), so it is commonly detected as a wastewater pollutant.

Environmental implications of β-sitosterol

  • Not likely to elicit toxic effects to aquatic life at concentrations detected in surface waters in Minnesota. Because it has the potential to bioaccumulate, secondary poisoning to wildlife eating aquatic organisms should be considered.
  • Has the potential to accumulate and persist in sediment. It has been detected in sediment, but at concentrations that will likely not adversely affect aquatic organisms.
  • Moderately volatile but not persistent in air, so long-range atmospheric transport of this contaminant is not a concern.

Toxic mode of action

β-sitosterol does not have a clear mode of action for acute toxicity. Information regarding acute toxicity to aquatic life was limited.

Relevant media for monitoring

Water, sediment, biota

Are there seasonal considerations for monitoring?

No. β-sitosterol is widely generated, and is likely to be found in wastewater consistently year-round.

Important degradates

Major biological transformation products include boldione, 24-ethylcholest-4-en-3-one, 3-oxochol-4-en-3-one-24-oic acid, and 3-oxopregn-4-en-3-one-20-carboxylic acid. None of these compounds are monitored in Minnesota.


Because this contaminant is a common wastewater pollutant, continued monitoring of β-sitosterol is warranted. Monitoring should focus on systems with effluent input, as this is where the concentrations are likely highest.

Monitoring of sediment would be beneficial, as this is where the contaminant may accumulate and persist.

CAS RN: 83-46-5

Alternate name(s): β-sitosterol

Primary use(s): Pharmaceutical

Priority: Medium